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Qualitative assessment of raw sewage effluents andaccumulation of heavy metals in some vegetablesShagufta Naheed a , N. Ariz a & Shahjahan Beg ba Environmental Protection Agency‐Punjab , 2 ‐ Lake Road, Lahore ‐ 2, Pakistanb P.C.S.I.R. Laboratories , Lahore — 16, PakistanPublished online: 17 Dec 2008.

To cite this article: Shagufta Naheed , N. Ariz & Shahjahan Beg (1988) Qualitative assessment of raw sewageeffluents and accumulation of heavy metals in some vegetables, Environmental Technology Letters, 9:3, 251-259, DOI:10.1080/09593338809384563

To link to this article: http://dx.doi.org/10.1080/09593338809384563

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Environmental Technologv Letters, Vol. 9, pp. 251-259© Publications Division Selper Ltd., 1988

QUALITATIVE ASSESSMENT OF RAW SEWAGE EFFLUENTSAND ACCUMULATION OF HEAVY METALS IN SOME

VEGETABLES

SHAGUFTA NAHEED AND N. ARIZEnvironmental Protection Agency-Punjab, 2 - Lake Road, Lahore - 2, Pakistan.

SHAHJAHAN BEGP.C.S.I.R. Laboratories, Lahore — 16, Pakistan.

(Received 25 August 1987; in final form 22 December 1987)

ABSTRACT

Raw sewage effluent significantly affected the growth andtaste of consumable vegetables such as sugar beet, carrots, spinach.Cauliflower, coriander, lettuce, turnip and radish. In addition, avariety of heavy metals was also present in the waste water. Themagnitude of their accumulation in crops was found to be in the orderof Na> Ka> Fe> Cu> Cr> Pb> Ni. Crops irrigated with ground waterexhibited the least accumulation of these metals.

INTRODUCTION

Disposal of untreated municipal waste water is a growingproblem in the developing countries as a consequence of uncontrolledincreasing human population. In general, raw sewage effluents ofmunicipal origin, after a series of selected screening operastions,are disposed into lakes, streams and/or, ultimately, rivers. InPakistan, raw sewage effluents are frequently utilized for theirrigation of agricultural land as a cheap soil conditioner toescalate the productivity of crops.

The long-term irrigation with . raw sewage effluentssignificantly influences the properties of receiving soils, e.g.texture, porosity, organic matter, nutrients and microbialactivities. The minor and major elements in waste water, mayaccumulate and persist in soil and cause enhanced plant uptake (1—4),as a result of enzymatic imbalance in plant metabolism. It is welldocumented (5-10), that, As, Co, Mn, Hg, Cd, Pb and Zn areaccumulated in the tissues of potatos, carrots, cabbage, and lettuceplants grown in the soil receiving raw sewage effluents. High rate ofirrigation with untreated sewage resulted in the quantitativeincrease of some metallic ions in these vegetables irrespective ofthe magnitude of their accumulation in plant tissues. Some metalssuch as Mn, Fe, Al, Cr, As, Se, Pb and Hg, are relatively littledangerous for the production of crops or accumulation in plants

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because of their low solubility in neutral or slightly acidic soil,or their usually low concentrations in waste water, as in the case ofSe, Mo and lïg. On the other hand, metals such as Cd, Cu, Mo, Ni andZn can accumulate in plant tissues (7). However, the magnitude ofuptake of these metals varies considerably depending upon the natureof sewage, soil conditions and genetic make up of plants(8). Thecontrol measures to decrease the level of micro elements,preferentially heavy metals associated with sewage effluents,however, are essential for receiving soil to prevent phytotoxicity ordegradation of crop quality by virtue of these metals which are thusaccumulated in food chain with sometimes serious consequences (7).

The present paper describes attempts made to assess monthlyperiodicity of some metals in raw sewage effluents, frequently usedfor irrigation, and their magnitude- of accumulation in consumablevegetables.

