Researchers Find Insufficient Data Available To Assess Sludge Risk

Tens of thousands of organic chemicals from homes, farms, industries, medical facilities, street runoff and businesses are treated in wastewater treatment plants. The resulting sludge -- rich in organic matter and nutrients but also potentially containing toxic metals, pathogens and pollutants -- often is applied to land to amend soil. Yet sludge concentration data for only 516 organic chemicals can be found in peer-reviewed and official government reports, Cornell University researchers announced this month.

Of those 516 chemicals, more than 80 percent are not on EPA's established list of priority pollutants or on its list of target compounds, said Ellen Z. Harrison, director of the Cornell Waste Management Institute and the lead researcher of the study.

"Thus analyses targeting these lists will detect only a small fraction of the organic chemicals in sludges," said Harrison, noting that federal rules have no requirements for testing sludges for such chemicals. Very little data is available for such chemicals as nitrosamines, which may pose a high risk. Where data are available, concentrations in sludges for many chemicals exceed the levels EPA use to determine whether soils at Superfund sites present enough of a risk to require a site-specific risk assessment.

"Relying on existing lists of chemicals, such as priority pollutants, will not identify many chemicals of current concern," Harrison concluded. Further surveys of organic chemical contaminants in sewage sludges and the risks they pose are sorely needed, she said.

The study will be published in a forthcoming issue of Science of the Total Environment and can be accessed at

This article originally appeared in the 07/01/2006 issue of Environmental Protection.

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