Research Open Dumping Site in Asian Developing Countries: A Potential Source of Polychlorinated Dibenzo-p-dioxins and Polychlorinated Dibenzofurans NGUYEN HUNG MINH,† TU BINH MINH,† MAFUMI WATANABE,† TATSUYA KUNISUE,† IN MONIRITH,† S H I N S U K E T A N A B E , * ,† S H I N I C H I S A K A I , ‡ ANNAMALAI SUBRAMANIAN,§ KARUPPIAN SASIKUMAR,§ PHAM HUNG VIET,| BUI CACH TUYEN,⊥ TOUCH S. TANA,# AND MARICAR S. PRUDENTEO Center for Marine Environmental Studies, Ehime University, Tarumi 3-5-7, Matsuyama 790-8566, Japan, Research Center for Material Cycles and Waste Management, National Institute for Environmental Studies, Tsukuba, Japan, Centre of Advanced Study in Marine Biology, Annamalai University, Parangipettai, India, Center for Environmental Technology and Sustainable Development, Hanoi National University, Hanoi, Vietnam, University of Agriculture and Forestry, Hochiminh City, Vietnam, Social and Cultural Observation Unit, Cabinet of the Council of Minister, Phnom Penh, Kingdom of Cambodia, and Science Education Department, De La Salle University, Manila, Philippines
Open landfill dumping areas for municipal wastes in Asian developing countries have recently received particular attention with regard to environmental pollution problems. Because of the uncontrolled burning of solid wastes, elevated contamination by various toxic chemicals including dioxins and related compounds in these dumping sites has been anticipated. In this study, concentrations of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and coplanar polychlorinated biphenyls (PCBs) were determined in soils from dumping sites in the Philippines, Cambodia, India, and Vietnam. Residue concentrations of PCDD/Fs and coplanar PCBs in dumping site soils were apparently greater than those in soils collected in agricultural or urban areas far from dumping sites, suggesting that dumping sites are potential sources of PCDD/Fs and related compounds. Observed PCDD/F concentrations in soils from dumping sites in the Philippines and Cambodia were comparable or higher than those reported for dioxin-contaminated locations in the world (e.g., near the municipal waste incinerators and open landfill dumping sites). Homologue profiles of PCDD/Fs in dumping * Corresponding author telephone/fax: +81-89-946-9904; e-mail:
[email protected]. † Ehime University. ‡ National Institute for Environmental Studies. § Annamalai University. | Hanoi National University. ⊥ University of Agriculture and Forestry. # Cabinet of the Council of Minister. O De La Salle University. 10.1021/es026078s CCC: $25.00 Published on Web 03/06/2003
2003 American Chemical Society
site soils from the Philippines and, to a lesser extent, from Cambodia and India reflected patterns of samples representing typical emissions, while profiles of agricultural or urban soils were similar to those of typical environmental sinks. This result suggests recent formation of PCDD/Fs in dumping site areas and that open dumping sites are a potential source of dioxins in Asian developing countries. Uncontrolled combustions of solid wastes by waste pickers, generation of methane gas, and low-temperature burning can be major factors for the formation of dioxins in dumping sites. Elevated fluxes of PCDD/Fs to soils in dumping sites were encountered in the Philippines, Cambodia, India, and Vietnam-Hanoi, and these levels were higher than those reported for other countries. Considerable loading rates of PCDD/Fs in the dumping sites of these countries were observed, ranging from 20 to 3900 mg/yr (0.12-35 mg TEQ/yr). PCDD/F concentrations in some soil samples from the Philippines, Cambodia, India, and Vietnam-Hanoi exceeded environmental guideline values, suggesting potential health effects on humans and wildlife living near these dumping sites. The estimated intakes of dioxins via soil ingestion and dermal exposure for children were higher than those for adults, suggesting greater risk of dioxin exposure for children in dumping sites. To our knowledge, this is the first comprehensive study on PCDD/Fs contamination in open dumping sites of Asian developing countries. On the basis of the result of this study, we have addressed a new environmental issue that open dumping sites are potential sources of PCDD/Fs and related compounds, and dioxin contamination in dumping sites may become a key environmental problem in developing countries.
