Hydrophilic trace organic contaminants in urban stormwater: occurrence, toxicological relevance, and the need to enhance green stormwater infrastructure

Hydrophilic trace organic contaminants (hyphil-TrOCs) are polar, often ionizable organic compounds of anthropogenic origin that have various applications in the urban environment e.g., as pesticides, plasticizers, and flame retardants. Hyphil-TrOCs can be washed off in storm events and enter surface waters via untreated urban stormwater discharges or combined sewer overflows. Though trace concentrations of these chemicals may pose a risk to ecosystem and human health, information on their presence in urban stormwater remains elusive. Monitoring and source apportionment of hyphil-TrOCs in urban stormwater is complicated by the vast number and sources of organic contaminants and the high variability in aqueous concentration over time and space. Here, we present the current state of knowledge on the occurrence and toxicological relevance of hyphil-TrOCs in urban stormwater. To mitigate negative impacts of contaminated surface runoff to receiving water bodies and to prevent sanitary or combined sewer overflows, many cities implement sustainable green stormwater infrastructure, also called best management practices (BMPs). Current knowledge suggests that conventional stormwater BMPs such as detention basins, constructed wetlands, and biofilters often fail to remove hyphil-TrOCs. We identify future research needs to enhance green stormwater infrastructure with respect to water quality and safe use of urban stormwater for non-potable applications or groundwater recharge and present potential benefits of geomedia amendments in BMPs (e.g., activated carbon or biochar-amended biofilters). We highlight the need to improve stormwater monitoring strategies by combining chemical and bioanalytical tools to better assess effects of complex chemical mixtures and the treatment performance of BMPs and assure safe stormwater use for water supply.