Which\nMicropollutants in Water Environments Deserve\nMore Attention Globally?

Increasing\nchemical pollution of aquatic environments is a growing\nconcern with global relevance. A large number of organic chemicals\nare termed as “micropollutants” due to their low concentrations,\nand long-term exposure to micropollutants may pose considerable risks\nto aquatic organisms and human health. In recent decades, numerous\ntreatment methods and technologies have been proposed to remove micropollutants\nin water, and typically several micropollutants were chosen as target\npollutants to evaluate removal efficiencies. However, it is often\nunclear whether their toxicity and occurrence levels and frequencies\nenable them to contribute significantly to the overall chemical pollution\nin global aquatic environments. This review intends to answer an important\nlingering question: Which micropollutants or class of micropollutants\ndeserve more attention globally and should be removed with higher\npriority? Different risk-based prioritization approaches were used\nto address this question. The risk quotient (RQ) method was found\nto be a feasible approach to prioritize micropollutants in a large\nscale due to its relatively simple assessment procedure and extensive\nuse. A total of 83 prioritization case studies using the RQ method\nin the past decade were compiled, and 473 compounds that were selected\nby screening 3466 compounds of three broad classes (pharmaceuticals\nand personal care products (PPCPs), pesticides, and industrial chemicals)\nwere found to have risks (RQ > 0.01). To determine the micropollutants\nof global importance, we propose an overall risk surrogate, that is,\nthe weighted average risk quotient (WARQ). The WARQ integrates the\nrisk intensity and frequency of micropollutants in global aquatic\nenvironments to achieve a more comprehensive priority determination.\nThrough metadata analysis, we recommend a ranked list of 53 micropollutants,\nincluding 36 PPCPs (e.g., sulfamethoxazole and ibuprofen), seven pesticides\n(e.g., heptachlor and diazinon), and 10 industrial chemicals (e.g.,\nperfluorooctanesulfonic acid and 4-nonylphenol) for risk management\nand remediation efforts. One caveat is that the ranked list of global\nimportance does not consider transformation products of micropollutants\n(including disinfection byproducts) and new forms of pollutants (including\nantibiotic resistance genes and microplastics), and this list of global\nimportance may not be directly applicable to a specific region or\ncountry. Also, it needs mentioning that there might be no best answer\ntoward this question, and hopefully this review can act as a small\nstep toward a better answer.