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(160) Biosolids Applied to Land: The National Academy of Sciences Recommendations.
Harrison, Ellen*,1, McKone, Tom2, 1 Cornell University, Ithaca, NY, USA2 University of California Lawrence Berkeley National Laboratory & School of Public Health, Berkeley, CA, USA
ABSTRACT- More than half of the 6.4 million tons of sewage sludges produced in the US are treated and then used as soil amendments. Sewage sludges are the semi-solid residue from municipal wastewater treatment plants. They contain nutrients and organic matter that can improve soils. They also contain contaminants and pathogens that are discharged to the sewer system from homes, businesses, industries and streets. Federal regulations governing land application were promulgated in 1993 and provide minimum standards that may be supplemented by state and local rules. The federal rules that establish contaminant standards for chemicals in sewage sludges are risk-based. A risk assessment that examined 14 pathways of exposure to people, agricultural crops, livestock, and selected environmental receptors was performed to develop the standards. A total of 9 inorganic elements are the chemical contaminants currently regulated under the federal rules. The rules pertaining to pathogens in land-applied sewage sludges are technology-based and no risk assessment was performed. Controversy surrounding both the practice of land application and the science behind the regulations as well as allegations of illness and even death resulting from use of sludges moved USEPA to commission a study by the National Research Council of the National Academy of Sciences. Released in July, 2002, the study found that there is uncertainty about the potential for adverse human health effects from exposure to biosolids. Thisconclusion is based on the lack of exposure and health information for exposed populations as well as the reliance of the current standards on risk assessment methods consistent with 1990 guidelines but now outdated. The committee also noted that current standards rely a on a sewage sludge survey dating from 1988, which needs to be updated. Committee recommendations include studies to examine exposure and health effects for workers and neighbors to sites where sludges are applied to the land, a new survey of chemicals and pathogens in sludges, reassessment of risks based on more recent methodology and including pathogens and development of improved pathogen detection methods and indicator organisms.
Key words: sludge, biosolids, national academy, land application
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