FACTSHEET ON WATER QUALITY PARAMETERS E. coli (Escherichia coli) £ coli (Escherichia coli) is a type of bacteria that lives in the intestines of people and animals. £ coli is commonly found in human and animal feces. Most strains of £ coli are harmless, but some can make people sick. Why do we measure E. coli? Water samples are collected to measure £ coli (Figure 1) to make sure water is safe for public recreation, such as swimming, fishing or canoeing. £ coli is considered an indicator organism, used to identify fecai contamination in freshwater and indicate the possible presence of disease-causing bacteria and viruses (pathogens). Individuals who swim or come in contact with water with elevated levels of £ coli and other fecal indicator organisms are at an increased risk of getting sick because of potential exposure to fecai pathogens. Common symptoms of ingesting a pathogenic strain of £ coli include vomiting and diarrhea. High numbers of £ coli (and other) bacteria may contribute to cloudy water, unpleasant odors, and increased oxygen demand (which may reduce levels of dissolved oxygen in the water). £ coli concentrations may be linked with other parameters such as high totai suspended soiids (TSS) and turbidity concentrations because the bacteria tend to higure 1. E. coli under a microscope. Credit: Photo courtesy of National Institute of Allergy and Infectious Diseases be found with particles. £ coli concentrations may also be linked with high phosphorus, nitrate, and biological oxygen demand (BOD) concentrations. What affects E. coli levels? £ coli is found in the feces of warm-blooded animals. £ coli from humans can reach surface water via wastewater treatment plant effluent, broken or leaky sewer pipes, and failing or poorly sited septic systems. £ coli from animals can enter waterbodies in stormwater runoff from feedlots, manure storage areas, or areas where there is wildlife. Livestock that are allowed to get into or near streams can introduce £ coli directly into surface water. For factsheets on other water quality parameters, visit: epa.gov/awma/factsheets-water-quality-parameters. For more information about the Clean Water Act Section 106 Grants Program, visit: epa.qov/water-pollution-control-section-106-q rants. ------- E coli What are EPA's recommended criteria for E coli? £ coli criteria are expressed as the number of colony- forming units (cfu) per 100 ml_. The two sets of criteria shown in Table 1 were developed using different methods for calculating illness rates from scientific data. They are based on studies that show a link between illness and fecal contamination in recreational waters. Both are considered protective of human health, and either can be used to assess recreational water quality. Recommendation 1 A geometric mean (GM) of 126 cfu per 100 mL and a statistical threshold value (STV) of 410 cfu per 100 mL measured. Recommendation 2 A GM of 100 cfu per 100 mL and an STV of 320 cfu per 100 mL measured. The GM is a statistic often used for bacterial counts in federal and state water quality standards. The GM of the monitoring samples should not exceed whichever criterion is selected from the two recommendations in any 30-day interval. The STV is similar to a 90th percentile, meaning that no more than 10% of samples should exceed it. EPA recommends weekly sampling to evaluate the GM and STV over a 30-day period and encourages more frequent sampling at more densely populated beaches. Table I. Two sets of E. coli criteria based on two different estimated illness rates. Recommendation 1 Estimated Illness Rate: 36 per 1,000 Indicator Organism Geometric Mean (cfu/100 mL) Statistical Threshold Value (STV- 90th percentile) (cfu/100 mL) £ coli (freshwater) 126 410 Recommendation 2 Estimated Illness Rate: 32 per 1,000 Indicator Organism Geometric Mean (cfu/100 mL) Statistical Threshold Value (STV- 90th percentile) (cfu/100 mL) £ coli (freshwater) 100 320 Source: Anderson and Rounds (2003) How do we measure E. coli? £ coli levels are measured by analyzing bacterial growth in laboratory analyses. This is commonly done by the membrane filter procedure, although color test kits have also been EPA-approved. Care must be taken when collecting water samples because all of the sampling containers must be sterile. More information on measuring £ coli can be found in EPA's Volunteer Stream Monitoring: A Methods Manual (1997). What are the challenges of using E. coli as a water quality parameter? Bacteria levels in waterbodies can be highly variable. In rainfall. This can make it challenging to pinpoint sources of streams, natural bacteria levels vary and change with elevated £ coli concentrations. 2 ------- E. coli What if there is an exceedance of the water quality criteria? ADVISORY .'ass vsassS"™"4""" Figure 2. Public advisory warns of high bacteria levels in water. Public advisories can include additional information such as the date of the posting and contact information to check on the status of the posting. Credit: Photo courtesy of USEPA When elevated £ coli concentrations are observed, it is important to respond in a timely manner by collecting additional data, posting a public notice (Figure 2), and/or closing the waterbody to recreational activities. Figure 3 summarizes general actions to take when responding to elevated concentrations. RESPOND QUICKLY u Take action immediately in the event of an exceedance to prevent human exposure to £ coli. Exposure can cause infection, diarrhea, and other illness in humans. Additional data may be needed to understand the cause of the exceedance. SHORTTERM ACTION Issue a public notice and post advisories to notify the public that the waterbody is closed to recreational activities. LONG TERM ACTION To prevent future E. coli exceedances, identify the source of the bacteria. Depending on the source, different steps will be necessary to remediate the problem and reduce the likelihood of future events. Figure 3. General actions to take when a sampling result shows an elevated concentration of E. coli. EPA 841F21007F | July 2021 ------- |