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Mercury contamination and potential impacts frommunicipal waste incinerator on Samui Island, ThailandDudsadee Muenhor a , Jutamaad Satayavivad a b , Wongpun Limpaseni c , Preeda Parkpian a d

, R. D. Delaune e , R. P. Gambrell e & Aroon Jugsujinda ea Post-Graduate Education in Environmental Toxicology, Technology and Management, Inter-University Program between Chulabhorn Research Institute, Asian Institute of Technology,and Mahidol University, Thailandb Laboratory of Pharmacology, Chulabhorn Research Institute, Bangkok, Thailandc Department of Environmental Engineering, Faculty of Engineering, ChulalongkornUniversity, Bangkok, Thailandd Environmental Engineering and Management, Asian Institute of Technology, Pathumthani,Thailande Wetland Biogeochemistry, Department of Oceanography and Coastal Sciences, School ofCoast and Environment, Louisiana State University, Baton Rouge, Louisiana, USA

Available online: 30 Jan 2009

To cite this article: Dudsadee Muenhor, Jutamaad Satayavivad, Wongpun Limpaseni, Preeda Parkpian, R. D. Delaune, R. P.Gambrell & Aroon Jugsujinda (2009): Mercury contamination and potential impacts from municipal waste incinerator onSamui Island, Thailand, Journal of Environmental Science and Health, Part A: Toxic/Hazardous Substances and EnvironmentalEngineering, 44:4, 376-387

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Mercury contamination and potential impacts frommunicipal waste incinerator on Samui Island, Thailand

DUDSADEE MUENHOR1, JUTAMAAD SATAYAVIVAD1,2, WONGPUN LIMPASENI3,PREEDA PARKPIAN1,4, R.D. DELAUNE5 , R.P. GAMBRELL5 and AROON JUGSUJINDA5

1Post-Graduate Education in Environmental Toxicology, Technology and Management, Inter-University Program betweenChulabhorn Research Institute, Asian Institute of Technology, and Mahidol University, Thailand2Laboratory of Pharmacology, Chulabhorn Research Institute, Bangkok, Thailand3Department of Environmental Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok, Thailand4Environmental Engineering and Management, Asian Institute of Technology, Pathumthani, Thailand5Wetland Biogeochemistry, Department of Oceanography and Coastal Sciences, School of Coast and Environment, Louisiana StateUniversity, Baton Rouge, Louisiana, USA

In recent years, mercury (Hg) pollution generated by municipal waste incinerators (MWIs) has become the subject of serious publicconcern. On Samui Island, Thailand, a large-scale municipal waste incinerator has been in operation for over 7 years with a capacity of140 tons/day for meeting the growing demand for municipal waste disposal. This research assessed Hg contamination in environmentalmatrices adjacent to the waste incinerating plant. Total Hg concentrations were determined in municipal solid waste, soil and sedimentwithin a distance of 100 m to 5 km from the incinerator operation in both wet and dry seasons. Hg analyses conducted in municipalsolid waste showed low levels of Hg ranging between 0.15–0.56 mg/kg. The low level was due to the type of waste incinerator. Wastesuch as electrical appliances, motors and spare parts, rubber tires and hospital wastes are not allowed to feed into the plant. As aresult, low Hg levels were also found in fly and bottom ashes (0.1–0.4 mg/kg and ≤0.03 mg/kg, respectively). Stack concentrationof Hg were less than 0.4 µg/Nm3. Since Hg emissions were at low concentrations, Hg in soil from atmospheric fallout near thisincinerator including uptake by local weeds were very low ranging from non detectable to 399 µg/kg. However, low but elevatedlevels of Hg (76–275 µg/kg) were observed in surface soil and deeper layers (0–40 cm) in the predominant downwind direction ofincinerator over a distance of between 0.5–5 km. Soil Hg concentrations measured from a reference/background track opposite ofthe prevailing wind direction were lower ranging between 7–46 µg/kg. Nevertheless, the trend of Hg build up in soil was clearly seenin the wet season only, suggesting that wet deposition process is a major Hg pollution source. Hg concentrations in the sea bottomsediment collected next to the last station track was small with values between 35–67 µg/kg. Based upon the overall findings, in termsof current potential environmental risk, the environment has not yet been appreciably contaminated from Hg emissions producedby this incinerator. However the increase of Hg measured in downwind direction of the incinerator should be monitored for futurepotential risk.

