"The Risks of Microscopic Organisms in Drinking Water"
Joan Rose, Ph.D., is an Associate Professor in the Department of Marine Sciences, College of
Public Health, University of South Florida. Her area of expertise is water pollution microbiology She has been involved in the investigation of recent waterborne outbreaks of Cryptosporidium, and she is well known for her participation in the NBC TV program "Dateline" which focused on the Cryptosporidium outbreak in Milwaukee. Dr. Rose has served on the National Academy of Sciences committee and the Science Advisory Board for the EPA and was recently invited to join the National Drinking Water Council. The following is a synopsis of her presentation at a 1995 Conference in Las Vegas.
In the U.S. we are facing degradation of our waterways by pollutants and microbial contaminants
resulting in an average of one million cases of waterborne disease per year. Microbial contaminants, such as Giardia, Cryptosporidium, and the new Cyclospora, are causing major outbreaks across the nation.
In the 1960's Giardia became a prevalent contaminant of health concern that prompted the enactment of the Surface Water Treatment Rule that stated that all surface water that may potentially be used for drinking water must be filtered. Unfortunately, problems with Giardia, viruses, newer protozoans (like Cyclospora), and, especially, Cryptosporidium are still occurring.
Chlorination has little effect on cysts and protozoans like Cryptosporidium. We are also finding that merely filtering surface water isn't solving the problem since most microbial outbreaks of this sort are occurring in ground water sources (of all the waterborne outbreaks between 1991-92, 77% occurred in wells). Even pristine water sources (which are closed to human activity) are not safe from microbial contamination since sources of microbial contaminants are not only human waste products, but also animal feces.
Giardia can be killed by long contact with chlorine, but Crypto is much more resistant. Filtration is the only effective way to get Crypto out of the water. Often, unfortunately, "rapid filtration" at the public utilities water treatment plants doesn't do the job, and Crypto makes it through to the public's tap water.
Recently, a new cyst, Cyclospora, has made its presence known. Like Crypto, it produces intestinal disorders and is resistant to disinfection. Unlike Crypto, Cyclospora oocysts must be mature before they are infectious (so, if the body clears the cysts before maturation, there will be no infection). It is also larger in size than Crypto and is, therefore, easier to filter out of the water.
Although most of the intestinal disorders caused by microbial infection affect a large segment of the population only like a stomach flu or traveler's diarrhea, over 5 million Americans (the immunocompromised, the aged, infants, and pregnant women) are at a much greater risk (possibly even of death). Emerging patterns of rainfall, sewage overflows, and animal excrement are leading experts to believe that microbial outbreaks are going to continue and probably worsen.
Filtration has become the focus for control of these microorganisms. Disinfection had always been the major barrier for control, but we are finding microorganisms that are resistant to disinfection. Filtration has got to be the focus here.