EPA Targets Waterborne Microbial Disease

The Environmental Protection Agency recently released for review a draft strategy for combating waterborne microbial disease. The draft calls for better integration of Safe Drinking Water Act and Clean Water Act programs, which have historically followed separate paths using differing indicators of contamination and differing approaches to addressing water quality problems.

The consequences of microbial water contamination are severe. The Centers for Disease Control and Prevention estimates that in the United States each year up to 940,000 cases of illness and possibly 900 deaths occur as a result of waterborne microbial infection. On a worldwide basis, diarrhea is the disease most likely to result in child mortality, with a global mortality estimate of 3.3 million deaths per year. Drinking of contaminated water is the most common source of exposure to organisms that cause pathogenic diarrhea.

There are as many potential microbial hazards as there are pathways into surface and ground water systems. One area of concern is the risk of human disease from animal-borne pathogens in water. It had been thought that most cases of waterborne enteric disease came from direct contact with pathogens in human feces or from human contact. However, fecal material from both humans and animals (especially mammals) can carry pathogens which cause disease in humans.

As humans have domesticated animals and populated previously pristine and rural areas, increased interaction has resulted in the evolution of new human pathogens; that is, microbes which previously had animals hosts have acquired the ability to infect humans, a process called zoonotic transfer. Examples include cryptosporidiosis and giardiasis.

"We cannot currently predict which microbes will clear the evolutionary hurdle from an animal host to humans. Every microbial class (bacteria, viruses, protozoa) has made that jump," the draft strategy states.

"Microbes evolve rapidly; they adapt to their environment by developing traits which can make them more effective parasites or pathogens. It is likely that innovative approaches will need to be developed to ensure that the many uses of water do not result in exposure to disease-causing organisms.

"Protection of source waters is necessary to provide or maintain high quality ambient waters that are swimmable and fishable and to manage watersheds more effectively so that we can reduce the burden on drinking water sources."

The draft strategy identifies EPA's top approaches to water protection, which include setting CWA ambient water quality criteria; managing sources of contamination, establishing treatment and monitoring requirements or discharge criteria for reused waters and unregulated industrial wastes; and establishing an agency panel to develop a microbial risk-assessment paradigm.

The draft strategy identifies on-site treatment systems and non-point sources of pollution as major areas of unregulated water body contamination. Estimates indicate that at any given time at least 10 percent to 30 percent of existing septic systems are significantly failing, the strategy states.

According to EPA, criteria for the microbiological quality of publicly owned treatment works wastewater discharges do not reflect their potential impact to downstream drinking water intakes. And there are no requirements to notify downstream users when discharges exceed limits due to accidents or upsets in the system.

Appropriate risk assessment protocols for waterborne infectious diseases would increase the accuracy of assessments used for developing regulations, prioritizing enhancements to public health protection, and for conducting outbreak investigations.

The goal of the strategy is to develop an integrated, coordinated approach to developing risk based criteria. These criteria could be based on exposure, and the application of a common set of fecal indicators across the various uses of water, rather than different indicators for specific uses. As new health protective criteria and indicator/monitoring requirements are developed for ambient water uses, EPA's goal is to ensure that they are uniform, consistent, and rational across uses.

Copies of the draft "Strategy for Waterborne Microbial Disease" are available on the EPA website, www.epa.gov.

James Laughlin
Editor