Polychlorinated biphenyls in apple snails from an abandoned e-waste recycling site, 2010–2016: A temporal snapshot after the regulatory efforts and the bioaccumulation characteristics
Graphical abstract
Introduction
Polychlorinated biphenyls (PCBs) are a class of chlorinated aromatic compounds in which one to ten chlorine atoms are attached to a biphenyl skeleton. Since the initial production of commercial PCBs in 1929, they had been extensively used for industrial purposes due to their highly chemical and thermal stability (Erickson, 2001). They were widely utilized as dielectric fluids in transformers, capacitor sand voltage regulators, and as plasticizers, lubricants, inks and surface coatings in carbonless copy paper (Erickson, 2001). These chemicals can be released to the environment during their production and the disposal of PCB-containing products. Because of their persistence, bioaccumulation potential and highly toxic effects, commercial PCB production ended in the USA, Western Europe and China during the 1970s (Erickson, 2001; Zhao et al., 2017), and worldwide formulation and application of PCBs was prohibited after the Stockholm Convention on persistent organic pollutants (POPs) in 2001 (UNEP, 2001). Despite the ban on the production and usages of PCBs, they continue to be of great concern because they can be emitted from fundamental sources such as old electrical and electronic products, and re-emitted from environmental reservoirs including soils, sediments, and other contaminated compartments (Breivik et al., 2007, Breivik et al., 2016; Zhao et al., 2017; Bogdal et al., 2014; Shanahan et al., 2015; Yadav et al., 2017; Li et al., 2018).
The primitive electronic waste (e-waste) recycling activities have caused heavy pollution of PCBs and other contaminants in developing countries such as China, India and Pakistan and some African countries (Wong et al., 2007; Chen et al., 2014; Iqbal et al., 2015). To deal with the worsening environmental problems in e-waste recycling sites, the Chinese local government has banned some crude processes of e-waste recycling such as open burning and acid washing since the late 2000s, leaving many abandoned e-waste sites in fields (Fu et al., 2012; Zhang et al., 2014; Wu et al., 2015; Wang et al., 2016). The local government also took some measures, e.g., covering the burning sites with uncontaminated soil, to control the re-emission of the pollutants (Wang et al., 2016). Despite of these efforts, extremely high levels of e-waste related contaminants were detected in the environment of the abandoned sites without further e-waste disposal and can still pose ecological risks (Zhang et al., 2014; Wu et al., 2015; Wang et al., 2016, Wang et al., 2017; Huang et al., 2018).
Apple snails (Pomacea canaliculata) are freshwater snails that naturally occur throughout the tropics and subtropics. They inhabit a wide range of ecosystems including natural streams, ponds, paddy fields and other waterways. Apple snails have a broad diet, preferring plant materials and decomposing organic matter (Kwong et al., 2010). Paddy fields constitute a more favorable habitat for apple snails than other ecosystems because of similarities in the environmental conditions (e.g., temperature, salinity, pH and flow velocity of paddy water) necessary for both rice production and for snail survival and development (Horgan, 2018). The ecology and biology of apple snail fit in with most of the essential characteristics of an ideal bioindicator, that is, bioaccumulation potential, wide distribution, narrow range of movement, short life-span, and ease in collection (Tanabe and Subramanian, 2006). These advantages make apple snail inhabited paddy field a suitable bioindicator for PCBs and other organic chemicals (Fu et al., 2011; She et al., 2013; Yuan et al., 2017).
Biomonitoring of PCB concentrations in abandoned e-waste recycling sites could provide information on PCB trends now that crude e-waste recycling activities have been banned. In this work, we present data from an abandoned e-waste recycling site in South China, using apple snail as a bioindicator. We collected the samples in 2010, 2012 and 2016 to evaluate whether PCB levels have continued to decrease following the stricter environmental regulations. Furthermore, we examined PCB levels in paddy soils and estimated the biota-soil accumulation factors (BSAFs) for these chemicals, to assess the bioaccumulation characteristics of PCBs in apple snails from the abandoned e-waste recycling site.
Section snippets
Sampling strategy
Apple snails (Pomacea canaliculata) were collected from 15, 16 and 11 adjacent paddy fields of an abandoned e-waste recycling site in South China (latitude 23°34′ N and longitude 113°01′ E), in April of 2010, 2012 and 2016, respectively. Apple snails collected from one paddy field were mixed as a pool sample which was composed of at least 20 individuals. The apple snails sampled for each year possess similar body length (3.0 ± 0.2 cm; mean ± SE). In the 2016 sampling, paddy soils (n = 11) were
Concentrations and congener profiles of PCBs
The concentrations of individual PCB congeners as well as the sum of the 28 PCBs detected (∑28PCBs) and the sum of the 7 marker-PCBs (∑7PCBs, including CBs 28, 52, 101, 118, 138, 153 and 180) in apple snails sampled in 2010, 2012 and 2016 are shown in Table 1. The concentrations of the ∑28PCBs in apple snails were 115 ± 15 (mean ± SE), 92 ± 11, and 53 ± 4.6 ng/g dry weight in the 2010, 2012, and 2016 sampling year, respectively. Previous studies have reported PCB concentrations in apple snails
Conclusions
The present study provides the recent levels and temporal trend of PCBs in apple snails living in paddy field of an abandoned e-waste recycling site in South China, a PCB hotspot with scarce dataset. Our results indicated that PCB levels have continued to decline over the period 2010–2016. However, recent PCB levels in the apple snails were still at significantly high levels, possibly resulting from the slow clean-up of these compounds without amended controls as well as fresh PCB input. The
Acknowledgements
Dr. Ying Zhang from the Pearl River Water Environment Monitoring Center is kindly acknowledged for assisting in instrumental analysis of part of the samples. This work was financially supported by the National Natural Science Foundation of China (grant 41373105), the Scientific Research Foundation of Anhui Normal University (grant 2017XJJ39), and State Key Laboratory of Organic Geochemistry, GIGCAS (grant SKLOG-201714). B.-X. Mai acknowledges the Local Innovative and Research Teams Project of
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