Chlorination disinfection byproducts in water and their association with adverse reproductive outcomes: a review

Objectives and methods-Chlorination has been the major disinfectant process for domestic drinking water for many years. Concern about the potential he alth effects of the byproducts of chlorination has prompted the investigati on of the possible association between exposure to these byproducts and inc idence of human cancer, and more recently, with adverse reproductive outcom es. This paper evaluates both the toxicological and epidemiological data in volving chlorination disinfection byproducts (DBPs) and adverse reproductiv e outcomes, and makes recommendations for future research. Results and conclusions-Relatively few toxicological and epidemiological st udies have been carried out examining the effects of DBPs on reproductive h ealth outcomes. The main outcomes of interest so far have been low birth we ight, preterm delivery, spontaneous abortions, stillbirth, and birth defect s-in particular central nervous system, major cardiac defects, oral cleft, and respiratory, and neural tube defects. Various toxicological and epidemi ological studies point towards an association between trihalomethanes (THMs ), one of the main DBPs and marker for total DBP load, and (low) birth weig ht, although the evidence is not conclusive. Administered doses in toxicolo gical studies have been high and even though epidemiological studies have m ostly shown excess risks, these were often not significant and the assessme nt of exposure was often limited. Some studies have shown associations for DBPs and other outcomes such as spontaneous abortions, stillbirth and birth defects, and although the evidence for these associations is weaker it is gaining weight. There is no evidence for an association between THMs and pr eterm delivery. The main limitation of most studies so far has been the rel atively crude methodology, in particular for assessment of exposure. Recommendations-Large, well designed epidemiological studies focusing on we ll defined end points taking into account relevant confounders and with par ticular emphasis on exposure characterisation are ideally needed to confirm or refute these preliminary findings. In practice, these studies may be im practicable, partly due to the cost involved, but this is an issue that can be put right-for example, by use of subsets of the population in the desig n of exposure models. The studies should also reflect differences of cultur e and water treatment in different parts of the world. To identify the spec ific components that may be of aetiological concern and hence to fit the mo st appropriate exposure model with which to investigate human exposure to c hlorinated DBPs, further detailed toxicological assessments of the mixture of byproducts commonly found in drinking water are also needed.