MATERIALS AND METHODS

EXPERIMENTAL

In the field experiments, eight vegetables such as sugar beet,carrots, cauliflower, coriander, lettuce, spinach, turnip and radishwere cultivated in three plots - each covered 10 sq.m. area. Thetexture of the soil was sandy loam, primarily constituted of 13.3%clay, 18.2% silt and 68.5% sand. The soil was conventionallyirrigated with clean ground water from a tube well, before thecommencement of growth experiments.

I. Growth Conditions

The vegetables were grown in the following threeconditions

a) crops irrigated with pure raw sewageeffluents,

b) Sewage effluents diluted with ground water(1:1) was used for irrigation, and

c) crops irrigated with ground water.

II. Vegetable Cultivars

In each plot, 10 g, healthy seeds of vegetables purchasedfrom "Punjab Seed Corporation", were sown at equal distance (10 cm.)and just beneath (2 cm.) the top soil. The field capacity of each potwas maintained at 70 ± 5% by irrigating with sufficient quantity ofwater according to the category of growth condition. The seedlingbegan to appear after one week. Crop harvested after eight weeksexcept coriander which because of its rapid growth, was harvestedafter six weeks. The growth of vegetables were assessed visually, aswell as on the basis of dry weight. There was no rainfall experiencedduring the growth period.

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ANALYTICAL

i . Raw Sewage Effluent

Monthly sampling of waste water was conducted 50 cm.beneath the surface of running sewage drain near experimental plots.

Changes caused by the growth of microorganisms in sewage water wereminimized by keeping the samples in the dark at 5 ±_ 1°C in arefrigerator for no more than 48 hours prior to the determination oftheir physio-chemical characteristics. Parameters such as colour,odour, pH, conductivity, alkalinity, chloride, total solids,dissolvled solids, suspended solids, BOD, COD, setleable solids,oils/fats, sulphides, nitrates, total nitrogen and metallic ions,were determined according to the methods described in "StandardMethods for the Examination of Water and Waste Water" (11). An AtomicAbsorption Spectrophotometer (Perkin Elmer, model 280) equipped withas air-acetylene flame system, was employed for the quantitativedetermination of metals in the raw-sewage effluents.

II . Metals in Vegetables;

Edible portions (2 kg.) of harvested plants werehomogenised separately and dried in oven overnight at approximately103°C for the determination of dry weight. 1 g. oven dried andfinely ground material was placed in pre-weighed porcelain dish, andplaced in muffle furnace adjusted at 470-500°C for 24 hrs. toobtain ash content. The ash war; dissolved in 5 ml. of 20% v/v HC1.Warmed the solution for complete solublization of ash in acidsolution. Filtered the solution through acid washed filter paper toremove insoluble portions by washing with hot water while filtering.

Heavy metals were quantified according to the methodologyrecommended in Analytical Methods of Atomic Absorption Spectro-photometer", using Atomic Absorption Spectrophotometer (Perkin Elmer,model 280) equipped with air-acetylene flame system.

RESULTS AND DISCUSSION

Quality of Raw Sewage Effluents

The data presented in Table-1 show variations in physio-chemical characteristics of raw sewage effluents of Municipal origin,from January to December, 1984. This community waste water has beenfrequently utilized for irrigation of agricultural land in thesuburbs of Lahore for many years.

In general, the waste water was a greyish, had as offensiveodour like H2S, and a pH which was almost neutral, throughout theyear. The quantified values of total solids and dissolved solidsranged from 850-960 mg I"1, and 560-620 mg I"1 respectively. The

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computed values of biochemical oxygen demand (BOD5) are between150 and 200 mg 1 , thus indicating a medium strength waste water.Similarly, chemical Oxygen demand (COD) exhibited a slight variationand ranged between 410-500 mg 1~ , in 1984. Despite theseparameters, the concentrations of sulphate, nitrates, chlorides, the•hardness and the alkalinity did not show any significant change. Anenormous amount of proteinaceous matter, an essential component ofcommunity waste water, increased the total nitrogen level because ofmicrobial degradation processes. An apparent increase in oil and fatfound in the range of 65-81 mg 1~ ,in comparison with setleablesolids, that is 2-3 mg 1"1, throughout the year.

