Conventional and Emerging Halogenated Flame Retardants in Marine and Estuarine Food Webs in Subtropical Hong Kong Waters: Accumulation Profiles, Trophic Transfer, and Source Identification

Halogenated flame retardants (HFRs) are emerging contaminants of concern because most of them are persistent, toxic, and bioaccumulative. Despite their potential ecological and public health impacts, environmental data on these compounds, especially as alternatives for polybrominated diphenyl ethers (PBDEs), are still very limited. PBDE levels in mussels and cetaceans in south China, including Hong Kong, have been found to be the highest among many Asian sites. High occurrence of these toxic and recalcitrant pollutants may be attributed to the heavy industrialization and urbanization in the Pearl River Delta (PRD) over the past decades. A recent study identified two new HFRs in Hong Kong cetaceans, and this finding lends support to the idea that a wide range of HFRs are in use in the region and are continuously being released into the coastal environment of south China. In addition, significantly higher levels of HFRs, including HFRs being used as PBDE alternatives, have been recorded in dolphins in comparison to porpoises inhabiting the northwestern and eastern waters, respectively. There is also an increasing usage of PBDE alternatives following the restriction/voluntary withdrawal of the production and use of PBDE commercial mixtures, namely pentabromodiphenyl ether (Penta-BDE) and octabromodiphenyl ether (Octa-BDE). Although some information on the distribution pattern and dietary preferences of local cetaceans is available, the sources of HFRs and how these emerging contaminants of concern accumulate in top predators are still unclear. Discerning the sources (e.g. point and non-point sources) and accumulation dynamics of HFRs in the cetaceans is both challenging and instructive. Compound-specific stable isotope analysis (CSIA) has been used to infer sources and fate of contaminants in the environment by measuring the ratio of stable isotopes in specific organic compounds. Recently, hyphenation with two-dimensional gas chromatography (2DGC) for CSIA has been proposed for use to characterize the source and fate of persistent organic pollutants due to its improved specificity and sensitivity. With the potential differences in isotopic fractionations in HFR sources from the respective habitats of the dolphins and porpoises, this project aims to test the hypothesis that the sources of HFRs in the PRD (northwestern waters of Hong Kong) are significantly different from those of the eastern waters of Hong Kong, and that these differences are reflected in the accumulation levels and profiles of target HFRs in dolphin and porpoise, respectively.