Academic journal article Environmental Health Perspectives

Balancing the Risks and Benefits of Drinking Water Disinfection: Disability Adjusted Life-Years on the Scale

Academic journal article Environmental Health Perspectives

Balancing the Risks and Benefits of Drinking Water Disinfection: Disability Adjusted Life-Years on the Scale

Article excerpt

To evaluate the applicability of disability adjusted life-years (DALYs) as a measure to compare positive and negative health effects of drinking water disinfection, we conducted a case study involving a hypothetical drinking water supply from surface water. This drinking water supply is typical in The Netherlands. We compared the reduction of the risk of infection with Cryptosporidium parvum by ozonation of water to the concomitant increase in risk of renal cell cancer arising from the production of bromate. We applied clinical, epidemiologic, and toxicologic data on morbidity and mortality to calculate the net health benefit in DALYs. We estimated the median risk of infection with C. parvum as [10.sup.-3]/person-year. Ozonation reduces the median risk in the baseline approximately 7-fold, but bromate is produced in a concentration above current guideline levels. However, the health benefits of preventing gastroenteritis in the general population and premature death in patients with acquired immunodeficiency syndrome outweigh health losses by premature death from renal cell cancer by a factor of [is greater than] 10. The net benefit is approximately 1 DALY/million person-years. The application of DALYs in principle allows us to more explicitly compare the public health risks and benefits of different management options. In practice, the application of DALYs may be hampered by the substantial degree of uncertainty, as is typical for risk assessment. Key words:, bromate, Cryptosporidium parvum, disinfection, drinking water, ozone, quality of life, risk assessment. Environ Health Perspect 108:315-321 (2000). [Online 21 February. 2000]

http://ehpnet1.niehs.nih.gov/docs/2000/108p315-321havelaar/ abstract.html

The microbiologic safety of drinking water is of paramount importance to public health (1). Source protection is generally accepted as the primary strategy to obtain microbiologically safe drinking water. However, many sources (surface waters in particular) are highly polluted and need extensive treatment before distribution to the consumer. Chemical disinfection is prominent in these treatment schemes. Highly oxidizing chemicals such as chlorine and ozone kill a variety of pathogenic microorganisms during treatment, and chlorine is applied in many countries as an additional safeguard in the distribution system. An important drawback of the use of these chemicals is the generation of disinfection by-products, which have suspected adverse effects on human health. This situation calls for a formal quantitative framework to compare the positive and negative health effects of drinking water disinfection and to assist in the design and operation of treatment plants (2).

Microbiologic risks are expressed as the annual individual probability of infection for a given consumption of drinking water. Chemical risks related to genotoxic carcinogens are usually associated with an increase in cancer incidence attributable to a lifetime exposure. The public health impact of these disease end points is very different and cannot be compared directly. Hence, decision making is difficult. We evaluated the applicability of a single measure of attributable disease burden to compare and balance health risks and benefits on a public health basis. The disability adjusted life-year (DALY) consists of the loss of healthy life years due to either premature mortality or morbidity. The DALY integrates several dimensions of the public health impact, such as the number of affected persons and the severity and duration of adverse health effects, and uses time as a unit of measurement. We illustrate our approach by a case study of ozonation of a hypothetical drinking water supply using surface water. We used Monte Carlo simulation to assess the uncertainty in our risk estimates, to account for biologic and seasonal variation in exposure and effects, and to accommodate uncertainty in parameter values. In accordance with the framework proposed by the U. …

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