Applying tissue-burden based quality benchmarks to assess the ecological risks of endocrine disrupting organotin compounds in Hong Kong waters

Abstract

Since their application as biocides in the 1960s, organotins (OTs), in particular tributyltin (TBT) and triphenyltin (TPT), have caused widespread adverse effects on marine organisms such as the induction of imposex (i.e., superimposition of male sexual characteristics - penis and vas deferens - on females) in over 200 species of neogastropods, and growth inhibition and deformities in oysters. A mandatory global ban on the use of OT-based antifouling systems has been enacted since September 2008. It is, therefore, anticipated that there will be a reduction of OT pollution in marine environments around the world. In this study, we measured the imposex status and tissue concentrations of OTs (i.e., mono-BT, di-BT and TBT, mono-PT, di-PT and TPT) in the rock shell Thais clavigera collected from 28 coastal sites of Hong Kong during summer 2010. The results indicated that T. clavigera from a number of sites contained high TPT concentrations and suffered from high degree of imposex. The average TPT tissue concentration was 11,108 μg kg-1 dry weight (dw) in T. clavigera collected from Aberdeen, which was 26 times higher than the maximum TBT tissue concentration in the animals obtained from Kadoorie Beach (i.e., 422 μg kg-1 dw). Using the Monte Carlo approach, an ecological risk assessment was conducted by computing the distribution of risk quotients (RQs); RQ is the ratio between a measured tissue concentration of the target pollutant (MTC) and predicted effects tissue concentration (PETC) (i.e., RQ = MTC/PETC). The results showed that 11.1% of T. clavigera across all sites in Hong Kong waters was at risk with RQ > 1 due to exposure to TPT, whereas the risk associated with TBT was relatively low (0.7% with RQ > 1). Kadoorie Beach, Butterfly Beach, Waterfall Bay and Aberdeen, the four sites which are close to the shipping facilities, were severely impacted by TBT, while all 28 sites were alarmingly heavily contaminated by TPT. As TPT is highly toxic and may trigger imposex in T. clavigera, the local rock shells are still under considerable threat associated with this pollutant even after the global ban of OTs in antifouling systems. This study highlights that TPT is a major environmental concern which deserves immediate actions to control its use and release, and to remediate its pollution in the marine environment of Hong Kong and the Pearl River Estuary.