An Assessment of Fecal Indicator Bacteria-Based Water Quality Standards

Abstract

Fecal indicator bacteria (FIB) are commonly used to assess the threat of pathogen contamination in coastal and inland waters. Unlike most measures of pollutant levels however, FIB concentration metrics, such as most probable number (MPN) and colony-forming units (CFU), are not direct measures of the true in situ concentration distribution. Therefore, there is the potential for inconsistencies among model and sample-based water quality assessments, such as those used in the Total Maximum Daily Load (TMDL) program. To address this problem, we present an innovative approach to assessing pathogen contamination based on water quality standards that impose limits on parameters of the actual underlying FIB concentration distribution, rather than on MPN or CFU values. Such concentration-based standards link more explicitly to human health considerations, are independent of the analytical procedures employed, and are consistent with the outcomes of most predictive water quality models. We demonstrate how compliance with concentration-based standards can be inferred from traditional MPN values using a Bayesian inference procedure. This methodology, applicable to a wide range of FIB-based water quality assessments, is illustrated here using fecal coliform data from shellfish harvesting waters in the Newport River Estuary, North Carolina. Results indicate that areas determined to be compliant according to the current methods-based standards may actually have an unacceptably high probability of being in violation of concentration-based standards.

Fecal Coliform and E. coli Concentrations in Effluent-Dominated Streams of the Upper Santa Cruz Watershed

“…Studies have shown that FIB survival in surface waters varies from hours to days or even months if protected by sediments which make identifying the source of the FIB concentrations difficult [37,38]. The decay rate of FIB in surface water is a function of many ecological influences; therefore, water quality management, best management plan (BMP) development, watershed modeling, and risk assessment practices need to incorporate better methods as to how FIB interact with the environment, and furthermore, how well FIB accurately model true pathogenic concentrations in the watershed [16,17]. Researchers and regulators continuously question which pathogen indicators are appropriate to determine safe exposure levels in recreational waters.…”

“…Current ambient water quality criteria for FIB in fresh waters are aimed to protect human health from gastroenteritis due to pathogenic exposure based on the estimated relative risk of 8 cases of gastroenteritis per 1000 swimmers [12]. The appropriateness of the methods used and FIB capability for correlating and identifying human health risk from pathogens has been debated in the literature [16][17][18][19]. Despite the ongoing debate, most states monitor for total coliforms, fecal coliforms, Escherichia coli (E. coli), fecal streptococci, or enterococci as indicators of potential pathogens in water resources.…”

Ecology of Vibrio parahaemolyticus and Vibrio vulnificus in the Coastal and Estuarine Waters of Louisiana, Maryland, Mississippi, and Washington (United States)

“…Dissolved oxygen (30,54,57), chlorophyll (6,20,31,33), and plankton (2,31,41,59,74) have also been found to be important in the ecology of vibrios. Regulatory authorities responsible for oversight of recreational waters and shellfish harvesting areas employ rainfall, fecal coliform counts, river stages, and, more recently, enterococcus counts to determine opening and closing of specific areas to protect public health (21,25,62,76). Standard microbiological approaches to classification and opening/closing of oyster harvest areas, which are unfortunately not useful for control of exposure to pathogenic Vibrio spp., continue to be used and are generally accepted for regulating exposure to other pathogens in the United States (36).…”

Design and rationale of a matched cohort study to assess the effectiveness of a combined household-level piped water and sanitation intervention in rural Odisha, India

“…E. coli was selected as a standard non-human specific indicator of fecal contamination, though the limitations of this indicator are well-established. [66][67][68] In order to better characterise human fecal contamination of the household environment, V. cholerae and Shigella spp. were selected based on prevalence in southern Asia, evidence of public health importance, and field laboratory limitations.…”