Keywords: Municipal waste incinerator, Hg emission and impacts, Hg accumulation in soil, sea sediment and vegetation.

Introduction

A rapid increase in industrialization and urbanization inmany developing countries in south-east Asia such asCambodia, Indonesia, Vietnam and Thailand is contribut-ing to crucial air, water, soil and environmental pollu-tion. Some of those critical problems are caused by mu-

Address correspondence to Dudsadee Muenhor, EnvironmentalEngineering and Management, Asian Institute of Technology,Pathumthani 12120, Thailand; E-mail: dudsadeem@hotmail.com; dudsadeem@hotmail.co.ukReceived September 16, 2008.

nicipal solid waste management. To cope with the largeamount of solid waste generated in any big city, incin-eration is widely chosen as a technology option.[1] Thismethod lessens the volume as well as the weight by 90%and 70%, respectively.[2−4] Likewise, the use of incinera-tors minimizes land space limitations, especially in denselypopulated areas.[5,6] In addition, the incineration techniquehas been known to eliminate certain infectious constituentsand toxic compounds. However, heavy metals such as lead,cadmium and mercury are concentrated in fly and bottomashes before final disposal at landfill site.[7,8] With the energycosts rising, this solid waste management method is oftenpreferable and enables energy recovery through steam andelectricity production.[9,10]

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Mercury in municipal waste in Thailand 377

Similar to other countries in the region, in Thailand, anumber of incinerators have been proposed and some madeoperational nationwide, 50 of which have been located inurban areas.[11] The two large-scale MWIs are currently op-erating in Phuket and Samui Islands with a capacity of250 tons/day and 140 tons/day, respectively, in order tomeet the growing demand for municipal waste disposal.This raises concerns among environmentalists and the pub-lic over the role of MWI in solid waste management.

MWI emits a variety of toxic pollutants such as mercury,cadmium, dioxin, sulfur dioxide nitrogen dioxide and par-ticulate matter.[10,12] Among toxic pollutants emitted, bothmercury (Hg) and dioxin are of particular concern becausethey are very toxic at extremely low concentrations in theenvironment and can bioaccumulate.[13] The harmful prod-ucts of MWIs are present in bottom ash, fly ash, dust parti-cles, combustion and stack gases and residues from pollu-tion control devices.[10,14] Mercury released from MWIs isdifficult to control because it exists as a gas or small parti-cle at the combustion temperature which can pass throughmost particulate control equipment.[15] As a result, MWIsare a potential source of Hg to the environment.[13,16] Forexample in south Florida, municipal waste incineration wasthe largest Hg emission source and was the major source ofHg found in wet deposition.[17]

Approximately 25% of the world municipal waste pro-duction or about 360 tons/y of Hg in the eleven developedcountries is processed in waste incinerators.[18] If not appro-priately managed, Hg emissions from MWIs may adverselyaffect human health and the ecosystem.[10,19,20]

In recent years, Hg pollution generated by MWIs has be-come the subject of serious concern and public outcry.[21,22]

A large number of studies worldwide reported that the Hgemitted from incinerators results in an expansion of Hg con-tamination in the environment.[23,24] Furthermore, a grow-ing number of both health and environmental concernsassociated with Hg provides evidences that Hg pollutionproblem requires urgent attention.[25−27]

Moreover, Hg is a global pollutant as it has the potentialfor long range atmospheric transport and deposition andre-emission of the deposited Hg (a process known as “leap-frogging”)[28] from its emission sources to remote areas asfar as Arctic regions.[3,10,29,30] And Hg can bioaccumulateand biomagnify resulting in increasing its toxicity. Such pro-cess can result in detrimental effects to people, wildlife andthe environment.

In addition to impacts to humans, elevated Hg in theenvironment also poses a serious risk for fish and fishconsuming wildlife such as bald eagles, herons, osprey,kingfishers, minks and others.[13,31,32] Atmospheric Hgemitted by MWIs is deposited by way of wet and dry pro-cesses to forest and aquatic ecosystems. It then bioaccu-mulates and biomagnifies in the methyl Hg form in thefood chain.[33] Such process can result in detrimental ef-fects to people, wildlife and the environment. Birds andmammals that eat fish as well as predators that eat fish-

eating animals are at risk because they are more exposedto methyl Hg than any other animals in ecosystem. Somehighly exposed wildlife species are being harmed by methylHg.[13]

In Thailand and perhaps its neighboring countries, infor-mation on Hg contamination and environmental impactsderived from MWI is still limited since this technology hasonly been recently practiced. The objective of the presentstudy is to thoroughly investigate potential Hg pollutionfrom incinerator to the surrounding environment includ-ing soil, water, sediment and vegetation. Hg deposition andaccumulation in soil, sediment and ground cover was as-sessed near a MWI on Samui Island, Suraththani Province,Thailand.

