George Article 151211 JournalofEnvironmentalScienceandEngineeringVol5No42011-0001

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Volume 5, Number 4, April 2011 (Serial Number 41)

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Journal of Environmental Science and Engineering

Volume 5, Number 4, April 2011 (Serial Number 41)

Contents Aquatic Environment

381 Treatment of Shrimp Pond Effluent Using Sedimentation Pond in the Tropics

L. Nyanti, B. George and T.Y. Ling

388 Determining the Best Mathematical Models of Stable Hydraulics Slop for Jajroud River with Analyzing and Comparing the Results by HEC-RAS

A.R. Mardookhpour

392 Nitrogen Derivatives of Irrigation in Chihuahua’s Parks with Wastewater Treatment Residuals

C.J. Navarro-Gómez, E. Herrera-Peraza, V. Collins-Martínez, M.S. Espino-Valdés and C. Barraza-Bolivar

Environment Monitoring

400 Workplace Assessment of Naphtha Exposure in a Tyre Manufacturing Industry

I. Norazura, H. Zailina, L. Naing, N. Rusli, H.H. Jamal and J. Mohd. Hasni

410 Determination of Fe, Cu, and Zn in Water Samples by Microcolumn Packed with Multiwalled Carbon Nanotubes as a Solid Phase Extraction Adsorbent Using ICP-MS

A. Ahmad and H.M. Al-Swaidan

420 Chlorophyll a and Trophic State in the Boka Kotorska Bay (Eastern Adriatic Sea)

S. Krivokapić and B. Pestorić

428 Monitoring Soil Moisture under Wheat Growth through a Wireless Sensor Network in Dry Conditions

M.N. Inagaki, T. Fukatsu, M. Hirafuji and M.M. Nachit

Environmental Chemistry

432 Dechlorination Behavior of Mixed Plastic Waste by Employing Hydrothermal Process and Limestone Additive

P. Prawisudha, T. Namioka, L. Liang and K. Yoshikawa

440 Photolysis and Rate Constant of 2,3-butanedione with OH Radicals in the Aqueous Phase under Tropospheric Conditions

L. El Maimouni, A. Ait Taleb and A. El Hammadi

Environmental Energy and Materials

446 Waste Plastic Conversion into Hydrocarbon Fuel like Low Sulfur Diesel

M. Sarker, M.M. Rashid and M. Molla

453 Swelling Properties of Water-Swelling Materials Exposed to Organic Water Pollution

S. Inazumi, M. Kobayashi, T. Wakatsuki and K. Shishido

Environmental Economics

460 Estimation Methodology of Short-term Natural Rubber Price Forecasting Models

A.A. Khin, M. Zainalabidin , S. Mad Nasir, E.C.F. Chong and A. Fatimah Mohamed

475 Economic Appraisal of Damages Caused by Forest Fires Adopting a New Prevention and Suppression System: The Case of Rhodes Island, Greece

A.S. Christodoulou, N. Theodoridis and K. Papastergiou

Environmental Assessment

483 Analyzing Climatic and Hydrologic Trends in Lebanon

A. Shaban

493 Low Blood Lead Concentrations and Cognitive Development of Primary School Children from Three Areas in Malaysia

H. Zailina, R. Junidah, M.E. Saliza, B.S. Shamsul and H.H. Jamal

500 Investigation of Hydrotreating of Vegetable Oil-Gas Oil Mixtures

J. Hancsók, M. Krár, T. Kasza, S. Kovács, C. Tóth and Z. Varga

508 An Energy and Exergy Analysis of a Microturbine CHP System

B.M.A. Makhdoum and B. Agnew

519 Potential Impacts of Climate Change on Water and Public Health in Alberta, Canada

K.K. Klein, R. Grant-Kalischuk, H. Bjornlund and P.L. Wilson

Journal of Environmental Science and Engineering, 5 (2011) 381-387

Treatment of Shrimp Pond Effluent Using Sedimentation Pond in the Tropics

L. Nyanti, B. George and T.Y. Ling Faculty of Resource Science and Technology, Universiti Malaysia Sarawak, Kota Samarahan 93400, Malaysia

Received: November 25, 2010 / Accepted: January 17, 2011 / Published: April 20, 2011.

Abstract: Aquaculture plays a major role in providing the needed protein. However, there have been reports of negative impacts of shrimp farming which include environmental pollution. Therefore, shrimp pond effluent had to be retained for treatment. Treatment in tanks showed good improvement in water quality but in sedimentation ponds it may not be the case. Therefore, the objective of this study was to determine the water quality of effluent retained in sedimentation pond for a duration of 76 hours. Results show that water quality at 1/3 depth was better than 2/3 depth. There was an improvement in water quality with reductions of TSS, BOD5, COD, nitrate-N, nitrite-N, SRP and TP ranging from 25-52% except for DO and TAN. In addition, there was fluctuation of each parameter during the duration of study. It is important to monitor the water quality prior to the release of effluent so that it coincides with low nutrients and acceptable DO and partial release of the top 1/3 portion is recommended. There is a limit on the reduction achievable by sedimentation ponds likely due to processes occurring in the sediment. For higher reductions, other methods of effluent management and recovery of nutrients have to be considered. Key words: Shrimp aquaculture, sedimentation pond, water quality, effluent treatment.

1. Introduction

Aquaculture is an important industry worldwide as it provides the needed protein for the growing population [1]. In Malaysia, aquaculture is actively being promoted due to its relatively clean and ample supply of water and extensive coastline. Among the aquaculture activities taking place is shrimp aquaculture which is carried out at the estuaries. Shrimp aquaculture is a lucrative industry as the shrimp were predominantly exported to developed countries. However, there have been reports of negative impacts of shrimp aquaculture in different parts of the world [2-6]. Those impacts include the poor management of effluents which impacted the environment. As a result,

B. George, research assistant, main research field: aquatic

biology. E-mail: [email protected]. T.Y. Ling, associate professor, Ph.D., main research field:

engineering science. E-mail: [email protected]. Corresponding author: L. Nyanti, associate professor,

Ph.D., main research fields: aquaculture and fish ecology. E-mail: [email protected].

in Malaysia, shrimp farm operators are required to channel shrimp pond effluents into the sedimentation ponds for retention prior to discharge. Studies of effluent retained in tanks showed good improvement of water quality after retention and those treatments with plants did better than without plants [7]. However, batch retention in actual sedimentation pond has to be studied as treatment of effluent in tanks may not simulate all the processes occurring in the earthen sedimentation pond which is used repeatedly. In Australia, efficiency of continuous flow sedimentation pond of different residence times in the treatment of shrimp effluent has been reported [8, 9]. However, in Malaysia, batch retention is commonly practised. Therefore, the objective of this study was to determine the change in the water quality of the retained water from harvested shrimp pond in the sedimentation pond.

2. Materials and Methods

This study was conducted at a commercial Penaeus


382

monodon shrimp farm of the Malaysian Fisheries Development Board (LKIM) at Telaga Air, Matang, located north east of Kuching division, Sarawak, Malaysia. The climate of the area is tropical equatorial which is warm and humid throughout the year. The harvested pond was about 1 ha in area and 1.2 m in depth and the sedimentation pond was about 1.4 ha in surface area and 0.9 m in depth.

Data collection was conducted in the sedimentation pond after all effluent from a shrimp pond had been discharged into the sedimentation pond during harvesting. Data were collected 2-hourly for the first 12 hours, 6-hourly for the next 24 hours and finally 10-hourly until the 76th hour. Temperature and DO values were recorded using Hydrolab Data Sonde Surveyor 4a with Water Quality Multiprobe (SN39301). pH was measured using a pH meter (Cyberscan 20). Water samples were collected at the end of the sedimentation pond at 2 depths, 1/3 from surface (30 cm) and 2/3 from the surface (60 cm). Three replicates were collected and composited before being analyzed for total suspended solids (TSS), 5-day biochemical oxygen demand (BOD5), chemical oxygen demand (COD), total ammonia-nitrogen (TAN), nitrate-nitrogen (nitrate-N), nitrite-nitrogen (nitrite-N), reactive phosphorus (RP) and total phosphorus (TP).

TSS and BOD5 analyses followed that of standard methods [10]. For the other parameters, water samples were filtered through a 0.45 μm pore size membrane filter before analysis using Hach procedures where concentrations were determined colorimetrically using the Hach Spectrophotometer DR2010 [11]. COD was determined using the reactor digestion method. Determination of nitrate-N and nitrite-N were based on cadmium reduction method and diazotization method respectively. TAN was analyzed using Nessler method. TP analysis was conducted according to the acid persulfate digestion method and the determination of concentrations of phosphorus in the digested solution and RP followed the ascorbic acid method. Paired-t test

was used to compare concentrations at 1/3 depth with that of 2/3 depth.

3. Results and Discussion

Fig. 1 shows the changes in water quality parameters as the shrimp pond effluent was retained in the sedimentation pond for 76 hours after harvesting. At 1/3 depth from the surface, temperature ranged from 27.1

℃ at 18th hr (5 a.m.) to 31.4 ℃ at 30th hr (5 p.m.). At 2/3 depth, temperature ranged from 27.4 ℃ at 11 p.m. to 31.4 ℃ at 5 p.m.. Shallower water showed higher temperature fluctuation than deeper water (Fig. 1). All pH values measured were above 7.5. For pH at 1/3 depth, it ranged from 7.67 to 8.91 and at 2/3 depth, it ranged from 7.83 to 8.86 and shallower water fluctuation was less compared to deeper water. At 76th hour, pH was high possibly due to phytoplankton photosynthesis as 1/3 depth TSS, nitrite, TAN and SRP were high and there was a corresponding high level of DO at that time.

Most of the DO readings were below 5 mg/L with the mean 1/3 depth value of 4.92 mg/L and 2/3 depth DO of 4.60 mg/L. They fluctuated depending on the time of the day the measurements were made. At 1/3 depth, DO ranged from 3.48 mg/L at 18th hour (5 a.m.) to 6.73 mg/L at 6th hour (5 pm) whereas at 2/3 depth, it ranged from 3.19 mg/L at 66th hour (5 a.m.) to 5.61 mg/L at 4th hour (3 p.m.). High DO values during the afternoon were due to photosynthesis of algae whereas the low DO values at 5 a.m. were due to algal respiration and consumption of oxygen by organisms in the breakdown of organic matter.

