Approximately 25% of all biosolids generated by domestic publicly owned treatment facilities in 2021 were applied to agricultural lands, creating numerous exposure scenarios for farm workers and the general public. Concentrations and loading rates for select elements in biosolids applied to agricultural lands are regulated under the Clean Water Act, but the potential exists for a wide array of organic compounds to survive the treatment processes and persist in these biosolids. Nontarget analyses (e.g., via liquid chromatography–high-resolution mass spectrometry; LC-HRMS) can be used to detect and identify these biosolid-associated organic compounds (BOCs). However, the detectable chemical space of a particular analysis is impacted by a variety of factors, including, for example, the chosen instrumental technique and the specific analysis conditions (e.g., mobile phase selection, ionization source). Defining the detectable chemical space can improve the interpretation and communication of nontarget analysis results; however, this remains challenging. A proof-of-concept chemical space mapping tool, the ChemSpace Tool, has been developed to address this need, which uses existing chemometric tools as well as filtering based on categories of chemicals identified in types of samples. We applied this tool to identify BOCs in biosolid specimens analyzed using LC-HRMS and 8 different instrumental conditions (4 mobile phase conditions x 2 ionization sources) in both positive and negative ionization modes. The ChemSpace Tool was implemented to define the identifiable and detectable regions of chemical space of the different biosolids. These results will be included in future work to detect and identify BOCs widely present in U.S. and international biosolids.

Implementing a chemical space mapping tool to improve interpretation of nontargeted analyses of biosolids: A proof-of-concept study

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