Introduction | Waterborne Pathogens and the Diseases They Cause | Microbial Water Contamination and Human Exposure | Drinking Water Treatment | Improvements ... and What You Can Do
As water moves through a watershed, it collects and drains into rivers, lakes, and groundwater. And it picks up microorganisms.
Most are harmless microbes that normally live in the soil and water, but the mix can also contain organisms that cause disease in people.
The majority of waterborne microorganisms that cause human disease come from animal and human fecal wastes. These contain a wide variety of viruses, bacteria, and protozoa that may get washed into drinking water supplies or recreational waters.
Groundwater bacteria (yellow area shown in white circle). Courtesy of MicrobeLibrary.org, © William Ghiorse, Cornell University.
Just a small drop of fecal matter can contain millions of microorganisms. Although many of these microbes occur naturally in our bodies, a few may be agents of disease.
Sewage, or wastewater, is not supposed to be released raw and untreated into the environment.
Most treated wastewater goes into rivers, lakes, and oceans. Occasionally, heavy rains overwhelm sewer systems, causing them to overflow. This can put communities at risk from high concentrations of microbial pollutants in raw, untreated sewage. Public health advisories notify citizens when such large discharges occur.
Not all human waste is treated in sewage treatment facilities. There are approximately 25 million septic tanks in the United States, receiving 175 billion gallons of wastewater. Pathogenic viruses, bacteria and other microbes in these wastes can sometimes escape and contaminate ground and surface waters.
Nearly 1.4 billion tons of animal manure are produced annually in the United States. These animal wastes carry concentrations of microbes as high as a billion organisms per gram of feces. Most are part of normal bodily flora, but some are potentially harmful to humans.
Infected cattle can excrete millions of E. coli O157:H7, Cryptosporidium, Giardia, and other microbes in their manure. Chicken wastes can carry the pathogenic bacteria Salmonella and Campylobacter.
In areas of intensive livestock production, manure-laden run-off is the main suspect in blooms of toxic microbes such as Pfiesteria in estuaries and coastal regions.
Fishkill. Courtesy of JoAnn Burkholder, Center for Applied Aquatic Ecology, NC State University.
Groundwater has historically been assumed to be safe without treatment to kill microorganisms. Layers of soil act as a natural filter, removing microbes and other particles as water seeps through.
More than 100 million Americans rely on groundwater as their source of drinking water. Only half of the communities that use groundwater sources disinfect the water prior to distribution. In rural and nonincorporated areas, almost none of the water is treated.
While soil acts as a natural filter, it isn’t 100% foolproof. Of 17 outbreaks of waterborne disease associated with drinking water recorded by the Centers for Disease Control and Prevention (CDC) in 1997–1998, 15 were associated with groundwater sources.
The health of our surface and groundwater drinking water supply is closely linked to the safety of our recreational waters and even our food supply.
Before 1990, pathogens were rarely found, or even looked for, in fresh fruits and vegetables in the U.S.
Since then, however, there have been a few headline-grabbing outbreaks of Salmonella-caused illness tied to imported produce. Outbreaks of hepatitis A have been reported from contaminated lettuce and strawberries; raspberries contaminated with the parasite Cyclospora have caused outbreaks of diarrheal illness.
During the winter season, most produce consumed in the U.S. now comes from Mexico and Latin America. Inadequate wastewater treatment means that irrigation waters used in many of these countries are laden with fecal microorganisms, including pathogens.
The water-to-food connection also impacts the American seafood industry: fish and shellfish can acquire pathogens from contaminated waters, a growing problem in the U.S.
About 42 percent of our estuary waters are contaminated by municipal, industrial, and agricultural wastes. As a result, bacteria, viruses, and toxic algae are the major causes of human disease associated with fish and shellfish.
Courtesy of JoAnn Burkholder, Center for Applied Aquatic Ecology, NC State University.
Ongoing or occasional microbial pollution can occur in natural bodies of water, such as lakes and oceans, as well as man-made pools and fountains.
While infrequent, outbreaks associated with wading or swimming in recreational waters can occur. In 1997–1998, 32 such incidents in 18 states made some 2,100 people ill.
Exposure to microbial pollution in recreational waters has caused outbreaks of gastrointestinal disease, hepatitis, meningitis, and respiratory, ear, eye, and skin infections. Exposure to toxin-producing algae can cause respiratory problems, making even a stroll on the beach risky during algal blooms, or “red tides.”
Some 729 U.S. beaches had to close for at least one day in the summer of 1998 due to unsafe levels of bacteria. Such closures happen every year.
Introduction | Waterborne Pathogens and the Diseases They Cause | Microbial Water Contamination and Human Exposure | Drinking Water Treatment | Improvements ... and What You Can Do
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