TSS values were high, ranging from 74-104 mg/L at 1/3 depth to 61-86 mg/L at 2/3 depth and they were higher at 1/3 depth than 2/3 depth. It decreased before increasing and fluctuated. TSS could be due to inorganic and organic particles [9]. The initial decrease in TSS was likely due to settling of inorganic particles which occurred quite rapidly and the subsequent fluctuation was possibly due to organic particles. TSS at shallower water was higher than deeper water likely


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Fig. 1 Water quality parameter in the sedimentation pond for 76 hours duration after completion of harvesting.

due to phytoplankton growth which decreases as a function of solar radiation penetration and in shrimp

ponds it was found to be concentrated in the top 10-20 cm of the water column [12].


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For nitrite-N, there was decrease and increase and fluctuation in nitrite and finally after 76 hours, the concentrations at both depths were lower than the initial concentrations. Nitrite-N at 1/3 depth concentration ranged from 0.063 to 0.107 mg/L and the values at 2/3 depth ranged from 0.059 to 0.104 mg/L with the highest occurring at 18th hour at 5 a.m.. Nitrate-N decreased to the lowest at 18th hour followed by an increase and subsequently decreased. Nitrate-N was significantly higher (p < 0.0005) in the 2/3 depth than 1/3 depth likely due to the significantly higher concentration of TAN in the 2/3 depth when compared to 1/3 depth (P = 0.007). At 18th hour, nitrate at both depths were very low which corresponded to high TAN. This is because at 18th hour, it was 5 a.m. and DO which was required for oxidation of TAN to nitrite and subsequently to nitrate was low. Therefore, there was an accumulation of TAN. TAN fluctuated throughout the duration of the experiment with final ammonia nitrogen higher than the initial concentrations. When organic matter is decomposed by bacteria, ammonia is produced in the process [13]. That explains the final TAN being higher than the initial TAN.

BOD5 ranged from 5.5 to 13.2 mg/L at 1/3 depth and 6.8-13.2 mg/L at 2/3 depth with the deeper water mean BOD5 significantly higher than shallower water (P<0.0005). COD values were much higher than BOD5 ranging from 102-155 mg/L at 1/3 depth to 123-163 mg/L at 2/3 depth. Values at deeper water were significantly higher than shallower water (P < 0.0005). This is most likely due to the higher oxygen demand of the degrading organic matter at deeper water which is nearer to the bottom sediment, exerting higher oxygen demand of the water above the sediment. According to Avnimelech and Ritvo [12], sediments are enriched with nutrients and organic matter by sedimentation of organic materials and bacteria developed and consume large amounts of oxygen.

At 1/3 depth, SRP range was 0.024-0.114 mg/L and at 2/3 depth, SRP ranged from 0.028 to 0.118 mg/L. For TP, at 1/3 depth, it ranged from 0.09 to 0.42 mg/L

and at 2/3 depth, the range was 0.13-0.44 mg/L. Initial values of TP observed in this study (0.19 and 0.26 mg/L) fall in the range (0.15-0.4 mg/L) reported by Preston et al. [9] in Australia. Both mean SRP and TP were higher at 2/3 depth than at 1/3 depth and the differences were significant (P = 0.004 and P < 0.0005 respectively). This is likely due to the uptake of phosphorus by phytoplankton which is more concentrated at the surface than at the deeper part of the pond and the release of phosphorus which occurs in the sediment results in more concentrated phosphorus at the bottom. It was observed that TP in the water increased to values that were above the initial concentrations. This could be due to the release of phosphorus from the sediment. In the sediment, phosphorus in feed and waste are mineralized and thus after the initial decrease in phosphorus there was an increase. Furthermore, phosphorus fluctuated due to uptake and release of phosphorus in the sediment. Sediment, algae and bacteria uptakes will reduce the concentration in water [14]. In sediment, P has been reported to be bound to Fe, Al and Ca, carbonates and organic matter. According to Boyd [15], iron pyrite accumulation is especially common for coastal soils and therefore Fe bound P is common. pH above neutral was reported to promote the release of Fe and Al bound phosphorus [16] and anoxic condition of the sediment also promote release of phosphorus from the pond sediment [17].

Percent reductions of different water quality parameters after 76 hours are shown in Table 1. DO decreased more at deeper water resulting in higher reduction in deeper water than shallower water. Overall, in the sedimentation pond, DO decreased by 2%. TSS reduction was 26% which was not that high likely due to phytoplankton biomass and also the value is affected by initial concentration which might not be high due to settling of particles before arriving at the sampling point at the end of the pond. According to Preston et al. [9], once the inorganic particulates were removed, there was greater light penetration which resulted in


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Table 1 Mean initial and final concentrations at 1/3 and 2/3 depths and their reductions in concentrations, mean of concentrations of the two depths and overall reduction after 76 hours.

Parameter Depth Initial Conc (mg/L)

Final Conc (mg/L) Reduction (%) Mean Initial Conc

(mg/L) Mean Final Conc (mg/L)

Overall Reduction (%)

DO 1/3 4.84 4.83 0.2 4.85 ± 0.02 4.74 ± 0.65 2.2 ± 2.3

2/3 4.86 4.65 4.3 TSS 1/3 103.7 76.7 26.0

93.0 ± 14.9 69.0 ± 10.0 25.8 ± 9.3 2/3 82.3 61.3 25.5

Nitrate-N 1/3 0.11 0.05 54.5 0.15 ± 0.04 0.07 ± 0.02 51.7 ± 6.8

2/3 0.18 0.09 50.0 Nitrite-N 1/3 0.098 0.065 33.7

0.095 ± 0.01 0.059 ± 0.01 38.1 ± 6.6 2/3 0.091 0.053 41.8

TAN 1/3 0.89 1.07 -20.2 0.93 ± 0.04 1.11 ± 0.05 -20.6 ± 3.0

2/3 0.96 1.15 -19.8 BOD5 1/3 9.7 7.3 24.7

9.9 ± 0.8 7.5 ± 1.6 24.8 ± 5.0 2/3 10.1 7.6 24.8

COD 1/3 154.7 102.0 34.1 158.9 ± 5.7 112.7 ± 20.8 29.2 ± 11.1

2/3 163.0 123.3 24.4 SRP 1/3 0.114 0.058 48.6

0.12 ± 0.02 0.07 ± 0.02 41.3 ± 15.7 2/3 0.118 0.079 33.3

TP 1/3 0.192 0.096 50.8 0.23 ± 0.06 0.11 ± 0.03 49.3 ± 8.1

2/3 0.259 0.134 48.1

higher phytoplankton density. According to Jackson et al. [8] who studied sedimentation ponds of different residence time, TSS was reduced by 60% with residence time of 0.7 day. In addition, BOD5 and COD only reduced 25% and 29% after 76 hours likely due to the large concentrations of algae and bacteria in the sediment which consumed oxygen during breakdown of organic matter [18]. For phosphorus, removal of SRP and TP were 41% and 49% respectively which fall in the range (28-67%) reported by Preston et al. [9]. Furthermore, this reduction was better than values of 35% and 15% for the sedimentation ponds with residence time of 2 days and 4.65 days respectively as reported by Jackson et al. [8]. Nitrate-N reduction was the highest among all the parameters studied. TAN removal was negative due to final TAN being higher than initial TAN as organic nitrogen in the sediment was converted to ammonia. Jackson et al. [8] reported removal rates of less than 23% for total nitrogen in sedimentation pond with different residence time.

Shrimps are poor eaters and mass balance showed that only 14.2% of the total input of phosphorus was recovered in harvest and 74.4% was deposited in the sediment [19]. According to Thakur and Lin [20], shrimp only assimilate 23-31% nitrogen and 10-13% phosphorus of the total inputs and the major sink of nutrients were in the sediment which accounted for 14-53% nitrogen and 39-67% phosphorus of the total input. During harvesting, the nutrient rich water was drained into the sedimentation pond and the pond bottom was also flushed with water to clean it transferring the nutrient rich bottom sediment to the sedimentation pond. Thus, in sedimentation pond bottom, organic matter from extra feed, shrimp waste and dead phytoplankton and dead aquatic organisms are decomposed by bacteria and in the process, ammonia is produced. In the presence of oxygen, ammonia-N is oxidized to nitrite and subsequently to nitrate. The fluctuation is likely due to a combination of these processes where the level of oxygen fluctuated.


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Fluctuations of pH and concentrations of DO and BOD5 were similar to the outdoor experiment where shrimp pond harvest water was placed in a tank to simulate sedimentation pond treatment [7]. However, fluctuations of TSS, COD, SRP, TP and TAN in the present study in the actual sedimentation pond were not observed when effluent was treated in the tank and the percent reductions in the present study were lower than those in the tank. This could be explained by the presence of nutrient rich sediment in the actual sedimentation pond where organic matter and phosphorus accumulated and processes such as oxidation of organic matter by microorganisms and uptake and release of phosphorus affects the oxygen demand, nutrients concentrations and indirectly TSS of the water above it.

In general, the surface 1/3 portion has better water quality than the 2/3 level. If space for sedimentation pond treatment is a problem, surface 1/3 portion can be considered for earlier release. Other than that, from Fig. 1, nutrients such as RP, TP and TAN and BOD5 and COD were low at the 12th hour and that could provide a window for the release of pond effluent. However, DO at that time was not the best for total release. Therefore, partial release could be considered as surface DO was above 4 mg/L.

4. Conclusions

Over the 76 hours the water quality was monitored, there was fluctuation in water quality parameters indicating interactions of different processes occurring in the sedimentation pond. Reduction of most nutrients and organic matter in sedimentation pond were not as high as that reported in the tank experiment possibly due to processes occurring in the sediment. Most of the water quality parameters showed improvement ranging from 25-52% except DO and TAN and better water quality for the top portion of the water. Therefore, if space is limited, water quality parameters need to be monitored and partial release could be conducted at suitable time, for example, the top portion of the water

can be discharged at the 12th hour when nutrients were low and surface 1/3 DO ( > 4 mg/L) was higher than bottom DO.

Acknowledgements

The authors acknowledge the financial assistance provided by University Malaysia Sarawak and the Malaysian Ministry of Higher Education and Mr. Ahim Noh of LKIM who assisted the authors during data collection.

