Spatial distribution and source identification of hydrophobic organic compounds (HOCs) on sedimentary microplastic in Hong Kong

The spatial distribution, composition and source of hydrophobic organic compounds (HOCs) including polyaromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and organochlorinated pesticides (OCPs) of the sedimentary microplastics (0.25–5 mm) in Hong Kong were investigated. The concentration of ΣPAHs ranged between 70.8 and 1509 ng g⁻¹ with inter-site differences although the regional difference was insignificant, indicating localised pyrolytic and petrogenic input of PAHs. The concentration of ΣPCBs (13–1083 ng g⁻¹) varied with both study sites and regions with higher concentrations obtained in the western waters, possibly due to the input from Pearl River. Significantly higher concentrations of OCPs on eastern shores highlighted fishing and aquaculture activities in South China Sea a potential major source of OCPs. DDT and its metabolites (DDX, ranged from 1.96 to 626 ng g⁻¹) were the dominant forms of OCPs (45%–80%). Since most of the DDX existed as DDT, this suggested that there was a fresh input of DDT into the microplastics. As microplastics and HOCs cannot be removed effectively from the environment, reduction of potential ecotoxicological risks should rely on minimizing the use of plastics and HOCs.