A variety of metallic ions in significant amounts are alsofound in raw-sewage effluents (12) as listed in table - 2. Acomparison of their concentration and monthly periodicity have alsobeen assessed in 1984. Major metals include Ca, Mg, Na and K. Amongthese metallic ions, Na maximised to 62.0 ppm in February whilst therest of these metals decreased in the sequence of Ca> Mg> K. Inaddition, concentrations of minor metals including heavy metals werealso found in excess and quantitatively decreased in the order of Fe>Cu> Cr> Zn> Pb> Ni. Furthermore, the higher computed values ofhazardous elements such as Cr and Pb in the waste water were 1.2 and2.0 ppm, in February and April, respectively.

TABLE 1. PHYSIOCHEHICAL ANALYSIS OF RAH SEHA6E.

Honths Colour(1984)

January Greyish

February 'NarchApril-HayJuneJulyAugust "September *October "Noveiber "Oeceiber '

Odour pH

Offen- 7.0siveH2S like

• 7.1

* 7.2" 7.0" 7.0" 7.1" 7.1" 7.0' 7.1" 7.2• 7.0" 7.0

Conduc-tivity

1050

11001000110010001100110010001080109011001100

TotalSolids

n e l " 1

900

960910950900952900850918890930925

Dissolved B0D5Solids

_]

560

600580610580600595600620550600590

*r210

220180200210210210200150160200200

COD

Vl475

500408464470490460450400410460460

SQ4—1

90

9010011090110120110106110100100

HOg

ngl

0.01

0.150.090.140.080.160.090.040.050.100.130.15

TotalAlkal-inity

332

345316344310340 .341310342344340342

CI

Œgl

73

7770777077767075767778

HardnessCaC03

-1 ,-1

231

242220240220242240220240240243244

TotalNitrogen

50

5452555058565555546060

Oiland

si"1

80

8179807581736580658081

SetleableSolids.

2.8

3.02.52.62.52.72.22.02.52.62.62.7

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TABLE 2.ELLLUENT

MONTHLY VARIATIONS IN MAJOR AND MINOR METALS IN RAW SEWAGE

Metals (ppm).

Months(1984)

JanuaryFebruaryMarchAprilMayJuneJulyAugustSeptemberOctoberNovemberDecember

Growth of

Ca

525550555055565057545655

Mg

181817181718181619171617

vegetables

Na

606255604858585256555658

K

1211131316151414151621616

Cu

1.41.61.31.41.21.41.51.21.21.21.41.5

Ni

0.050.080.060.090.050.070.100.050.040.040.030.04

Fe

5.06.05.05.55.04.54.34.15.04.56.05.9

Cr

1.01.31.01.20.91.01.20.90.81.01.21.2

Pb

0.30.30.42.00.52.00.100.070.050.050.080.08

Zn

1.01.21.11.10.90.50.40.30.090.10.30.1

Sewage-Sludge is generally recognised as a valuable resourcefor agriculture, supplying nutrients in the form of nitrogen,phosphorous and organic matter to improve the soil conditions forcrop growth (7). The data in Table - 3 present a visual assesmentregarding gorwth of some consumable vegetables i.e, sugar beet,carrot, cauliflower, coriander, lettuce, spinach, turnip and radishin different growth conditions.