Introduction Contamination by polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) is a growing concern because of the toxic effects on human health and wildlife. These compounds were unintentionally formed during various combustion processes and are impurities of chlorinated chemicals that were used in large quantities as herbicides and wood preservatives. Combustion is believed to be the major source of PCDD/Fs to the environment (1). Once emitted, PCDD/Fs undergo various processes such as dispersion and reaction in/through the atmosphere, deposition into the earth’s surface, and eventually accumulation in human and wildlife tissues (2, 3). In recent years, a number of extensive investigations have been conducted in some developed nations such as the United States, United Kingdom, and Japan to elucidate the transport behavior, global fate, and emission/deposition of PCDD/Fs using soils as a suitable sampling matrix (3-8). Research in the United States indicated that municipal waste incineration was a considerable source of PCDD/Fs to the atmosphere and that a global emission rate derived from municipal waste incineration was 1130 kg/yr (5). In the United Kingdom, Jones and co-workers measured PCDD/F concentrations in various environmental compartments and suggested that volatilization from soils was one of the major sources of dioxins to the atmosphere (3). VOL. 37, NO. 8, 2003 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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More details can be found at http://deevio.tripod.com/mixednuts/history.html.
2000 2000 2001 Perungudib Tay Mo Dong Thanh India (Chennai City) Vietnam (Hanoi) Vietnam (Hochiminh)
a
1999 1999/2000 Stoeung Meanchey
Philippines (Quezon City) Cambodia (Phnom Penh)
b
More details can be found at http://www.chennaicorporation.org/depart/Waste.htm. c na, not available.
1300 1360 4000 1 400 000 50 000 300 000 from 1985 till now from 1997 to 1999 from 1990 to 2001 5 1 3 13 9 8
remark
low-temp burning obsd low temp and burning by waste pickers obsd low-temp burning obsd uncontrolled burning obsd low-temp burning obsd 200 200 230 000 30 000 from 1993 till now from 1979 till now 4
3 15
nac
capacity (t/day) area (m2) working time (year) control sites dumping sites collected year site names country
no. of samples
Samples. Soil samples were collected in open dumping sites in Manila (Philippines), Phnom Penh (Cambodia), Chennai (India), and Hanoi and Hochiminh (two cities in Vietnam) during 1999-2001. Details of samples and characteristic of dumping sites are given in Table 1. The sampling map and other relevant information can be found in the Supporting Information. Those open dumping sites are located close to human habitat, and there are large numbers of people scavenging in these dump sites for collecting recycling wastes. In dumping sites in Cambodia, uncontrolled burning of solid wastes was observed. Some figures of open dumping sites in Cambodia and India can be found in the Supporting Information. Soil samples were collected at depths from 0 to 10 cm at five points with an area of approximately 25 m2 and combined together and considered as a representative sample. Urban or agricultural soils were also collected at some locations far from the dumping site areas (at least 30 km from dumping sites). Soil samples collected from these locations hereinafter are referred to as “control sites” relative to dumping sites. Soils were kept in clean plastic bags, maintained at 4 °C, transported to laboratory, and stored at -20 °C until chemical analysis. Chemical Analysis. Chemical analyses of PCDD/Fs and coplanar PCBs followed the method of the Environmental Agency of Japan with some modifications. Soil samples were dried and sieved using a 2-mm sieve before analysis. About 10-30 g of dry soil samples was extracted in a Soxhlet apparatus with toluene for 16-20 h. 13C12-labeled PCDD/Fs (2378-T4CDD/F, 12378-P5CDD/DF, 123678-H6CDD/F, 123789H6CD/F, 1234678-H7CDD/F, OCDD/F) and 13C12-labeled coplanar PCBs (CB-77, CB-81, CB-118, CB-126, CB-156, CB167, CB-169, and CB-189 for the respective coplanar PCBs; 13 C12-labeled CB-118 for CB-105, CB-114, and CB-123; and 13 C12-labeled CB-156 for CB-157) were spiked to the con-
TABLE 1. Information of Soil Samples and Dumping Sites in Asian Developing Countries
Materials and Methods
Payatasa