Materials and methods

Study area

Based on earlier records and a recent field survey conductedin Samui Island, a municipal waste incinerator (MWI) isthe only major Hg pollution source for the island (Fig. 1).Therefore the study of Hg pollution around the municipalsolid waste incineration plant of the island is of great in-terest. If a significant portion of Hg in the waste has beenemitted to the atmosphere during the 7 years the plant hasbeen in operation, a certain amount of Hg would be de-posited at or near the site. Environmental samples werecollected around the incinerator and areas likely impactedby Hg emissions from the stack of the MWI.

The Samui incineration plant has a capacity of 140tons/day (70 tons/day × 2 units). Location of the plantand other facilities are presented in Figure 1. This inciner-ator has heat recovery units and one 59 m high stack. Theflue gas cleaning system is a bag filter for collecting dustand calcium hydroxide injection system to remove both hy-drochloric acid (HCl) and oxides of sulfur (SOx). There isno Hg control equipment installed on the system.

Sampling and sampling preparation

A series of samples including Hg sources (municipal solidwaste, fly ash, bottom ash leachate from the incinerator)and Hg deposits in soil, sediment and ground cover specieswere collected at the study site (Samui municipal waste in-cinerator). Samples were collected during the years 2005and 2006. Secondary data dating back to the year 2000, thedate the plant began operating, were also obtained from themunicipality. This information was used for earlier compo-sition of solid waste fed into the incinerator.

Municipal solid waste composition and Hg content

Municipal solid waste composition was characterized usinga standard method when the waste arrived before being

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Fig. 1. Plant site location map on Samui Island (Koh Samui), Thailand.

fed into the incinerator. For Hg content, the solid wastewas sampled at the same points as samples collected formunicipal solid waste for measuring its composition. Thesamples obtained were air-dried, crushed, and then storedin clean PVC bags and refrigerated (controlled at 2◦C) in adry box until Hg analysis.

Mercury content in precipitation, bottom ash, fly ashand leachate

Precipitation (rain water) was collected around severalbuildings near the Samui incinerator during the wet sea-son of 2005 (August to December). Whereas, bottom andfly ash including leachate were sampled from the outputsources at the Samui incinerator. All samples were kept inPVC vials in the refrigerator controlled at 2◦C until analysisfor Hg concentrations.

Mercury content in ground cover species

Local plant species covering the ground near the municipalwaste and fly ash landfill located at the study site were col-lected. Eight native plant species were identified and sam-ples (above ground as well as root portion) were collected.All plant samples were air-dried and ground to pass througha 100 mesh sieve and then stored in PVC bags in a dry boxuntil analysis.

Soil and sediment sampling

A total of 83 soil and sediment samples were collected forHg analysis from 8 stations during the wet season in August,2005 and from 5 stations during dry season in January, 2006.At each station, soil was manually sampled at three depthintervals (0–15, 15–25 and 25–40 cm). Sediment sampleswere collected from the surface (0–5 cm) of sea bottom at 4selected points using a pre-cleaned sediment core samplingdevice inserted into the bottom sediment.

Soil was sampled at thirteen stations (a wet season, 8stations, and dry season, 5 stations) within 100 m to 5 kmdownwind of the Samui incineration plant. The minimumdistance of 100 m from the plant was chosen to avoid sam-pling of soil polluted by direct breakage of Hg containingequipment.[34] Reference or background concentrations ofHg, including natural and anthropogenically elevated Hgin soils, were also estimated from 39 samples taken between100 m and 5 km at sampling stations which was opposite ofthe prevailing wind direction in both wet and dry seasons.The estimation of Hg background concentrations did notconsider differences in composition of soils in the samplingarea such as organic matter or clay content, which can ac-count for variation in Hg background values. The valuesobtained from this study are therefore, only a rough esti-mation of Hg background concentrations.[34] All soil andsediment samples were stored in PVC packages at 2◦C andlater air dried prior to performing Hg analysis.

