What Is The Role Of Microbes In Water Quality?

Many U.S. citizens believe that thanks to our advanced technology and enlightened public policy we can consume without risk the food and water that are readily available to most of us, as citizens of a rich and privileged country. Some of those who subscribe to this buoyant and comforting attitude, however, may have lately experienced second thoughts. Because of various recent and widely reported incidents, many people are feeling concerned about the quality and safety of our food and water.

Cup of contaminants

This is not surprising; some of these incidents have resulted in serious, widespread sickness, even death. For example, several incidents were reported of people becoming sick from eating undercooked beef at fast-food restaurants. In other incidents, more than 70 people became sick and one died in late 1996 from drinking Odwalla apple juice, a brand sold at health food stores, and last year lettuce from a small producer sickened at least 61 people in the U.S. Northeast. The latter two incidents were related to a strain of E. coli bacteria. Water too has raised public health concerns.

Microbial pathogens or contaminants in drinking water are being blamed for various gastrointestinal illnesses that have occurred in different parts of the country. U.S. citizens, in the unlikely event they had even given much thought to contaminated drinking water, would have considered it a condition out of the past or one associated with developing countries. Now waterborne sickness from microbial contaminants, some with strange and unlikely sounding names-e.g., Cryptosporidium, Giardia, Legionella, and Norwalk virus-has become a seemingly modern concern even for people living in the United States.

Estimates project from seven to about 30 million Americans each year develop a gastrointestinal illness, possibly from drinking contaminated water. EPA also provides a wide range of figures when estimating the nation's annual medical and lost productivity costs due to waterborne illnesses, from $3 billion to $22 billion. Of much greater concern are the deaths related to microbial contaminants in drinking water.

The Centers for Disease Control and Prevention estimates 900 to 1,000 people die each year from microbial illnesses from U.S. drinking water. Other estimates run as high as 1,200 deaths. Although difficult to pin down, such figures indicate the existence of a serious problem.

Microbial Contaminants in History

Microorganisms are present everywhere in our environment, in soil, air, food, and water. Also called microbes, microorganisms are living organisms, generally observable only through a microscope. Our exposure to them causes harmless microbial flora to establish in our bodies, although some microbes are pathogens and can cause diseases. These diseases are considered waterborne if the pathogens are transmitted by water, to infect humans or animals that ingest the contaminated water. Diseases transmitted by water are primarily those found in the intestinal discharges of humans or animals The presence of microbial contaminants in drinking water has plagued humans throughout history.

In fact, outbreaks of cholera, typhoid fever, and dysentery are recurring themes in early U.S. history. For example, in 1850 and 1851, an especially aggressive outbreak of cholera occurred in Sonora, an area that included Tucson at that time. More than 1,000 people died in northwestern Sonora, while in Tucson the 122 deaths that occurred in 1851 far exceeded the number of recorded births that year which was 19. Due to microbial pathogens, a harsh reality confronted those seeking gold and glory in the hills of California. "Diarrhea," reported a doctor in Sacramento, "was so general during the fall and winter months and degenerated so frequently into a chronic and fatal malady that it has been popularly regarded as the disease of California...."

Waterborne microbial pathogens cause a whole range of diarrheal diseases. The hazards of fecal contamination and the principles of basic sanitation were recognized early. The occurrence of such outbreaks alerted people to the hazards of drinking contaminated water and prompted investigations into ways to prevent the occurrence of waterborne illnesses. Public health officials eventually achieved success in controlling the more common forms of waterborne diseases, at least in the United States and other developed countries.

Progress was due to the adoption of public health measures as well as the implementation of important water treatment techniques, such as filtration, disinfection, and sewage treatment. Some believed the battle, if not won, was at least under control.

Emerging Contaminants

Waterborne microbial contaminants, however, have attracted renewed attention, both within the scientific community and among the public. Once thought to be under control, they are now referred to as the "emerging drinking water contaminants." What in fact is emerging is an expanded awareness of the presence of previously undetected microbial contaminants in drinking water and their effects on human health.