Despite the fact that PCDD/F contamination has been extensively studied in developed nations, very little is known about their behavior, fate, and ultimate sources in developing countries. In recent years, public media have voiced concern regarding the open dumping sites in Asian developing countries where large amounts of municipal solid wastes have been dumped. Unfortunately, in most of the developing countries in Southeast Asia, such open dump areas are located near human habitats; therefore, exposure to various toxic chemicals that originated from dumping sites are of serious concern because of the effects on human health, wildlife, and environmental quality (9). Uncontrolled burning of solid waste by waste pickers, generation of methane gas, lack of advanced waste incineration technology, and natural lowtemperature burning are major problems in dumping sites in Asian developing countries at present. These are favorable factors for the formation of dioxins and dibenzofurans. Because of these reasons, we anticipated elevated contamination by PCDD/Fs in dumping site environments in Asian developing countries. Our laboratory has conducted a comprehensive research to find an answer to the question of whether open dumping sites in Asian developing countries are potential sources of dioxins and related compounds. In this study, soil samples were collected in open dumping sites from the Philippines, Cambodia, India, and Vietnam, and concentrations of PCDDs and related compounds such as PCDFs and coplanar polychlorinated biphenyls (PCBs) were measured. Soils from agricultural and urban areas, located far from dumping sites, were also examined for PCDD/Fs to elucidate the differences in dioxin accumulation in dumping sites and agricultural areas and whether dumping sites are sources of PCDD/Fs. The annual loads of dioxins into dumping site areas were also estimated to give further insight into the fate of dioxins in tropical environment.
centrated extract as internal standards. For checking the extraction efficiency, we used repeated Soxhlet extraction procedure (2 times) for soil samples. PCDD/Fs in the second extracts remained at the residues less than 5% of the concentrations in samples the used the first extraction. The extract, after adding internal standards, was then applied to a multilayer silica gel column, and PCDD/Fs and PCBs were eluted with hexane. The hexane was concentrated and further passed through an activated carbon-impregnated silica gel column to separate mono-ortho coplanar PCBs and PCDD/ Fs and non-ortho coplanar PCBs. The first fraction eluted with 25% dichloromethane in hexane contained mono-ortho coplanar PCBs. The second fraction eluted with toluene contained PCDD/Fs and non-ortho coplanar PCBs. The first fraction was then further cleaned up by passing through an activated alumina column, and PCB congeners were eluted with hexane. 13C-labeled CB-105, CB-157, and CB-180 and 1234-T4CDD and 123789-H6CDD prepared in decane were added into the final solutions of first and second fractions, respectively. All fractions were microconcentrated and injected into a high-resolution gas chromatograph coupled with a high-resolution mass spectrometric detector (HRGCHRMSD) for quantification. Mono-ortho PCBs were quantified using a gas chromatograph (Agilent 6980N series, Wilmington, DE) with an autoinjection system and a benchtop double-focusing mass selective detector (JEOL, GC-Mate II, Tokyo, Japan) at a resolving power of >2000. The GC column used was DB-1 fused silica capillary (0.25 mm × 60 m; J&W Scientific Inc., Folsom, CA) having 0.25 µm film thickness with deactivated fused silica guard columns at both ends. The quantification of non-ortho coplanar PCBs and PCDD/Fs was performed using a GC (Agilent 6890N series) coupled with a highresolution mass selective detector (JEOL JMS-700D) at a resolving power of >10 000. A DB-5ms (0.25 mm × 60 m; J&W Scientific Inc.) fused silica capillary column was used for separation of non-ortho PCBs and hepta- and octa-CDD/ Fs; and a Chrompack CP-Sil 88 (0.25 mm × 60 m, 0.1 µm film thickness; Varian, Walnut Creek, CA) capillary column for tetra- to hexa-CDD/Fs. Equipment were operated at an EI energy of 38 eV, and the ion current was 600 µA. PCDD/F and coplanar congeners were monitored by selective ion monitoring mode at the two most intensive ions of the molecular ion cluster, except for P5CDD at ions of M+ and [M + 2]+. All the congeners were quantified using the isotope dilution method to the corresponding 13C12-labeled congeners if the isotope was within 15% of the theoretical ratio and the peak area was more than 5 times noise or procedural blank level. Detection limit for tetra- and penta-CDD/Fs was 1 pg/g dry wt; hexa- and hepta-CDDs was 2 pg/g; OCDD/F was 5 pg/g dry wt; and non-ortho coplanar PCBs was 1 pg/g dry wt. A procedural blank with every set of 6 samples was analyzed to check for interfering compounds and to correct samples values, if necessary. Recoveries for 13C12-labeled PCDD/Fs and coplanar PCBs, which were added prior to multilayer silica gel column, ranged within 60-120%. Variation of concentrations between duplicate analyses of soil samples was within 15% for congener concentrations with signal-to-noise (s/n) ratio >50 and was within 30% for those with s/n ratio of 5-50.
