Due to rapid advances and improvements in equipment features and capabilities, the lifespan of most electronic devices continues to decline rapidly 1. When these electronic devices reach the end of their service life, they are discarded and considered as electronic waste (e-waste). Every year, 20 to 50 million tons of e-waste are generated worldwide, from which a large quantity of toxic chemicals can be released during e-waste disposal, posing potentially harmful effects to the environment (http://www.grid.unep.ch/product/publication/download/ew_ewaste.en.pdf) 1. Clearly, assessment of the occurrence and potential impact of e-waste–derived toxics has become increasingly critical. It is not only essential for responsible assessment of ecosystem integrity and human health, but it is the cornerstone of the responsible pursuit of continued global economic and societal development. After all, the e-waste problem is not just a problem for China per se, but it is representative of a global issue.
China, as the world's largest importer and recycler of e-waste, has been faced with mounting e-waste problems in recent years 2. There are at least two reasons for this e-waste deluge. The first is the accelerating domestic demand within China for electronic equipment and devices. A good example is the increasing use of personal computers in China, due to its rapid development as a world leader in global technology and business. Largely due to this increased demand for computers, China has generated roughly 1.1 million metric tons of e-waste annually since 2003 (http://www.worldwatch.org/node/3921). Greenpeace estimates that there will be 178 million new computer users in China by 2010 (http://www.greenpeace.org/china/en/campaigns/toxics/e-waste/the-e-waste-problem). The second reason for China's alarming e-waste situation is the tremendous amounts of e-waste that have been illegally imported into China, greatly exacerbating the e-waste problem. Although China has made great strides in its efforts to mitigate environmental impacts caused by e-waste disposal, e-waste–derived pollution in China has persisted, and is likely to increase if existing e-waste management efforts continue to fail.
We recently identified enhanced law enforcement and global collaboration as the key factors to counteract and solve the e-waste problem in China 3. However, to quantify the magnitude of the e-waste problem, which was not done in the previous assessments 1, 3, accurate and updated information concerning e-waste–derived chemicals is needed. Previous reviews 4–6 and reports (http://www.greenpeace.org/international/news/e-waste-toxic-not-in-our-backyard210208, http://www.ban.org/E-waste/technotrashfinalcomp.pdf) have mainly focused on e-waste management practices, while environmental and human exposure to e-waste–derived chemicals has not been adequately addressed. In the last few years, a large number of studies conducted in China have investigated the environmental occurrence of persistent halogenated compounds (PHCs), including polybrominated diphenyl ethers (PBDEs) 7–9, polychlorinated biphenyls (PCBs) 7, 8, 10, polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) 10–13, polybrominated biphenyls (PBBs) 7, 8, tetrabromobisphenol A (TBBPA) 14, polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs) 10, and chlorinated polycyclic aromatic hydrocarbons (ClPAHs) 14, originating from e-waste, and thus providing sufficient data for an adequate assessment of the e-waste issue. However, to our knowledge, no review of organic contamination originating from e-waste handling in China has been conducted so far. Therefore, this review will summarize the occurrence of PHCs in various environmental media near e-waste sites in China and compare them to reference locations. Human exposure to e-waste–derived chemicals will be assessed simultaneously.
STRATEGY OF THIS REVIEW
The main purpose of e-waste recycling is to recover valuable metals, such as copper, aluminum, and gold 4, hence metal pollution from e-waste in China has been addressed extensively elsewhere in the literature 5, 15–21. A much more underaddressed issue is the environmental and human exposure to PHCs released during e-waste handling.
In the course of primitive e-waste dismantling, which is typically the case in China, various toxic organic chemicals are being released into surrounding environmental media 5, 14, 22, 23. Particularly worthy of future attention are brominated polycyclic aromatic hydrocarbons (BrPAHs), which are known to form during incineration 24–26 (one of the unsafe e-waste recycling operations). In this review, PBDEs, PBBs, PCBs, PCDD/Fs, PBDD/Fs, and ClPAHs are the main target contaminants for examination. The present review will chiefly compare the environmental levels of PHCs between exposed and control sites from the same surveys. We also attempt, where possible, to compare the conclusions drawn by the various authors cited in this review.
