Waste Management xxx (2014) xxx–xxx

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Environmental effects of heavy metals derived from the e-waste recycling activities in China: A systematic review Qingbin Song, Jinhui Li ⇑ State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Tsinghua University, Beijing 100084, China

a r t i c l e

i n f o

Article history: Received 6 May 2014 Accepted 14 August 2014 Available online xxxx Keywords: E-waste Environmental effect Heavy metal Environmental media China

a b s t r a c t As the world’s leading manufacturing country, China has become the largest dumping ground for e-waste, resulting in serious pollution of heavy metals in China. This study reviews recent studies on environmental effects of heavy metals from the e-waste recycling sites in China, especially Taizhou, Guiyu, and Longtang. The intensive uncontrolled processing of e-waste in China has resulted in the release of large amounts of heavy metals in the local environment, and caused high concentrations of metals to be present in the surrounding air, dust, soils, sediments and plants. Though the pollution of many heavy metals was investigated in the relevant researches, the four kinds of heavy metals (Cu, Pb, Cd and Cr) from e-waste recycling processes attracted more attention. The exceedance of various national and international standards imposed negative effects to the environment, which made the local residents face with the serious heavy metal exposure. In order to protect the environment and human health, there is an urgent need to control and monitor the informal e-waste recycling operations. Ó 2014 Elsevier Ltd. All rights reserved.

Contents 1. 2. 3.

4. 5.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Review methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Results and discussions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1. Air. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2. Dust . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3. Soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4. Sediments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5. Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1. Introduction The disposal of electronic and electric waste (e-waste) has caused a serious environmental problem, especially in developing countries. China, as the world’s leading manufacturing country, ⇑ Corresponding author. Address: Rm. 805, Sino-Italian Ecological Energy Efficient Building, Tsinghua University, Beijing 100084, China. Tel.: +86 01062794143; fax: +86 01062772048. E-mail address: [email protected] (J. Li).

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has become the largest dumping ground for e-waste (Chi et al., 2011; Song et al., 2012a, c, 2013). E-waste is a crisis not only of quantity but also of toxic components. E-waste recycling in China, especially informal e-waste recycling, has clearly become a major source of toxic heavy metals (Luo et al., 2011; Tang et al., 2010b; Wong et al., 2007). Heavy metals are widely used in the manufacturing of a variety of electronic products, such as lead and cadmium in circuit boards, cadmium in computer batteries, and copper in electrical wiring (Achillas et al., 2013; Song et al., 2012b; Stevels et al., 2013; Zeng and Li, 2013;

http://dx.doi.org/10.1016/j.wasman.2014.08.012 0956-053X/Ó 2014 Elsevier Ltd. All rights reserved.

Please cite this article in press as: Song, Q., Li, J. Environmental effects of heavy metals derived from the e-waste recycling activities in China: A systematic review. Waste Management (2014), http://dx.doi.org/10.1016/j.wasman.2014.08.012

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Q. Song, J. Li / Waste Management xxx (2014) xxx–xxx

