Prioritization of biosolids-borne unregulated organic compounds

The land application of biosolids offers benefits over landfilling and incineration by improving soil health and plant nutrition. Unregulated Organic Compounds (UOCs) in biosolids have led to concerns that may impede the beneficial use of biosolids. This study presents a prioritization scheme to identify the highest-priority biosolids-borne UOCs that risk human health. A database of 906 identified chemicals in US biosolids was developed. The primary filtering process based on the class of chemicals further reduced the number of chemicals to 460. Based on the availability of quantifiable UOCs concentrations in biosolids, the number of UOCs was reduced to 298. A criterion of the highest measured biosolids chemical concentration to toxicity (rat LD₅₀) ratio of <0.001 was further used to reduce the final list to 124 UOCs. A scoring scheme was developed that included occurrence, mobility, persistence, bioaccumulation, and toxicity. Results were used to understand the fate of chemicals in soil and their potential effect on human health. The final assessment was based on the sum of five scenarios by adding scores of two or more of the parameters. Forty-six high priority and 78 low priority UOCs were identified after the final scoring evaluation. This study prioritizes UOCs based on exposure, fate, and potential hazards in soil amended with biosolids and recommends further investigation of high priority UOCs.