Drinking water treatment with chlorine dioxide and potential health effects

The authors review the available toxicological and epidemiological data with the intent of assess the potential human health adverse effects that may be associated with the use of chlorine dioxide as disinfectant in drinking water treatment and with its prominent disinfection by-products, chlorite and chlorate. Although scientific data available today provides little evidence that properly controlled disinfection of drinking water with chlorine dioxide poses significant hazards to human health, there are some substantial gaps in the data. Toxicological data obtained from experimental animals is an essential component of hazard identification process, however, because of the high doses that are ordinarily used in these studies, knowledge of the mechanisms, or at least modes of action, are required to confidently estimate risks in humans at low doses. Without such data, default assumptions are applied to the descriptive data which tend to result in guidance values that are unnecessarily restrictive. Conversely, epidemiological studies focus directly on human responses to ambient exposures of a chemical. The major problems associated with epidemiological studies of chlorine dioxide-disinfected water relate to exposure assessment. The levels of chlorine dioxide or of its oxyhalide anions in drinking water vary widely in time and space in water treatment systems that currently employ chlorine dioxide, depending on generation technologies, feedstock chemicals, treatment objectives and quality of the local water. Moreover, individual exposure is greatly modified by different personal habits and by their changes over time. Furthermore, when studying ambient exposures it is frequently difficult to be certain that effects observed are attributable to the chemicals being studied among many other chemical, environmental, and even genetic contributions to disease in the population. Further toxicological and epidemiological research is therefore needed both to clarify the mechanisms of action, the potential synergic effects, the individual genetic susceptibility to oxidants and to identify adequate personal exposure assessment matrixes combining together chemical levels in water and information on personal habits able to modify subjects exposure.