Risk characterization from multipathway exposure associated with land applying biosolids by accounting for multimedia mass loss.

摘要

For over two decades the 40 CFR Part 503 has been the regulatory framework guiding land application of biosolids in the US. During this period public perception about the practice has worsened as evidenced by increases in partial and full biosolids land application bans across the US. In this work, the Multimedia, Multipathway and Multi-receptor Risk Assessment (3MRA) model was applied to four biosolids land application sites across the US (two sites in WA, one site each in VA and GA) to evaluate human health risk concerns from regulated (As and Cd) and non-regulated (B(a)P and DEHP) chemical constituents present in biosolids. The excess cancer risk from ingesting soil contaminated with As and Cd was higher than 1x10-6 when accounting for the background concentration. However, after separating the risk to reflect just the land application practice, the excess cancer risk estimates for the soil ingestion pathway were well below the acceptable risk criteria (several orders of magnitude lower). The non-cancer risk, for both As and Cd, was below 1. As and Cd remained mostly in the zone of biosolids incorporation. The combined As and Cd mass lost to all pathways for a 20-year consecutive application scenario was less than 15%. The classes of organic environmental toxins evaluated also did not cause concern. Both B(a)P and DEHP aerobically degraded and less than 3% remained in the zone of biosolids incorporation after a 100-year consecutive biosolids application based on model predictions. Scenarios considering biosolids application at typical agricultural rates did not result in groundwater impairment for the sites evaluated; however, scenarios with biosolids applications that are similar to a surface disposal practice resulted in groundwater impairment. In addition to this work, sites across the US (in WA, VA and GA) were evaluated for groundwater impairment scenarios. The results from this effort clearly point towards no additional excess cancer (>1x10-6) or non-cancer (HQ>1) health risks associated specifically with the practice of land application of biosolids for agricultural production for the sites and chemical contaminants evaluated.