However, e-waste is not the only source of PHCs in the environment. For example, PCDD/Fs can be released from various sources other than e-waste handling 27–30. In addition, only 3% of the global production of flame retardants is used in electronic apparatus 31. Consequently, only small portions of PBDEs, PBBs, and TBBPAs, the major constituents of brominated flame retardants (BFRs), found in the environment are derived from e-waste. Other PHCs such as ClPAHs can also be emitted from incineration of municipal solid wastes and certain industrial processes 14, 32. Unfortunately, there is no effective method to clearly differentiate PHCs derived from e-waste versus other origins, which is one of the major challenges in the current review. In this context, data on PHCs not explicitly involving e-waste disposal activities are not included for assessment. Data acquired from various environmental media near several major e-waste processing and control sites in China are summarized, their impact on human exposure is assessed, and possible health risks will be identified. Furthermore, the amounts of PBDEs, PBBs, TBBPA, PCDD/Fs, ClPAHs, and polybrominated phenols (PBPs) accumulated in the environment of China due to e-waste handling activities are estimated, rather than measured. It should be noted that the amounts of PCDD/Fs and ClPAHs are possibly underestimated because they are mainly formed from the disposal processes, but not embedded in e-waste 14, 32. Finally, human exposure to e-waste–derived PHCs and associated health risk are reviewed.
DISPOSAL OF E-WASTE IN CHINA
Guangdong Province of South China is the main recipient of e-waste, which is distributed to e-waste dismantling sites in other provinces or municipalities such as Hunan, Zhejiang, Shanghai, Tianjin, Fujian, and Shandong (Fig. 1). Guiyu in Guangdong Province has been a focal point of international attention because it houses one of the world's largest e-waste dismantling and recycling facilities. In addition, Longtang and Dali in Guangdong Province, Taizhou in Zhejiang Province, and Huanghua in Hebei Province also host large-scale e-waste processing facilities typically employing hundreds of workers (Fig. 1). Additionally, e-waste processing centers of varying sizes and scales are operational in Hunan Province and Jiangxi Province (Fig. 1) 1, 3, but a large number of illegal dismantling sites throughout China still remain unknown to media, citizens, and officials.
E-waste recycling operations in China are mostly crude and unsafe. Typical recycling techniques include toner sweeping, open burning, cathode-ray tube cracking and dumping, circuit board recycling, acid stripping of chips, plastic chipping, and melting and direct dumping of waste residues 5, 33.
It should be addressed that unsafe recycling procedures not only result in serious contamination of surrounding areas, but also impacts further regions via various transfer pathways such as riverine runoff, air and dust transport, or exportation of contaminated fish 34, 35.
Indoor air will not be assessed in the current review, because the presence of PHCs is not solely due to e-waste dismantling processes. The levels of PHCs in ambient air of e-waste recycling sites are the best parameters to assess impacts of e-waste on the surrounding environment. Recently, researchers have reported a limited number of PBDE measurements in air from e-waste dismantling regions. In 2009, Chen et al. 36 were the first to report the diurnal variability of PBDEs in the atmosphere. The average concentrations of 11 BDE congeners (Supplemental Data, List S1) were 11.7 ng/m3 in daytime and 4.83 ng/m3 at night in Guiyu, while the concentrations were lower at the reference site with 0.38 ng/m3 in daytime and 0.24 ng/m3 at night. Two years earlier, the atmospheric concentration of PBDEs (Supplemental Data, List S2) in Guiyu (21.5 ng/m3) was approximately 140 times higher compared to Hong Kong (0.15 ng/m3) (Fig. 1), and approximately 70 times that of Guangzhou (0.29 ng/m3) (Table 1 and Fig. 1) 37. Li et al. 38 also observed higher levels of PBDEs (Supplemental Data, List S3), PCDD/Fs (Supplemental Data, List S4), and PCBs (Supplemental Data, List S5) in ambient air around e-waste recycling sites of Taizhou compared to other urban sites (Table 1). The atmospheric concentrations of PCDD/Fs (Supplemental Data, List S4) in Guiyu were 64.9 to 2,365 pg/m3 (Table 1), the highest values documented so far worldwide 10. High levels of PBDD/Fs (Supplemental Data, List S6) were also found in the same survey (Table 1) 10. The results obtained by Li et al. 38 suggested that the high levels of PBDD/Fs in Guiyu air were indicative of the impact of e-waste recycling activities in the region. In addition, the high levels of atmospheric dioxins in Guiyu also impacted the adjacent areas of Guiyu, such as Chendian, where the levels of atmospheric PCDD/Fs (Supplemental Data, List S4, Table 1) and PBDD/Fs (Supplemental Data, List S6, Table 1) were at the high end of the range commonly found in urban areas around the world 10. In Taizhou, the average concentration of PCDD/Fs (Supplemental Data, List S4) in the air around e-waste facilities was 14.3 ng/m338, not as high as that in Guiyu, but still strongly indicative of impacts on air quality by e-waste (Table 1). All these surveys have clearly shown that ambient air in e-waste dismantling sites has been severely contaminated by PHCs.