Zeng et al., 2014). Driven by profits, the recycling of e-waste using primitive processes is being carried out extremely actively in a few locations in China. It is becoming an important new source of environmental pollution in these regions (Chi et al., 2011; Fujimori and Takigami, 2014; Wang et al., 2010; Song and Li, 2014). The unregulated processing of E-waste usually recovers gold and other valuable metals by applying some simple techniques such as burning, melting, and using acid chemical bath. These activities can cause severe pollution of highly toxic heavy metals (such as Cu, Cd, Pb and Hg) in aquatic and terrestrial ecosystems, and even to the atmosphere (Deng et al., 2007; Gullett et al., 2007; Wei and Liu, 2012). E-waste processing sites are usually located in fields adjacent to land used for agricultural purposes, especially for the informal e-waste recycling in China. Heavy metals could penetrate the soils where vegetables and crops are grown by contaminating irrigation water and through direct deposition by air. Plants can take up these metals from soil by their roots, transport them upwards to their shoots, and finally accumulate them inside their tissues (Li et al., 2011b; Zhao et al., 2010), although there are large variations among different plant species in terms of metal accumulation ability (Gullett et al., 2007; Li and Yu, 2011). In addition, direct foliar uptake of heavy metals from the atmosphere can also occur during plant growth (Zhao et al., 2010). It is well known that heavy metals persist in the environment and lead to poisoning at low concentrations through bioaccumulation in plants and animals or bio-concentration in the food chain (Fu et al., 2008; Luo et al., 2011; Zhang and Hang, 2009). Oral ingestion of contaminated food has been proved to be an important pathway for the transfer of heavy metals from the environment to human bodies. In humans, lead interferes with behavior and learning abilities; copper results in liver damage; and chronic exposure to cadmium increases the risk of lung cancer and kidney damage (Balakrishnan Ramesh et al., 2007; Bhutta et al., 2011; Chan and Wong, 2013; Esteban-Vasallo et al., 2012; Grant et al., 2013; Yan et al., 2013). Children are particularly susceptible to heavy metal exposure due to high gastrointestinal uptake and the permeable blood–brain barrier (Guo et al., 2010; Huo et al., 2007; Li et al., 2011c; Ogunseitan, 2013). Although many studies have investigated and discussed the environmental pollution of heavy metals from e-waste recycling in China, to the best of our knowledge, no systematic reviews have been performed. Furthermore, significant findings related to heavy metal pollution of e-waste in China have been recently published. Considering the above-mentioned situation, this study reviews the current state of knowledge on heavy metal pollution from e-waste in China, with almost all the representative available data now. The main objectives of this study were to provide comprehensive information on the current environmental effects of heavy metals in China. This study can provide a large amount of valid data for the governments and companies to improve the e-waste recycling system to be more efficiently and environmentally friendly.

2. Review methods We conducted a systematic search of the published literature, which focused on the environmental effects of heavy metals from e-waste recycling sites in China, as determined in panel studies. To focus our study, we did not consider other pollutants (PBDEs, PCBs, and PCDD/Fs) or studies in other countries (such as India, and African nations). We excluded studies reporting results in reviews, letters to the editor, and abstracts, and those that did not report an outcome related to heavy metal effects from e-waste. We conducted an extensive literature review using databases such as Web of Knowledge, Science Direct, Google Scholar, CNKI (database of Chinese journal) up to October 2013, with the search terms: (e-waste OR electronic waste OR WEEE), (heavy metals OR Pb OR Cd OR Hg OR Cu OR Cr), and pollution OR environmental effects). We used broad search terms to ensure that publications were not overlooked, and many were then excluded. Our search was not restricted to the English language, nor by any other means. Relevant articles published in languages other than English, especially Chinese, were translated. We also assessed reference lists of included studies for other relevant research. After preliminary screening, studies deemed relevant were retrieved for assessment. Eligibility was assessed independently, and disagreements were resolved by consensus, for all of the included reports. Finally, a total of 25 research articles were found. The basic information referred in this study, which including the location, recycling type, the environmental medias, and sampling sites, was shown in Table 1.

3. Results and discussions 3.1. Air High levels of heavy metals in the air will impose serious environmental and biological problems (Eckelman and Graedel, 2007; Ejiogu, 2013; Ettler et al., 2008). Increased risks of mortality and morbidity have been associated with elevated levels of total suspended particles (TSP) in ambient air, especially for fine particles with aerodynamic diameter less than 2.5 mm (PM2.5) (Deng et al., 2006; Park et al., 2002). Bi et al., 2010 investigated the concentrations of 11 kinds of heavy metals (Pb, Cd, Ni, Cu, Sb, etc.) in TSP from the PCBs recycling workshop in Guiyu. The results (Table 2) indicated that all of the 11 heavy metals, taken together, account for about 1% of the TSP. The level of Pb in TSP (4.42 lg/m3) was higher than that of the other heavy metals, exceeded 28.5 times the upper bracket of air Pb levels for non-urban European sites ( Zn (181.12 mg/kg) > Pb (129.56 mg/kg) > Cr (1.89 mg/kg)  Cd (1.12 mg/kg), and Cu, Pb and Cd concentrations in the pond sediments were 7.0–17.0-, 2.3–3.0- and 1.9–2.4-fold those in the Lingdingyang sediment, respectively. At another typical e-waste recycling site, Taizhou, the heavy metal contamination of surface sediment in the Nanguan River was also conducted by Chen et al., 2010. Compared with the Liangjiang River, the Nanyang

