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The government is using outdated science in assessing the health risks of more than 3 million tons of sewage sludge used as fertilizer each year, a panel of scientists said yesterday.
When the Environmental Protection Agency set standards in 1993 on the use of "biosolids" for treating soil, it used an unreliable 1988 survey to identify hazardous chemicals in sewage sludge from wastewater treatment plants, said the National Research Council panel.
Since then, the panel said, the technology for detecting pathogens and the methods for assessing health risks posed by chemicals in the sludge have developed significantly.
"There is a serious lack of health-related information about populations exposed to treated sewage sludge," said the panel's chairman, Thomas A. Burke, a health policy and management professor at Johns Hopkins University's Bloomberg School of Public Health.
The panel's 270-page report, which had been requested by EPA, found no documented scientific evidence of the EPA's standards failing to protect public health. But it said the agency needs to do more scientific work so it can "reduce persistent uncertainty" about the risks to people from exposure to chemicals and disease-causing pathogens in sludge used as fertilizer.
The EPA hasn't done a substantial reassessment to determine whether its standards are supported by current scientific data and risk assessment methods, the panel said, noting that it had made a similar recommendation in 1996.
After sewage sludge is treated to limit concentrations of some chemicals and reduce pathogens, it is commonly known as biosolids, which can be applied as fertilizer to farms, forests, parks, golf courses, lawns and home gardens.
About 5.6 million tons of sewage sludge are used or disposed of each year in the United States, and 60 percent of it is used as fertilizer. The rest is buried in landfills or incinerated. Dumping sewage into the ocean was banned in 1992.
In February, a report by the EPA's inspector general found the government has done too little research to ensure humans are safe from the viruses, bacteria and toxins in the sludge.
The agency also was faulted for continuing to rely heavily on a 1990 survey that contained sampling "inconsistencies" and used reporting methods that "undermined the reliability of the data" instead of conducting new scientific studies.
However, panel member Ian Pepper, who directs the National Science Foundation Water Quality Center at the University of Arizona in Tucson, said decreasing heavy metal concentrations have made biosolids safer than a decade ago.
Benjamin Grumbles, deputy assistant administrator of EPA's Office of Water, said the report confirms the agency's view that the existing sewage sludge regulations protect human health.
Republican Sen. Charles E. Grassley of Iowa said after seeing the report that he worries the public "simply has to take the EPA's word" that its sludge standards are effective.