Is sludge safe? (Recycling).

The U.S. Environmental Protection Agency (EPA) should initiate a hefty research program into the human health risks of using treated sewage sludges ("biosolids") on land, according to a National Research Council committee report released in July. The report, titled Biosolids Applied to Land: Advancing Standards and Practices, was requested by the EPA to address public health concerns and to fulfill a Clean Water Act requirement to periodically reassess the science behind the so-called Part 503 rule.

This rule sprang from the Clean Water Act and came into effect in 1993. It established management practices for land application of sewage sludges, concentration limits, loading rates for chemicals, and treatment and use requirements designed to control and reduce pathogens as well as the number of bugs, birds, and rodents that the sludge might attract.

The study identified three major gaps in the scientific basis of the rule: a lack of knowledge about potential human health effects and exposure, a need for an updated risk assessment-of chemical contaminants, and a need to assess the risk posed by pathogens in sludge. The committee also found that there is no documented scientific evidence of adverse human health effects from treated sewage sludges applied to land in accordance with the EPA's regulations.

However, according to committee chair Thomas Burke, a public health professor at The Johns Hopkins University in Baltimore, Maryland, this finding was "tempered by the fact that there are few studies available on human exposure to biosolids, and that, even when they are investigated locally, there are no means of tracking health allegations nationally."

Reaction to the report has been favorable from all sides. The EPA and the water and sludge industry welcomed the finding of no proven health problems. Environmental groups and concerned scientists welcomed the research agenda.

The Part 503 rule has been controversial since its inception in 1993. It divides sludges into two classes based on pathogen content. In Class A biosolids, pathogens are below detection levels, whereas Class B biosolids have detectable levels of pathogens. However, the risk from pathogens was never formally assessed for the biosolids rule, nor has the potential exposure of neighbors to pathogens and contaminants resulting from wind dispersion or runoff been taken into account. Municipalities and counties in some states including California, Virginia, Florida, and New Hampshire have instituted land application bans or restrictions on sludge application.

The increase in land application of biosolids has engendered an increase in health complaints, says Burke. These complaints are anecdotal, but they may be important, he adds.

"I am increasingly convinced that in some places people are getting sick, sometimes very sick, from Class B sludge applications," says Ellen Harrison, director of the Cornell Waste Management Institute in Ithaca, New York. Her organization has tracked down some 40 allegedly sludge-related health incidents affecting over 300 people as of August 2002. Respiratory and gastrointestinal symptoms are most common. Other frequent complaints include nosebleeds, flu-like symptoms, fatigue, and burning eyes, throat, and nose.

To find out whether health effects can be linked to biosolids exposure, the committee recommends that unexpected outbreaks or unusual exposures be studied along with preplanned exposure assessment studies of farmers, sludge workers, and nearby residents. In addition, a few well-designed epidemiological investigations of exposed populations should be conducted to see if there is a causal association between biosolids exposure and adverse health effects.

The committee urges a new survey of contaminants in sludge to include pathogens and organic contaminants of emerging concern such as flame retardants and detergent surfactants. A new risk assessment incorporating probabilistic methods and allowing for regional differences in climate and soils should also be conducted, the committee finds.

The EPA has until April 2003 to craft a response and request public comment, in accordance with a legal agreement from a previous lawsuit related to sludge regulations. Any research program will involve funding across and outside of the agency, says Alan Hais, associate director of the EPA's Health and Ecological Criteria Division, adding that such research will cost millions of dollars.