Application of risk assessment techniques to microbial monitoring data: a South-African perspective

Abstract

The feasibility of applying microbial risk assessment techniques in South Africa was evaluated by assessing risks associated with enteric viruses in raw and treated drinking water. Maximum daily risks associated with treated drinking water were in the range 2x10(-2) - 7x10(-1). If levels of viruses in treated drinking water were approximated from those in raw water by assuming reductions during treatment of 4 log, 5 log and 6 log, maximum daily risk estimates were 4x10(-2) - 4x10(-1), 5x10(-3) - 1x10(-1) and 5x10(-4) - 1x10(-2), respectively. A number of complicating factors were identified. Detection limits were high and volumes of water monitored were low. There was no information on viral pathogen removal during treatment. Application of risk assessment techniques within these limitations clearly showed the volume of water monitored to be the most important factor limiting detection of low risk levels. The sampling and concentration of large water volumes (at least 100 l) for microbial analysis was identified as an urgent need.