This study is the first linking adverse health effects in humans to the land application of Class B biosolids to be published in a medical journal. It was co-authored by David Lewis, a UGA research microbiologist also affiliated with the U.S. Environmental Protection Agency (EPA)'s National Exposure Research Laboratory; David Gattie, assistant professor of agricultural engineering at the University of Georgia's College of Agricultural and Environmental Sciences; Marc Novak, a research technician at UGA's School of Marine Sciences; Susan Sanchez, assistant professor of veterinary medicine at UGA; and Charles Pumphrey, a physician from Prime Care of Sun City in Menifee, Calif. The article appeared this month in the British medical journal, BMC Public Health.
Researchers found that affected residents lived within approximately one kilometer (0.6 miles) of land application sites and generally complained of irritation after exposure to winds blowing from treated fields. A prevalence of Staphylococcus aureus infections, a condition commonly accompanying diaper rash, was found in the skin and respiratory tracts of some individuals. Approximately 25 percent of the individuals surveyed were infected, and two died. The 54 individuals surveyed lived near 10 land application sites in Alabama, California, Florida, New Hampshire, Ohio, Ontario, Pennsylvania and Texas. S. aureus is commonly found in the lower human colon and tends to invade irritated or inflamed tissue.
"The EPA did not consider S. aureus to be a significant public health risk even though it is a leading cause of hospital-acquired infections and is commonly found in sewage," said Lewis. "When approving sludge for use as a fertilizer, EPA looked at chemical and pathogen risks separately without considering that certain chemicals could increase the risk of infection."
Chemicals such as lime, which is added during sludge processing, can irritate the skin and respiratory tract and make people more susceptible to infection, according to Lewis. The American Chemical Society recently published another article on pathogen risks from sludge by Lewis and Gattie in their journal Environmental Science & Technology.
Though modern treatment can eliminate more than 95 percent of the pathogens, enough remain in the concentrated Class B sludge leaving treatment plants to pose a health risk, according to Lewis and Gattie.
On July 2, the National Research Council of the National Academy of Sciences (NAS) concluded that there may be public health risks from using processed sewage sludge as a commercial fertilizer. Approximately 60 percent of an estimated 5.6 million tons of dry sludge is used or disposed of annually in the United States.
The NAS report entitled "Biosolids Applied to Land: Advancing Standards and Practices" cites growing allegations that exposure to Class B sludge, the most common form, is causing illnesses and sporadic deaths among residents. The report concludes that certain types of exposure, such as inhalation of sludge particles, "were not adequately evaluated" previously and no work has been done on risks from mixtures of pathogens and chemicals found in sludge. In 1989, an EPA study found 25 groups of pathogens in sludge, including bacteria such as E. coli and salmonella; viruses, including hepatitis A; intestinal worms; harmful protozoa; and fungus.
Sludge also includes traces of household chemicals poured down drains, detergents from washing machines, heavy metals from industry, synthetic hormones from birth control pills, pesticides, and dioxins, a group of compounds that have been linked to cancer.
Fertilization of land with processed sewage sludge, or "biosolids," has become common practice in Western Europe, the United States and Canada. Local governments, however, are increasingly restricting or banning the practice in response to residents reporting adverse health effects.
"Most people are not aware this is going on in the U.S.," said Gattie. "Most people don't realize that a concentrated sludge of waste products is being processed into a cheap commercial fertilizer and applied to fields near our homes. 'Biosolids' does not connote 'sewage' to most people." He notes this practice has become more common after ocean dumping of sewage was prohibited.