Table 1. Concentrations of total suspended particles (TSP), polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), and polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs) in ambient air samples collected from e-waste recycling and reference sites in China
Tree bark can be regarded as a good passive air sampler for PHCs due to its high lipid content and large surface area 39. Polychlorinated dibenzo-p-dioxins and dibenzofurans (Supplemental Data, List S4), PBDEs (Supplemental Data, List S7), and PCBs (Supplemental Data, List S8) were detected in tree bark from Luqiao in Taizhou (Fig. 1), an e-waste recycling area, with the mean concentrations of 0.1, 1.4, and 6.5 µg/g lipid weight, respectively. Among all target analytes, 2,3,4,7,8-PeCDF and PCB-126 were the main contributors to toxic equivalencies (TEQs), accounting for 36 and 81% of the TEQs of PCDD/Fs and PCBs, respectively. The high levels of PCDD/Fs, PBDEs, and PCBs in tree bark indicate the impact of e-waste dismantling activities on the local environment, which is also confirmed by the homolog and congener profiles of these organic contaminants 40.
Numerous publications have discussed the occurrence of PBDEs and PCDD/Fs in Chinese soil, but only a few reports have focused on soil impacted by e-waste recycling. Leung et al. 41 examined the spatial distribution of PBDEs (Supplemental Data, List S9) and PCDD/Fs (Supplemental Data, List S4) in five types of soil in Guiyu, with the total PBDE concentrations (normalized to dry sample wt) in decreasing order: acid leaching (2,720–4,250 ng/g) > printer roller dump site (893–2,890 ng/g) > duck pond (263–604 ng/g) > rice field (34.7–70.9 ng/g) > reservoir (control site) (2.0–6.2 ng/g). Since printer circuit boards contain PBDEs, it is possible that PBDEs were stripped off printer circuit boards in acid baths during the acid leaching process and then disposed into the adjacent soil. It is notable that the levels of PBDEs are significantly higher in combusted residues (33,000–97,400 ng/g dry wt) than in acid leaching site soil (2,720–4,250 ng/g dry wt) 41. This indicates the potential impact of combusted residues on the ambient environmental media.
Fengjiang (Fig. 1), an e-waste recycling site in Taizhou, eastern China, houses one of the largest e-waste recycling facilities in China and has a nearly 30-year history of processing e-waste. A previous study 32 measured PCDD/Fs (Supplemental Data, List S4) in surface soil collected in the vicinity of Fengjiang (Fig. 1), at the Wenling reference site (Fig. 1), as well as from cultivated surface soils from several other provinces in China. Levels of PCDD/Fs (Supplemental Data, List S4) in soil from the e-waste recycling site (854–10,200 pg/g) were significantly higher than those in both the reference sites (72.8–456 pg/g) and the cultivated soils (3.44–33.8 pg/g) from the various other regions in China (Table 2). Similar results were also obtained in Guiyu, as the levels of PCDDs/Fs (Supplemental Data, List S4) decreased in the following order: from e-waste recycling sites including acid leaching, duck pond, rice field, and printer roller dump sites to the reference site (a reservoir) 41. Combustion of e-waste contributes far more significantly than other disposal methods to the levels of PCDD/Fs in the ambient environment 41. Therefore, the elevated levels of PCDD/Fs at the acid leaching site suggested the proximity of the possible combustion sources. High PCDD/Fs levels at the duck pond and the rice field (where no open burning has occurred in nearby areas) might be due to atmospheric transport and deposition of the pollutants from nearby incineration of e-waste 41. In summary, crude e-waste processing methods such as acid leaching and open burning are the major contributors of PBDEs and PCDD/Fs to the terrestrial environment in China 41. The lower concentrations of PCDD/Fs in the reference site and cultivated soil indicate that PCDD/Fs can spread from where they are generated, to other areas via atmospheric transport. Figure 2 shows a significant positive correlation between the levels of PCDD/Fs in dust and soil samples from Taizhou, suggesting that PCDD/Fs emitted from incineration of e-waste are initially discharged to ambient air and dust, and then deposited into soil later.
