Have risks associated with the presence of synthetic organic contaminants in land-applied sewage sludges been adequately assessed?

Land application has become the dominant means for sewage sludge disposal in the United States. In 1993, the EPA concluded that synthetic organics therein posed an insignificant risk, based on the results of the 1988 National Sewage Sludge Survey, the view that most persistent organics are no longer in commerce and that industrial pretreatment further reduces their release to municipal treatment plants. However, we detected high concentrations of several problematic compounds in biosolids that were overlooked in the risk assessment, including persistent, bioaccumulative polybrominated diphenyl ethers and estrogenic nonylphenols. These results and other findings call into question the assessment's certainty.