Inactivation of indicator microorganisms in estuarine waters

In the United States, shellfish growing areas are classified, in part, usin g standards based on the densities of either the total or fecal coliform gr oups in surface waters. However, the standards currently employed may not r eliably index the presence of certain enteric pathogens, particularly enter ic viruses responsible for human illnesses, even though both the pathogens and indicators derive from the same fecal contamination. To some extent, th is may be due to differences in the survival of these pathogens in the envi ronment relative to that of the bacterial indicators. This investigation wa s conducted to assess the effects of temperature, salinity, dissolved oxyge n, geographic location, season, and solar radiation on the survival of sele cted indicator microorganisms in estuarine waters. The indicators examined included fecal coliforms, Escherichia coli. Clostridium perfringens, and ma le-specific bacteriophage (MSB), a potential indicator of enteric viruses. In situ experiments were performed in estuarine waters of Alabama and Rhode Island. Among the parameters examined, sunlight and/or temperature most significant ly affected indicator decay rates. In general. the effects from exposure to sunlight accounted for up to 83, 84, and 99% of the density reductions of MSB, C, perfringens and fecal coliforms, respectively. Thus, the effects fr om sunlight were greatest on fecal coliforms and much less pronounced on MS B and C. perfringens. For fecal coliforms. the effect of sunlight was more pronounced during the winter than the summer. In the absence of sunlight, t he rate of MSB decline was strongly negatively correlated with estuarine wa ter temperatures and dissolved oxygen. Overall. fecal coliform decay rates were dissimilar to those found for MSB. From this. it would appear that fec al coliforms may not be reliable indicators of viruses in estuarine waters. Published by Elsevier Science Ltd.