Deep seafloor plastics as the source and sink of organic pollutants in the northern South China Sea

• Published in: The Science of the total environment Vol. 765; p. 144228
• Main Authors: Dasgupta, Shamik, Peng, Xiaotong, Xu, Hengchao, Ta, Kaiwen, Chen, Shun, Li, Jiwei, Du, Mengran
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 15.04.2021
• Subjects: cis-chlordane; DDE (pesticide); DDT (pesticide); environmental assessment; HCH (pesticide); heptachlor; heptachlor epoxide; isomers; marine environment; Marine pollution; metabolites; microplastics; Organochlorine pesticide (OCP); Plastics; Polychlorinated biphenyl (PCB); polychlorinated biphenyls; risk; South China Sea; trans-chlordane; transportation; South China Sea; South China Sea; Polychlorinated biphenyl (PCB); Marine pollution; Plastics; Organochlorine pesticide (OCP)
• ISSN: 0048-9697; 1879-1026; 1879-1026
• DOI: 10.1016/j.scitotenv.2020.144228

Large plastic litter (as opposed to microplastics and plastic pellets) could adsorb organic pollutants and thus pose a serious threat to the marine environment. We report high levels of polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) adsorbed to plastic litter sampled from depths of 1800–3100 m in the Xisha Trough region of the northern South China Sea (NSCS). ∑PCBs on plastics ranged from 126.9–142.1 ng/g, with tri-PCBs accounting for 92–97% of the total PCB concentrations in all samples. Levels of ∑OCPs varied from 4280 to 5351 ng/g (average 4690 ng/g), with a total of 19 compounds detected in the seven samples. While no parent DDT (dichlorodiphenyltrichloroethane) was detected, op′-DDE (metabolite of DDT) was most abundant, with concentrations ranging from 947.5–1551.7 ng/g. ∑CHLs (heptachlor + heptachlor epoxide A + heptachlor epoxide B + cis-chlordane + trans-chlordane) ranged from 1083.1–1263.7 ng/g (mean 1153 ng/g) and accounted for 24% of ∑OCPs. Various compositional ratios of HCH (hexachlorocyclohexane) and DDT metabolites improved our understanding of the sources and transport pathways of OCPs. The total absence of DDT may be a “ghost indicator” of no recent DDT inputs into the oceans. There could well be inputs of DDT, but only as the degraded metabolites DDE and DDD when they are adsorbed to seafloor plastic litter. A comparison of HCH isomer ratios in seafloor plastics with technical HCH ratios revealed that HCHs were possibly not from early residues but from later inputs. An ecological risk assessment of the contaminants indicated a high risk from ∑DDTs, p,p-DDE, and γ-HCH in all the sampled locations. Finally, we propose a descriptive model depicting the movements and transportation of PCBs and OCPs from the ocean surface to seafloor plastics in the NSCS. [Display omitted] •High concentrations of persistent organic pollutants (POPs) in deep seafloor macro-plastics of northern South China Sea•Absence of parent DDT, but high levels of metabolite DDE was detected in the seafloor plastics•Sources of DDT metabolites and hexachlorocyclohexane (HCH) isomers were predicted depending on various compositional ratios•Ecotoxicological parameters indicate adverse effects of pollutants on benthic lives•A model is proposed depicting different pathways and movements of contaminants from surface to seafloor plastics