Implications of coliform variability in the assessment of the sanitary quality of recreational waters

Abstract

SUMMARYThe most widely used indicator of the sanitary quality of recreational waters is the coliform group of bacteria. Present techniques of coliform enumeration are imprecise, and this fact is too often overlooked in routine water quality surveys as well as in research efforts seeking quantitative relationships between coliform density and the health effects of recreational waters. To illustrate this point, three years of data gathered by the New York City Department of Health as part of their routine beach water sampling programme were re-analysed, taking the limited precision of each coliform estimate into account. Re-analysis showed 56600 of the data were not significantly different (P > 0 05) from the standard being used. This large percentage of the data was of little value in determining the acceptability of the waters being sampled relative to the standard being used and thus represented a substantial waste of time and expense. Of the remaining data, half indicated acceptable water quality and half indicated unacceptable water quality relative to the standard. These three years ofdata, therefore, gave little information on the acceptability of the water quality at this location with respect to the standard being used. The data further suggest significant differences in coliform density within sample dates. It is recommended that in future water quality surveys, or in studies of the health effects of recreational waters as related to coliform density, emphasis should shift from maximizing the number of sample dates to maximizing the number of replicate determinations made per sample date.

Variations in microbial indicator densities in beach waters and health-related assessment of bathing water quality

“…Taking into account the variability of microbial indicator densities, it is not advisable to judge the acceptability of beach-water quality based on the microbial indicator density obtained on one sampling occasion, or on the mean density of a number of samples obtained in a day (which covers only part of a tidal cycle), no matter how precisely these densities were measured. Fleisher [7] has suggested emphasis should shift from maximizing the number of sampling date to maximizing the number of replicate determinations made per sampling date, in order to improve the precision in estimating coliform counts. This objective would better be achieved by adopting the membrane filtration method, which gives more precise microbial counts than the MPN method [8].…”

“…Previous studies have indicated that an understanding of the time-related variations in microbial indicator densities in beach-waters is essential for properly assessing the microbiological quality and swimming-associated health risk levels of bathing beaches [5][6][7]. The purpose of this paper is to (a) describe the daily and hourly variations in microbial indicator densities at Hong Kong beaches; (b) evaluate the importance of tide and bather numbers in causing such fluctuations; and (c) explain some of the observations by elucidating the sources of the indicator microorganisms in bathing waters.…”

Application of microbial source tracking methods in a Gulf of Mexico field setting

“…Epidemiological studies conducted over the past 30 years have supported the correlation between the levels of certain IO and the risk of gastroenteritis in recreational water users (Cabelli et al. 1979, 1982; Fleisher 1985; Fleisher et al. 1993); however, various factors can confound this relationship, including ubiquitousness and extended survival of certain IO in the environment (Davies et al.…”