Table 2. Concentrations (ng/g dry wt) of chlorinated polycyclic aromatic hydrocarbons (ClPAHs), polybrominated diphenyl ethers (PBDEs), and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in soils from e-waste recycling and control sites in China
Sampling from an e-waste recycling facility in Taizhou, with urban soil as reference.
The main formation of ClPAHs from PAHs is through chlorination of the parent compounds during e-waste disposal. The concentration of ClPAHs (Supplemental Data, List S10) in soil from an e-waste recycling facility in Taizhou equaled 26.8 ng/g dry weight (Table 2). The mean concentration of ClPAHs (Supplemental Data, List S10) in e-waste debris (59.1 ng/g) was lower than that in dust (103 ng/g) from the e-waste recycling facility 14. This indicates that the e-waste disposal process, rather than the electronic components, is the major contributor of ClPAHs 14, similar to PCDD/Fs (e-waste open burning) 32. Nevertheless, improving the e-waste recycling techniques should be an effective way to contain e-waste associated contamination in soil.
Relatively few studies have been conducted to investigate the occurrence of PBDEs in sediment influenced by e-waste disposal. Overall, the levels of PBDEs in sediment impacted by wastewater discharges from e-waste recycling sites are higher than those from reference areas. For example, river sediments from Liangjiang River of Guiyu contained higher concentrations of PBDEs than sediments receiving wastewater from a non–e-waste source due to discharge from acid leaching of e-waste (http://www.greenpeace.org/raw/content/international/press/reports/recycling-of-electronic-waste.pdf). Penta-BDEs were the most abundant components in sediment from Guiyu with total concentrations ranging from 11.7 to 6,270 ng/g 42. In the last three years, there has been only one study 43 of PCDD/Fs in sediment influenced by e-waste recycling activities in Guiyu. The concentrations of PCDD/Fs (Supplemental Data, List S4) decreased with increasing distance from e-waste recycling sites (Guiyu): Liangjiang riverbank sediments (35,200 pg WHO-TEQ [World Health Organization toxic equivalency]/g dry wt) > sediment proximate to residential areas (21.2–2,690 pg WHO-TEQ/g dry wt) > downstream zone sediments (1.69–3.49 pg WHO-TEQ/g dry wt).
Two noteworthy studies on the occurrence of PBDEs in birds have been published 44, 45. The first study 44 measured PBDEs (Supplemental Data, List S11) in eight birds of prey collected by the Beijing Raptor Rescue Center during 2004 to 2006 and found that congener profiles differed among some species, but were generally dominated by heavily brominated congeners such as BDE-153, -183, and -209. In addition, BDE-209 was dominant in most samples, which is most likely attributable to the significant manufacture, use, and disposal of deca-BDE containing products in China. Among the eight bird species examined, PBDE concentrations were the highest in common kestrel (muscle: 6,760–17,840 ng/g lipid wt; liver: 5,700–18,700 ng/g lipid weight) 44, while common buzzards contained the lowest PBDE concentrations (muscle: 94.7–269.3 ng/g lipid wt; liver: 72.6–229.4 ng/g lipid wt) 44. The difference is probably due to the degree of exposure. A previous study indicated that such factors as the dietary habits, body conditions, age, and gender of individual birds may be important 46.
The second study 45 determined PHCs in five bird species collected from 2005 to 2007 in Qingyuan County of Guangdong Province (Fig. 1), noted as the second largest e-waste recycling region behind Guiyu in South China. The levels of PCBs (Supplemental Data, List S12) in five bird species ranged from 960 to 1,400,000 ng/g lipid weight (Supplemental Data, Fig. S1) 45. Polychlorinated biphenyls were the dominant contaminants in all birds, accounting for 81 to 92% of the total PHC concentrations 45. Polybrominated diphenyl ethers (Supplemental Data, List S13) and organochlorine pesticides (OCPs; Supplemental Data, List S14) contributed almost equally to the total concentrations, ranging from 37 to 2,200 and from 530 to 4,300 ng/g lipid weight (Supplemental Data, Fig. S1), respectively 45. This distribution pattern was different from the other studies which indicated that the levels of OCP in birds were higher than those of PCBs or PBDEs 44, 47–54. The distribution pattern of PHCs in birds from Qingyuan suggested that industrial sources (PCBs and PBDEs) are more important than agricultural sources (OCPs) in the region. In particular, the extensive e-waste recycling activities are most likely a significant contributor to the high levels of PCBs and PBDEs in birds.
