Inactivation of indicator microorganisms in estuarine waters

In the United States, shellfish growing areas are classified, in part, using standards based on the densities of either the total or fecal coliform groups in surface waters. However, the standards currently employed may not reliably index the presence of certain enteric pathogens, particularly enteric viruses responsible for human illnesses, even though both the pathogens and indicators derive from the same fecal contamination. To some extent, this may be due to differences in the survival of these pathogens in the environment relative to that of the bacterial indicators. This investigation was conducted to assess the effects of temperature, salinity, dissolved oxygen, geographic location, season, and solar radiation on the survival of selected indicator microorganisms in estuarine waters. The indicators examined included fecal coliforms, Escherichia coli, Clostridium perfringens, and male-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 significantly 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 from sunlight were greatest on fecal coliforms and much less pronounced on MSB and C. perfringens. For fecal coliforms, the effect of sunlight was more pronounced during the winter than the summer. In the absence of sunlight, the rate of MSB decline was strongly negatively correlated with estuarine water temperatures and dissolved oxygen. Overall, fecal coliform decay rates were dissimilar to those found for MSB. From this, it would appear that fecal coliforms may not be reliable indicators of viruses in estuarine waters.