Occurrence and Ecological Risk of Organotins in the Marine Environment of Hong Kong

Description

Since 1960s, organotin compounds (OTs), such as tributyltin (TBT) and triphenyltin (TPT), have been extensively used as active ingredients in antifouling paints on ship hulls, submerged marine infrastructures and mariculture cages, and as biocides in agricultural and textile industries. They are highly toxic and can cause morphological abnormalities in marine organisms at low concentrations (ng/L). The best-documented example is OT-mediated imposex (i.e., the superimposition of penis and vas deferens on females) in gastropods. In September 2008, the Marine Environment Protection Committee of the United Nations’ International Maritime Organization adopted a global prohibition on the use of OT-based biocides on sea-going vessels (i.e., the AFS Convention). The Hong Kong SAR Government eventually established the relevant legislation (Cap. 413N) for regulating the use of OTs on ships on January 1, 2017. While being a densely populated coastal city, Hong Kong serves as the 7th busiest container port in the world. Historically, our marine environment has received a large amount of OTs originated from shipping activities, surface runoff, partially-treated wastewater and discharge from the Pearl River. Our previous studies indicated that there were serious contaminations of OTs, especially TPT in our marine environment between 2010-2016. Extremely high concentrations of TPT were found in local coastal marine sediments. However, OT contamination situation after the implementation of the AFS Convention and the impact of TPT to benthic community remain largely unknown. Therefore, we will, first, examine the contamination status of OTs in the marine environment of Hong Kong post-implementation of the AFS Convention by examining imposex status in the marine gastropod Reishia clavigera and concentrations of various OTs in the gastropod, seawater and sediment samples during 2022-2024 and by comparing the results with relevant historical data. Second, we will conduct both laboratory and field studies to investigate the impact of TPT and OTs on the benthic community in sediments using the environmental DNA (eDNA) metabarcoding approach. Through microcosm experiments, we will reveal the dynamic change of eDNA in sediment after spiking environmentally relevant concentrations of TPT or OTs, and identify the sensitive species. Concurrently, we will establish the relationship between the benthic biodiversity (as depicted by eDNA) and OTs contamination in sediments collected from the field. The results will enable us to evaluate the effectiveness of the management intervention and law enforcement on reducing OTs contamination in the marine environment, determine the effect thresholds of OTs, and assess their ecological risks to the benthic ecosystem.