The concentrations of e-waste–derived PHCs measured in human samples are given in Table 3.
Table 3. Concentrations of persistent halogenated hydrocarbons in human samples from e-waste recycling and reference sites in China. Polybrominated diphenyl ethers (PBDEs), polychlorinated biphenyls (PCBs), polybrominated biphenyls (PBBs), polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinated dibenzofurans (PCDFs) are the sums of various numbers of congeners as specified in the footnotes
The median PBDEs (Supplemental Data, List S15) concentration (580 ng/g lipid) in serum from residents of Guiyu (Fig. 1, Table 3), e-waste recycling center in South China, was three times higher than that of Haojiang (Fig. 1) (190 ng/g lipid) where aquaculture dominates (Table 3) 55. Similarly, serum PBDE (Supplemental Data, List S15) concentrations of residents from Guiyi were 382 ng/g lipid in the exposure group and 158 ng/g lipid in the control group (Table 3) 56. Hair analysis of residents around e-waste recycling sites in Zhejiang Province resulted in PBDE (Supplemental Data, List S16) levels approximately 10 times higher compared to a reference site (Fig. 1 and Table 3) 8. In Luqiao (Fig. 1), an e-waste recycling site in Taizhou, the concentration of PBDEs (Supplemental Data, List S7) in hair was as high as 870 ng/g lipid (Table 3) 57.
Polychlorinated biphenyls and polybrominated biphenyls
No significant difference was observed in the concentrations of PCBs in serum samples (Supplemental Data, List S18) collected from people residing near the e-waste site (Guiyu) and control site (Haojiang) 55 (Table 3). The concentration of PCBs in serum of Guiyu residents (69 ng/g lipid) was only slightly higher than that for Haojiang residents (65 ng/g lipid) 55 (Table 3). However, hair samples from the e-waste recycling sites (Tongshan, Panlang, Xiazheng, and Xinqiu) of Taizhou contained higher levels of PCBs (Supplemental Data, List S19) and PBBs (Supplemental Data, List S20) than those from control site (Yandang) 8 (Fig. 1 and Table 3). This is probably because different human subjects are significantly influenced by varying exposure routes 58. Exposure of hair to PHCs is obviously more direct than that of serum. Contaminants in hair are likely to be derived from direct atmospheric deposition, whereas those in serum may have also undergone various additional and complex biological processes of absorption, distribution, and metabolism 59. In addition, it is worth noting that depositions on hair are much more likely to reflect short-term contamination which is more prone to variation. A recent study 60 showed that the concentration of PCBs (Supplemental Data, List S17) in human milk from Guiyu reached as high as 9.50 ng/g lipid. Overall, human exposure to PCBs in e-waste recycling sites is significantly increased than that in control sites. Moreover, occurrence of PCBs and PBBs is expected to mainly derive from their historical use in electronic equipment.
Polychlorinated dibenzo-p-dioxins and dibenzofurans
A recent report suggested that e-waste recycling was the most significant source of PCDD/F contamination in China 32. Therefore, e-waste recycling should be regarded as possibly the major contributor of human exposure to dioxins in China. The concentrations of PCDD/Fs (Supplemental Data, List S4) in human milk samples from a group of pregnant women in Taizhou were higher than those at a reference site (Hangzhou) 58 (Fig. 3). Similarly, the TEQ values in Taizhou human samples (21.0–33.8 pg WHO-TEQ/g lipid) were all higher than those in reference site samples (5.59–11.9 pg WHO-TEQ/g lipid) 58. It is notable that the levels of PCDD/Fs in all Taizhou human milk samples and 80% of the Hangzhou human milk samples exceeded the European Union's maximum permitted level in milk (3 pg WHO-TEQ/g lipid) 58, 61. Moreover, Taizhou human milk samples had the highest levels among the samples from other parts of China during 2000 to 2005, while Hangzhou samples contained similar levels to those from non–e-waste recycling sites 62–65 around the world. The levels of PCDD/Fs in placenta and hair from Taizhou were also at the high end of the global range 58. This further confirms that the relatively heavier body burdens of contaminants in residents near e-waste recycling sites are attributable to e-waste recycling activities.
