Ecological Risk Assessment of Retinoic Acids in Urbanised Coastal Marine Ecosystems 

Retinoic acids (RAs), which are metabolites of vitamin A, can disturb the development of embryos or foetuses in vertebrates at elevated levels (i.e., teratogens). A laboratory study demonstrated that 9-cis-RA could induce an abnormal development of male sexual organs in females of the marine gastropod,Reishia clavigera(i.e., imposex). A study in China showed that freshwater cyanobacteria could produce such teratogenic RAs in Lake Tai. We have recently demonstrated, for the first time, that a number of marine microalgae and cyanobacteria species can produce RAs, and their RAs can trigger up-regulation of certain imposex- and stress-related genes in head ganglia and digestive gland of femaleReishia clavigera. We have also observed that all-trans-RA at environmentally relevant concentrations can delay the developmental time of the marine copepodTigriopus japonicus.However, toxicological effects of these RAs on other marine organisms and the underlying toxic mechanisms are still largely unknown. As an urbanised coastal city, the marine environment of Hong Kong receives a large amount of partially treated wastewater effluent and contaminated surface runoff, and thus our water bodies often suffer from nutrient enrichment with frequent events of harmful algal blooms (so called ‘red tides’). If marine microalgae and/or cyanobacteria can generate and release high concentrations of RAs especially during their blooms, such RAs may cause abnormal development of marine organisms and lead to devastating impacts on marine biodiversity and natural resources. Additionally, RAs can be excreted through urination from humans and animals, and hence they commonly occur in partially treated wastewater effluents and their receiving waters. Using Hong Kong’s marine environment as an example of urbanised coastal ecosystems worldwide, this study will first investigate spatiotemporal variations of the types and magnitudes of RAs contamination in marine seawater with respect to their sources (i.e., wastewater effluents, storm waters, and those associated with marine microalgae and cyanobacteria, especially during their blooms). Second, we will examine the toxic effects of standard RAs, and RAs associated with microalgae or cyanobacteria on various marine organisms such as larvae of barnacles, copepods, gastropods, sea urchins and tube-worms through standard ecotoxicity tests. By integrating the results of the environmental fate and toxic effects of RAs to marine organisms, we will probabilistically assess their current ecological risks in local coastal marine ecosystems. Finally, we will make use of next generation sequencing and quantitative real-time PCR techniques to investigate the toxic mechanisms of RAs onTigriopus japonicaswhose genome is available.