Inadequacy of Using Individual Pollutants to Assess Comprehensive Hazard Effects of Road Deposited Sediments: Implications for Stormwater Reuse Safety

Road deposited sediments (RDS) are the key carrier of pollutants deposited on road surfaces during dry days. When rainfall events occur, RDS can be washed-off into stormwater runoff along with pollutants attached, undermining stormwater reuse safety. The conventional approach to assessing the hazard effect of pollutants attached to RDS in terms of stormwater reuse is to analyze individual pollutant groups and their quantity. However, it is well known that many pollutants are present together rather than individually. This raises a question: do conventional approaches permit a comprehensive understanding of how appropriately the RDS polluted stormwater can be reused?

In order to answer this question, this study undertook a toxicity test of pollutants attached to RDS using Chinese hamster ovary cells (CHO). Organic pollutants were used as the testing pollutant group. It is noted that comparative toxicity of RDS is not strongly related to total solids (commonly seen as the key carrier of pollutants) and chemical oxygen demand (COD, representing organic matters). Additionally, the comparison results of spatial distributions of toxicity (in this study) and individual pollutants in previous studies did not show a similar trend. These results imply that toxicity should be also used to indicate how stormwater can be safely reused while solely investigating individual pollutants can not adequately show a comprehensive hazard effect in terms of ensuring stormwater reuse safety. Based on study outcomes, a new assessment approach considering both pollutant and toxicity were proposed. This will assist on effective stormwater reuse and ensuring their reuse safety.