Survival of Clostridium spores in river water and in sand from a slow sand filter

Spores of sulphite-reducing clostridia (SSRC; incl. C. perfringens) have been introduced in water quality monitoring for microbial safety of drinking water because of their higher resistance to water disinfection processes than E. coli. Interpretation of this parameter, however, is hampered by lack of quantitative data on the spore decay rates. We determined decay rates of environmental Clostridium spores in river water and in filter sand in a twelve year microcosm study at different temperatures. Decay was not significant at 3°C and limited at 15°C. First order decay rates in water and sand were in the same order of magnitude and ranged from of 0.001 up to 0.0023 d⁻¹. Molecular typing of isolates of surviving SSRC showed diversity in the species at different temperatures. From the results in combination with literature data it was concluded that there is heterogeneity in the longevity of environmental SSRC. There is a need for more information on the survival of C. perfringens spores which is essential for interpretation of this parameter in water microbiological quality control.