Also emerging in the field of environmental microbiology, as new microbial pathogens are being discovered and research is underway to develop improved methods for detecting and treating microbial in drinking water. Microsporidia is an example of an emerging pathogen that is attracting attention. Potentially waterborne, this pathogen is recognized as causing disease among AIDS patients, although healthy persons also may be susceptible to microsporidia.

Because of its small size, microsporidia may survive filtration, and studies thus far indicate that the pathogen will be fairly resistant to many drinking water disinfectants. With more research and the development of improved detection methods, researchers will be able to better determine the occurrence of microsporidia, both in humans and the environment.

Some researchers believe this microorganism may eventually need to be monitored and controlled in drinking water supplies. H. pylori is another emerging pathogen. Common among people exposed to poor hygienic conditions from childhood, H. pylori also has been found, although much less frequently, among the socio-economic advantaged. Its source is not known, but water is thought to be a likely route of transmission. H. pylori causes inflammation of the stomach and seems to be a factor in the development of duodenal ulcers. It also is thought to play a causal role in the chain of events leading to gastric cancer. The occurrence of H. pylori ranges from less than one percent of the population of industrialized nations to three to eight percent in developing countries. Researchers continue to study this pathogen.

These and other microbial contaminants are increasingly attracting the concern of public health authorities as well as an interdisciplinary array of experts in such fields as microbiology, engineering, epidemiology, and risk assessment.

Where Do They Come From?

Waterborne diseases result from drinking fecally contaminated water. To explain the presence of microbial contaminants in drinking water is to describe a circuitous route, from a human or animal source back to a human or animal via drinking water. Microbial contaminants follow a fecal-oral route. Bacteria, viruses, and protozoa are the microorganism groups containing pathogens of primary concern in the study of waterborne disease.

Human sources account for viruses, while both animal and human waste contribute protozoa to water. For example, cattle are considered the source of much Cryptosporidium, and Giardia is often traced to beavers. Both Cryptosporidium and Giardia are protozoa. Each day the average human excretes about 38 grams of urea, mostly urine, and 20 grams of solids in feces. The excreta contains billions of microbes. These microbes cannot only survive but also multiply in water and are made up of a wide range of organisms, including pathogenic microbes, which even healthy people excrete.

Others who have a disease or who are carriers of a disease-producing microorganism are a more obvious source of waterborne infections. Estimates indicate that about five percent of those who have contracted an enteric or intestinal disease remain life-long carriers, even after having recovered from the disease. That these intestinal microbial contaminants can infect a drinking water source may at first seem puzzling, especially to citizens of a country that prides itself on its public health standards.

Yet through natural flow or accident, various types of water can interconnect and flow together. For example, stormwater runoff from residential, rural, and urban areas can carry waste material from domestic pets and wildlife, to collect in surface waters and even enter groundwater. Through accident or equipment failure, sewage, a rich source of microbial contamination, might come into contact with drinking water.

Also, defective on-site wastewater disposal or septic systems in rural and other residential areas can contribute large numbers of coliforms and other bacteria to both surface water and groundwater. These contaminants occur widely and are not limited to areas inhabited by humans. A deer or other wildlife feeding by a clear-flowing, pristine stream in an untrammeled forested area is an appealing image. This hardy specimen of wildlife, however, can contribute contaminants to the stream to infect a downstream hiker enjoying a sip of spring water direct from the source. Cattle also add contaminants to water in isolated areas. Cattle graze many backcountry areas and drink from streams that then flow to other areas or into other water sources. Fecal contamination can occur in indirect and seemingly unlikely ways. Authorities suspect the contamination of Odwalla apple juice was caused when the processing plant pressed a decayed apple that had fallen to the ground and came into contact with feces, possibly from a deer. This sickened 70 people and resulted in one death.

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