Contamination and distribution of phenyltin compounds in the marine environment of Hong Kong

Abstract

Organotin compounds (OTs) are amongst the most prevalent endocrine-disrupting chemicals occurring in urbanized coastal regions around the world, especially in Asian area, because of their extensive use in antifouling paints, agricultural, and industrial activities. Due to their notorious effects on various marine organisms, the International Maritime Organization (IMO) of the United Nations implemented a global prohibition on the usage of OT-based antifouling agents on ship hulls of sea-going vessels in September 2008. Hong Kong has only enacted a new legislation to regulate their use on ship hulls since January 2017. There is a dearth of information regarding the occurrences of these compounds, especially phenyltin compounds (PTs), in the marine environment of Hong Kong, their distribution in different environmental compartments, and their ecological and human health risks. Moreover, the toxicokinetics of these compounds in fishes, as well as their potential to be magnified along the trophic cascade, have also been poorly studied. This multifaceted investigation, therefore, aims to unveil these aforementioned knowledge gaps. First, this study has revealed that Hong Kong is seriously contaminated by PTs, as shown by their high concentrations in the seawater, sediment, and marine biota samples. The results of the ecological risk assessment based on environmental concentrations of TPT showed that local marine organisms are at high risks, especially benthic organisms because these compounds can strongly adsorb onto marine sediments. Human consumption of benthic fish species such as Playcephalus indicus, Siganus canaliculatus, and Oxyurichthys tentacularis could cause potential health risks as their hazard quotients of PTs exceeded the unity. Upon environmental exposure, TPT can be bioaccumulated and distributed the tissues of marine organisms. In the second study, tissue distribution profiles of TPT in four marine fish species revealed that TPT preferentially accumulated in the liver among fifteen analyzed tissues and organs. The tissue distribution profile was further extrapolated to reveal toxicokinetic aspects of TPT, including metabolism and elimination of TPT in fish. Muscles were found to contribute most to the total TPT burden in the whole fish, and were identified as the best predictive tissues for estimating TPT burden in fish. The last part of this thesis investigated the contamination profile of PTs in two resident marine mammals, namely Indo-Pacific humpback dolphins (Sousa chinensis) and finless porpoises (Neophocaena phocanoides). High concentrations of PTs were identified in their muscles, implying potential adverse effects of PTs on resident marine mammals in the region. Dietary uptake was found to be the major pathway of PT bioaccumulation in these organisms, which was demonstrated by the significant trophic magnification of TPT and total PT along marine food chains. The overall results demonstrated that Hong Kong’s coastal marine environments, including seawater, sediment and marine organisms are heavily contaminated with PTs. Exposure to these contaminants can pose health risks to the marine organisms and subsequently to humans upon consumption of contaminated seafood. In view of that, immediate management actions should be carried out by the Hong Kong SAR Government in order to protect marine lives from risks associated to the occurrence and exposure to these compounds.