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River, and the ponds in Longtang, Cu and Cr levels in the Nanguan River (Cr: 316.52 mg/kg; Cu: 4787.5 mg/kg) were higher, and a high As level (11.93 mg/kg) was also detected. From Table 5, we can also see that there was a consistent progression for the heavy-metal contamination: Cu > Zn > Pb > Ni > Cr  Cd, indicating that the heavy metals in the sediments of the rivers were mainly from the e-waste recycling processes. 3.5. Plants Heavy metal contamination in plant samples is a reflection of the metals’ presence in the soil, as demonstrated by similar patterns between the two sources. Heavy metals in food plants can accumulate in the human body through the food chain, and can lead to psychotic disorders and many debilitating diseases. Heavy metal contamination in food plants has therefore become an increasing concern. Rice is the dominant agricultural crop in China and ranks second by quantity in global agricultural production; hence maintaining its quality is critical to human health. Most plant contamination studies in China have consequently focused on the heavy metal contamination of rice, as shown in Table 6. According to Fu et al., 2008, all heavy metal concentrations, except for Co, were higher in rice hulls than in polished rice. The mean level of Pb in polished rice reached 0.69 mg/kg, 3.5-fold higher than the maximum allowable concentration (MAC) (0.20 mg/kg) set as the safety criteria for milled rice (NY5115-2002). Cd content in 31% of the rice samples exceeded the national MAC (0.20 mg/kg), as did the arithmetic mean, albeit only slightly. In addition, Cd and Pb contents in local rice were much higher than in commercial rice samples from the control areas. Heavy metal concentrations, except for Co, were higher in rice hulls than in polished rice. Similarly, Fu et al., 2013 also reported that the concentrations of Cd, Cu, and Pb in the e-waste-dismantling area were significantly higher than those in the non-e-waste-dismantling area (p < 0.05), a result which showed a close connection between e-waste dismantling activities and elevated Pb, Cu, and Cd levels. Levels of Pb showed a significant decreasing trend during the sampling period (2006–2010), whereas the other three elements (Cu, Cd and As) remained relatively constant or even increased. Zhao et al., 2010 and Zhao et al., 2011 investigated the enrichment index from soil to rice. The enrichment index varied significantly (P < 0.05) with heavy metals in paddy fields, and the content of heavy metals in rice generally followed the order Cd > Zn > Cu > Ni. Furthermore, the study also revealed that high soil OM and sand would increase the accumulation and availability of heavy metals in rice. Very few studies have been conducted on the heavy metal levels in other plants collected from e-waste processing sites, although there have been some. The values of heavy metal concentration reported by Alabi et al., 2012, in other plants, were much higher than those in rice, suggesting that the plants in these two studies had a higher enrichment index. According to Alabi et al., 2012, Cu and Pb levels were the most predominant contaminants among the heavy metals in Guiyu, especially for plants growing along the roadside. For the other four heavy metals (Cr, Ni, Cd, and Mn), the mean heavy metal levels in the e-waste dumpsite were higher than those along the roadside. Luo et al., 2008c investigated the mean concentrations of heavy metals in four types of plants growing in e-waste open burning areas in Longtang. These plants showed clear evidence of heavy-metal pollution, especially from Cu and Cd; studied species included: Eucalyptus spp. (Cu), Dicranopteris dichotomy (Pb) and Neyraudia reynaudiana (Cd, Zn and Cu). The roots of all four plants exhibited the highest enrichment effects of heavy metals, followed by leaves and stalks. According to Luo et al., 2011, the highest concentrations of Cu, Pb, and Zn in shoots were found in the wild plant samples, at