Results and Discussion Residue Levels. Average concentrations of PCDD/Fs in soils from dumping sites were the highest in the Philippines, followed by soils in Cambodia, India, Hanoi, and Hochiminh, Vietnam in that order (Table 2). A full database of concentrations of individual soil samples from all the surveyed Asian countries can be found in the Supporting Information. Elevated residues were found in soils from dumping sites in
the Philippines and Cambodia, ranging from 44 000 to 75 000 and from 330 to 200 000 pg/g dry wt, respectively. In particular, few soil samples in Cambodia had extremely high concentrations of PCDD/Fs (up to 200 000 pg/g dry wt). Soils from the dumping site in Hochiminh City, Vietnam, accumulated the lowest PCDD/F residues (ranging from 130 to 260 pg/g dry wt). Soils collected from agricultural or urban areas located far from dumping sites were considered as the control samples for corresponding dumping soils. Interestingly, the control levels of PCDD/Fs ranged from 33 to 370 pg/g dry wt, which was substantially lower than those in soils from dumping sites in most of the countries surveyed, except in Hochiminh (South Vietnam) (Table 2). The magnitude of contamination of dumping site soils was apparently greater than that in control sites, suggesting that open dumping sites are a potential source of dioxins and related compounds in Asian developing countries. The trend of contamination by non- and mono-ortho coplanar PCBs was somewhat similar to that of PCDD/Fs with the concentrations ranging from 900 to 42 000 pg/g dry wt in dumping sites and from 3 to 160 pg/g dry wt in control sites (Table 2). Their contribution to total TEQs was also different between dumping and control sites, which were 10-57% and 5-20%, respectively. In dumping sites, the highest coplanar PCBs concentration was found in the Philippines, and the lowest was in Hochiminh, Vietnam. However, their concentrations in the control group were the highest in Hochiminh followed by Hanoi (North Vietnam), India, and Cambodia (control site in the Philippines was not investigated). This result indicates considerable background contamination of coplanar PCBs in Vietnam. In general, elevated accumulation of PCDD/Fs and coplanar PCBs in landfill soils from the Philippines, Cambodia, and India is of concern and suggests that the formation of dioxins in these dumping site areas was significant in addition to the atmospheric deposition. Considering that there were no municipal waste incinerators located near such dumping sites (Table 1), uncontrolled burning of solid wastes by waste pickers and low-temperature burning with the formation of natural (methane) gas are probably the plausible explanations for the formation of dioxins in dumping sites. Observed PCDD/F residue levels in control sites from the Philippines, Cambodia, India, and Vietnam in this study were comparable or lower than levels reported for general soils from other countries, while soils collected in the dumping sites showed much higher levels (Table 3). To our knowledge, this is the first comprehensive data of PCDD/Fs and related compounds in dumping soils from Asian developing countries, which were comparable or greater than those in soils from dioxin-contaminated sites reported in developed nations. Our result, therefore, highlights the role of dumping sites as a significant source of PCDD/Fs. Residue levels of PCDD/Fs from the soils of dumping sites were also compared with those in soils from other locations around the world that were reported as dioxincontaminated sites (Table 3). In the present studies, sampling was conducted at the dumping sites (representing the sources) and control sites (representing background locations). The cited data from literature represent the concentrations in soils from the environments that are impacted from the municipal waste incinerator, open landfill dumping sites, and HCH manufacturing waste site (11-15). In such studies, soils were collected from the sources, from the control sites, and along gradients in the vicinity of the sources. Nevertheless, these levels also reflect the magnitude of contamination in the source allocations. We compared our data to those from these studies to understand the magnitude of dioxin contamination in dumping sites from Asian developing countries and to demonstrate the role of these dumping sites as significant sources of dioxins and dibenVOL. 37, NO. 8, 2003 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 2. Concentrations (pg/g dry wt) of PCDD/Fs and Coplanar PCBs in Soils from Dump Sites and Control Sites in Asian Developing Countries Philippines dumping site concn T4CDD P5CDD H6CDD Hp7CDD OCDD T4CDF P5CDF H6CDF Hp7CDF OCDF