TABLE - 3 VISUAL ASSESSMENT OF GROWTH OF VEGETABLES

Growth ConditionsVegetables Condition'A

Irrigationwith 100 %Sewage

Condition 'B'Irrigation with50% sewage & 50%ground water

Condition 'CIrrigationwith pureground water

Sugar beetCarrotsCauliflowerCorianderLettuceSpinachTurnipRadish

GoodAbundantExcellentExcessiveExcessiveAbundantGoodAbundant

AverageAverageGood

AverageAverage

Poor

It has been found that, the vegetables vigrously flourished incondition A, which might be attributed to the abundantly available

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nitrogen, phosphorous and sulphur incorporated with a variety ofminerals in untreated sewage effluent (13). On the other hand, incondition B, vegetables indicated average and good growth. The reasonmight be the dilution of concentrated nutrients, for the optimalrequirements of healthy crop. Dry weight of the vegetables is also anindication of growth (Table -5). Crops showed a considerableincrease in dry weight when irrigated with clean ground water -condition C. Maximum water retention in the tissues resulted incondition A, due to the bioavailability of enriched nitrogenousmatter to the crops. This oversupply may delay crop maturation byencouraging excessive vegetative growth, a constraint of enzymaticabnormalities in the metabolic system of plant cells (14-16). Theleast amount of available nutrients are transported in ground water,thus encouraging growth was not observed in condition-C. Similarobservation's were also recorded in the case of sweet corn (17).

Influence of Waste Wateron taste of Vegetables

There are many complaints regarding the taste of vegetables,harvested from agricultural land frequently irrigated with raw sewageeffluents, in the vicinity of Lahore City. A panel of ten persons,was deputed to evaluate the taste of the vegetables grown in thedifferent conditions, shown in table - 4. Generally, a bitter, wateryor slaty taste developed in radish, turnip, sugar beet, spinach,lettuce and cauliflower when grown in condition A - irrigated withraw sewage effluents, hence unacceptable to all the members of panel,

acceptability improved in condition B, and appreciablypleasent and sweet in condition C. The apparent change in

The tastechanged totaste may be attributed to metabolic alterations during growthprocesses. According to our findings, the taste acceptability isdirectgy proportional to the growth in the three conditions.

TABLE 4 - TASTE OF VEGETABLES GROWN IN DIFFERENT CONDITIONS.

Taste of Vegetables

VegetablesIrrigation with100 X raw sewage

Irrigation with50 X raw sewageand 50 % ground

Irrigation with100 X groundwater

Sugar beetCorrotsCaulifloweCorianderLettuceSpinachTurnipRadish

Slightly bitterNormalBitterNormalBiLterBitter waterBitterBitter water

PleasentNormalPleasentNormalSlightly bitter

SweetSweet pleasentPleasentNormalPleasentNormalPleasentSweet, Pleasent

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Accumulation of Heavymetals in Vegetables

The discharge of sewage effluents prior to physical, chemicaland/or biological treatments, are facets of water cycle which resultsin exposure of plants to micro-pollutants, particualrly heavy metals.The data presented in Table - 5 exhibit the quantitative variationsin accumulated heavy metals such as Cr,Pb,Cu, Ni, Na and K, in thetissues of sugar beet, carrot, cauliflower, coriander, lettuce,spinach, turnip and radish, as a result of different growthconditions. A substential amount of these metals accumulated invegetables grown in condition A - crops irrigated with raw sewageeffluents. Amongst these metals, the higher computed value of Na(70,000 ppm) was recorded in lettuce which slightly decreased inspinach (60,000 ppm) as compared to other metals, is also indicativeof greater intrinsic values of accumulation in plant tissues.Subsequently, an appreciable increase in K(50,000 ppm) was also foundin coriander. Lettuce, spinach and coriander are considered likely toaccumulate Fe at higher levels as compared to other crops, turnip atmoderate levels, and sugar beet, carrot, radish and cauliflower, atlow levels. Similarly, lettuce and coriander exhibited the uptake ofCu at higher values than other crops, in conditon A. In contrast, Crand Pb fall within a fairly narrow range, i.e. 40 ppm and 35 ppm,respectively. Despite these metallic ions. Ni persisted in leastquantity in spinach and lettuce, as compared with other metals, whenirrigated with raw sewage effluents.