Please cite this article in press as: Song, Q., Li, J. Environmental effects of heavy metals derived from the e-waste recycling activities in China: A systematic review. Waste Management (2014), http://dx.doi.org/10.1016/j.wasman.2014.08.012

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Q. Song, J. Li / Waste Management xxx (2014) xxx–xxx

Table 5 Environmental pollution of heavy metals in sediment. Location

Sampling time

Sampling site

Sample size

Concentrations

References

Guiyu

2003.8

Duck pond-A, duck pond-B, Lianjiang River-1, River-2, River-3, reservoir

–

Leung et al. (2006)

Guiyu

2006.4

Lianjiang River and Nanyang River

–

Longtang and Shijiao Taizhou

2005.11 and 2006.9 2007.6

Pond, and Lingdingyang

–

Nanguan River

–

Cd: 0; 0.3; 0.1;0.9; 0.5; 0.1 mg/kg; Cr 21.2; 43.5; 17.6; 29.2; 27.3; 3.4 mg/kg; Cu 32.2; 30.9; 113; 528; 20.1; 6.3 mg/kg; Ni 20.6; 20.8; 10.1; 120; 12.6; 11.3 mg/kg; Pb 57.7; 53.1; 316; 94.3; 118; 39.4 mg/kg; Zn 79.6; 84.5; 86.8; 249; 175; 45.2 mg/kg Liangjiang: Cd: 0.24; Cr: 35.32; Cu: 66.7; Ni: 51.51; Pb: 54.97; Zn: 133.72 mg/kg; Nayang: Cd: 6.28; Cr: 65.39; Cu: 2153.88; Ni: 293.95; Pb: 394.5; Zn: 482.75 mg/kg Pond: Cu: 766.16 mg/kg; Zn: 181.12 mg/kg; Pb: 129.56 mg/kg; Cr: 1.89 mg/kg; Cd: 1.12 mg/kg Ni: 153.38; Pb: 377.33; Cd:6.31; Cr: 316.52; Cu: 4787.5; Hg: 1.55; As:11.93 mg/kg

Wang et al. (2009a, b)

Luo et al. (2008a, b, c) Chen et al. (2010)

Table 6 Environmental pollution of heavy metals in plants. Location

Sampling time

Sampling site

Sample size

Concentrations

References

Guiyu

2009.8 and 2010.10

Sorghum bicolor, Moench and rice stalks

20–30

Alabi et al. (2012)

Taizhou Wenling

2005.11 2006.10

Rice and hull Rice grain

13 96

Fengjiang

2006–2010

Rice and hull

99

Longtang

2005.8

4 types of plants

12

Longtang

2007.9

Shoots of vegetables, rice, and wild plants

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E-waste dumpsite site: Pb: 11.41; Cu: 28.98; Cr: 2.66; Ni: 13.35; Cd: 2.92; Mn: 122.5 mg/kg Guiyu roadside: Pb: 18.74; Cu: 32.61; Cr: 1.92; Ni: 2.49; Cd: 0.90; Mn: 60.86 mg/kg No details Cu: 3.09 mg/kg; Cd: 0.072 mg/kg; Ni: 0.221 mg/kg; Zn: 20.69 mg/kg Rice: As: 0.119 vs. 0.137; Cu: 4.944 vs.2.560; Cd: 0.449 vs. 0.058; Pb: 0.250 vs. 0.118 mg/kg Hull: As: 0.274 vs. 0.222; Cu: 10.455 vs. 3.393; Cd: 0.473 vs. 0.049; Pb: 4.013 vs. 0.914 mg/kg Roots: Pb: 31.14; Cu: 302.93; Zn: 41.47; Cd: 0.81 mg/kg; Stalk: Pb: 7.91; Cu: 21.79; Zn: 31.77; Cd: 0.64 mg/kg; Leaf: Pb: 12.26; Cu: 49.25; Zn: 40.29; Cd: 0.58 mg/kg Vegetables: Cd: 2.62; Cu: 20.37; Pb: 5.79; Zn: 134.66 mg/kg; Rices: Cd: 0.43; Cu: 42.3; Pb: 13.6; Zn: 94 mg/kg; Wild plants: Cd: 1.59; Cu: 94.47; Pb: 54.; Zn: 143.2 mg/kg

