Fertilizer From Sewage Linked To Illness, Deaths

by Kim Carlyle

Researchers found that affected residents lived within approximately one kilometer of land application sites generally complained of irritation after exposure to winds blowing from treated fields. Approximately 25 percent of the individuals surveyed were infected, and two died.

"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 David Lewis, a microbiologist also affiliated with the EPA's National Exposure Research Laboratory. "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 co-author David 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 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.

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.

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, which appeared in the British medical journal, BMC Public Health.