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Human Health Risk Implications of Multiple Sources of Faecal Indicator Bacteria in a Recreational Waterbody
Citation:
Soller, J., M. Schoen, A. Varghese, A. Ichida, A. Boehm, S. Eftim, N. Ashbolt, AND J. Ravenscroft. Human Health Risk Implications of Multiple Sources of Faecal Indicator Bacteria in a Recreational Waterbody. WATER RESEARCH. Elsevier Science Ltd, New York, NY, 66(12):254-264, (2014).
Impact/Purpose:
This study aims to estimate human health risks from recreational exposure to waters impacted by various mixtures of fecal contamination (as represented by enterococci) from diverse sources including sewage, animal sources and sources that contribute enterococci but not pathogens (non-pathogenic sources). This work is unique in that it specifically examines risk in waters impacted by mixed sources of enterococci, and considers confounding effects from ‘naturalized’ enterococci. Health risks are estimated for exposure to water containing combinations of sources as each source varies within the total enterococal contribution. The estimated health risks were compared to US EPA’s benchmark risk using the previously established QMRA approach introduced above. The implications for the regulation of U.S. recreational waters that are impacted by mixed contamination sources are discussed and needed research is highlighted
Description:
We evaluate the influence of multiple sources of faecal indicator bacteria in recreational water bodies on potential human health risk by considering waters impacted by human and animal sources, human and non-pathogenic sources, and animal and non-pathogenic sources. We illustrate how risks vary with the proportion of culturable indicator bacteria (enterococci) in water bodies derived from these sources and estimate corresponding enterococci densities that yield the same level of health protection that the recreational water quality criteria in the United States provides (benchmark risk). The benchmark risk is based on epidemiology studies conducted in water bodies impacted by human faecal sources. The key result is that the risks from mixed sources are driven predominantly by the proportion of the contamination source with the greater ability to cause human infection (potency), not necessarily the source(s) of greatest faecal load. Predicted risks from exposures to mixtures comprised of 10–30% enterococci from human sources were 0.5 - 1 orders of magnitude lower than the risks expected from purely human sources when contamination is recent and enterococci levels are at current water quality criteria levels. For human/non-pathogenic, human/pig, and human/chicken faecal mixtures at relatively low human contribution, the predicted culturable enterococci densities that correspond to the benchmark risk are substantially greater than the current water quality criteria values, but not substantially different from each other. These findings could significantly influence the regulation of recreational waters and help motivate research to manage recreational waters.