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[3] S.D. Costanzo, M.J. O’Donohue, W.C. Dennison, Assessing the influence and distribution of shrimp pond effluent in a tidal mangrove creek in north-east Australia, Marine Pollution Bulletin 48 (2004) 514-525.

[4] J.H. Primavera, Overcoming the impacts of aquaculture on the coastal zone, Ocean and Coastal Management 49 (2006) 531-545.

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Determining the Best Mathematical Models of Stable Hydraulics Slop for Jajroud River with Analyzing and

Comparing the Results by HEC-RAS

A.R. Mardookhpour Department of Civil and Water Engineering, Islamic Azad University, Branch of Lahijan, Guilan 1616, Iran

Received: November 10, 2010 / Accepted: December 25, 2010 / Published: April 20, 2011.

Abstract: This paper deals with an analysis of selected equations used for the determination of a stable longwise slope calculation of torrential rivers of Jajroud in east of Tehran. Irregularity of the gradient, accompanied by heavy bed-load experiencing abrupt changes of the flow as a result of heavy rainfalls of short duration and high intensity, these are typical features impacting the behavior and characteristics of torrential rivers. The determination of the stable bottom slope, when the river bed is kept unpaved but still provides resistance against harmful effects of rapids, becomes an essential objective of the study. Three methods are used to determine the stable slope: the first is based on tangent tension (shear stress theory), the second observes a (critical) non-scouring cross-sectional velocity (critical mean channel velocities), and the third applies the bottom layer velocity (the critical bed velocities). The mathematical hydraulic model HEC-RAS v. 3.1.3 has been used for the verification of the methods in this research study. Key words: Stable bed slope, shear stress theory, critical mean channel velocities, critical bed velocities, HEC-RAS software.

1. Introduction

Typically, the hydraulics of torrential rivers is quite different if compared with those of lowlands. Irregularities of the lengthwise river-bed gradient and a significantly varying grain-size distribution of the bed-load are specific features of such rivers [1]. The bed-load is usually blended and it consists of sandy, gravelly, and cobble-formed grain particles. Sudden changes in the flow rate triggered by flash rainfall of short duration and high intensity usually hit solely small drainage areas [2]. This is also a typical feature of such channels behaviors. High flow rate results in losses of the bed-load from the channel bottom and from the river banks [3]. Thus, the sediment deposition during the decrease of the driving force becomes an unavoidable consequence. One of the basic objectives

Corresponding author: A.R. Mardookhpour, Ph.D., main

research field: water engineering. E-mail: [email protected].

of the respective studies is the determination of the stable bed slope of the channel that would resist the driving force during the design floods [4]. The creation of a sustainable bottom slope depends not only on the sediment grain-size distribution, but also on the saturation with water of the bed-load [5]. The theoretical scope of the study aims mainly at three methods of the stable bed slope analysis [6].


The methods are based on the shear stress theory, on the critical mean channel velocities distribution, and on the critical bed velocity that is based on the bottom velocities [7]. The hydraulic model HEC-RAS v. 3.1.3 has been used for the method verification in the Jajroud river [8, 9]. On the basis of shear stress theory, Shields theorem dominates the situation by Eq. (1):

Is = [0.06 × (ρm – ρw) ×de]/(ρw × R) (1) On the basis of critical mean channel velocities

distribution, Manning and Strickler theorem dominates

Determining the Best Mathematical Models of Stable Hydraulics Slop for Jajroud River with Analyzing and Comparing the Results by HEC-RAS

389

the situation by Eq. (2): Is = Vv

2/[Ks2 × R4/3] (2)

On the basis of the critical bed velocity that is based on the bottom velocities, Novak theorem dominates the situation by the Eq. (3):

Is = 0.0035× C2 × de/R (3) Also the following equation has been used for the

conversion of k and n coefficients, n = R1/6/[18 × log (a × 12.2 × R/K)] (4)

Where: Is–stable bed slope (m/m); ρm–bed-load material density (kg/m3); ρ–water density (kg/m3); de–effective grain diameter (m); R–hydraulic radius (m); Vv–critical mean channel velocities (m/s); k–coefficient, bottom roughness (m); n–Manning’s roughness coefficient; Ks–mean velocity coefficient of wetted perimeter,

unpaved channel bed; a–the constant in Manning-Stickler’s equation

related to the value of de; C–characteristic of the sediment load. The hydraulic model HEC-RAS has been used to

quantitatively analyze the above equations [10]. The Jajroud river is a sinistral tributary river at its

fluvial kilometer 2.0 and the mean slope of the channel is 4%. Some of the other data of river are as follows:

Total catchments area = 5.964 km2; Forest coverage= 47%; Length of watershed = 1.73 km; Watershed shape factor = 0.653; Torrential coefficient = 0.118. Fig. 1 shows the sketched diagram of the river. Also Table 1 lists the N-year discharges. Table 2 shows the hydraulics characteristics of

sediments in each reach or investigated span of river for grain size distribution.

3. Results and Discussions

The evaluation of the channel capacity, the flow velocity, and the proposed stable slope of the river-bed

Fig. 1 The sketched diagram of the river.

Table 1 Design discharges.

N (years) 1 2 5 10 20 50 100 (m3/s) 0.9 1.2 2.2 2.9 3.7 5.4 6.9

Table 2 Hydraulic characteristics of sediments.

Cρw ρm adeReach5.581000 2650 18.290.0635.581000 2650 16.780.125.581000 2650 15.310.161

covers 3 choices of the river reaches, all characterized by the effective grain size of de = 0.06 m, de = 0.10 m and de = 0.16 m. The above-mentioned data set-ups were computed for 2 flow rates of Q100 = 6.9 m3/s and Q5 = 2.2 m3/s. Fig. 2 shows the velocity distribution in cross section of the river. It should be noted that the span of the river for computations has altitude between 1564 till 1563 and for briefing it is shown by deducting 1000 m.

Steady-state calculations under non-uniform flow conditions were performed for three selected river- reaches, all characterized by the effective grain size de. The discharge, mean flow velocity, and geometric characteristics of the cross sectional profiles were identified by virtue of the modelHEC-RAS. On the basis of these data the individual equations have been verified and the results summarized into the pictures and graphs as shown in Figs. 3-8.

The basis for the calculation of the stable bottom slope became the classical Shields equation (1) based on the shear stress philosophy. A good agreement was also shown with the calculation after Manning-Strickler (2). The Eq. (3) of Novak indicates

389


390

Fig. 2 Velocity distributions in cross section, flooded by Q5 and Q100.

Fig. 3 Analysis of Shields, Manning strickler and Novak for Q5 = 2.2 m3/s and de = 0.06 m.




00.01

0.020.030.040.050.06

0.070.080.09

de= 0.06 m

Is (m

/m) Shields

Manning-Strickler Novak

0

0.01

0.02

0.03

0.04

0.05

0.06

de =0.16 m

Is (m

/m) Shields

Manning-Strickler Novak

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

Is (m

/m)

ShieldsManning-StricklerNovak

de = 0.06 m

0

0.005

0.01

0.015

0.02

0.025

0.03

de = 0.1 m

Is(m

/m)

Shields Manning-StricklerNovak


391



somewhat higher values of the slope stability. The difference between the extreme results amounts to 19% (Figs. 7 and 8). In general, it can be stated that the model accuracy increases with the reliability of granulometric analysis of the bed-load and discharges. For the Jajroud river both Shields and Manning-strickler theories have good agreements with analyzing results by HEC-RAS software. It is proposed that the mathematical formulas of Shields and Manning-strickler that have both good convergence with HEC-RAS analysis would be applied by researchers , although the Novak formula has good agreement with analyzing results by HEC-RAS software within Q < 2.2 m3/s and de < 0.1 m.

4. Conclusions

The theoretical scope of the study aims mainly at three methods of the stable bed slope analysis. The methods are based on the shear stress theory, on the critical mean channel velocities distribution, and on the critical bed velocity that is based on the bottom velocities. The hydraulic model HEC-RAS v. 3.1.3 has been used for the method verification in the Jajroud river. The results obtained from utilizing Shields, Manning-Strickler, and Novak formulas show the Novak theory indicates somewhat higher values of the slope stability. The difference between the extreme results amounts to 19%. It is recommended that for submitting a mathematical method for Jajroud river, the researches uses Shields or Manning-strickler formulas because of good agreement and convergence with HEC-RAS analysis.

References [1] O. Akan, Open-Channel Hydraulics, Eldenier,

Amsterdam, Netherland, 2006, pp. 87-99. [2] M. Chaudry, Open-Channel Flow, 2nd ed., Springer, USA,

2008, pp. 145-176. [3] A. Chadwick, Hydraulics in Civil and Environmental

Engineering, 4th ed., Taylor and Francis, London, 2004, pp. 65-98.

[4] H. Chanson, The Hydraulics of Open Channel Flow, 2nd ed., Elsevier, USA, 2004, pp. 112-146.

[5] T.W. Sturm, Open Channel Hydraulics, Mc-Graw Hill, New York, USA, 2001, pp. 89-106.

[6] F. Krovak, On the Determination of the Stable Bed Slop of a Channel Using Mathematics Models, Czech University, Czech Republic, 2007, pp. 12-19.

[7] P. Kovar, P. Cudlin, M. Herman, F. Zemek, Analysis of flood events on small river catchments using the KINFIL model, Journal of Hydrology and Hydromechanics 50 (2002) 157-171.

[8] D.E. Overton, M.E. Meadows, Storm Water Modeling, Academic Press, London, 1976, pp. 200-214.

[9] S.C. Chapra, Numerical Methods for Hydraulics Engineering, 5th ed., Mc-Graw Hill, New York, USA, 2006, pp. 167-186.

[10] HEC-RAS, Hydraulics Engineering Centers River Analysis System, US Army Corps of Engineers, USA, 2006, pp. 23-35.

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

de =0.16 m

Is (m

/m)


0 0.002 0.004 0.006 0.008 0.01

0.012 0.014 0.016 0.018

0.02

de =0.1 m

Is (m

/m)


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Nitrogen Derivatives of Irrigation in Chihuahua’s Parks with Wastewater Treatment Residuals

C.J. Navarro-Gómez1, E. Herrera-Peraza1, V. Collins-Martínez1, M.S. Espino-Valdés2 and C. Barraza-Bolivar2 1. Department of Environmental and Energy, Center for Advanced Materials Research S.C, Chihuahua, Chih 31109, México.