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Mercury in municipal waste in Thailand 379

Mercury analysis and determination

All samples were acid digested by wet oxidation follow-ing U.S. EPA Method 3050 (HNO3 extraction in autoclavefor 30 minutes).[35] After digestion, the samples were di-luted with water and were analyzed for the total Hg con-centration by inductively coupled plasma-optical emissionspectroscopy (ICP-OES, OPTIMA 2100DV) with hydridegeneration system according to U.S. EPA Method 6010.[36]

Mercury concentrations determined for samples collectedat each station were interpreted by comparison the resultsobtained from samples collected from a non-Hg contami-nated track (reference/background track).

Results and discussion

Composition of municipal solid wastes

The composition of municipal solid waste (MSW) fromthe Samui municipality before feeding into the incineratorhas been thoroughly characterized by the institutions incharge of the facility. Results are presented together withthose of two other cities in Thailand; one from BangkokMetropolis and the other from Phuket Province (Table 1).The latter is quite similar in geographical and weather con-ditions to Samui Island with increased growth in tourismand services. Both locations now use incineration to dis-pose of solid waste due to limited available landfill spacefor disposing of waste.

Table 1. Composition of municipal solid waste (MSW) within(a) Bangkok Metropolis, (b) Phuket Municipality and (c) SamuiMunicipality of Thailand, 2003.

Composition (%)

(a) (b) (c)Items Bangkok[40] Phuket[37] Samui[37]

Combustible 94.52 88.58 82.90Food and organic

substances30.59 59.33 28.75

Plastic & foam 23.18 17.76 25.78Paper 13.41 8.07 13.08Wood & leaves 8.53 na* 6.42Cloth 8.10 1.66 4.76Leather & rubber 0.58 0.59 2.55Unclassifiable 10.13 0.99 1.56Non-Combustible 5.48 11.97 16.91Glass 2.55 4.56 6.63Metal & aluminum 1.33 1.73 6.16Stones & ceramics 0.68 na* na*Bones & shells 0.92 na* na*Other — 5.68 4.12

Total 100 100 100

∗ na = not available.

Table 2. Composition of MSW at Samui Incineration Plant,Suratthani Province, Thailand, August, 2005.

Items Composition (%)

Combustibles 72.84Food scraps 34.03Plastic and foam 9.85Paper 12.54Wood and leaves 8.66Cloth 5.97Leather and rubber 1.79Non-Combustibles

Glass, brick, shells, bones, stones,ceramics, and metal, etc.

27.16

Total 100

Note: Analysis was conducted in August, 2005.

The overall finding indicated that Samui’s MSW con-tained combustible substances similar to those of Bangkokand Phuket municipal waste. The main waste material werefood and organic wastes, followed by plastics, paper andwood and leaves etc. The site was slightly higher (17%)in non-combustible materials. Recent analysis of Samui’sMSW carried out in August, 2005 as part of this studyshowed still higher amounts of non-combustible materi-als (27%) (Table 2). This could imply that waste segrega-tion, from upstream to down stream including collection,transport and transfer till disposal is not being successfullyapplied in support of waste reuse-recycling program beingpromoted by municipalities of Thailand.

The non-combustible materials contained glass and met-als including cans and bottles which represented 12% ofthe total waste.[37] These indicate there is an opportunityto lower the amount of non-combustibles by means of re-source recovery before disposal (incineration).

Composition of the MSW from selected countries includ-ing Thailand is presented in Table 3. This analysis is usefulfor relating country income level, and living standard.[38,39]

It is known that wealth and the industrialization level ofthe country in addition to geographic and climatic factorsplay a role in type and amount of waste generated. Forexample, countries in Asia such as China, Indonesia andThailand have higher food and organic wastes than theUnited States and European countries. Paper is found inhigher amounts in the United States, Europe and Japan.This reflects that higher income countries with greater in-dustrialized and commercial development use more pre-processed and packed foods, resulting in a high fraction ofpackaging materials such as paper/cardboard and plasticsin MSW. This observation can also be used to some extent torelate economic growth and development in each country.

Trend of MSW composition in Thailand

Information concerning the composition of MSW is cru-cial for defining waste management measures. Among

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Table 3. Composition of municipal solid waste (MSW) in selected countries.

