Solid Waste & Recycling


Sewage sludge studies point to serious health risks

Recent studies confirm that the practice of applying sewage sludge to farm fields can pose serious and even fatal h...

Recent studies confirm that the practice of applying sewage sludge to farm fields can pose serious and even fatal health risks to humans and animals. Data indicates that people exposed to fields and gardens fertilized with sewage sludge run a higher risk of developing untreatable, potentially deadly viral and bacterial infections and cancer.

"Interaction of Pathogens and Irritant Chemicals in Land-Applied Sewage Sludges (Biosolids)," a study that appeared in the BMC Public Health, a British medical journal, suggests that Class B sewage sludge (byproducts of human waste) often contain pathogens. When mixed, these pathogens create potent new strains of staphylococcus aureus (staph), the most common bacteria found in sewage sludge. According to lead author David Lewis, a microbiologist with the U.S. EPA at the University of Georgia, the new strains are almost impossible to fight off with antibiotics.

For two years researchers from the University of Georgia monitored the symptoms and medical conditions of participants near sewage sludge application sites in Canada and the U.S. Reported complaints included skin rashes, sore throats, flu-like symptoms, and even two deaths. According to Dr. Lewis, the staph found in sewage sludge is much more dangerous than in a normal environment because it contains waste flushed down the toilet in hospitals where individuals are treated for virulent strains of staph. The study also expresses concern about other harmful viruses not killed by treatment processes currently used for Class B sludge.

Furthermore, Dr. Coleman Rotstein, an infection specialist who heads the Canadian Infectious Diseases Society, calls for urban centres to stop spreading thousands of tonnes of treated human waste on farm fields until the practice is proven safe.

According to Dr. Rotstein, in light of the Walkerton, Ontario water tragedy (when seven people died and 2,300 became ill as a result of E.coli contamination) and recent U.S. studies, there should be a moratorium on spreading liquid or semi-solid sludge within 10 kilometres of any populated area. Ottawa city council recently acted on the association’s advice and voted to suspend spreading sludge on farms, even though landfilling it will cost an estimated $1.5-million a year.

Legislation such as Ontario’s new Nutrient Management Act might eventually control sludge use. The Act cleared the committee hearing stage in the Ontario Legislature on May 13, 2002. The bill would use Commissioner Dennis O’Connor’s Walkerton Inquiry report and further research to develop best practices and regulations.

SW&R’s articles about sewage sludge — available at the "back issues" section at — include: award-winning "Sludge Fight" in the December/January 2002 edition; "A Solid Approach to Control the Content of Sludge" and "Will the U.S. EPA Clean Up its Sludge Policy?" in the April/May 2002 edition; and "The Right to Harm" in the October/November 2001 edition.

To read the U.S. National Research Council Report on Biosolids Applied to Land visit and to read the "Interaction of Pathogens and Irritant Chemicals in Land-Applied Sewage Sludges (Biosolids)" study visit

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