Heavy metal contamination of sedimentary microplastics in Hong Kong

This is the first study of heavy metal (As, Cd, Ni, Mn, Cu) contamination of microplastics on sandy beaches in Hong Kong. Three study sites are located in the eastern waters (Pak Lap Wan, Stanley Bay, Tung Lung Chau Island) and the remaining sites in the western waters (Tai Pai Tsui, Ha Pak Nai and Shui Hau Wan). The mean concentration of Mn (52.88 mg kg^-1) was the highest and followed by Cu (4.09 mg kg^-1), Ni (0.36 mg kg^-1), As (0.07 mg kg^-1), and Cd (0.06 mg kg^-1). Western sites have significantly higher concentrations of Ni but eastern sites higher concentrations of Cd. Inter-site differences were found with a significantly higher concentration of Cd (0.15 mg kg^-1) at Shui Hau Wan than Tai Pai Tsui (< LOD) and Ha Pak Nai (< LOD). The concentration of Ni was significantly higher at Ha Pak Nai (1.09 mg kg^-1) than Tai Pai Tsui (0.08 mg kg^-1) and Pak Lap Wan (0.04 mg kg1 ). The results indicate that the source was different for different metals. As a large number of marine biological species are known to ingest microplastics, the study of heavy metal contamination of microplastics will help assess the potential risk of bioaccumulation and biomagnification of heavy metals through trophic transfer.