Composition

Countries Year Paper/cardboard Plastics Glass Metal Food/organic Textiles Other

France 1990 31 10 12 6 25 4 12Ireland 1992 34 15 5 4 24 3 15Switzerland 1990 31 15 8 6 30 3 7UK 1999 29 7 10 8 25 3 18United States 2001 36 11 6 8 23 7 9Japan 2003 40 20 10 6 17 — 7China 2006 9 13 2 1 65 — 10Indonesia 2003 13 11 1 1 65 — 9Thailand 2003 12 11 6 4 43 5 9

these are (i) assessing the factors that govern waste pro-duction, (ii) evaluating the adverse effects on the humanhealth and environment of specific compounds found inMSW, (iii) planning the MSW handling infrastructureand (iv) selecting the proper waste treatment and disposalstrategies.[41−43] Based on the above criteria with more fo-cus on points 2 and 4, here we describe trends in changingcomposition of MSW collected from the Samui incinera-tion plant, Suratthani Province and Bangkok MetropolitanAdministration (BMA), Thailand. The Surathani Provincerepresents a municipality influenced by rapid economicgrowth and development including hotels, resorts, supermarkets and restaurants. The services’ sector at this loca-tion is designed to accommodate moderate to high incometourists coming in from temperate regions. Whereas BMAwaste represents a centralized mega cities located in a trop-ical environment with slow progress in implementing wastereuse-recycling program. Figures 2 and 3 illustrate tempo-ral distribution in MSW composition at Samui incinerationplant and within BMA, respectively.

Similar to other mega cities in Thailand, BMA, foodwaste represented the largest composition of wastes gen-erated and will likely remain the case for the near future(Fig. 3). The average composition for this waste category

was between 30–35% by weight. Whereas plastics and foamranked second behind food wastes showing an increasingtrend with time. Yearly average values began to increasein 1998 (20%) increasing to 25% in 2004. This trend is pro-jected to increase due in part to urbanization and migrationof rural people to Bangkok seeking better job opportunity.Paper is ranked third in BMA waste with a slight decreasefrom 15% to 10% as of 2004. BMA still elects to use landfillfor waste disposal with 70% of total waste collected beingdisposed in landfills. Other waste disposal techniques forconsideration in the near future include composting and in-cineration. Currently BMA and few large hospitals (>500–1,000 beds) treat infectious and medical wastes by their ownincineration plants.

In recent years, composition of solid wastes at Samui mu-nicipality varied only slightly from month to month consist-ing primarily of large quantity of food, plastics, paper andincombustible materials (Fig. 2). This could be explained inpart by a rapid population growth resulting from increase intourism and service sectors. These are the two key factors re-sulting in plastics and food wastes including incombustiblesbeing generated at greater percentage over other categories.We hypothesized that plastics, paper and some unclassifiedmaterials are dominant waste sources incinerated at this

Fig. 2. Composition of MSW at Samui Incineration Plant, 2000–2005.

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Mercury in municipal waste in Thailand 381

Fig. 3. Composition of MSW within BKK Metropolis, 1993–2004.

island over the past 7 years. As a result, certain amount oftoxic compounds could be emitted to the environment. Dueto lack of information available on impact of emission tothe people and habitats within the area, a tracer study wasproposed to measure Hg deposited in soil and vegetation asan indicator of MSW incineration on Samui Island assum-ing there is no other significant sources for Hg emissionsexcept this incineration plant.

Mercury in municipal solid waste

There has been an increased interest in the presence of Hgin municipal solid waste (MSW). Research activities asso-ciated with the Hg component of MSW have been concen-trated in Europe and the United States. Table 4 summarizesimportant studies carried out between the year 1986–2007.The table provides a comparison of the results of this studywith other studies in which Hg concentrations in MSW have

Table 4. Summary of studies (1986–2007) on Hg content of MSW in selected countries.

Country Waste type mg/kg MSW Reference

Sweden MSW 0.5–3.0 [48]Germany MSW 5 [49]Switzerland MSW 0.83 ± 0.81a [50]Switzerland MSW 2(b) [50]Germany Domestic garbage 3–4 [51]Sweden Municipal refuse 1–5 [52]Germany Domestic refuse 4.1 [53]Germany & Switzerland Domestic refuse 2–5 [53]USA & Europe (1990) MSW 4 [18]USA (1990) MSW 3–4 [18]Europe MSW 0.5–9 [54]Sweden Household waste 5c [45]Sweden Household waste 1d [45]Germany MSW 0.3–14 [55]USA & Europe (2002) MSW 2 [18]Switzerland Household waste 4.2 ± 2.3 [56]Switzerland Mixed waste 2.9 ± 1.5 [56]Germany (2002) MSW 1.4 [57]China Food stuff 0.0005–0.48 [26]Western Europe MSW 2–7 [58]USA MSW 1–6 [59]USA Combustible fraction of MSW 0.66–1.9 (1.2) [60]Thailand (Samui incineration plant) MSW 0.15–0.56c This study, 2006

aWith battery collection system & determined by the analysis of incineration products.bWithout battery collection system & determined by the analysis of incineration products.cUntreated waste in an industrialized area.dWaste is sorted and batteries are extracted.

