The evolution of chemical risk in a Chinese river catchment exposed to untreated wastewater

The risks posed by chemicals released with domestic wastewater can be reduced by treating wastewater prior to its release, but in developing countries such as China, many of its settlements lack the infrastructure to treat its domestic wastewater. Improving our understanding of the risk posed by these chemicals in catchments that are partially served by sewage treatment works would enable this risk to be better managed. The spatially explicit chemical risk assessment model Geo-referenced Regional Exposure Assessment Tool for European Rivers was used to determine how chemical risk varies across the East River catchment, southeast China, in response to the construction of new sewage treatment works and to population change between 2010 and 2020. We evaluated the risks from two naturally occurring estrogens, estrone and 17β-estradiol, as well as two personal care product ingredients, triclosan and triclocarban. Model predictions suggest that chemical concentrations initially decrease substantially because of the rapid construction of new sewage treatment works throughout the catchment, but as the rate of construction slows and population continues to increase, chemical risk increases, with concentrations for most chemicals rising to levels greater than in 2010. We then explored the potential impact of treating 100% of domestic wastewater within the catchment, which we estimated would sufficiently reduce chemical risk for triclocarban and estrone. Subsequently, to try to reduce the risk posed by triclosan, we theoretically reduced its usage until concentrations were lowered to levels below the predicted no effect concentration. The results from this analysis suggested that triclosan usage would need to be reduced by approximately 90% to reach safe concentrations in the East River catchment.