2. Faculty of Engineering, The University Autonomy of Chihuahua, Chihuahua, Chih 31000, México

Received: October 11, 2010 / Accepted: December 13, 2010 / Published: April 20, 2011.

Abstract: Since 2000 Chihuahua City has distribution system Waste Water Treatment (WTR), watering city’s green areas. The need to cover the growing demand for drinking water has encouraged the use of non-potable water where water quality is not an issue despite being used by 10 years ago, it is not known whether nitrogen compounds derived from WTR pose risks to the environment and public health. Therefore, in order to minimize health and environmental risks, this is needed to assess the impact and policy support for water use. The aim of this study is to determine the constitution and the concentration of nitrogen compounds through selection and characterization of park’s representative. It’s divided into physical properties and main parameters that affect nitrogen transformations. It was determined that sand was material that allowed more favorable oxidation and reduction of nitrate in soil and atmosphere, opposite of the clay. When used WTR, nitrates, nitrites and ammonia nitrogen were identified in the subsurface and NOx and N2O were identified in the atmosphere. When drinking water was used, none of these compounds was found. However, it was determined that despite having high concentrations of nitrates, the WTR was within the limits allowed by the Mexican standard for the use of WTR in public places. Key words: Wastewater treatment, oxide nitrous, nitrate, unsaturated zone.

1. Introduction

The city of Chihuahua is located in Northern Mexico between 105° and 106° West longitude and 28° and 29° North latitude, this is the latitude of the largest deserts in the world. The climate is arid to semiarid, with 415 mm average annual rainfall and average annual evaporation of 2,900 mm (Fig. 1) [1].

Rainfall is intensity and short time that does not promote the infiltration and therefore aquifer recharge. The groundwater is 100 percent water supply for the city. The city’s growth has been related to the accelerated

C.J. Navarro-Gomez, Ph.D., professor, research fields:

drinking water supply and groundwater prospecting and impact of treated wastewater. E-mail: [email protected].

Corresponding author: E. Herrera-Peraza, Ph.D., professor, main research fields: modeling and simulation atmospheric, renewable energy and environment protection. E-mail: [email protected].

Fig. 1 Statistics of average monthly precipitation and temperature with a time series of 1941-2007.

development of industrial sector in recent years. As a result, it has had to face the drinking water demand supply by means of the addition and operation of new wells deeper than 400 m being the most important aquifer Chihuahua-Sacramento (ACHS), source of drinking water supply located in urban areas. This has caused pressure on the continuous and uninterrupted


393

aquifer whose water table declines ranging from 2 to 3 meters in wells of drinking water [2]. The over pumping from ACHS in just 20 years has dropped from 30 meters at the water table in the wells for supply drinking water [3] being in the aquifer, the extraction of groundwater 2.5 times greater than recharge [4] standard to evaluate the balance between recharge and exploitation of aquifers in Mexico (NOM- 011-CNA-2000) [5], the overexploitation and low- drinking water supply and increased demand, application originated where potable quality is not required by their replacement with treated wastewater (WTR).

The reuse basically compresses the hydrological cycle in a global scale uncontrolled locally controlled. Water reuse is a proven tool and appropriate management of water scarcity resources [6]. Since 2000, the city of Chihuahua has a pipeline distribution system that supplies WTR green areas of the city. The WTR is the process of activated sludge from two wastewater treatment plants. The Board Municipal Water and Sanitation Chihuahua (JMAS) institution responsible for water supply and sewerage implemented a WTR in all parks and gardens in the city [7]. This makes it possible to recharge induced by infiltration of irrigation return derived from the green areas [8, 9]. This hits directly in the unsaturated zone [10], which has at least 100 meters deep on average ACHS, this thickness is of vital importance to the processes and changes in the quantity and quality of WTR. Given that these effluents have high concentrations of nutrients as phosphorus and ammonia nitrogen, and despite the low levels of organic matter, these are sufficient to cause reactivation or development of microorganisms. In addition they are susceptible to favor the nitrogen transformations that lead more to their oxidized forms [11] with the risk of nitrate leaching due to the unsaturated zone and favoring contamination [12], and the possible release into the atmosphere of nitrogen oxides [13]. In Mexico, it is little known of the impacts of irrigation with WTR,

in August 2009 rule was published concerning the possible effects of the recharge with this type of source (NOM-014-CONAGUA-2009) [14], but this rule does not emphasize the impact of the unsaturated zone, to issue the precursor of greenhouse gas (nitrous oxide), to be consistent with the trends to reduce or avoid climate change. In case of arid Chihuahua is very important as the two factors that vitiated the Mexican standard. The interest of this research is to understand the processes and transformations that occur from continuous irrigation during the ten years of the green zones WTR, and to identify and describe positive and negative impacts generated by this practice. The purpose is obtained through the valuation of a green representative surface. The experimental site has a surface of 1200 m2, corresponding to gardens of the north treatment plant (NTP) (Fig. 2).

This is intended to define the frequency of monitoring and surveillance in the unsaturated zone or in nearby wells in order to evaluate the existence of recharge and evaluate gas emissions. The International Panel on Climate Change (IPCC, 2001) estimates that 46% comes from agricultural activities, assuming that the irrigation of green areas as agricultural activity. At the moment, with preliminary results of the monitoring and sampling, statistical evaluation was using software as Hydrus, Comsol and Minitab.

2. Experiment

The first step was the knowledge of the geographical

Fig. 2 Green areas irrigated with WTR in Chihuahua city.


394

position of the green areas where this process is happening with WTR irrigation in the city of Chihuahua, 19,000 hectares are occupied by urban areas, of which 368 correspond to green areas [15]. At least 20 areas because of their size are capable of analysis given the opportunity to present and quantify the phenomenon of infiltration, evaporation and gas emission (Fig. 3).

The area selected as representative of the green areas was chosen in the gardens of NTP’s, that’s where it began with the WTR irrigation since 1996, when it was built, this surface is 1200 m2; the next step was characterization of this place. Several items are needed for evaluation as: water, vegetation, soil and rock material, these elements or parameters to represent are our constant experimentation on the part of experimental is described in detail the follow up to their representation and evaluation.

Besides the features described above physical form must identify irrigation and meteorological variables that influence on nitrogen transformations and processes of WTR; most important weather variables are temperature, wind, humidity and precipitation, we are using at time series of more than 30 years at the observatory of the city [16], but in order to gauge the specific microclimate of the NTP, a Vaisala station was installed.

The database of the weather observatory show that the lower temperature peak hours occur from 6:30 to

Fig. 3 Surface with WTR irrigation, in Google Earth, 2010.

7:30 a.m., and the higher maximum temperature peak occur from 14 to 15 hours; this determines its influence on the transformations of nitrogen in WTR, the sampling interval of meteorological values was each day [17]. Tables 1 and 2 outline the conduct of the regional weather variables based on data from the observatory, with a historical series over 30 years, the distribution of precipitation and average temperature oscillation in the climate of the region were defined in Fig. 1, the period between July to September, is where have the highest accumulation of rain, were 50 days, in the missing days are recorded rainfall amounts negligible, there were 4 days with rainfall greater than 25 mm; then that is almost 25 percent of the annual cumulative precipitation. All these data affect the climate statistics analysis of the transformations and derivatives of N contained in the WTR, as they may be diluted the compounds concentrations. The Vaisala station data in order to define the microclimate in the gardens of NTP, not yet established a track record of Table 1 Physical and chemical characteristics of soil at 40 cm of depth.

Variables Method Asset Units N total MicroKjeldahl 0.679 % P removable Olsen 54.53 ppm MO Wakley y Black 15.3 pH Potenciometer 7.4 Conductivity Electrical Conductivity 2.16 ohms/cm

Sand 64.44 % Loam 25.84 % Clay 9.72 % Textural Classification Bouyoucos Sandy

Loam

Bulk density 1.07 kg·m-3 Humidity 17.7 % NO3 Brucina 267.3 kg·Ha

Table 2 The values of different parameters of the fitted function with its corresponding deviations.

Parameters N-NH3 N-NO3 N-NO2

y0 (mean value in y) 48 ± 10 3.1 ± 0.5 0.08 ± 0.01 xc (mean value in x) 207 ± 6 221 ± 4 221 ± 4 w (2 × standard deviation) 252 ± 82 122 ± 11 113 ± 12

A (Amplitude) -7652 ± 554 1501 ± 183 281 ± 38 χ2 26.13 5.01 0.26


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complete cycles of observations in the different meteorological variables that will carry through June 2010. However one can observe a trend similar to the regional weather observatory, only if there is a temperature difference ranging from 1 degree.

In order to assess the mechanism of transformation of nitrogen contained in the WTR and applied to the gardens, where one of the mechanisms is denitrification, which is the release of nitrogen oxides from the soil to the atmosphere. One of the gases emitted is oxide nitrous (N2O) [18]. The content of bacteria in WTR involved in the production of N2O is called denitrifying and has the genetic potential to produce, by the action of some oxide nitrous reductases. The conversion of NO3 to nitrogen (N2) [19], this is because the rate of mineralization of organic matter (OM), which produces NO3 descending to deeper soil layers; A lower content of OM, the leaching process is slower because of the absence of bacteria, since carbon or any organic compound based on this element are a source of energy for these organisms, but other nutrients as the same nitrogen (N). In the form of nitrates (NO3) and ammonia nitrogen (NH4) [20] sampling was defined for this process in two areas, one on the soil or root and the other in the unsaturated zone within 1 m depth of the surface. The first depth sampling due to gas emition by the roots, which govern the population dynamics of denitrifying bacteria [21], was sampling in depth where there is level of oxygenation. The oxide reductase is repressed by O2, which also inhibits the formation of reductase probably by competition from electrons. The reduction of NO3 to NO2 is observed. The relative humidity or moisture content is important, when there is high water content, greater than 70-80% of available water for prolonged periods is important for the occurrence of denitrification [22]. The emission of gas is related to soil texture as follows: clayey soils have higher levels of MO and hence higher microbial activity [20], and soil, and finally the pH. The development of soil bacteria promotes denitrification, additional at pH < 4.

