Previous studies of microbial behaviour in situ have used dialysis sacs and diffusion chambers to permit contact of contained microorganisms with the external aqueous milieu. Their main limitation is a slow response to changes in water quality, preventing adequate simulation of field conditions. This study used the ECODYNE system™, a new device responsive to real time changes in water quality. It consists of a hollow fibre membrane module and fluid reservoir which separates the test microorganisms from the external environment. Use of a mixture of Escherichia coli, Enterococcus dwans, MS-2 phage, poliovirus type 1 (Sabin) and hepatitis A virus (HM-175) allowed direct comparison of their survival in river water under identical conditions over a period of at least 24 hours. The results can be summarised as follows: a) survival patterns of E. coli in nutrient rich river water were highly variable, b) a ten-fold or greater increase in numt)ers of E. coli was sometimes observed in twth latwratory and field tests, c) no regrowth was ever observed with E. durons, and its titre declined faster than that of E. coli, and d) over the first 24 hours, the phage survival was similar to that of the human pathogenic viruses. The observations regarding the variable survival of E. coli and its potential for regrowth raise questions about its suitability as a water quality indicator. MS-2 phage shows promise as an indicator of viral pollution, but requires further study. The ECODYNE system proved highly suitable in this study, and shows potential for other environmental interaction/environmental fate studies including ecotoxicological investigations and monitoring.

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