The Science of Recycling Sewage Sludge

Sept. 6, 2002

National Academies Op-Ed Service Archives

by Thomas A. Burke

From the privies of colonial times to today's regional wastewater treatment facilities, the safe management of human waste has presented a fundamental environmental challenge. Today, the national wastewater treatment infrastructure deals with millions of tons of domestic waste generated annually; it is a cornerstone of our efforts to keep the nation's waters clean. To manage the ever-increasing volume of sewage, technology has been developed that enables us to recycle some of it to the environment. The recycling plan includes applying treated sewage sludge, called biosolids, to agricultural and other lands as fertilizer.

The U.S. Environmental Protection Agency regulates biosolids that are applied to land. Approximately 3 million dry tons are used annually. Although land application has been practiced for decades, it has not been without controversy. In recent years a number of communities have protested the practice, and there have been anecdotal reports of illness.

Two years ago, at the request of EPA, the National Research Council convened a committee to examine the scientific basis of EPA's regulatory requirements for applying biosolids to land. I served as chair of that committee, and in July the committee's report, Biosolids Applied to Land: Advancing Standards and Practices, was released. The consensus report called on EPA to update the scientific basis of its requirements, to improve our knowledge about chemicals and disease-causing pathogens that may be present in biosolids, to evaluate concerns about health effects and exposure, and to make a stronger investment in the agency programs overseeing biosolids application and management. The report outlined positive steps the agency can take to evaluate and manage risks, respond to stakeholder concerns, and protect public health. But because some press accounts focused only on criticisms of EPA's past efforts, and do not fully reflect the findings and recommendations of our report, I would like to clarify our findings.

First, we found no evidence of an urgent public health risk from exposure to land-applied biosolids, based on our review of the scientific literature. Currently, there are no studies documenting adverse health effects from land application of biosolids, even though land application has been practiced for years. But this finding was tempered by the fact that few studies are available on human exposure to biosolids, and that, even when they are investigated locally, there are no means of tracking health allegations nationally. Based on the lack of epidemiological studies and a need to address the public's concerns, we recommended that EPA support studies of populations exposed to biosolids, such as workers or communities near application sites, and investigate reports of unusual illness or exposure.

Second, we need to update our understanding of the components of biosolids, particularly in light of changes over time in chemical uses, wastewater treatments, and technology. An updated assessment is needed periodically to identify possible changes in the composition of biosolids and to verify that the regulatory requirements are still valid. Therefore, one of our major recommendations is that EPA conduct a new national sewage sludge survey to examine both chemicals and pathogens.

Third, EPA has not reassessed the chemical and pathogen standards since it established them in 1993. EPA based its regulations on its understanding of the most hazardous chemical and microbial components at that time. We support this approach, but advised EPA that it needs to periodically reassess whether the existing regulatory standards are supported by the latest scientific data, improved technology, and methods for estimating risk. These periodic assessments will require additional resources at EPA and state agencies.

EPA's biosolids regulatory program must move forward, as should any regulatory program that has been in place for a number of years. The good news is that better scientific tools are available now to help EPA gather needed data and monitor land-application practices. Science does not remain static, nor should our efforts to protect public health and the environment.

Thomas A. Burke, Ph.D., is a professor at the Bloomberg School of Public Health, Johns Hopkins University, Baltimore.

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