3. Results and Discussion

In order to delineate the characteristics field work was divided into 4 lines of work such as: irrigation with WTR, soil, gas emissions and unsaturated zone.

3.1 Irrigation with WTR

Through a campaign of observation and lift irrigation system in the gardens of the north plant, in order to know the time and exposure conditions of the irrigated area, it was found that irrigation is done through PVC lines 2 and 4 diameter, the duration is 2 hrs, 365 days a year, even in rainy season. The watering schedule is from 7 to 9 a.m., method is aspersion irrigation and flooding in some parts, layer of water which goes above 10 cm, was taken daily water samples at the outlet of the irrigation system at that time in order to characterize the WTR, hence from the analysis of changes generated and considerating weather parameters on two points of time at 7 a.m. to consider the minimum or base behavior of daily temperature and 14 hours to consider maximums, was taking parameters weather each 15 minutes. The monthly average result of the analysis of WTR, obtained from the daily, is shown in Fig. 4.

3.2 Soil

As for the characterization of soil fits a sampling plan based on the Mexican standard (NMX-AA- 132-SCFI-2006) [23], which states the criteria for sampling, with this defined 4 physical sampling points

Fig. 4 Results of the monthly average WTR analysis, obtained from the daily show.


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spatially distributed in the plots of the gardens of NTP, which excavated and sampled to know the profile of it, that was to shallow depths where the horizons marked change of stone material, which were : 15, 40, 80, 100 and 130 cm. Geohydrological conditions are determined by the stabilization method and variable load permeameter with tensiometer-TDR equipment. The soil was considered as 40 cm, where horizon of root and soil samples is deeper to determine the rock material of the unsaturated zone. The results obtained in laboratory soil are shown in Table 1. For denitrification potential of soils in the gardens of the four surveys were conducted following NTP manuals, and a composite sample was obtained at 40 cm vertical depth; the measure of denitrification potential of soils was conducted by the acetylene block method.

3.3 Gas Emission

The N2O production measures were made at 14 hours, for which two collectors are inserted to depths of 15 and 40 cm: the sampling method was through closed suction chamber, its analysis in a gas chromatographic detector electron capture, however the production of N2O was obtained based on relation between the favor factors of N2O emission, such as: MO, moisture, pH, soil classification and the water concentrations of NO3, NO2 and NH3 in WTR.

The reaction of nitrogen transformation is given as follows: the first step is the conversion of nitrate to nitrite, and then produces nitrous oxide and nitrogen gas. The last three compounds are gaseous and can be released into the atmosphere (Eq. (1))

NO -3 NO -

2 NO N2O N2 (1) The denitrification potential decreases with depth

[24], being then the maximum values of denitrification in sampled points 15 and 40 cm for being shallow and rich in organic matter with denitrification rate of 5.7 mg N/kg soil/day. Conducted scientific analysis in terms of vegetation cover (grass), nitrogen content in plant cover in NTP is 2.78%.

3.4 Unsaturated Zone

For the present study were made activities site to define the rock material where the unsaturated zone, a correlation was made of methods of interpretation, such as interpretation of satellite images regional geology, geomorphology, structural geology, physiographic, lithology and stratigraphy from deep wells near the area of NTP (Fig. 5), was taken piezometry historic information in wells to define groundwater preferential flow of water quality. There are deeps in wells drinking of water table in average 102 m was defined deep vadose zone by application of geophysical methods in experimental site.

The geological description of area is located in the Sierras and Basin Province, according to the classification of Erwin Raisz (1964) [25], saws arranged in a northwest-southeast. Geomorphically, the area is settled in a valley of tectonic origin, i.e., those blocks of rock that formed part of the Sierra Nombre de Dios has been displaced over time vertically, with jumps. That is larger than 200 m. On these blocks displaced “down” particles have been deposited granular products of the disintegration of the rocks of the upper parts and materials that have been washed away and transported by streams during the rainy season, starting his tour in the highlands de la Sierra Santo Domingo. The description of events and units are made based on lithological mapping and mapping of the Mexican Geological Service (Letter Chihuahua) (Fig. 5). Regional geological structures

Fig. 5 Regional geological interpretation.


397

affect the study area, which are the result of orogeny, a transcurrent tectonics and finally an extensional event that resulted in the current morphology. There are normal faults oriented NNW-SSE. In order to investigate the physical characteristics of the materials that make up the subsoil in the area where is located the NTP, it required the application of an indirect method, using geophysics using electrical resistivity method through the implementation of Vertical Electrical Sounding (SEV), using two types of arrangements, the form or arrangement of placing the electrodes were known as Schlumberger and Wenner. Schlumberger arrangements were identified from 01 to 04 and identified Wenner 05-08 (Fig. 6).

The first three units are identified relatively resistivity of sand with thickness no greater than 4 m, detected after a unit with low resistivity values between 9 to 18 Ohm-m, that corresponded at clay-silts material with a thickness of 17 m. With resistivity value of 70 Ohm-m is detected associated with volcanic rock.

Application of these methods was able to obtain readings of the responses to the introduction of electric current through which one could associate the measurements being made from the surface with the types of materials that make up the subsoil. For the present work 8 lines of vertical electrical sounding (SEV) were carried out, with distances between 60 and 500. In four of them used the unit is not uncommon that volcanic rock is in the basement every time due to the presence of graven formation of this unit was displaced “down” and is now in the ground covered with granular materials. Units that are detected by their composition are interspersed layers of sand, gravel and clay with a thickness no greater than 20 m, except the drive where volcanic rocks are identified.

A Gaussian distribution was result of behavior of parameters in WTR as: nitrate, ammonia and nitrite. It’s due fundamentally to season heat and Table 2 shows the values of different parameters of the fitted function with its corresponding. The fitted function was Eq. (2). Study is composed of ten geoelectrics units

Fig. 6 Location of vertical electric sounding (SEV’s).

(Fig. 7).

(2)

The inverse behavior of ammonia respect to nitrates and nitrites is due to transformation of denitrification and that is favored for the weather conditions in the period between June to August which correspond to 95% of the distribution (Fig. 8).

4. Conclusions

The presence of dissolved oxygen in the process eliminates the enzyme system necessary for the development of denitrification in soil and water. Nitrate is converted into gas (NOX) and one of inducing this change is the increase in pH. Temperature affects the rate of removal of nitrate and microbial growth. The organisms are sensitive to temperature changes. One can see that in the months of June to August where are the highest temperatures and the tendency of the behavior of nitrate and nitrite derivatives WTR ammonia in these months are higher, so it is possible to predict at that time a increased emission of nitrous oxide. Comparing the number of data analysis: nitrates, nitrites with meteorological variables (precipitation, relative humidity and temperature), one can conclude that the trend of increase of nitrates and nitrites in WTR is affected when temperature increase and not correlated enough to set the relative humidity and precipitation.


398

Fig. 7 Geoelectrics profiles showing the units and thicknesses of rock material in the subsoil of NTP.

Fig. 8 The graphical behavior of the concentration of ammonia, nitrates and nitrites.

Another factor affecting the emission of nitrous oxide soil texture because the soil is mostly sandy to shallow depths, where oxygenation occurs and the process of regression to the atmosphere of the components of the WTR. One can assume that the quantities of emission of nitrous oxide are not important. But requires more sampling in the period from June to August, where temperatures are highest and to define correlation with nitrous oxide emissions. In order to establish a monitoring plan, that should be included in the Mexican Standard.

According to the study objective and based on the interpretation of geophysical surveys, one can conclude that subsoil in experimental site is compound for granular units as sand and clay, playing as an area that corresponded to an old channel of the Sacramento River, at other times, so the same for existing materials

can be interpreted as being material deposited by the river or pertaining to abandoned meanders. The unsaturated zone based on the interpretation of geophysical studies which concluded that the subsoil of NTP are in granular units, which corresponds to an old channel of the Sacramento River, so that existing materials can be interpreted as the material which shall be deposited by the river or in connection with abandoned meanders, with average depths of 100 m, given the regime of irrigation and precipitation as well as the intercalated clay materials gives a very slow infiltration rate, rather than having to constantly refill as that given in the NTP, has not allowed this has come to impact the groundwater quality as there is no evidence in the pits on the presence of nitrate or nitrite, making it necessary to build wells at different depths of observation units defined by resolved in the SEV stratigraphic, and sampling at least once a month to have enough information in the unsaturated zone impacted by irrigation with WTR, before assessing nitrate contamination in the aquifer or recharge the purpose artificial.

References [1] National Institute of Statistics and Geography INEGI,

Statistical Yearbook of the State of Chihuahua, 2008. [2] National Water Commission, Chihuahua-Sacramento

aquifer piezometry measurements, Technical Report, 2006.

[3] Board Municipal Water and Sanitation Chihuahua, Diagnosis modeling and planning sectors, Technical Report, 2007.

[4] NOM-011-CNA-2000, Establishes specifications and the method for determining the annual average availability of national waters for exploitation or use Official, Journal of the Federation, 2002.

[5] National Water Commission, Availability and balance of groundwater in Chihuahua-Sacramento aquifer, Technical Report, 2000.

[6] B. Durham, A.N. Angelakis, T. Wintgens, C. Thoeye, L. Sala, Water Recycling and Reuse, A Water Scarcity Best Practice Solution, European Environment Agency, AQUAREC, 2006.

[7] Board Municipal Water and Sanitation Chihuahua, Regulation for the construction of water and sanitation


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subdivisions in Chihuahua City, Chihuahua State Congress, 2000.

[8] M.V. Esteller, Aquifer vulnerability against the use of wastewater and sludge in agriculture, Latin American Journal of Hydrogeology 2 (2002) 103-113.

[9] Intergovernmental Panel on Climate Change, Climate change and water resources, Impacts and Responses, IPCC Technical Paper, Chapter 3, 2008, pp. 35-41.

[10] T. Harter, Y.S. Onsoy, K. Heeren, M. Denton, G. Weissmann, J.W. Hopmans, et al., Deep vadose zone hydrology demonstrates fate of nitrate in eastern san Joaquin valley, Journal California Agriculture 59 (2005) 124-132.

[11] S.R. Maggioto, Fluxes of oxidized nitrogen gases from fertilized agricultural field, Ph.D. Thesis, The University of Guelp, 2000, pp. 6-38.

