Program     Ocean Circulation, Ecosystem and Hypoxia around Hong Kong Waters       Poster Occurrence, distribution and risk of contaminants of emerging concern in marine ecosystem of the South China Sea P-SPS4-09 Mirabelle M. P. Tsui* , State Key Laboratory in Marine Pollution (SKLMP), City University of Hong Kong, Hong Kong SAR, China Lianguo Chen, State Key Laboratory in Marine Pollution (SKLMP), City University of Hong Kong, Hong Kong SAR, China Qi Wang, State Key Laboratory in Marine Pollution (SKLMP), City University of Hong Kong, Hong Kong SAR, China Xin Li, State Key Laboratory in Marine Pollution (SKLMP), City University of Hong Kong, Hong Kong SAR, China James C. W. Lam, Paul K. S. Lam, State Key Laboratory in Marine Pollution (SKLMP), City University of Hong Kong, Hong Kong SAR, China Presenter Email: mpmtsui2@cityu.edu.hk Coastal eutrophication is caused by excessive nutrient loading which stimulates phytoplankton blooms when physical, chemical, and biological conditions are favorable. It may lead to harmful algal blooms (HABs) and hypoxia, both of which threaten the ecosystem. The aquatic environment of the Pearl River Estuary (PRE) is chronically contaminated by contaminants of emerging concern (CECs) such as per- and polyfluoroalkyl substances (PFASs) and organic ultraviolet (UV) filters. These chemicals are released to the aquatic environment during their production, usage and disposal into wastewater treatment plants. They have accumulated in the top predators in the southern China region and are posing a risk to marine wildlife. In this project, our team has conducted chemical and toxicological studies in order to (1) identify pollution sources of various CECs and their effects on HABs, (2) investigate the accumulation and transportation of these contaminants through the food web and (3) assess their eco-toxicological disruption to the ecosystem. In the chemical analysis part, the measured environmental concentrations (MECs) of CECs in water and sediment were determined by validated quantitative analytical methods; while their transport, fate and ecological impacts in the RES were also monitored. Moreover, PFASs can be used as tracers for the identification and validation of ocean circulation; while coprostanol, one of the fecal stanols can be used as a marker of sewage in the river-estuary-shelf system (RES). In the toxicological part, an exposure platform, using marine medaka (Oryzias melastigma) as model species, was established in order to study the toxic effects of CECs and determine the predicted no effect concentrations (PNEC) under chronic toxicity condition. Recently, the C-8 PFAS homologue, perfluorooctanesulfonate (PFOS), has been listed as a persistent organic pollutant by the Stockholm Convention, which drives the phasing out of this substance. As an alternative, the shorter chain C-4 perfluorobutanesulfonate (PFBS) is synthesized to meet the market demand. However, the increasing usage of PFBS has led to contamination of environment. The toxicological effects in marine organisms after a life-cycle exposure to PFBS on the disruption of the thyroid endocrine system and the impairment of visual function in eyes were investigated. By combining the data obtained from both chemical and toxicological studies, risk quotients can be calculated and thus environmental risks in the RES can be assessed.