6 300 6 700 11 000 5 800 12 000 8 600 4 900 3 300 1 800 500
total PCDD/Fs range non-ortho coplanar PCBs mono-ortho coplanar PCBs total coplanar PCBs range a
TEQsa 15 110 55 32 1.2 24 170 90 15 0.05
Cambodia dumping site concn 5 500 6 900 5 300 1 200 1 400 4 600 2 700 1 900 520 140
TEQs
concn 12 12 16 11 39 18 10 9.1 3.4 1.4
TEQs
concn 920 1 000 1 300 800 1 900 490 330 290 230 110
TEQs 1.8 12 7.3 4.2 0.19 1.3 11 7.9 1.4 0.01
control site concn 0.55 0.57 1.1 3.4 21 1.1 0.8 1 1.4 1.9
TEQs
dumping site concn
TEQs
concn 5 5.5 26 56 270 9.2 1 95% of the total TEQs) in most of the soil samples from dumping and control sites in the Asian countries surveyed (see data in Table 7 in Supporting Information for further details). The formations of coplanar PCBs have been hypothesized through three alternative processes including release from commercial PCBs mixtures, emission from combustions, and to a lesser extent, solar photolysis of higher chlorinated PCBs (19). In the United Kingdom, Alcock et al. (20) reported that TEQ input of coplanar PCBs from Aroclor formulations into environment was mainly contributed by PCB congeners CB77, -105, -118, -156, and to a lesser extent CB-126. Combustion source emissions were dominated by non-ortho PCBs, in which congener CB-126 predominantly contributed to total TEQs (19). Besides, it should be noted that CB-126 could be also formed during the domestic burning process (21). Our result suggests that uncontrolled burning of solid wastes in dumping sites in Asian developing countries could be a source of coplanar PCBs.
TABLE 4. Estimated Flux of PCDD/Fs to Soils in Dumping Sites from Asian Developing Countries in Comparison with Those to Soils from Other Countries in the World flux (ng m-2 yr-1) country
mean
range
references
Philippines 17 000 13 000-21 000 present study Cambodia 2 900 31-19 000 present study India 990 290-4 500 present study Vietnam-Hanoi 4 100 83-34 000 present study Vietnam-Hochiminh 67 3.8-160 present study Hong Kong 2 800 840-4 030 6 Australia 13 10-16 6 Lake Baikal. Russia 9 6 Thailand 2 6 Indiana, USA 1 280 1 260-1 290 6 Michigan, USA 80 52-110 6 British Columnbia, 64 4.2-350 6 Canada Yukon Territory, 6.6 1.2-15 6 Canada Brazil 2.2 6 United Kingdom 180 170-220 6 Spain 100 72-130 6 Germany 97 51-140 6 Norway 26 6
TABLE 5. Estimated Load of PCDD/Fs to Dumping Site Areas in Asian Developing Countries
FIGURE 2. Homologue profiles of PCDD/Fs in soils from agricultural and urban areas (control sites) in Asian developing countries in comparison to the profile of samples representing environmental sinks (urban soils). Vertical bars represent the percentage of each homologue to total PCDD/F concentrations. F and D refer to dibenzofurans and dibenzo-p-dioxins, respectively. Numbers Figures indicate the degree of chlorination. Data for environmental sink samples were cited from ref 18. Data for soils in Philippines were cited from ref 6. Flux and Load of PCDD/Fs to the Dumping Sites. Recently, Hites and co-workers (4-6) have demonstrated that soil is a useful environmental matrix to estimate the deposition of PCDD/Fs on a global scale. This is because soil can act as a passive collector of atmospheric deposition and is easy to collect worldwide. In addition, soils are excellent reservoirs of dioxins and related compounds as these chemicals are very persistent in soils with long biological half-lives, approximately 9-15 yr (4). In this study, we used the same approach that was reported by Hites and co-workers (4-6) to estimate the flux of PCDD/Fs to the soils and their load to the dumping site areas in Asian developing countries. Flux to soils can be calculated by the following equation:
F ) CM/(St)
(1)
