Soil Contamination due to E-Waste Disposal and Recycling Activities: A Review with Special Focus on China

This paper presents a review of soil contamination resulting from e-waste recycling activities, with a special focus on China, where many data have been collected for a decade. Soils in the e-waste areas are often contaminated by heavy metals and organic compounds, mainly polycyclic aromatic hydrocarbons (PAHs), polybrominated diphenyl ethers (PBDEs), polychlorinated and polybrominated biphenyls (PCBs and PBBs), dechlorane plus (DP), hexabromocyclododecanes (HBCDs), polychlorinated and polybrominated dibenzo- p-dioxins (PCDDs and PBDDs), and polychlorinated and polybrominated dibenzofurans (PCDFs and PBDFs), while other compounds, not systematically monitored, can be found as well. Pollutants are generally present in mixtures, so pollution situations are complex and diversified with a gradient of contamination from agricultural soils to hot spots at e-waste sites and mainly in open burning areas. It has been proved that pollutants were transferred to the food chain via rice in China, and that the population was threatened since high levels of various pollutants were detected in blood, placentas, hair, etc., of residents of e-waste sites. Eventually, soil remediation techniques are reviewed. Although there are many available techniques devoted to heavy metals and persistent organic pollutants, the current techniques for the e-waste sites, where these contaminants coexist, are very sparse. Phytoremediation has been investigated and co-cropping appears as a promising approach for the slightly contaminated agricultural soils. In some cases, different remediation techniques should be combined or trained, while the influence of coexisting contaminants and the removal sequence of contaminants should be considered. In hot spots, physical and chemical techniques should be used to reduce high pollution levels to prevent further pollutant dissemination. This review highlights the urgent needs for 1) characterization of pollution status in all the countries where e-wastes are recycled, 2) research on fate and toxicity of pollutant mixtures, and 3) development of combined techniques and strategies to remediate agricultural fields and hot spots of pollution.