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Sorting Out the Science of Sludge

By Michael Purdy

“It’s 10 o’clock. Do you know where your poop is?” jokes Thomas Burke, PhD, MPH, professor of Health Policy and Management and co-director of the Risk Sciences and Public Policy Institute. 

Burke recently chaired a National Research Council panel on the potential health risks of a primary usage of sewage sludge: as a fertilizer for farmland, parks, landfills, old strip-mining sites, and home lawns and gardens. The United States banned ocean dumping of sewage sludge in 1992. The rate of recycling of sludge as fertilizer has increased since then; it’s estimated  that 60 percent of the 5.6 million dry tons of sewage sludge disposed of annually is applied as fertilizer.

“This is not on the radar for many policymakers, particularly given the attention on potential terrorist attacks, but as more farmland is lost to development, and more people live closer to areas where these materials are applied, more people are becoming exposed to this practice,” Burke says. The panel found a number of anecdotal reports of illnesses attributed to exposure, ranging from mild conditions to severe chronic health problems.

The panel’s final report, presented to the EPA on July 2, recommends a thorough reassessment of the health risks of sludge as fertilizer, and expanded resources for oversight.

“We don’t appear to have a public health crisis yet,” Burke comments, “but good public health is about prevention.”

 Techniques for assessing health risks have improved significantly since a 1988 study that many current  EPA rules are based on, and Burke and the other members of the panel believe it’s important to see those improved techniques applied to potential concerns about sludge. Potential risks include pathogens, like viruses, bacteria, and parasites; inorganic contaminants like metals; and pharmaceutical contamination.

“The large majority of these applications of sludge don’t appear to be causing problems, but this report is a call for sorting out the science,” says Burke. “We want to take the next step and make sure we prevent adverse exposures and effects.”