ESTIMATED ANNUAL LOADING OF E-WASTE–DERIVED PHCS IN THE ENVIRONMENT OF CHINA
Based on the concentrations of PHCs in e-waste debris and volumes of e-waste generated in and imported to China every year, the amount of e-waste–derived individual PHCs accumulated in the environment of China (Ii; tons/year) can be estimated with the following equation:
where k is a conversion factor, V (tons/year) is the annual total amount of e-waste generated in and imported to China, and Ci (ng/g) is the concentration of the ith compound in e-waste. Each year, the gross amount of e-waste in China (from both domestic generation and importation) is estimated to be at 15 to 36 million metric tons/year (the procedure for estimation is detailed in the Supplemental Data), including 1.1 million metric tons (http://www.worldwatch.org/node/3921) generated in China and 70% of the amount of the globally generated e-waste (∼20–50 million metric tons) that is shipped to China 32.
It should be noted that the annual mass loadings of PHCs from e-waste are estimated for the years 2006 to 2010 in the present review (detailed in the Supplemental Data). In addition, there are uncertainties of the estimation due to the data's uncertainty, especially, the volumes of e-waste. With the values of CPCDD/Fs32 and CClPAHs14 in e-waste debris and V at 15 to 36 million tons, the annual loadings of e-waste–derived selected congeners and total PCDD/Fs and ClPAHs accumulated in the environment of China were estimated (Tables 4 and 5). Because the accurate contents of BFRs in e-waste remain somewhat unclear, the annual loadings of PBDEs were estimated based on the procedures used for PCDD/Fs and ClPAHs with minor modifications. Plastics, which constitute a major portion of flame retardant consumption, generally account for approximately 20% of the total weight in electronic equipment 66. Therefore, V is replaced with the gross amount of plastics in e-waste (Supplemental Data) in Equation 1. Furthermore, the concentrations of BFRs in plastics instead of CBFRs66 were used to estimate the annual loading of BFRs (Table 6).
Table 4. Estimated annual mass loadings of e-waste derived polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in the environment of Chinaa
Concentrations of ClPAHs in electronic shredder waste 14. Individual congeners include 3,9-dichlorophenanthrene (3,9-Cl2Phe), 3-monochlorofluoranthene (3-ClFlu), 8-monochlorofluoranthene (8-ClFlu), 1-monochloropyrene (1-ClPyr), 3,9,10-trichlorophenanthrene(3,9,10-Cl3Phe), 7-monochlorobenz[a]anthracene (7-ClBaA), 6-monochlorobenzo[a]pyrene (6-ClBaP).
Table 6. Estimated annual mass loadings of e-waste–derived polybrominated diphenyl ethers (PBDEs), tetrabromobisphenol A (TBBPA), polybrominated biphenyls (PBBs), and polybrominated phenols (PBPs) in the environment of China
The low end for the annual loading of PBDEs from e-waste could reach approximately 76,200 tons/year, including approximately 70,600 tons/year from importation and approximately 5,600 tons/year from domestic generation (Table 6; the procedure for estimation is detailed in the Supplemental Data), with deca- and none-BDE congeners dominating the PBDE composition. This is consistent with the fact that heavily brominated BDEs are major constituents in electronic goods and e-waste 67. In addition, the annual loading of PBBs, TBBPA, and PBPs have been estimated in a similar way (Table 6). Table 6 indicates that e-waste importation contributes more than domestic generating to the annual loading of e-waste–derived PHCs in the environment of China. The estimated amount (∼70,600 tons/year) of PBDEs is fairly consistent with our previous estimated amount of approximately 35,000 tons/year for PBDEs imported to China 34. The difference basically reflects different values for the relative abundance of plastics in e-waste used in the estimations, i.e., 10% based on an assumption used in our previous study 34 and 20% from the literature 66 used in the present review.
The estimated annual loading of PCDD/Fs from e-waste is low (Table 4). For example, the amount of the most toxic component, 2,3,7,8-TCDD, annually accumulated from e-waste is estimated at only 1 g/year. In reality, electronic components generally contain low levels of PCDD/Fs. It is the recycling process that may produce large amounts of PCDD/Fs 32. Apparently, the amounts of PCDD/Fs inherited from e-wastes are not reflective of the levels of environmental and human exposure to e-waste–derived PCDD/Fs. Similar to PCDD/Fs, ClPAHs are also produced mainly during combustion of municipal solid waste including e-waste 14. The annual loading of ClPAHs from e-waste reaches up to 890 kg/year (Table 5). If ClPAHs emitted from e-waste recycling processes are taken into account, the amount of ClPAHs accumulated in the environment of China should well exceed 890 kg/year. In this regard, the environmental behavior and fate of ClPAHs sourced from e-waste are worth further investigations because their toxicity is similar to that of dioxins 14. It is notable that the global e-waste generation rate is increasing rapidly 68; therefore, the annual mass loading of e-waste–derived PHCs in the environment of China is expected to maintain an upward trend in the near future if the e-waste situation remains unresolved.
