Abstract

In 2000 the Dutch National Institute for Public Health and the Environment (RIVM) conducted a drinking-water monitoring programme for the Dutch Inspectorate for the Environment (IMH), using the non-routine parameters, iodide (I-) and iodate (IO3-). Samples were taken from a total of 232 drinking water production plants and analysed for iodide and iodate in both raw water and drinking water. The concentrations found for iodide and iodate in both raw water and drinking water occurred in the same range, with all values being very low. The average concentrations found for raw water were <0.5 ug/l IO3- (range: 0.5-9 ug/l) and 7.3 ug/l I- (range: 0.5-94.1 ug/l). The average concentrations found for drinking water were 3.0 ug/l IO3- (range: 0.5-42.6 ug/l) and 2.1 ug/l I- (range: 0.5-28.3 ug/l). The purification process evidently has an influence on the equilibrium between iodide and iodate; in general, raw water is seen to contain more I- and drinking water more IO3-. This equilibrium is mainly pH (acidity) and pE (electron activity) related. There is no regulation on maximum levels for iodide and iodine in the Netherlands, nor do the EG, WHO or EPA have any guidelines. The results here show that it is not yet necessary to regulate levels for either iodide or iodate, though the data on toxicity of both substances are limited. In general, there is no reason to measure the compounds I- and IO3- more frequently, but it is recommended that the measurements be repeated, this time including I2, at the drinking-water plants with the highest levels of I- and IO3-.