94.3, 54.8, and 143 mg/kg, respectively. However, the highest concentration of Cd in shoots (2.62 mg/kg) appeared in the vegetable samples. Luo et al., 2011 also reported that the accumulation of heavy metals in the edible parts of vegetables could have a direct impact on the health of nearby inhabitants, because vegetables produced from gardens are mostly consumed locally. The concentrations of Cd and Pb in most vegetables exceeded the food safety limit in China (GB2762-2012), with the average levels of Cd and Pb being 4.7 and 2.6 times the maximum permissible levels, respectively. 4. Discussion China has historically been one of the largest recipients of e-waste. In the last ten years, the Chinese government has also implemented some measures and policies to reduce informal recycling (Li and Yu, 2011; Zeng et al., 2013), e.g. the e-waste import to Guiyu and Taizhou has been reduced, and at the same time, about 92 formal e-waste recycling enterprises, which were included in the subsidy list of ‘‘Processing Fund for Electrical and Electronic Equipment’’, have been established in China. However, most researches did not specify the sampling time, or used different sampling sites, therefore it was very difficult to identify trends. There are two other reasons why the decreasing trend was not clear. One is because the policies and measures were not effectively implemented, and informal recycling processes in China still exist, due to their lower cost compared to the formal sector (Ruan et al., 2011; Terazono et al., 2006). In addition, the characteristics of lipophilicity, bioaccumulation and biomagnification, can cause

Fu et al. (2008) Zhao et al. (2010, 2011) Fu et al. (2013)

Luo et al. (2008a, b, c) Luo et al. (2011)

these pollutants from e-waste recycling to accumulate in the food chain and food-stuffs. Therefore, it is necessary to wait until the effects of the new management policies and other measures of e-waste control can show up in future studies. According to the above researches, it can be known that the heavy metal pollution of e-waste in China has been spreaded from the e-waste recycling facilities (especially for the informal sector) to the surrounding environment (air, dust, soil, sediment, and plants). Some effective measures should be carried out to relieve the environmental pollution of heavy metals. In order to better understand the potential environmental and health risk of heavy metals pollution, a long-term risk assessment needs to be carried out on the leachability and migration potential of these toxic metals at the contaminated sites. Due to high concentration of heavy metals in the e-waste recycling sites, especially for the three traditional e-waste recycling sites (Taizhou, Guiyu, and Longtang), the residents are facing a potential higher exposure of heavy metals than are persons in the control areas studied. Children are a particularly sensitive group because of high-risk behaviors (hand-to-mouth activities in early years, higher risk-taking behaviors in adolescence) and their changing physiology (higher comparative uptakes of air, water and food, and lower toxin elimination rates) (Grant et al., 2013). It also appears that neonates, due to the mothers’ exposure to e-waste, were faced with potential health effects, and e-waste exposure has threatened the neonates in e-waste recycling areas. e.g. the neonates from the e-waste exposure areas has been influenced by the heavy metals, including mental health outcomes, growth, changes in cellular expression, and DNA effects (Alabi

Please cite this article in press as: Song, Q., Li, J. Environmental effects of heavy metals derived from the e-waste recycling activities in China: A systematic review. Waste Management (2014), http://dx.doi.org/10.1016/j.wasman.2014.08.012

