Using zebra mussels to monitor Escherichia coli in environmental waters

Use of the zebra mussel (Dreissena polymorpha) as an indicator of previousl y elevated bacteria concentrations in a watershed was examined, The ability of the zebra mussel to accumulate and purge Escherichia coli over several days was investigated in both laboratory and field experiments. In laborato ry experiments, periodic enumeration of E. coli in mussels that had been ex posed to a dilute solution of raw sewage demonstrated that (i) maximum conc entrations of E. coli are reached within a few hours of exposure to sewage, (ii) the tissue concentration attained is higher than the concentration in the ambient water, and (iii) the E, coli concentrations take several days to return to preexposure concentrations when mussels are subsequently plate d in sterile water. In field experiments conducted in southeast Michigan in the Clinton River watershed, brief increases in E. coli concentrations in the water were accompanied by increases in mussel concentrations of E, coli that lasted 2 or 3 d. The ability of mussels to retain and to concentrate E. roll made it possible to detect E. coli in the environment under renditi ons that conventional monitoring may often miss. Sampling caged mussels in a river and its tributaries may enable watershed managers to reduce the sam pling frequency normally required to identify critical E, coli sources, the reby providing a more cost-effective river monitoring strategy for bacteria l contamination.