Occurrence and origin of triazine herbicides in a tropical coastal area in China: A potential ecosystem threat

Tropical coastal ecosystems are particularly at threat from land-sourced pollution, resulting from the input of harmful substances from a multitude of emission sources. Although not intensively studied to date, this concerns also the contamination of coral reefs with pesticide classes apart from the frequently reported organochlorine pesticides. We therefore investigated the occurrence and spatial distribution of these compounds in water samples from the northeast coast of Hainan, a tropical Chinese island. The study area included two sensitive coastal habitats: a shallow bay and fringing coral reefs with seagrass beds. The results revealed the occurrence of photosystem(II) triazine herbicides at most sampling stations in the coastal waters, especially of prometryn (maximum concentration 440 ng L-1). A chemical characterization of aquaculture pond waters gave evidence that aquaculture was the source of this contamination. Prometryn was detected in many sampled ponds and could thus be useful as source-specific molecular indicator to trace aquaculture emissions in coastal areas. Concentrations of triazine herbicides in the study area (<10-440 ng L-1) were lower than reported acute effect concentrations for dinoflagellates, seagrass and algae. Thus, no acute toxic effects on local coral reefs and seagrass beds are expected. Chronic exposures of sensitive species to low concentrations of the detected triazine herbicides have to date not been studied. Therefore, we cannot exclude deteriorating effects in the long-term, especially in combination with other stressors such as rising sea surface temperature, which can enhance the sensitivity to pollutants. Future studies in other world regions should consider prometryn and further triazine herbicides as harmful pollutants from aquaculture emissions.