Microbial Risk Assessment Modeling for Exposure to Land-Applied Class B Biosolids.

摘要

Biosolids has been used as a soil amendment to enhance agricultural production. While providing benefits to agriculture, land application of biosolids may introduce pathogens into the environment and present human health risks. There have been several studies on the link between land-applied biosolids and human health. However, land-application sites vary, making it important to have models that can be implemented for a site-specific assessment of risk.;This study developed and applied a spreadsheet-based tool, named The Spreadsheet Microbial Assessment of Risk: Tool for Biosolids (SMART Biosolids), which links quantitative microbial risk assessment with microbial fate and transport modeling. The SMART Biosolids model estimates risk associated with exposure to pathogens from land-applied biosolids through five pathways: inhalation of aerosols from land application sites, consumption of groundwater affected by land-applied biosolids, direct ingestion of biosolids-amended soils, consumption of water contaminated by runoff from a land application site, and ingestion of plants impacted by land-applied biosolids. Currently the model is able to quantify risks for six pathogens: Giardia lamblia, Cryptosporidium, Salmonella, Shigella, enterovirus, and adenovirus, and examine the exposure concentrations for four indicators: coliphage, E.coli, Enterococci, and fecal coliforms.;The application of the SMART Biosolids model to a specific site with typical application found that the risks generated across pathways, in descending order, are from ingestion of biosolids-amended soils, ingestion of contaminated surface water, ingestion of contaminated vegetables, inhalation of aerosols from application sites, and consumption of contaminated groundwater. A sensitivity analysis indicates that microbial parameters, especially decay rates and dose-response parameters, are strongly correlated to the risk estimates. For the groundwater pathway, the hydraulic parameters, including hydraulic conductivity, saturated water content, residual water content, and dispersion, need to match site-specific environmental conditions. This study compiles the most current pathogen occurrence, fate, and decay data and develops a comprehensive exposure model for biosolids-derived pathogens. The assessment tool has the capability to archive the most up-to-date knowledge and to be updated as additional information becomes available in the future.