TABLE 5 - HEAVY «ETALS IN VE6ETA8LES IM DIFFERENT GROWTHCONDITIONS.

Vegetables

Sugar Beet

Carrots

Cauliflower

Coriander

Lettuce

Spinach

Turnip

Radish

GrowthCondition

ABCA8CABCABCABCABCABCA8

. C

DryMeiqht Z

11.7212.215.06.78.410.359.211.212.11.6

11.512.17.57.58.16.066.59.06.18.89.95.095.135.59

Cr

20108221084020102010525106402010401210302010

Pb

178220123352010233122171030201020761096

Heavy MetalsFe

3302401602001301209080282800120060044504604003400020001250120010005001109692

(PPI)Cu

30201250352536121212050302301248066.0050.040.040.025.015.0504035

Ni

5.03.02.010.07.01.012.03.01.013.06.02.019.08.04.020.015.012.09.04.02.010711

Na

30,00024,00015,40018,00015,40013,20012,6006,4005,40036,00028,00010,00070,00060,00030,00060,00042,00030,00040,00030,00011,00030,00020,00010,000

K

22,00010,0008,00022,00016,00015,20024,0002,4002.200

50.00044,00020,00046,00036,00025,00032.00030,00028,00024,00022,00018,00022.00010.0001,800

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Comparatively, concentrations of these heavy metalsconsiderably dropped in growth conditions B and C, that is cropsirrigated with diluted raw sewage effluents and clean ground water,respectively. Sodium and potassium fall within a narrow range,whereas greater difference exist between Fe and other metals such asCr. Pb and Ni.

It is well established that waste water originating fromindustrialized urban areas contain elevated levels of potentiallytoxic elements (5,15). In general, nitrogen is a regulator in that itgoverns to a considerable degree the utilization of metallic ions,particularly Na and K(14). Paye (15) found the increased quantititesof trace metals such as AI, Cd, Cu.Fe.Cr, Mn, Ni, Pb and Zn persistedin the roots of corn (Zea mays L.), as compared with edible portions.On the other hand, the studies of Kloke (21) reveal that thereproductive organs of a plant contain lesser amount of heavy metals.Leaves, straw, stems and other similar organs, however, obviouslycontain higher amounts compared to the amounts in the reproductiveorgans. The concentration of metals in carrot and radish is normallylower than those of leaves. It has also been investigated (9-23)that, As,Co, Mn, Hg, Cd, Pb and Zn persist in greater quantity, inthe tissues of potatos, carrots, cabbage and particularly in lettuceas a result of sewage irrigation.

In conclusion, the comparison provides additional informationthat, accumulation of heavy metals in crops as a result of irrigationwith raw sewage effluent, is in the order Na> K> Fe> Cu> Cr> Pb> Ni.The persistance of such metals, eventually decreases when crops areirrigated with diluted sewage effluent or clean ground water. Thetaste acceptability also corresponds to the quality and quantity ofheavy metals persisted in the tissues of consumable vegetables.Thus, the salty taste of vegetables indicated the accumulation of Naand K in greater amount, grown in condition A. This might beattributed to the increasing metal concentrations in receiving soil(6,11,13-16). Comparatively, a moderate level of heavy metals foundin vegetables when irrigated with diluted raw sewage effluent and thetaste of vegetables was slightly bitter or pleasent. In addition, thehigher the heavy metals in soil, the higher is the amount of thesehazardous elements in plants.Evidently (24,25), with respect toseveral elements crop genetics factors are more improtant than soiland environment. Tissue analysis gives insight into the status ofplants relative to the onset of toxicity as well as indicating thepotential transfer of metallic ions into food chain. Therefore, whensewage effluent is applied to agriculural land to improve the cropproductivity, it is essential to limit the input of heavy metals intothe receiving soil within the safe limit(25,27,29).

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