Abstract

Kibaki Okemo, John Saitoti and Njeru Masakhalia

Land application of biosolids has been shown to benefit degraded rangeland; however, soil metal accumulation has been a concern. To date, nine heavy metals found in land applied biosolids are regulated by the United States Environmental Protection Agency. Concern increases when application rates exceed the agronomic rate. The objective of this study was to monitor changes in soil metal accumulation from a one-time biosolids surface application on disturbed rangeland in Western Utah. Two types of biosolids, aerobically digested and lime stabilized, were applied at rates up to twenty times (20x) the estimated agronomic rate. Biosolids were not incorporated into the soil. Levels of heavy metals were recorded at five different soil depths, 0.2, 0.6, 0.9, 1.2 and 1.5 m. The one-time application was evaluated over a two year period. No significant consistent trend between metal concentration, biosolids application rate, biosolids type, year, and soil depth was found. It was concluded that metal concentrations in this study were below the cumulative loading rate from the 40 Code of Federal Regulations (CFR) Part 503 rule. These findings can help alleviate concerns about environmental and health risks due to metal accumulation from biosolids land application.