HUMAN EXPOSURE TO PHCS FROM E-WASTE IN CHINA
Environmental fate and effects of contaminants related to e-waste recycling activities in China have recently received extensive review elsewhere in the literature 42. Therefore, only a brief review of human exposure to e-waste–derived PHCs 7, 32, 55, 56, 58 is presented here. In general, risk groups such as e-waste workers are higher exposed to e-waste–derived chemicals than the general population.
Yuan et al. 56 examined whether e-waste–derived PBDE exposure was correlated with serum PBDE levels of risk groups. They recruited 49 subjects from an e-waste site in Guiyu and Chendian (reference site) located 50 km from the e-waste site. As discussed previously, residents of the e-waste site were exposed to PBDEs (Supplemental Data, List S15) more than those of the reference site. In addition, Yuan et al.'s 56 results indicated no association between the duration of exposure to PBDEs and oxidative DNA damage. However, extended exposure to PBDEs may have an effect on the levels of thyroid-stimulation hormone and genotoxic damage among the exposed population 56. As a result, Yuan et al. 56 speculated that other e-waste–derived PHCs, in addition to PBDEs, may also affect the balance of thyroid hormone homeostasis, suggesting that chronic exposure to PHCs may lead to significant biological effects. Obviously, more comprehensive studies are needed to confirm these biological effect activated by e-waste–derived PHCs.
In Guiyu (Fig. 1), the highest concentration of serum BDE-209 (3,100 ng/g lipid) was detected in a male subject and was higher than in any other human samples reported so far 55. Again, Guiyu residents are also exposed to considerably high levels of PCDD/Fs (Supplemental Data, List S4) 10. The daily intake doses of PCDD/Fs (Supplemental Data, List S4) in Guiyu were between 68.9 (summer) to 126 (winter) and 122 (summer) to 223 (winter) pg of WHO-TEQ/kg per day for adults and children, respectively. These values far exceed the WHO 1998 tolerable daily intake limits (1–4 pg of WHO-TEQ/kg per day 10) and daily intake limits in regions around medical solid waste incinerations 69, 70. Furthermore, the daily intake dose (122–223 pg of WHO-TEQ/kg per day) for children was approximately twice as much as those (68.9–126 pg of WHO-TEQ/kg per day) for adults 10, suggesting that children are particularly vulnerable to the impact of improper e-waste disposal practices. For example, 80% of children in Guiyu suffer from respiratory diseases 10. Moreover, dioxins from Guiyu may have been transferred to Chendian via atmospheric transport (Fig. 1), resulting in increased health risk to local residents 10. An assessment 58 on human body loadings of PCDD/Fs (Supplemental Data, List S4) at Taizhou suggested that the estimated daily intake of PCDD/Fs in six-month breast-fed infants from the e-waste site (Taizhou) was twice that from the reference site (Hangzhou) 58.
Normally, food consumption is the most important route for human exposure to organic pollutants for the general population 71–73. Other exposure routes such as dermal contact, water drinking, and dust inhalation are less important. As more toxicants derived from e-waste enter into the food supply 2, human exposure to harmful chemicals via food consumption will continue to rise. Zhao et al. 7 investigated the total dietary intakes of PBDEs (Supplemental Data, List S16), PCBs (Supplemental Data, List S19), and PBBs (Supplemental Data, List S20) by local residents of an exposed group (residing in an e-waste recycling site at Taizhou) and a control group (residing in Yandang of Zhejiang Province; Fig. 1). The exposed residents had contaminant levels approximately two to three times higher than those in the residents of the control group (Fig. 4). This again indicates that e-waste recycling activities continuously pose a health threat to the environment and humans in China, especially to people living near e-waste dismantling sites. It is notable that nondietary intake of PCDD/Fs accounts for approximately 85% of total daily intake for e-waste recycling workers, which is much higher than that (<30%) for the general population 32. Furthermore, ingestion of contaminated food can further increase exposure to PCDD/Fs for e-waste recycling workers.
