Electronic waste, or e-waste, refers to obsolete electronic devices for disposal, including TVs, desktop and laptop computers, mobile computers (notebooks, netbooks, tablets, e-book readers), cellular phones, printers, copiers, video players, telephones, and information and communications technology (ICT) equipment (United Nations Environment Programme, 2009). According to the latest estimate from Solving the E-waste Problem (StEP) Initiative, the annual global production of e-waste reached 48.9 million metric tons in 2012, and will be 65.4 million metric tons in 2017 (StEP, 2014).
A significant proportion (~23%) of e-waste generated in developed countries is exported to developing countries for recycling, predominantly by informal sectors that are not regulated, lack occupational and environmental pollution control, and cause widely spread environmental contaminations (Breivik, Armitage, Wania, & Jones, 2014; LaDou & Lovegrove, 2008; Sthiannopkao & Wong, 2013). These informal sectors often use convenient locations, such as residential homes, public roads, and river sides, to recycle e-waste with simple handheld tools and methods (e.g., cutting, hammering, heat melting, acid washing, and burning). Workers involved in the informal sectors rarely use personal protective equipment such as gloves, goggles, respirators, and work clothes.
Electronic devices contain many toxicants: lead (Pb, in cathode ray tube [CRT] TVs or monitors), cadmium (Cd, in batteries and resistors), mercury (Hg, in batteries, switches, and flat panel screens), hexavalent chromium (Cr[VI], in steel housing), polyvinyl chloride (PVC, in cables and computer housing), and polybrominated diphenyl ethers (PBDEs, as flame retardants in printed circuit boards, plastic covers, and cables) (Ramesh, Parande, & Ahmed, 2007). Electronic devices also contain other potentially toxic metals including antimony (Sb), barium (Ba), beryllium (Be), cobalt (Co), gallium (Ga), indium (In), molybdenum (Mo), nickel (Ni), platinum (Pt), thallium (Te), tungsten (W), vanadium (V), and metals that are nutrients but excessive intake can be toxic, including iron (Fe), copper (Cu), and zinc (Zn) (Julander et al., 2014). NonPBDE flame retardants, including tetrabromobisphenol A (TBBPA) and hexabromocyclododecanes (HBCDs), also exist in e-waste (Tsydenova & Bengtsson, 2011).
Further, the heating and open-fire burning used in informal sector e-waste recycling in developing countries can generate toxic polycyclic aromatic hydrocarbons (PAHs) and dioxins/furans (Chen, Dietrich, Huo, & Ho, 2011). Evidence is strong regarding extensive occupational and environmental contaminations in locations where informal sector e-waste recycling boomed in the past two to three decades, particularly in China, India, Ghana, Nigeria, and other developing countries (Asante et al., 2011; Bi et al., 2007; Chan et al., 2007; Feldt et al., 2014; Huo et al., 2007; Leung et al., 2010; Li et al., 2011; Ling, Han, & Xu, 2008; Ni, Chen, et al., 2010; Tue et al., 2010; Wang et al., 2011; Xu et al., 2015; Yang et al., 2013; Yang et al., 2015; Zheng et al., 2008).
Little is known, however, about public health related to e-waste recycling in developed countries. This line of inquiry has great relevance to the future global e-waste movement, resource recovery, application of environmentally friendly recycling technologies, and occupational and environmental protection standards. In this review, we attempt to summarize the current status of e-waste recycling in the U.S. in relation to public health, with the aim to raise awareness toward prevention of unnecessary exposure to toxic metals and organic chemicals in obsolete electronic devices. Additionally, the information will be helpful for developing countries to address their own public health problems arising from a mix of e-waste influx from developed countries and rapidly increased domestic e-waste generation. Common among the aforementioned countries is a lack of formal sector e-waste recycling policy and safe practices.
Piling Up of E-Waste
According to the StEP Initiative, the estimated annual e-waste production in the U.S. is 9.4 million metric tons in 2012, or 30 kg per resident (StEP, 2014). The U.S. Environmental Protection Agency (U.S. EPA), however, estimated that 3.4 million tons of "selected consumer electronics," which covers personal computers and displays and peripherals, TVs, mobile devices, and hardcopy devices, was generated in the municipal solid waste (MSW) stream in 2012 (U.S. EPA, 2014). U.S. EPA also estimated that 440 million new electronic devices were sold in 2010, and the weight of devices tend to be smaller due to the increase in flat panel TVs and monitors and the decline of CRT TVs/ monitors and desktop computers (U.S. EPA, 2011). The Consumer Electronics Association (CEA) estimated that the average U.S. household owned approximately 24 electronic devices in 2008 (CEA, 2008). American families are storing an average of 4.1 small (
Pb is a major toxicant in e-waste, particularly in CRT TVs and monitors. It is estimated that an average of 7.3% of the mass of a CRT TV is Pb (1-2 kg Pb/device) and 3% of the mass of a CRT monitor is Pb (0.5 kg Pb/device) (U.S. EPA, 2007). About 90,751 metric tons of Pb exist in the approximately 84 million obsolete TVs stored in U.S. households in 2010. In addition to Pb, these obsolete TVs contain 0.72 metric ton Hg, 1.35 metric ton Cd, and 286 metric ton Cr, and many other metals, PVCs, and plastics (Milovantseva & Saphores, 2013a).