Q. Song, J. Li / Waste Management xxx (2014) xxx–xxx

et al., 2012; Zhang et al., 2011; Zheng et al., 2013). A precautionary approach towards exposure, especially in children and neonates, seems warranted. Considering the potential environmental and health risk of heavy metals, many technical suggestions to protect the environment and guarantee the health of workers have been put forward and may be implemented in the future. The e-waste recycling workshops: (1) more effective collection and treatment facilities should be adopted to prevent the waste gas, waste water and solid waste emission into the surrounding. (2) Special highly-effective protective measures, such as mask and gloves, offer the most direct protection to the workers. (3) The e-waste recycling operation, especially the manual dismantling and separation, should be carried out within improved recycling facilities that afford a closed or semi-closed environment. (4) If each physical part of the automatic line (e.g., shredder, grinder, and separator) were to be isolated by acoustic hoods, the diffusion of particles into the surroundings would be greatly reduced, so that the concentrations of particles could be kept at a low level. It is also necessary to enhance the interior air purification by the bag-house. The potential polluted soil, sediments, and plants: (1) the China government should carry out the systematic field survey to determine the pollution status of the soil; (2) based on the pollution status, the government should implement the effective measures or technologies to solve the issues. This review was restricted in China (even most relevant researches focused on China), and the researches in other countries (e.g., India, Africa) were not introduced. At the outcome level, when evaluating the environmental pollution in the air, dust, soil, sediment, and the plants, the concentrations of heavy metals in the environmental medias were different with the distribution of sampling points, but we mainly adopted the mean values of heavy metals. Therefore, this could bring some results bias, due to lack of the distribution analysis of heavy metals distribution. A formal application of available statistical methods for assessing presence of this bias was not feasible for this broad review. A search for unpublished findings, which may decrease publication bias, was not performed.

5. Conclusions This review of data on the environmental effects of heavy metals from e-waste recycling processes in China suggests that the measured levels of heavy metals in environmental compartments (e.g. air, soil, sediment, dust, and plants) derived from the primitive e-waste processing operations. The intensive uncontrolled processing of e-waste in China has resulted in the release of large amounts of heavy metals in the local environment, and caused high concentrations of metals to be present in the surrounding air, dust, soils, sediments and plants. The exceedance of various national and international standards imposes negative effects to the environment. These findings provide clear evidence that there is an urgent need for reducing the negative impacts due to the e-waste recycling activities. Under the progressive development of pilot projects and domestic e-waste legislation in China over the past five years, the formal e-waste recycling industry in China has shown considerable growth in both treatment capacity and quality. The growth of the formal sector is important for lessening the environmental and health impacts of e-waste treatment in China (Song et al., 2012c, 2013; Zeng et al., 2013b). However, since the livelihoods of large population groups depends on the income from recycling activities, informal collectors continue to play a major role in the collection and recycling of e-waste, and informal processing often leads to detrimental effects on both the environment and the

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health and safety of workers and local communities (Chi et al., 2011; Xue et al., 2012). In the coming years, unfortunately, both formal and informal sectors will probably continue to operate. An integrated system which combines informal collection, manual separation and formal refining has been proposed as an optimal approach to maximize the collection and recycling rates of e-waste whilst minimizing the environmental concerns in China (Chi et al., 2011, 2014). In the system, the collection, dismantling and reuse can still be managed by the informal sector, providing income for those disadvantaged informal workers; meanwhile, metal recovery and final disposal should be done by the formal sector. In future, the following efforts can be the more important to relieve the environmental pollution of e-waste in China. (1) How to more effectively implement the e-waste laws and legislations into practice. (2) How to ensure the e-waste flow into the formal recycling enterprises. (3) How to guarantee the Best Available Techniques (BAT) adopted in the e-waste recycling processes. (4) How to guarantee the subsidy for recycling e-waste. (5) In addition, it is also very necessary to increase public awareness about e-waste issues (such as the residents’ behaviors, attitudes, and willingness to pay for recycling e-waste).

Acknowledgements The work was financially supported by National Key Technologies R&D Program (2014BAC03B04), China Postdoctoral Science Foundation (2013M540966), and a special fund of the State Key Joint Laboratory of Environmental Simulation and Pollution Control (11Z02ESPCT).

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