Although human exposure to pollutants is an extremely complex scenario that is difficult to accurately characterize, the concentrations of PHCs from e-waste in human tissues can directly reflect the magnitude of exposure. Figure 5 summarizes the concentrations of PHCs from e-waste in human tissues from both e-waste recycling and control sites. It is obvious that the levels of PHCs were always higher in residents residing near e-waste recycling sites than those living at control sites. For e-waste recycling workers, nondietary exposure is more severe than dietary exposure. Moreover, consumption of contaminated foods would further aggravate the situation, in addition to occupational exposure. Figure 5 indicates that residents in control sites also show signs of exposure to PHCs. The difference may be the magnitude of exposure between the e-waste recycling workers and general populations, considerably similar to the difference between the levels of PHCs in the environmental compartments of e-waste recycling and reference sites. For example, the concentrations of PHCs were significantly higher in soil and air from e-waste sites than those from reference sites (Fig. 6). It should be noted that PHCs originated from e-waste can be transported to other regions via varying modes, such as riverine runoff 34 or aerial movement 10, and the occurrence of PHCs in reference sites is a witness to this possibility.
Zhao et al. 74 recently estimated the burdens of PBBs (Supplemental Data, List S20), PBDEs (Supplemental Data, List S16), and PCBs (Supplemental Data, List S19) in cancer patients living near the e-waste recycling sites in Zhejiang, China. The levels of PBBs in kidney, liver, and lung tissue (181–192 ng/g lipid) 74 were 10 times those reported for the United States general population (3–8 ng/g lipid) 75. The PBDE levels (174–182 ng/g lipid) 74 were comparable to those for the general population of the United States (23–399 ng/g lipid) 75–77, but significantly higher than those in the populations of Japan (0.7–2.9 ng/g lipid) 78, Singapore (0.5–12 ng/g lipid) 79, and Europe (3.9–18 ng/g lipid) 80–84. Furthermore, the levels of PCBs (257–399 ng/g lipid) were similar to those reported in the populations of European industrialized countries 74. The high levels of PHCs in the cancer patients' tissue samples may correlate with the high cancer incidence near the e-waste recycling sites 74.
The comparative analyses conducted in the present review have reconfirmed that improper e-waste dismantling activities result in severe contamination of the surrounding environments by PHCs. All data suggest that the contaminant levels, and especially organic contaminant levels, in various environmental media near e-waste recycling sites are substantially higher than those of reference sites. Consequently, people living near e-waste recycling sites and adjacent regions are subject to increased health hazard. Most affected are e-waste dismantling workers due to direct exposure to PHCs in the ambient air through inhalation and dermal contact. Long-range transport of these toxins can also subject residents in adjacent regions to unintended health risks. Moreover, other disposal methods, such as informal dumping and acid leaching, have also been identified as ways to contaminate natural resources such as soils, crops, drinking water, livestock, fish, and shellfish, which would increase human exposure to PHCs via food and water consumption. With the rapid increase in the quantities of obsolete or end-of-life electronic goods, e-waste has become a pressing global pollution issue. The situation in China is obviously even more severe, due to the combination of China's burgeoning domestic demand for electronic and other fire retardant-laden commercial products and the continuing importation of e-waste from outside China. It is notable that the global e-waste generation rate is increasing rapidly 68; therefore, the annual mass loading of e-waste–derived PHCs in the environment of China is expected to maintain an upward trend in the near future if the e-waste situation remains unresolved. These findings clearly justify the need for further monitoring and better control of e-waste recycling activities in China.
Supplemental Data. Estimating the gross amounts of e-waste in China; Estimating the inventories of PBDEs in e-waste in China; References.
Lists S1–S20. Lists of PHCs for previous studies.
Figure S1. Occurrence of polychlorinated biphenyls (PCBs) (List 12), polybrominated diphenyl ethers (PBDEs) (List S13), organochlorine pesticides (OCPs) (List S14), and PBB 153 in waterbird species from the Pearl River Delta, China 6. (63.4 KB DOC)
Financial support from the National Natural Science Foundation of China (40588001, 40821003, and 40532013) is greatly appreciated. We also thank Michael Watson for his critical review and editing of the manuscript. This is contribution No. IS-1177 from GIGCAS.