The amount of toxic metals in the entire e-waste stream (beyond TVs) is difficult to calculate because of the variety of electronic devices and constituents used in the production processes. U.S. EPA estimated, however, that some 42,986 metric tons Pb and 106 metric tons Hg exist in select e-waste streams generated in 2005 alone in the U.S. (U.S. EPA, 2007). Figure 1 shows the estimated percentages of material composition in that e-waste stream generated in 2005. Even a metal of 0.01% in weight of e-waste is equivalent to 125 metric tons. A large quantity of toxic metals in the e-waste stream poses a serious public health problem that needs to be addressed systematically.
Despite the trend of replacing CRT TVs and monitors with flat panel products, CRT TVs and monitors in use or in storage will need 10-20 years to be phased out to become e-waste. Therefore, before an eventual decline of the amount of Pb in e-waste, preventing just Pb exposure from handling e-waste is a daunting task. Accompanying the reduction of Pb in e-waste, Hg levels will increase because of the increasing use of flat panel displays, cold cathode fluorescent lamps, and Hg-containing switches. Additionally, arsenic (As) in the form of gallium arsenide in light emitting diodes, mobile phones, and solar panels may increase significantly in the e-waste stream. Brominated flame retardants, particularly deca-BDEs, have been added to plastics of certain electronic products in large amount, and later become toxicants in e-waste. About 30% of e-waste plastics contain flame retardants, and 40% of these plastics contain bromines or chlorines (Vehlow et al., 2002). In TV products that used brominated flame retardants, it was estimated that up to 10% to 15% of the weight of high impact polystyrene polymers used in the back covers was deca-BDEs, often used in conjunction with antimony trioxide as a synergist (Lassen, Havelund, Leisewitz, & Maxson, 2006). The market demand of deca-BDEs in 2001 was 24,500 metric tons in the U.S., and about 80% of deca-BDE use in this country was in electronic enclosures, such as the front and back plates of TV sets (The Lowell Center for Sustainable Production, 2005).
U.S. EPA estimated that of the 3.4 million metric tons of e-waste ready for disposal in 2012, 2.42 million tons (71%) ended up in landfills. This presents a lost opportunity to recover metal resources in e-waste, but the low cost of landfill technology was the driving factor of its conventional use in this country (U.S. EPA, 2014). Pb was a major toxicant of concern in landfilling e-waste, as the standard toxicity characteristic leaching procedure (TCLP) the U.S. used to determine leaching hazards identified high concentration of Pb (>5 mg/L) in the leachates, which is above the regulatory level classifying hazardous waste (Townsend, 2011). TCLP is a conservative procedure for environmental safety that assumes the worst-case scenario (low pH, thus more metal release). Experimental conditions similar to real-world engineered sanitary landfill might not produce as high Pb concentrations in the leachates (Jang & Townsend, 2003; Spalvins, Dubey, & Townsend, 2008). Nevertheless, Pb can leach out of e-waste in the landfill and be absorbed by solids around it, and Pb might eventually find its way into landfill leachates after a long time or under certain environmental conditions such as rain (Li, Richardson, Mark Bricka, et al., 2009; Li, Richardson, Niu, et al., 2009). Research from four Australian landfills with 6% e-waste in MSW streams suggests increased concentrations of Pb, along with Al, As, Fe, and Ni, above drinking water guidelines in groundwater samples at the landfill sites (Kiddee, Naidu, Wong, Hearn, & Muller, 2014). In this study of four landfill sites, one site operated since 2005 with a capacity of 200,000 ton/year. It had the highest groundwater Pb levels: up to 38 [micro]g/L (almost 4 times higher than the local drinking water guideline of 10 [micro]g/L).
In addition to metals, brominated flame retardants, especially PBDEs, were found to be leaching out from e-waste in landfills (Choi, Lee, & Osako, 2009; Danon-Schaffer, Mahecha-Botero, Grace, & Ikonomou, 2013a; Kiddee, Naidu, & Wong, 2013; Kiddee et al., 2014). Deca-BDEs go through a debromination process in the environment to become lower-brominated congeners; however, the latter will need a longer period of time...