[12] M.V. Esteller, I. Morell, C. Almeida, Physics-chemical processes in a vadose zone during the infiltration of treated wastewater used for irrigation, Journal Environmental Geology 40 (2001) 923-930.

[13] Y. Master, R.J. Laughlin, U. Shaviv, R.J. Stevens, A. Shaviv, Gaseous nitrogen emissions and mineral nitrogen transformations as affected by reclaimed effluent application, Journal Environmental Quality 32 (2003) 1167-1172.

[14] Nom-014-CONAGUA-2003, Requirements for recharge of aquifer with treated wastewater, Official Journal of the Federation, 2009.

[15] Municipal Planning Institute, Plan of Urban Development from Chihuahua City 2007-2010, 2006.

[16] National Water Commission, National Weather Service Climatology, 2010.

[17] National Water Commission, Water Atlas, 2009. [18] R.G. Prinn, R.F. Weiss, P.J. Fraser, P.G. Siimmonds, D.M.

Cunnold, F.N. Alyea, et al., A. McCulloch, History of chemically and radioactively important gases in air deduced from ALE/GAGE/AGAGE, Journal Geophysics 105 (2000) 17751-17792.

[19] L.R. Tate, Soil Microbiology, 2nd ed., John Wiley & Sons, Inc., New York, USA, 2000.

[20] P. Marschner, C.H. Yang, R. Lieberei, D.E. Crowley, Soil and plant specific effects on bacterial community composition in the rhizosphere, Soil Biol. Biochem. 33 (2001) 1437-1445.

[21] J.W. Van Groenigen, G.J. Kasper, G.L. Velthof, Van Den Polvan Dasselaar,P.J. Kuikman, Nitrous oxide emissions from silage Maite fields under different mineral nitrogen fertilizer and slurry applications, Plant and Soil Journal 263 (2004) 101-111.

[22] R. Knowles, Denitrification in soil, Department of Microbiology, JCO, Canada, Technical Report 46, 1982, pp. 43-70.

[23] NMX-AA-132-SCFI-2006, Soil sampling, identification and quantification, and sample handling, Official Journal of the Federation, 2006.

[24] H.J. Di, K.C. Cameron, Nitrate leaching in temperate Agro ecosystems: Sources, factors and mitigating strategies, Nutrient Cycling in Agro Ecosystems 46 (2002) 237-256.

[25] Raisz Erwin, Atlas of global geography, GlobalHarper Editor 40, 1944.


Workplace Assessment of Naphtha Exposure in a Tyre Manufacturing Industry

I. Norazura1, 2, H. Zailina1, L. Naing3, 4, N. Rusli3, 5, H.H. Jamal6, 7 and J. Mohd. Hasni6 1. Department of Community Health, Faculty of Medicine and Health Sciences, University Putra Malaysia, Selangor 43400,

Malaysia

2. Department of Technology Management, Faculty of Manufacturing Engineering and Technology Management, Universitiy

Malaysia Pahang, Lebuh Raya Tun Razak, Gambang, Kuantan, Pahang 26300, Malaysia

3. School of Dental Sciences, University Sains Malaysia, Kelantan 16150, Malaysia

4. Institute of Medicine, University Brunei Darussalam, Jalan Tungku Link, Gadong BE 1410, Brunei Darussalam

5. School of Medicine and Health Sciences, Monash University, Johor Bahru 80100, Malaysia

6. Department of Community Health, Faculty of Medicine, University Kebangsaan Malaysia, Kuala Lumpur 56000, Malaysia

7. International Institute for Global Health, United Nation University, UKM Medical Centre, Kuala Lumpur 56000, Malaysia

Received: November 19, 2010 / Accepted: January 17, 2011 / Published: April 20, 2011.

Abstract: A qualitative and quantitative workplace assessment was carried out to determine naphtha exposure in a tyre manufacturing industry. A qualitative chemical health risk assessment was conducted to identify naphtha hazard at the workplace. Quantitative assessment using Portable VOC Monitor, Automatic Sampling Pump and personal air sampling pump was used to determine VOC concentrations, organic solvents, and individual air naphtha respectively. The risk rating of naphtha was estimated to be 5. The mean VOC concentration was in the range of 2.43 to 92.93 ppm. Repair area had the highest VOC concentration while the lowest was in the moulding area. Each work station had significant differences for VOC concentrations (p < 0.001). Laboratory analysis found various solvents including 2-methyl pentane, hexane, methyl cyclopentane, heptane, cyclohexane and toluene which were present in the liquid naphtha. Only xylene has been detected in the making and moulding areas with a range of 2 to 5 ppm. Meanwhile, the air naphtha concentrations of the exposed workers were significantly higher than those unexposed. The risk of naphtha exposure was qualitatively significant and not adequately controlled. Naphtha was detected in all work stations since it is the main solvent used. The “Repair Area” was significantly more contaminated than the other area. Key words: Environmental monitoring, risk assessment, volatile organic compound (VOC), naphtha, personal air sampling.

1. Introduction Majority of industrial solvents are volatile and the

common term “volatile organic compounds (VOC)” covers an extensively large group of compounds. VOC is a class of organic compounds with boiling points from 50 to 100 ℃ up to 240-260 ℃ depending on the sampling and analytical techniques [1]. A high-capacity to dissolve lipid-soluble materials as

Corresponding author: H. Zailina, professor, research field:

occupational health risk assessment. E-mail: [email protected].

well as sufficient volatility to permit simple removal of the solvent is the major requirements for solvent applications in several industries. Industrial operations of a number of industries are closely related with the use of organic solvents, as an important group of industrial chemicals. Industrial solvents have a wide applications in the manufacture of a variety of products, for example cosmetics, detergents and soaps, drugs, dyes, pigments, explosives, fertilizers, inks, pesticides, paints, plastics, shoe, tyre and others. Thus, organic solvents play an important role in the rapid development


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of the industrial sectors. Naphtha is an organic solvent which is classified as

petroleum distillates group, obtained by fractional distillation of petroleum. Petroleum distillate is composed of several hundred aliphatic and aromatic hydrocarbons, used as cleansing agent, thinner, paint, adhesive, fuel and other applications especially in industrial setting. Basically, there are three types of naphtha which are used in industrial setting: coal tar naphtha (heavy), wood naphtha (intermediate) and petroleum naphtha (light). Naphthas are used as organic solvents for dissolving or softening rubber, oils, greases, bituminous paints, varnishes and plastics [2]. In tyre manufacturing industry, hydrotreated light naphtha made up of aliphatic hydrocarbon (n-hexane) and aromatic hydrocarbons (benzene, ethylbenzene) is used as an adhesive, cleansing as well as segregative agent [3]. In other rubber-based industry, it is demonstrated that extraction naphtha was among the predominant volatile compounds in the analysis of 4 brands of glue used as adhesives in repairing of rubber conveyer belts [4].

Therefore, this workplace assessment plus exposure assessment within the individual breathing zone is necessary as an early preventive measure of controlling or maintaining the acceptable level of contaminants concentrations.


Pre-assessment using Chemical Health Risk Assessment (CHRA) concept was applied to identify naphtha hazard as well as to assess naphtha exposure among workers in a tyre manufacturing industry in Malaysia. This consisted of determining the degree of naphtha hazard, assessing the exposure and evaluating the existing control measures. This exposure assessment was implemented by considering the following factors: (i) the likelihood of contact of the work unit with naphtha; (ii) how naphtha is released into the work environment; (iii) the method of handling naphtha; (iv) the way naphtha enters the body; (v) the

frequency and duration of exposure and (vi) the intensity or magnitude of each exposure. Since the exposure level can be influenced by the adequacy of control measures at the workplace, the existing control measures were assessed whether they are adequate or not in terms of their suitability, use, effectiveness and maintenance [5].

A walk-through survey was initially done to observe the working environment of the plant and workers’ job activities throughout the tyre manufacturing process to identify various monitoring stations involving naphtha used for the environmental monitoring in this industry.

Area sampling was carried out using direct reading sampler namely Portable VOC Monitor (MiniRAE 2000), Model PGM 7600 using a Photo-Ionization Detector to monitor volatile organic compound (VOC), while Automatic Sampling Pump Model ASP-2000 (SampleRAE) was used to monitor the selected organic solvents [6]. It gives real time measurements and activates alarm signals whenever the exposure exceeds preset limits. This area sampling was carried out in several work areas using naphtha. The monitoring was conducted in each work area for 15 minutes. The protocol for sampling activities was carried out according to NIOSH/JICA [7]. Work area units using naphtha, its distribution and action as well as work areas of workers were identified. Sampling points were carried out on the intersections of horizontal and vertical lines at an interval of six meters throughout the industry. Air samples were measured at 100 cm above the floor for 15 minutes each by using direct reading samplers. Sampling was conducted during work operations.

A bulk sample of liquid naphtha was collected for detailed analysis of organic solvents using Gas Chromatography Mass Spectrometry (GC-MS). The organic solvent analysis was carried out using the NIST Standard Reference Database 1A, NIST/EPA/NIH Mass Spectral Library (NIST 98) and NIST Mass Spectral Search Program Version 1.6 [8].

Personal air sampling pump was used for the active


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sampling of naphtha as recommended in guidelines on monitoring of airborne contaminant [9]. The determination of time-weighted average (TWA) concentrations of naphtha in the worker’s breathing zone was made using a charcoal tube (100/50 mg sections, 20/40 mesh) as an absorbent. According to NIOSH Manual of Analytical Methods #1500 [10], ends of the sampler was broken before sampling and was attached to personal air sampling pump Model PAS-500 with flexible tubing. Then, the personal pump was attached to worker’s lapel throughout an 8-hour work shift for 2 hours. Samples were collected at a maximum flow rate of 0.2 liter/minute (TWA) until a maximum collection volume of 4 liters was reached. After 2 hours sampling, the samplers were capped with plastic caps and packed securely for shipment before analyzing in the laboratory

For the laboratory analysis, the concentration of air naphtha from the sorbent tube was analyzed by using gas chromatography with flame ionization detector (GC/FID). This laboratory analysis was carried out in Industrial Hygiene Analytical Laboratory according to the standard methods adopted from NIOSH Manual of Analytical Methods #1500 [10].

