VEQI - Surface Water Quality Indicator

Surface Water
by Leah Halfon, MPH

Public drinking water supplies depend on surface waters such as lakes, rivers, streams and reservoirs, in addition to ground water sources in rural settings. The Safe Drinking Water Act (SDWA) passed in 1976 and revised in 1990 and 1996 authorizes the Environmental Protection Agency to set primary standards for water contaminants to ensure adequate protection for both human and ecological health, and secondary standards for aesthetic purposes such as taste, odor and color. The primary standards called, Maximum Contaminant Levels (MCL's) regulate concentrations of biologics, chemicals, physical agents and radiologics.

However, despite federal initiatives to provide safe exposure levels, surface waters are prone to contamination by microorganisms, hazardous chemicals, metals, improper disposal of human and animal wastes, agricultural pesticides and urban run-off. Filtration and chlorinated disinfecting processes implemented in the 1900's have reduced human exposures to such infectious agents.

Nonetheless, waterborne outbreaks have been increasing recently especially in children, elderly and the immunocompromised. These outbreaks have been associated with bacteria, viral and parasitic pathogens, and have occurred through water consumption, food sources and skin contact in recreational waters. Health effects of these agents include gastroenteritis, dysentery, cholera, neurological disorders, kidney malfunctions and reproductive complications. The most notorious bacterial pathogen is Vibrio cholerae, a deadly organism responsible for cholera outbreaks in countries with poor sanitation.

Other disease-causing bacteria include Shigella species from sewage contamination and Campylobacter and Escherichia coli from zoonotic sources of agricultural run-off. Legionella and Mycobacterium species are unique environmental pathogens that multiply in areas of high sediment accumulation. Legionella pneumonia is thought to be the cause of bacterial pneumonia cases in the United States. Both bacteria have pronounced effects on immunocompromised populations. Viruses such as Hepatitis A, Norwalk virus and rotaviruses are among the most pervasive waterborne viral pathogens leading to gastrointestinal diseases in humans.

By far, the most widespread waterborne infectious agents are the protozoans Cryptosporidium parvum and Giardia lamblia. Alone these two parasites account for an estimated 600 million infections worldwide. Although Cryptosporidium parvum is a relatively new pathogen, it poses significant challenges to public health and water authorities. Originating in animals such as cows, sheep and even household pets, C. parvum exists in surface waters contaminated by agricultural and animal wastes. Once the Cryptosporidium oocytes invade filtration systems, they remain resistant to the chlorinating and disinfecting processes. Therefore, a breakdown in water filtration procedures can ultimately lead to human exposure to Cryptosporidium. Public concern over C. parvum as an emerging infectious agent arose after the 1993 incident in Milwaukee, WI, where 403,000 people became ill with Cryptosporidiosis.

Other measures of surface water quality included turbidity, an indicator of the presence of bacteria, viruses and other microorganisms, and total coliform, the amount of germ causing bacteria from contaminated animal and human wastes. In addition, overabundance of nutrients is particular important to ecosystem integrity. Excess amounts of nutrients, such as nitrogen and phosphorous, permeate waters from agricultural run-off, sewage effluents and deforestation. Elevated nutrient levels in watersheds can disrupt plant and soil interactions, increase soil acidification, produce toxic effects on freshwater biota and lead to eutrophication. Eutrophication is a direct result of anthropogenic and man-made contributions of nutrients to water sources and is characterized by an increase in algae, phytoplankton and dinoflagellate "blooms" that alter the pH, biological oxygen demand (BOD), odor and temperature of affected waters. Depletion of oxygen can be detrimental to fish sustainability, while certain dinoflagellates and bacteria are capable of producing toxins that poison nearby fish or shellfish.

With the increase in emerging pathogens resistant to contemporary methods of protection, it is imperative to monitor surface and source waters that receive agricultural wastes and to upgrade failing disinfection and filtration systems in order to protect the public health from waterborne diseases. It is critical that federal, state and local water pollution standards are constantly monitored and evaluated to provide the best protection from harmful contaminants that infiltrate our nations water sources.

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