where F is depositional flux to soils (ng m-2 yr-1); C is the concentration in soils, M is the mass of soils collected (g), S is the surface area of soil sample (m2), and t is the accumulation time of PCDD/Fs in the soil compartment (yr). For soils in open dumping sites, t values were calculated on
load
country
dumping site area (m2)
(mg/yr)
(mg TEQ/yr)
Philippines Cambodia India Vietnam-Hanoi Vietnam-Hochiminh
230 000 30 000 1 400 000 50 000 300 000
3900 87 1400 210 20
35 1.1 8.8 3.2 0.12
the basis of the time when dumping sites began to be used and the time when soil samples were collected (see Table 1 for further details). Accordingly, we set t values for soils in dumping sites in the Philippines; Cambodia; India; Hanoi, Vietnam; and Hochiminh, Vietnam, at 7, 21, 15, 3, and 11 yr, respectively. The loading rate (R) of PCDD/Fs to a dumping site (considered as the annual amount of PCDD/Fs received by surface area of the dumping site; mg TEQs/yr) can be calculated by multiplying flux value to surface area (A) of the dumping sites:
R ) FA
(2)
Estimated fluxes of PCDD/Fs to soils in dumping sites in the Philippines, Cambodia, India, and Vietnam in comparison with agricultural/urban soils from other countries are given in Table 5. It is interesting to note that fluxes to dumping site soils from the Philippines and Cambodia were greater than those from other locations in the world, including some contaminated sites in Hong Kong and Indiana, USA (Table 4). This result clearly supports the fact that dumping sites are potential sources of PCDD/Fs. Fluxes to control soils were apparently lower than those to dumping site soils. Considering the homologue pattern of soils from control sites, it can be suggested that soils from control sites were mainly originated from atmospheric depositions. Elevated fluxes observed in dumping sites in the present study could be attributed to uncontrolled combustion processes in a large open landfill area. The load of PCDD/Fs to the dumping sites, which were estimated using the equation as mentioned above, indicates VOL. 37, NO. 8, 2003 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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that dumping sites in the Philippines and India with a huge area of approximately 23 and 140 ha could receive the highest annual amount of 3900 and 1400 mg/yr PCDD/Fs (35 and 8.8 mg TEQs/yr), respectively (Table 5). The dumping site in Hochiminh, Vietnam, had the lowest loading rate due to the less contamination of PCDD/Fs in soils. As for comparison, total annual fluxes to the Kanto region in Japan, one of the most polluted areas in the world, were estimated and were found to range from 50 to 900 g TEQ with a total area of 32r t000 km2 (approximately 3 millions ha) (8). The area of dumping sites in India is 140 ha, which is 21 000 times smaller than that of the Kanto region; and this area was estimated to receive 8.8 mg TEQs/yr. These estimation data suggest that dumping sites in India and the Philippines may be a significant reservoir for PCDD/Fs. Possible impacts on human health and wildlife living near dumping sites are of great concern and deserve further comprehensive studies. Risk Assessment. The formation of PCDD/Fs in open dumping sites in Asian developing countries has raised a considerable public concern to human health for not only communities living near the dumping sites but also for people who live far away because PCDD/Fs may undergo atmospheric transport and deposit in such distant areas. For risk assessment of soils contaminated by dioxins and related compounds, the Agency for Toxic Substances and Disease Registry (ATSDR) proposed guidelines recommending that areas having soil concentrations within the range from 50 to 1000 pg TEQ/g should be evaluated for bioavailability, ingestion rates, community concerns, etc. and that soils with concentrations over 1000 pg TEQs/g should be considered for stronger actions such as health studies, exposure investigations, etc. (22). The Japanese Government recently issued new standards for dioxins in soil that established a level of 1000 pg TEQ/g for the maximum acceptable level, and those within 250-1000 pg TEQ/g must be kept under surveillance (23). Results of this