The reuse of biosolids as fertilizer for farming has several benefits, including being a ready source of nutrients for plant growth, reduction in the use of chemical fertilizers, reduced costs for sewage treatment, and reduced disposal of biosolids in landfills. The Clean Water Act (CWA) requires EPA to review biosolid regulations every two years to identify additional chemicals that may need to be regulated because of potential harm to human health and the environment”. Currently, regulation of chemical content in biosolids is limited to a few metals and PCBs. For years EPA has been collecting data in biennial reviews regarding chemical concentrations in biosolids, chemical toxicity, and environmental fate and transport, but has not performed risk assessments that would lead to decisions about the necessity for regulations. Currently, EPA is preparing to perform a risk assessment for PFAS compounds in biosolids, but these are not the only chemicals that may warrant further consideration. Given the effort required to perform a multi-media, multi-pathway risk assessment, we gathered data and implemented a ranking system for the hundreds of remaining chemicals found in biosolids to identify those chemicals with the highest potential risk. First a comprehensive review of the literature was performed to identify concentration data for chemicals detected in sewage sludge. This review included a search of the primary literature via PubMed, and a thorough review of any published U.S. EPA Biennial Reviews available at the time (2005 – 2017). Information related to hazard and environmental fate and transport was also collected from these reviews, and numerous other data sources. We then ranked each of the chemicals of interest based on the framework developed by U.S. EPA for the Toxic Substance Control Act (TSCA). The TSCA framework ranks chemicals based on exposure (we used concentration for this metric), human health effects, and persistence/ bioaccumulation. Consistent with TSCA’s approach, each of the three categories was ranked on a 3-point scale and the total score was based on adding the contributions of each category for maximum score of 9. Starting with a list of 223 constituents, 175 were determined to have sufficient data available and were ranked. A total of eight chemicals received the highest ranking of 9. These rankings can be used to prioritize chemicals for risk assessment. We would like to acknowledge the funding we received for this project from the Texas Commission on Environmental Quality.
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