3. Results

3.1 Chemical Health Risk Assessment

Observation through a walk-through survey showed that tyre manufacturing process uses naphtha as a main raw material during mixing, making, repairing and finishing processes. Table 1 shows the use of naphtha in several work units. Results from the workplace assessment based on the qualitative Chemical Health Risk Assessment (CHRA) [5] process showed that hazard rating (HR), magnitude rating (MR), and exposure rating (ER) were 4, 5, and 5 respectively (Tables 2 and 3). From the risk matrix table, the risk rating (RR) of naphtha exposure for this qualitative estimation was 5, and was concluded as significant and not adequately controlled (C3). This assessment was based on the observation during storage, movement,

Table 1 Application of naphtha in several work units.

Work process Application of naphtha used Cut plies for bead fillers To separate the stuck plies Assemble ply cut into pocket To separate stuck plies

Making raw cover

To apply on bead surface To apply on the tread joint before consolidating To be used during turn back of pockets To apply on pocket surface before application of treads/sidewall To decoy the raw cover from the former

Orbi stripping To spray onto surface of raw coverprior to application of orbistrip compound

Raw cover moulding To clean or wipe raw cover before loading and curing

Spraying cover To be used during cleaning or wiping raw cover at bead region before sending for moulding

(1) Repair or rework on defective tyres (2) Buffing defective area of the tyre

To wipe the tyre after ironing To clean or wipe finished repaired tyre To clean the buffed spots

Table 2 Hazard rating for naphtha. *Physical form

*Classification of hazard

*Risk phrases

*Skin notation

Hazard rating

Liquid Toxic

R36, R45 R48/20/21, R62 R65, R67

Yes 4

*Source: MSDS, 2006.

Table 3 Magnitude and exposure ratings for naphtha*.

Routes of entry Existing controls

Suitable and effective Yes/No

Maintenance testing and examination

Eyes None No - Skin Thermaprene glove No Yes Inhalation Fan No Yes Ingestion Safe work practice Yes Yes

*Frequency of entry = 4-7 hr/shift; degree of chemical release = high; degree of contact/inhale = high; MR = 5; ER = 5.

handling and using, transportation and disposal of naphtha. Naphtha is stored at the central material store, transferred to the naphtha booth as an intermediate area of storage before used by serviceman using specified container. The degree of chemical release was found to be high as naphtha were kept beside worker in uncovered container. The degree of chemical absorbed


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was also high due to heavy work. As reported, there were cases of chemical splashes. Assessing exposures during normal operation or spillage, leaks or accidental entry into the body were considered.

3.2 Occupational Profile

Further statistical analysis based on questionnaires was carried out to compare the occupational exposure and other related factors between the exposed and unexposed groups. More than half of the exposed group (86.5%) worked in shift (Table 4) since the production line operated for 24 hours. There were 3 shifts which were scheduled by the management division. This working shift was significantly different between the exposed and unexposed groups (p < 0.001). It was also found a significant difference in terms of the type of work handling as well as the nature of work between both groups (p = 0.002 and p < 0.001 respectively). Respondents in both groups mainly performed their job activities manually; 58.8% for the exposed group while 41.2% for the unexposed group. However, in term of the nature of work, the percentage of doing moderate work was the highest (81.7%) among the exposed group. Meanwhile, the unexposed group performs mainly the light work (84.5%). From the 119 exposed group, 47.9% of them were exposed to naphtha for more than 4 hours during their work shift, while 52.1% were exposed for less than 4 hours along their daily working shift.

3.3 Individual Factors

Table 5 shows the factors related to the individual safety and health concern on the exposure to naphtha. Most of them (66.4%) were affected by the smell of chemical in their work environment. More than half gave the negative perception on their current health status (57.1%). A total of 57 (47.9%) respondents felt better outside the workplace. In addition, the perception of the exposed group was significantly different than the unexposed group (at least p = 0.004). Nevertheless, both groups had poor habit such

Table 4 Working condition of respondents.

Variable n Exposed group (N = 119)

Unexposed group (N = 72)

χ2 a

(df) p

Freq. (%) Freq. (%) Shift work Yes 96 83 (86.5) 13 (13.5) 47.95 < 0.001***No 95 36 (37.9) 59 (62.1) (1) Type of work handling Manual 148 87 (58.8) 61 (41.2) 9.90 0.002** Semi- automatic 37 32 (86.5) 5 (13.5) (1)

Nature of work

Light 58 9 (15.5) 49 (84.5) 83.61 < 0.001***Moderate 93 76 (81.7) 17 (18.3) (2) Heavy 37 34 (91.9) 3 (8.1)

a Chi-square test for independent; ** Significant at p < 0.01; *** Significant at p < 0.001.

Table 5 Perception on naphtha exposure in the workplace.

Variable n Exposed group (N=119)

Unexposed group (N=72)

χ2 a

(df) p

Freq. (%) Freq. (%) Smell of chemical Yes 96 79 (82.3) 17 (17.7) 34.36 < 0.001***

No 68 26 (38.2) 42 (61.8) (2) Not sure 27 14 (51.9) 13 (48.1) Worry about own health and safety Yes 86 68 (79.1) 18 (20.9) 26.64 < 0.001*** No 74 30 (40.5) 44 (59.5) (2) Not sure 26 19 (73.1) 7 (26.9) Feel better outside workplace Yes 73 57 (78.1) 16 (21.9) 11.05 0.004** No 39 20 (51.3) 19 (48.7) (2) No diff. 75 42 (56.0) 33 (44.0) Smoking habit Yes 110 71 (64.5) 39 (35.5) 0.12 0.725

No 71 44 (62.0) 27 (38.0) (1)

a Chi-square test for independent; ** Significant at p < 0.01; *** Significant at p < 0.001.

as smoking. Both groups had high percentage of smokers (exposed group = 59.7%; unexposed group = 54.2%) and the mean number of cigarette smoked daily showed no significant difference.

3.4 Environmental Air Monitoring

Environmental air monitoring using direct reading


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sampler was carried out in several work stations that involved naphtha application (Table 6). It was shown that this industry was exposed to volatile organic compound (VOC) since all work stations had environmental concentration of at least 4.00 ppm, with the median of 5.20 (IQR 8.25) ppm (Table 7). There were significant differences in VOC concentrations between the work stations (p < 0.001) (Table 8). The “repair” area had the highest VOC concentration while the “moulding” area had the lowest VOC.

Laboratory analysis of a bulk sample of liquid naphtha found a variety of the mixtures of organic solvents such as 2-methyl pentane, hexane, methyl cyclopentane, heptane, cyclohexane and toluene which were present in Table 9. In the contrary, only 3 organic solvents namely n-hexane, benzene and methyl benzene were cited in the Material Safety Data Sheet (Table 10). N-hexane represented the highest concentration (10.00-30.00%) as compared to others. Surprisingly, only xylene had been detected mainly in the making and moulding areas with the range of 2 to 5 ppm (Table 11).

3.5 Personal Air Sampling

Personal exposure assessment was carried out among the workers from each work stations. Respondents Table 6 Monitoring stations in tyre manufacturing industry.

Work unit Function/task

1. Making I Make the layers of plystock onto the wheel rim to maintain the shape of the tyre to form the uncured tyres.

2. Making II Make the layers of plystock onto the wheel rim to maintain the shape of the tyre to form the uncured tyres.

3. Plystock preparation (pocket)

Rolling of the uncured rubber onto a sheet of fabric to form a continuous sheet of rubber coated fabric and then these sheets are cut by the cutter into appropriate lengths and at the proper angle.

4. Repair Trim the finished tyres, to remove excess rubber and doing inspection of the finished tyres for defects and repairs.

5. Cover spray Spraying tyres with mold release agents to prevent them from sticking to the curing presses.

6. Moulding Tyres are cured or vulcanized in molds under heat and pressure to produce the final product.

Table 7 Volatile organic compound (VOC) concentrations at various locations in the tyre manufacturing industry.

Station name VOC concentrations (ppm)

(sample period = 15 minute/station) Minimum Maximum Mean (s.d)

Making I 2.40 31.80 9.27 (8.35) Making II 6.10 16.40 9.82 (3.03) Plystock preparation (pocket) 2.50 32.10 5.63 (7.47)

Repair 2.20 546.10 92.93 (153.63)Cover spray 3.00 18.30 8.55 (4.85) Moulding 1.10 4.00 2.43 (0.91)

Table 8 Comparing VOC concentrations between work stations in the tyre manufacturing industry.

Work station n Median (IQR) X2 statistic (df)a P valuea Making I 15 4.80 (9.10) 40.83 <0.001***Making II 15 9.10 (3.90) (5) Plystock preparation (pocket)

15 3.40 (1.50)

Repair 15 21.60 (125.00) Cover spray 15 6.70 (8.20) Moulding 15 2.25 (1.33)

a Kruskal-Wallis Test; *** Significant at p ≤ 0.001. Table 9 Screening of the organic solvents in the sample of liquid naphtha.

Organic solvents CAS No. 2-methyl pentane 0000107-83-5 Hexane 000110-54-3 Methyl cyclopentane 000096-37-7 Heptane 000142-82-5 Cyclohexane 000108-87-2 Toluene 000108-88-3

Table 10 Composition of naphtha.

Chemical name CAS Concentration (%)n-hexane 110-54-3 10.00 - 30.00 Benzene 71-43-2 ≤ 0.10 Ethylbenzene 100-41-4 ≥ 0.10 - ≤ 0.30

Source: MSDS, 2006. Table 11 Xylene concentrations in the tyre manufacturing industry. Station name Xylene (ppm) Making I 5 Making II 5 Plystock preparation (pocket) 2 Repair 0 Cover spray 0 Moulding 5


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from both exposed (production division) and unexposed (administrative division) groups were sub-sampled to determine the air naphtha concentrations within their breathing zone. The personal air naphtha concentration was determined among 35 workers from the exposed group and 11 workers from the unexposed group. Results showed that the personal air naphtha concentration of the exposed group was significantly higher than the unexposed group (z = -4.21; p < 0.001), with the median of 37.65 (IQR 36.35) and 0.34 (IQR 4.51) mg/m3 respectively.