study revealed that many soil samples in dumping sites contained TEQ concentrations exceeding 250 pg/g TEQs (Figure 3), suggesting the necessity of continuous monitoring. Particularly, some soils from Cambodia and Hanoi dumping sites contained TEQ concentrations beyond the level of 1000 pg/g, suggesting their potential for causing adverse health risk for humans and wildlife. It is clear that living in areas contaminated by PCDD/Fs will lead to exposure to those chemicals via either direct ways (such as inhalation, dermal absorption) or indirect ways (e.g., soil ingestion, consumption of food grown or raised in the areas, etc.). In the present research, we are able to assess two exposure pathways including soil ingestion and dermal exposure. The assessment was implemented for two categories: people in dump sites (exposed group) and people in control sites (control group) because of our observation during sampling surveys that there have been as much as hundreds of people daily scavenging in the duping sites (e.g., in the Philippines, Cambodia, and India) or even residing there (e.g., in the Philippines). Humans ingest a small amount of soil indirectly in food and other sources including inhalation particles. The ingestion rate may be twice as high for children (63 mg/day) as for adults (26 mg/day). On the other hand, humans can also be exposed directly to soil and dust particles in air via dermal absorption, which takes place on body skin (24). It should be noted that PCDD/Fs are highly lipophilic; therefore, consumption of possible contaminated foods may cause much higher dioxins intake than a portion of soil ingestion and dermal exposure. For such reason, our assessment may only demonstrate a part of the total intake of dioxins. Human intake of dioxins via soil ingestion was calculated based on the eq 3, and similarly, absorption by dermal exposure was estimated from eq 4, which was simplified from the original descriptions (24). The total intake via ingestion 1500
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FIGURE 3. Concentrations of PCDD/Fs (pg/g TEQs dry wt) in soils from dumping sites in Asian developing countries in comparison with various environmental guideline values. (1) 50 pg/g TEQs dry wt, recommended by ATSDR for bioavailability, ingestion rates, pathways, etc.; (2) 250 pg/g TEQs dry wt, recommended by Japanese Government for the continuous monitoring necessity; (3) 1000 pg/g TEQs dry wt, Japanese Standard and level proposed by ATSDR for stronger actions and research on exposure and health studies. See text for further details of guideline values. includes two factions, one is from ingestion of soil and the other is from ingestion of dust:
DUtotal ) DUsoil + DUdust ) (AID × IFsoil × Csoil)/ Wt + (AID × IFdust × Csoil)/Wt (3) where DUtotal, DUsoil, and DUdust (pg TEQ kg-1 day-1) are total ingestion of contaminant and fraction for soil and dust, respectively; AID (kg/day) is ingestion of soil particle amounts; IFsoil and IFdust are ingestion factor for soil and dust, respectively; Csoil is TEQs concentration in soil (pg/g dry wt). Total absorption via dermal exposure (DAtotal) similarly is the sum of absorption by soil (DAsoil) and absorption by dust (DAdust):
DAtotal ) DAsoil + DAdust ) (DAEout × EFout × Csoil)/ Wt + (DAEin × EFin × Csoil)/Wt (4) where DA is dermal absorption (pg TEQ kg-1 day-1); DAEout and DAEin are skin coverage with dust outside and inside; EFout and EFin are exposure factors for appropriate absorptions of outside and inside skin, respectively. Those factors represent for exposing time, ratio of soil/dust, etc. (24). See Appendix I and II in the Supporting Information for details of calculations. Human exposure to PCDD/Fs in soil is considered to be different for children and adults due to the differences in the ingestion rate as well as body weight of children and adults. Various parameters for estimating intake of dioxins through soil ingestion can be found in the Supporting Information, and estimated intakes of dioxins for children and adult are
in Asian developing countries, are indispensable. Temporal trends of contamination of PCDD/Fs and organochlorine insecticides also deserve comprehensive investigations.