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382 Muenhor et al.

been obtained by analyzing the inputs or outputs from in-cinerators. The range of Hg constituents of MSW is widedue to the fact that the waste composition varies with lo-cation, period, place and country.[2,18] Hg concentrationsfound in MSW are dependent on the prevalence of Hg con-taining products in the waste and the type of collectingsystems used for Hg containing waste products.[41] Never-theless, the Hg content of MSW can be reduced to <1 mgkg−1 if the waste is sorted and batteries fluorescent lamps,thermometers and electrical switches etc., are extracted.[45]

Quite low levels of Hg (0.15–0.56 mg/kg) were reported inthe study because of MSW containing electrical appliances,motors and spare parts, rubber tires and hospital wastes arenot fed into the plant.[46] However still trace level of Hg arefound due to natural Hg impurities in high volume materi-als such as plastics, paper, glass/bottle coatings and paintresidues.[10,44,47]

Mercury emission from municipal waste incinerators

Stack concentrations of Hg from different countries includ-ing the Samui incineration plant, Thailand are summarizedin Table 5. Note should be made here that Hg concentra-tions from the stacks varied depending on waste source aswell as incinerator technology. For example, higher stackconcentrations of Hg are expected from traditional inciner-ators over advanced incinerators, providing that feed wastesare similar in composition and characteristics. When com-paring the amount of Hg released to the atmosphere fromthe stack at the Samui incineration plant with the others,the level of Hg is low, less than 1 ppb (0.4 µg/Nm3). Basedupon Hg concentration emitted, this suggests that contam-ination and risk to human and environment at the site arenot likely to occur. However adverse effects on the envi-ronment from cumulative deposits of low concentrations

Table 5. Stack concentrations of mercury.

Stack concentrationsCountry of Hg µg/Nm3 Reference

MWI, Samui,Thailand

< 0.4 [61]

MWI, Switzerlanda 140 ± 130 [56]MWI, Switzerlandb 160 ± 150 [56]MWIs Europe,

Canada & the USAc100 – 2,200 [16]

MWIs Europe,Canada & the USAd

30 – 200 [16]

MWI, China 33 [5]

MWIs, Taiwan 6 [19]

MWIs, Germany 7–11 [1]

aIncineration of household waste.bIncineration of mixed waste.cTraditional incinerators.dAdvanced incinerators.

of Hg on soil, sediment and local plant species around theincinerator may develop over time. Therefore environmen-tal samples were obtained for determining possible Hg ac-cumulation and perhaps contamination near the site overtime.

Mercury impacts from municipal waste incinerators

Concurrent with increased uses of municipal waste incin-erators (MWIs) for municipal solid waste destruction thereare more public concerns about potential human healthand ecological impacts.[8] Mercury emissions produced byMWIs can have adverse effects on both human health andthe environment.

Human health impacts

There are three potentially exposed populations from MSWincineration: (1) the incinerator workers, especially thosewho clean and maintain the Hg control devices; (2) the lo-cal population residing near the MWIs, which is exposedprincipally through any inhalation of airborne emissions,and (3) the larger regional population, located at remotearea from incinerators, but who consume food potentiallycontaminated by one or more incinerators and other com-bustion sources that emit Hg.[16,26,62,63]

Mercury emissions from MWIs can reach a target popu-lation via several pathways. They include direct inhalationof Hg polluted air, consumption of Hg contaminated food,ingestion of Hg contaminated soil and dust, dermal con-tact of Hg contaminated soil and dust, and maternal breastmilk consumption.[39,64,65] Nevertheless, the soil and dustdermal contact is often neglected due to its contribution tothe total exposure being very small.[64]