4. Discussion

As far as naphtha is concerned as a chemical hazardous to health, and is used as the main raw material in this tyre manufacturing industry, a workplace assessment was carried out to identify the information in terms of its harmful effects, nature and degree of exposure. Naphtha is complex and varies in composition, some of the constituents are well characterized and have their own occupational exposure limits (OELs) while for others the information may be more limited [11]. Therefore, the results on qualitative assessment based on the information obtained from the MSDS and other sources were obtained from the chemical health risk assessment (CHRA) process. A CHRA was carried out in the making area since the highest quantity of naphtha was used for more than 7 hours daily. Workers were expected to be exposed to naphtha continuously throughout their work shift.

In general, the exposed group was exposed to naphtha as naphtha were used in their job tasks during mixing, making, repairing and finishing. However, the degree of exposure differed because they use naphtha in different quantities and frequencies as an adhesive, segregative as well as a cleaning agent. The more frequent or the long duration naphtha is used, the higher is the degree of exposure. The greater the amount of naphtha being absorbed into the body or in

contact with eyes/skin, the higher is the degree of exposure. At least 300 litre of naphtha was used monthly, with the highest concentration of 3000 litre used in the Making Area. Thus, most of the exposed group were recruited from this work area. Almost 50% of them were exposed to naphtha for more than 4 hours during their work shift since the production area is operated for 24 hours with 3 work shifts.

Besides that, the workers were also exposed to various chemicals since they usually apply naphtha together with other chemicals in their job tasks. For example, in the Cover Making area, a spray gun is used to manually spray a chemical namely Y150X onto the inside of the raw cover. Once completed, the masking tape at the joint areas were removed and oversprayed are wiped with naphtha. The raw covers were then left to dry before being transported to the moulding area. Therefore, the workers tend to expose to more than one chemical at a time. Studies found the effects of multiple chemical exposure to be additive, synergistic or potentiated [12].

Other factors such as occupational profile, lifestyle and individual perceptions on naphtha exposure are important to be studied as each individual have different degree of susceptibility towards contaminants or hazards. Personal characteristics and social circumstances can be responsible for sensitivity to, and recovery from, disease and illness [13]. Type of work tasks and nature of work influenced the exposure levels to the exposed workers. Most of their work tasks involved the moderate physical activities such as standing, working with machines or walking, with moderate lifting or pushing. The heavier the physical activities performed, the higher the breathing rate or air intake. Thus, more naphtha vapor was inhaled, and eventually will affect the body system including the neurobehavioral functions. The nature of hazard also depends on the particle size distribution and bioavailability; and effectiveness of personal protective devices which can influence the level of exposure towards the air contaminants [14]. Other than


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that, the severity of this effect can be influenced by individual habit such as smoking which will exacerbate the neurobehavioral function as cigarettes contain hydrocarbon substances. This study has included workers who smoke who were then matched with the unexposed group since majority are smokers.

Quantitative monitoring using photoionization detector (PID) instrument showed that workers were exposed to volatile organic compound (VOC) since all work stations detected significant VOC concentrations. The variation of exposure concentrations were caused by air currents, movements of pollutant from sources, and changes of vaporized solvent volume as suggested by Kumagai and Matsunaga [15]. The exposure concentration varied with time and high short-term exposure may occur during the work shift. It may cause adverse health effects even the 8-hr TWA value is lower than the OEL. According to Henderson [16], PID-equipped instruments are generally the best choice for measurement of VOC at exposure limit concentrations. However, the specific chemicals were not determined as they only provide a single aggregate reading for all of the detectable substances present at the time. This equipment is suitable to determine the short term exposure limit (STEL) at any time of working shift. The STEL which is defined as a 15-min time weighted average (TWA) exposure that should not be exceeded at any time during a work shift even if the 8-hr TWA is within the Threshold Limit Values (TLV) for particular chemicals, in order to protect workers from the acute health effects [14]. Therefore, the present study only referred to the TLV of petroleum distillates (naphtha) which made up of 2-methylpentane, hexane, methyl cyclopentane, heptane, cyclohexane, toluene, benzene, ethylbenzene, and xylene. Based on the TLV adopted from National Institute of Occupational Safety and Health [17], Occupational Safety and Health Act [18] and American Conference of Governmental Industrial Hygienist [14] standards, the overall VOCs concentration for all work areas found in this study were below these limits (Table

12), suggesting the air quality at the workplace is generally within the “safe” level.

Referring to the type of work processes, the “repair” area was found to be the most polluted area as compared to others such as making, plystock preparation, cover spray and moulding. The same scenario was found in a rubber conveyor belts industry whereby the extraction naphtha hydrocarbons used as glue solvent were predominant in all air samples collected on charcoal in the “repair” shop [4]. In repair area, naphtha is applied onto the defected surface of tyre with a very high temperature. Work process involving high temperature usually releases more vapour. The condition become worse when the work process involved the batch process which usually cause higher releases of vapour as compared to continuous process. In repair area, naphtha is applied using very high temperature but the process is not continuous. This area released more vapour with a wide range of concentration as compared to others even though the amount of naphtha used in other area is greater than repair area. The exposure also depended on the number of defective tyre, whereby with more defective tyres, the more naphtha used in the work area. Therefore, there was a wide range of VOC concentrations within 15 minutes of the sampling period, whereby the maximum VOC were above the standard values.

Results from bulk sample analysis, direct reading sampler as well as MSDS showed various solvent mixtures present in naphtha. Though benzene, ethylbenzene and xylene were not detected in the qualitative analysis of this study, the presence of these organic solvents in the working environment of this industry was reported in Ref. [19]. While those which were present qualitatively were not confirmed by quantitative study such as benzene and ethylbenzene were most probably found only in trace quantities. These substances were determined in very low concentrations below the limit of detection of the applied analytical methods. This also indicated that components of petroleum distillate for naphtha


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Table 12 Exposure limits for selected organic solvents.

Chemical name Exposure Limit

aNIOSH (REL)

bOSHA (PEL TWA) C/ST IDLH

Petroleum distillates (Naphtha) Synonym: Aliphatic petroleum naphtha Petroleum naphtha Rubber solvent

350 mg/m3 500 ppm c400 ppm c1590 mg/m3

aC 1800 mg/m3 1100 ppm

2-Methylpentane NA NA NA NA n-Hexane 50 ppm 500 ppm

c500 ppm d500 ppm

dST 1000 ppm 1100 ppm

Methyl cyclopentane NA NA NA NA n-Heptane 85 ppm 500 ppm

c400 ppm d400 ppm

aC 440 ppm dST 500 ppm 750 ppm

Cyclohexane 300 ppm 300 ppm c300 ppm d100 ppm

NA 1300 ppm

Toluene 100 ppm 200 ppm c50 ppm d20 ppm

aC 300 ppm 500 ppm

Benzene Ca 0.1 ppm

1 ppm c0.5 ppm d0.5 ppm

aST 1 ppm bST 5 ppm dST 2.5 ppm

Ca 500 ppm

Ethylbenzene 100 ppm 100 ppm c100 ppm d100 ppm

aST 125 ppm dST 125 ppm 800 ppm

Xylene 100 ppm 100 ppm c100 ppm d100 ppm

aST 150 ppm dST 150 ppm 900 ppm

aNIOSH, 1997; bOccupational Safety and Health Administration, U.S.A.; cOccupational Safety and Health Act (Use and standards of exposure of chemicals hazardous to health Regulations) Malaysia; dACGIH; C: a ceiling value should not be exceeded at any time; ST: short-term exposure limit; IDLH: Immediately dangerous to life and health concentrations; Ca: Potential occupational carcinogens.

compound are not constant and sometimes do not conform to its real components. It was believed that the composition of personal samples taken for occupational exposure evaluation would be even more uniform [10]. Therefore, personal air sampling was carried out in this present study to evaluate naphtha exposure within the breathing zone of workers.

For personal exposure, the personal air naphtha concentrations among the exposed group were significantly higher than the unexposed group. Although this air naphtha concentration was much lower than 350 mg/m3 of the Recommended Exposure Limit (REL) adopted from NIOSH, it does not mean the workplace is safe. There were evidences of significant health effects especially for the chronic

effects among workers exposed to lower level of solvents exposure in various industries. For example, in other tyre manufacturing industry, an early impairment of the respiratory system was detected among the workers who were exposed to naphtha below the Occupational Exposure Limit [20]. There was also an inverse relationship between air naphtha concentration and lung functions ability. Moreover, industrial workers primarily males aged 20 to 65 years old who are exposed occupationally to chemicals as part of their daily activities are among the group of chemically sensitive individual [21, 22]. Workplace that contaminated with chemicals such as adhesive, industrial air contaminants, pesticide in building fumigation, smoke, soldering fume, solvents, and


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vapours from paints may precipitate symptoms in the chemically sensitive individual. It has been suggested that most initiating symptoms are not from heavy exposures, but exposure background with low levels of chemical exposure is more likely to be associated with multiple chemical sensitivity as compared to high exposure background [23]. A review by Winder [22] concluded that toxicity at the low end of a dose-response relationship is improbable, but not impossible. Therefore, the health surveillance should be carried out for early detection.

5. Conclusion

Volatile organic compounds were detected in various work areas, however, they vary with specific types and the amount used as well as the type of work processes found at the particular work station. The repair area is the most contaminated area. The personal air monitoring clearly showed that exposure level to naphtha among the exposed group was significantly higher than the unexposed group. The ambient air quality of the industry excluding the “repair” area as well as the personal air naphtha among workers was considered safe as both exposure levels were below the Threshold Limit Values. Nevertheless, attention to the chronic adverse health effects of lower level of chemical exposure should be given for safe and healthy working environment.

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[3] MSDS (Material Safety Data Sheet), Shell Chemicals, Singapore, 2006.

[4] J.P. Gromiec, W. Wesolowski, S. Brzeźnicki, K. Wróblewska-Jakubowska, M. Kucharska, Occupational exposure to rubber vulcanization productsduring repair of rubber conveyor belts in a brown coal mine, J. Environ. Monit. 4 (2002) 1054-1059.

[5] DOSH (Department of Occupational Safety and Health),

CHRA Manual, 2nd ed, Ministry of Human Resources, Malaysia, 2000.

[6] RAE Systems Service Department, Operation and Maintenance Manual, RAE Systems Inc, California, 2001.

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