Contamination and risk of heavy metals in soils and sediments from a typical plastic waste recycling area in North China

Highlights

• Surface soils and sediments have suffered from moderate to high metal pollution.

• High Cd and Hg pollution presented in both soils and sediments.

• The non-carcinogenic risk from soil metals to local children is unacceptable.

• Crude plastic waste recycling is a significant metal source to the environment.

Abstract

Plastic wastes are increasingly being recycled in many countries. However, available information on the metals released into the environment during recycling processes is rare. In this study, the contamination features and risks of eight heavy metals in soils and sediments were investigated in Wen'an, a typical plastic recycling area in North China. The surface soils and sediments have suffered from moderate to high metal pollution and in particular, high Cd and Hg pollution. The mean concentrations of Cd and Hg were 0.355 and 0.408 mg kg⁻¹, respectively, in the soils and 1.53 and 2.10 mg kg⁻¹, respectively, in the sediments. The findings suggested that there is considerable to high potential ecological risks in more than half of the soils and high potential ecological risk in almost all sediments. Although the health risk levels from exposure to soil metals were acceptable for adults, the non-carcinogenic risks to local children exceeded the acceptable level. Source assessment indicated that heavy metals in soils and sediments were mainly derived from inputs from poorly controlled plastic waste recycling operations in this area. The results suggested that the risks associated with heavy metal pollution from plastic waste recycling should be of great concern.

Introduction

The quantities of end-of-life plastics from households and industries have increased markedly in recent decades (Thompson et al., 2009). Plastic waste treatment is becoming a vital task worldwide because these wastes are resistant to degradation and are leading to various environmental problems, including plastic pollution in the ocean (Rochman et al., 2013, Jambeck et al., 2015). In the past, plastic waste was usually landfilled together with municipal solid waste. Low sustainability, increasing cost and decreasing space for landfills are forcing consideration of alternative options for plastic waste disposal. Recycling has become the primary policy for treating plastic waste in many countries (Al-Salem et al., 2009, Hopewell et al., 2009). Material recycling is becoming the key disposal method for plastic waste in developing countries because of the relatively low investment and simple technology requirements, although energy recovery and chemical recycling are encouraged in some developed countries (Al-Salem et al., 2009, Hopewell et al., 2009).

Many plastic wastes contain or are contaminated with harmful chemicals. It was reported that the chemical ingredients of more than 50% of plastics are hazardous (Lithner et al., 2011). Some hazardous chemicals are also widely used as specific targeted additives in plastic products. For example, brominated organics and phthalate esters (PAEs) have been extensively applied in plastic products as flame retardants and plasticizers, respectively. These additives also include other flame retardants and plasticizers, pigments, stabilizers, and reinforcement components, which are composed of heavy metals or metal compounds (Dimitrakakis et al., 2009, Luo et al., 2011, Nakashima et al., 2012, Rochman et al., 2013). In some products, the contents of these dangerous additives are high or extremely high (Morf et al., 2007, Dimitrakakis et al., 2009, Stenvall et al., 2013). For example, the upper concentration ranges of Pb and Sb were reported at 100–2000 mg kg⁻¹ and 2–13 g kg⁻¹, respectively, in the plastic fraction of waste electrical and electronic equipment (WEEE) (Morf et al., 2007). In addition, plastic wastes can potentially absorb various priority pollutants from the environment to some extent (Nakashima et al., 2012, Rochman et al., 2013). Hence, many toxicants could be released into the environment during the milling, washing and melt processing of material recycling of plastic wastes, especially with the rather primitive and crude facilities used.

Pollutant release from material recycling has not received much attention. Such contamination is traditionally undervalued perhaps because this recycling is only a mechanical process and is conducted at relatively low temperatures (<300 °C in the extrusion). Several studies have recently reported the emission of harmful compounds from material recycling processes. Dozens of volatile organic compounds were identified in the air and the workers suffered acute and chronic health risks in poly(acrylonitrile-butadiene styrene) (ABS) and polystyrene (PS) recycling workshops (Huang et al., 2013, He et al., 2015). High levels of polycyclic aromatic hydrocarbons and PAEs were also measured in the air from a polyvinyl chloride (PVC) plastic waste recycling plant (Tsai et al., 2009, He et al., 2015). Our previous research reported that high concentrations of polybrominated diphenyl ethers (PBDEs) occurred in the environment and in human hair in a plastic recycling area in China and their potential risks should be of great concern (Tang et al., 2014). Available information about the toxicant emissions and pollution characteristics from these processes is still rare.

The occurrence of material recycling of plastic waste by environmentally unfriendly and primitive technologies in developing countries, especially in Asia, Africa and Latin America, has increased in recent years (Pacheco et al., 2012, Huang et al., 2013, Yang and Buekens, 2014). In China, the total recycling of plastic wastes increased from 16.1 million tonnes in 2008 to 24.9 million tonnes in 2013; of the plastic recycled, primitive material recycling of plastic waste is common (Wei and Zhang, 2014). So far, little is known about the release of heavy metals into the environment in plastic waste recycling areas where primitive methods are used, and the potential ecological and human risks of heavy metals from such sites remain unknown. Using Wen′an, in northern China, as a case study for plastic waste recycling, the objectives of this study were to conduct a reconnaissance survey to investigate and characterize the level and risk of toxic metals in soils and sediments. The results will improve our understanding of the extent of heavy metal pollution caused by plastic waste recycling and provide information to plan risk management measures.