Viruses and Bacteria in Coastal Waters and Shellfish

The fate of viruses and pathogens discharged into the ocean in municipal effluent is not known for certain. They probably become inactivated in the same manner that coliform bacteria are—through sedimentation, predation by marine bacteria and filter-feeders, damage by ultraviolet light or abrupt changes from reducing to oxidizing environment, or because of some antiviral agent present in the sea. Past observations and measurements suggested that viruses survive longer in seawater and shellfish than do human enteric bacteria, but only the results of field studies can confirm this with certainty and provide guidance for wastewater discharge and public health policy. Thus the objectives of our research this year were to (1) determine the concentrations and rates at which enteric viruses enter the sea via municipal wastewater effluents, (2) measure concentrations of viruses in the digestive glands of mussels suspended from buoys near outfalls, and (3) determine the relationship between virus and coliform concentrations in mussels and seawater. We measured coliforms and viruses (and occasionally salmonella) in 34 samples of primary and secondary effluents and 39 mussels from sea buoys and shore stations; the coliforms in 26 samples of the seawater to which the mussels were exposed were also determined. In addition, tests were run to determine the efficiency of our virus recovery methods. Our most important finding to date is that viruses can be detected in shellfish near outfalls and do appear to survive relatively longer in mussels than do total coliforms. We estimated coliform-to-virus ratios in effluent, seawater, and mussels. Using a formula based on conventional first-order decay rates that was developed for the conditions of this study by Dr. T. Hendricks of the Project, virus inactivation rate was compared to coliform dieoff rate: The relative time required for 90 percent of the viruses in seawater to be inactivated was estimated to be three to six times as long as that for total coliform.