Individuals living near or working at MWIs can be ex-posed directly through the inhalation of Hg emissions.Those who live near MWIs can also be exposed indirectlythrough ingestion of locally produced foods or water pol-luted by Hg deposition to soil, plant and surface water. Pop-ulations living at some distance from MWIs are exposedthrough a different mix of environmental pathways. Atthese distances, Hg has sufficient time to go through severalphysicochemical transformations and can cycle into andout of soil, plant and surface water. At regional scales, Hgexposure through contact with water, food, soil and housedust appear to be the most important pathways.[8,10,65] Interms of human exposure to Hg, fish consumption is animportant exposure pathway for the general population,especially coastal populations and others that consume alarge amount of fish. The inhalation of air-borne Hg is an-other critical source for people working or residing in areaswith atmospheric exposure to Hg such as communities inthe vicinity of the MWIs and surrounding small-scale goldmining activities.[26,65,67]

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Mercury in municipal waste in Thailand 383

In this study, exposure of incineration workers and lo-cal population living near the Samui incinerator was notevaluated, however related exposure studies of workersat MWIs were evaluated. Results indicated that workersare the group of far higher risk for detrimental healtheffects than individual inhabitants in the surroundingcommunities. In the past, workers at incineration facil-ities have been exposed to high levels of dioxins andtoxic heavy metals, particularly, mercury, cadmium andlead.[10]

Mercury levels in selected environmental samples

Mercury concentrations in precipitation (rain water), bot-tom ash, fly ash and leachate extracted from different pub-lished reports including results from this study are presentedin Table 6.

Mercury in precipitation under natural conditions, as ex-pected, is quite low with levels in ng/L concentration range.Concentrations are higher in urban areas as compared torural or remote areas due mainly to sources of Hg emissionsfrom transportation, industry and utilities. Low Hg levelwas detected from rain water at the site (Samui incinerator)with the values between 9–12 ng/L. This would suggest verylow stack concentration of Hg (<0.4 µg/Nm3) togetherwith tropical monsoon environment reducing the risk de-rived from Hg deposited by rain. Mercury levels in bottomand fly ashes of Samui incinerator in this study were lowerwhen compared with other studies and also less than thatfor the Phuket incinerator reported by Labunska et al.[70]

Similar to other locations, ash from the Samui incinera-tor are considered as hazardous waste and are disposed in

Table 6. Mercury levels in various environmental samples.

Item Hg level References

PrecipitationSweden #1 1–50 ng/L [48]Sweden #2 1–30 ng/L [68]Remote oceanic 2–26 ng/L [69]Rural areas 1.3–90 ng/L [69]Urban areas 6–122 ng/L [69]Samui incinerator 9–12 ng/L This study, 2007

Bottom ashMWI residues <0.035 mg/kg [63]MWI residues 0.1–1.0 mg/kg [16]Phuket incinerator 0.2–1.2 mg/kg [70]Samui incinerator 0.03 mg/kg This study, 2007

Fly ashMWI ashes 59.1–65 mg/kg [60]MWI residues 0.03–0.29 mg/kg [60]Phuket incinerator 1–1.8 mg/kg [70]Samui incinerator 0.4 mg/kg [70]Samui incinerator 0.1 mg/kg This study, 2007

LeachateSamui incinerator 1.0 µg/L This study, 2007

Table 7. Mercury concentrations in collected ground coveringplants.

Plant species Hg concentration Samplingand plant part (µg/kg) location

Urochloa subquadriparaAboveground 51–54 A pile of solid

wastesRoot 161–265Mimosa pudico L.,

Aboveground nd A pile of solidwastesPod 95

Chloris barbata Sw.,Aboveground nd Fly ash landfillRoot 29

Eriochloa procera (Retz.)Aboveground nd Fly ash landfillRoot 233

Digitaria microbachne(Presl.)Aboveground nd Fly ash landfillRoot nd

Dactyloctenium aeguptium L.,Aboveground 191 Fly ash landfillRoot 399

Chloris barbata Sw.,Aboveground 181 Fly ash landfill

nd = Non Detectable (Detection Limit Range of ICP = 1–10 ppb).Method Detection Limits = 0.25 µg/L.

a landfill site to avoid the risk from other pollutants con-tained in the ash even though very low Hg levels were foundin the ash.

Mercury levels in plants

Mercury concentrations in plants collected from differentlocations around the waste stock pile and fly ash landfill sitein wet season of Samui incinerator are shown in Table 7.