TABLE 6. Estimated Intakes of PCDD/Fs for Children and Adults via Soil Ingestion and Dermal Exposurea soil ingestion country
dermal exposure
adult
child
adult
Dumping Sites Philippines 1.8162 0.1596 Cambodia 1.3279 0.1167 India 0.1730 0.0152 Vietnam-Hanoi 0.3406 0.0299 Vietnam-Hochiminh 0.0089 0.0008
0.3258 0.2382 0.0310 0.0611 0.0016
0.3790 0.2771 0.0361 0.0711 0.0019
0.00113 0.00012 0.00065 0.00073
0.00132 0.00014 0.00076 0.00085
Cambodia India Vietnam-Hanoi Vietnam-Hochiminh Wilrijk, Belgiumb
child
Control Sites 0.00633 0.00056 0.00067 0.00006 0.00365 0.00032 0.00406 0.00036
Waste Incinerators 0.06810 0.00787 0.01470 0.00730
a Intakes were estimated using formulars reported by Nouwen et al. (24), see text for further details. b Data were cited from Nouwen et al. (24).
given in Table 6. Intakes of dioxins were estimated to be the highest in people of the Philippines, followed by Cambodia, India, Hanoi (North Vietnam), and Hochiminh (South Vietnam). Intakes of PCDD/Fs for the exposed group were about 2-200-fold greater than those for the control and thus underline greater health risk threatening these people. Intake of dioxins via soil ingestion and dermal sorption contributed only a small portion to the total intake. If people consume foods (e.g., milk, meat, vegetables) produced in the vicinity of incinerators, dioxin intake via foods could account for more than 95% of the total intake (24). It is worth noting that Nouwen et al. (24) classified up to 5 scenarios in their study based on the different exposure patterns (food consumption, residence areas, etc.). Thus, exposure levels actually varied widely from this group to the others. Regardless of these differences, if considering the worst case and assuming that people in dumping sites have similar habits of food consumption, total dioxin intake was estimated to be in the range of 3-36 pg TEQ (kg of body wt)-1 day-1, which exceeds the WHO tolerable daily intake (TDI) value of 10 pg TEQ (kg of body wt)-1 day-1. Recently, the WHO intends to lower this TDI value to a range from 1 to 4 pg TEQ (kg of body wt)-1 day-1 (25). Similarly, The Japanese Government issued a new TDI of 4 pg TEQ (kg of body wt)-1 day-1 of dioxins for humans (23). These recommended TDI values would obviously increase concern over health risk of people living near dumping site areas. Further investigations should be focused on children and infant as they are the most susceptible group and have higher exposure levels to dioxins. Recommendations and Directions for Future Research. To our knowledge, this is the first comprehensive study on PCDD/Fs pollution in open dumping sites in Asian developing countries. Our result provides clear evidence that dumping sites in Asian developing countries are potential sources of PCDD/Fs and dioxin-like PCBs. On the basis of the results of this study, we have addressed a new environmental issue that open landfill dumping areas in developing countries may be a “hot spot” of pollution by toxic chemicals. Thus, dioxin contamination may become a key environmental problem in Asian developing countries in the 21st century. Possible toxic effects on human health and wildlife living near dumping areas should be studied in future, and this is a critical step for further considerations of the necessary control measures toward protecting environmental quality. Monitoring studies on exposure to other chemicals such as organochlorine insecticides, which were used in large quantities in the past and have been used until very recently
Acknowledgments The authors thank the staff of the Center for Environmental Technology and Sustainable Development, Hanoi National University, Hanoi; of the University and Agriculture and Forestry, Hochiminh City, Vietnam; and of the Centre of Advanced Study in Marine Biology, Annamalai University, India, for their valuable support during our sampling surveys. This study was supported by a Grant-in-Aid from the Scientific Research on Priority Areas (Project No. 13027101) of the Japanese Ministry of Education, Science, Sports, Culture and Technology and by the Scientific Research (Project No. 12308030) of Japan Society for the Promotion of Science. Financial assistance was also provided by “Formation and Behavior of Dioxins and their Related Persistent Organic Pollutants in Uncontrolled Combustion Processes” from the Waste Management Research Grants of the Ministry of the Environment; the Sumitomo Foundation; and the Core University Program between Japan Society for the Promotion of Science (JSPS) and National Center for Natural Science and Technology, Vietnam (NCST). The award of the JSPS Postdoctoral Fellowship for Researchers in Japan to T.B.M. (P00323) and M.W. (04166) is acknowledged.
Supporting Information Available Additional text, tables, and figures. This material is available free of charge via the Internet at http://pubs.acs.org.
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Received for review August 22, 2002. Revised manuscript received January 28, 2003. Accepted January 29, 2003. ES026078S
