Sewage sludge standards need new scientific basis

The report conducted by the Committee on Toxicants and Pathogens in Biosolids Applied to Land, concludes that the Agency should update its standards using better methods for assessing health risks, and further study is needed into whether sewage sludge causes health problems for workers who apply it to land and for people who live nearby.

Under a 1993 Clean Water Act rule designed to protect public health and the environment, sewage sludge can be applied to land if it is sufficiently treated to limit concentrations of certain chemicals and reduce disease-causing pathogens.

However, “there is a serious lack of health-related information about populations exposed to treated sewage sludge”, according to committee chair Thomas A Burke, professor of the Department of Health Policy and Management at John Hopkins University Bloomberg School of Public Health, Baltimore. “To ensure public health protection, EPA should investigate allegations of adverse health effects and update the science behind its chemical and pathogen standards,” he said.

The application of sewage sludge to land is a growing and increasingly controversial practice. Since 1992, when a ban on ocean dumping was instituted, applying biosolids to land has reduced the amount of sewage sludge that would otherwise need to be buried in landfills or incinerated. About 5.6 million tonnes of sewage sludge are used or disposed of each year in the United States, and 60% of that is used for land application.

Since the biosolids rule was established in 1993, methods for assessing health risks posed by exposure to chemicals have evolved substantially. The EPA used an unreliable survey in 1988 to identify hazardous chemicals in sewage sludge when it set the standards, and other chemicals have since been found to be of potential concern, says the National Academies’ report.

Accordingly, the Committee concludes that a new survey and revised risk assessments are needed, which not only reflect the potential for regional variations in climate, water flow, and biosolids characteristics, but should also be designed to protect individuals against realistic maximum exposures.