The levels of Hg found in plants varied and were speciesdependent. Within the same species such as Chloris barbata,Hg uptake by the plant was found to be in proportion to thelevel in soil. The above ground portion of plant from fly ashlandfill sites contained a higher Hg level (181 µg/kg) thanfrom plants collected from a pile of solid wastes. Findingsfrom this study suggested that roots extracted Hg from soiland retained the Hg in root tissue resulting in the above-ground portion having less Hg in plant tissue as comparedto the root. This was clearly indicated by Dactylocteniumaeguptium L., of which the Hg level in root (399 µg/kg) wasalmost 2 times higher than found in aboveground portion(191 µg/kg).

In some Mimosa species, a leguminous weed, the plantstended to have trace level of Hg (95 µg/kg) in pods but werenot detectable in its aboveground part. Since there is littleHg mobilization within the plant, the Hg found in pods ofMimosa could be from dry deposition of dust containing

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Hg from either the soil or atmospheric fallout. Based onplant analysis only, it seemed that surface soil of the flyash landfill had slightly higher Hg contamination over asoil at solid waste pile. However, Hg uptake by the plantsmay not reflect total amount accumulated in soil since plantabsorbs only bioavailable fraction which is incomparable tototal content of Hg found in soil. Therefore soil analysis wasconducted to further confirm how much Hg was depositedin soil and for assessing risk associated with soil pollutionwith Hg.

Mercury levels in soil and sediment

The levels of Hg in soil and sediment collected during wetand dry seasons are presented in Figures 4 and 5, respec-tively. Elevated Hg in soil was measured downwind of site.This trend of Hg build up was clearly seen in the wet sea-son suggesting that wet deposition of emitted Hg, derivedfrom the incinerator plant, is a major pollution source.As expected, Hg was distributed a shorter distance fromits source in wet season (1–4 km) than in the dry season(>4 km). Whereas in those higher Hg level sites, concen-trations seemed to increase with an increasing soil depth.

This phenomenon suggested that bound Hg from surfacesoil (0–15 cm) mobilized downward perhaps together withorganic carbon moving into deeper layers of soil (15–25 cmand 25–40 cm). Wind direction and velocity together withheavy and wide spread rainfall predominated in wet sea-son. This is a key factor including quite high temperature(25◦–34◦C) governing atmospheric fallout of Hg onto theSamui Island. Based on this survey, a distance between 1 to4 km from the incinerator was observed as the distance inwhich Hg is deposited during the wet season. This evidencewas confirmed by elevated Hg accumulation in soil at thosesampling stations. Beyond this point (>4 km) the level ofHg in soil dropped off to near reference/background con-centrations.

Sediment samples from four points were also collectedin both wet and dry season (Figs. 4 and 5). Results indicatethat bottom sediment having very low levels of Hg withthe values between 36–61 µg/kg in wet season and non-detectable level in dry season, respectively. In terms of envi-ronmental risk, Hg source from the incinerator may not yetpose any significant danger to the environment includingsoil, sediment and ground covering plant species. Howeverwith a trend of Hg buildup and movement in deeper profile

Fig. 4. Mercury concentrations in soil and sediment, wet season.

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Mercury in municipal waste in Thailand 385

Fig. 5. Mercury concentrations in soil and sediment, dry season.

layers of soil including bioaccumulation by some weed plantspecies, a monitoring program for assessing Hg contamina-tion should be conducted every 3–5 years. This is becausesuch low concentrations of Hg in soil may contain fractionsthat become bioavailable for plant uptake, and making Hgtoxic to other species both within soil and above groundorganisms such as food crops, animals and human throughvarious exposure pathways.

Conclusions

Mercury is a contaminant of worldwide importancebecause it is toxic, persistent, can bioaccumulate and bio-magnify, and has the potential to undergo long-range at-mospheric transport and deposition. From the findingsreported in this study, low Hg levels were detected in all en-vironmental compartments evaluated including MSW, flyand bottom ashes, leachate, precipitation, soil, sedimentand vegetations in the vicinity of the Samui solid waste in-cineration plant. Based on Hg levels, this study revealedthat these environmental media have not yet been appre-ciably polluted by Hg emissions produced by the incinera-

tion. However, it is suggested a plan be implemented for thefuture monitoring of Hg contamination in the environmen-tal adjacent to the waste incinerator. The aforementionedcomplex environmental chemistry and toxicity of the Hgincluding long-term emissions generated by the waste in-cinerator over time may lead to future Hg contaminationin the environment and may result in detrimental effects onecosystems and human health.

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