Balancing the Risks of Drinking Water Disinfection: Daly's on the Scale. Arie H. Havelaar, Microbiological Laboratory of Health Protection, telephone +31 30 2742826, fax +31 30 2744434, e-mail Arie.Havelaar@rivm.nl, Guus A. E. M De Hollander, Peter F. M. Teunis, Eric G. Evers, Henk J. Van Kranen, Ans J. F. M. Versteegh, Joke E. M. Van Koten and Wout Slob, National Institute of Public Health and the Environment (RIVM), P.O. Box 1, 3720 BA Bilthoven, The Netherlands
Chemical disinfection of drinking water is an important public health strategy. The health benefits from inactivation of pathogens should be balanced against risks from disinfection by-products. We examine the use of integrated measures of health-related quality of life for this purpose. Our approach is based on the established risk assessment approach for chemicals and micro-organisms but attempts to estimate actual risk in the human population and expresses the severity of all health outcomes on a common scale. We illustrate our approach by a case study of ozonation in a hypothetical) drinking water supply using surface water. In the scenario without disinfection, exposure to Cryptosporidium parvum due to drinking water consumption results in a risk of infection of approximately 10-3 per person per year. Ozonation leads to a 5-fold reduction of the concentration of C. parvum. Bromate is produced in a concentration of approx. 3 mug/l. For hazard characterisation, we consider acute gastro-enteritis and mortality in the immunocompetent and the immunocompromised as end-points of microbial infection and renal cell cancer resulting as end-point of bromate exposure.
For all disease end-points, we estimate the age at onset, the clinical course, mortality rates and recovery rates. We aggregate the outcomes of different diseases, using the concept of Disability Adjusted Life Years (DALY). The health benefits due to inactivation of pathogens are of the same order of magnitude as health losses by formation of bromate, if conventional (conservative) methods are used to extrapolate toxicological data. However, using a probabilistic approach we demonstrate that the cancer risk may be overestimated, hence ozonation would be favourable for public health. Our method requires a considerable amount of high quality data, which are only partly available. Hence, these preliminary results must be interpreted with caution.
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