Application of QSTR Models for Developmental Toxicity and Mutagenicity-Differences Regarding the Impact of the Halogen Atoms. R. M. Bruce, C. J. Moudgal, and V. K. Gombar, US Environmental Protection Agency, Glaxo Wellcome, Inc., NC
QSTR models can be a useful component of hazard identification in Risk Assessment; especially in cases were there is a paucity of toxicology data. Haloacetic acids (HAAs) along with trihalomethanes (THMs), haloacetonitriles (HANs) and other disinfection by-products (DBPs) are produced as a result of disinfecting water. THMs are the most commonly occurring group of DBPs in drinking water followed by the HAAs. Both the THMs and HAAs are comprised of a series of halogenated analogues; however, the brominated and iodinated analogues are less well characterized toxicologically. In the absence of toxicological data regarding the mutagenicity and developmental toxicity of the entire class (12 HAAs), QSTR submodels were used to assess these health-related endpoints. With respects to the toxicology of HAAs, the chlorinated analogs in contrast to the brominated and iodinated analogues have been more thoroughly characterized. The mono- and tri- halogenated analogues were predicted as developmental toxicants. However, only the mono- and a few of the di-halogenated acetic acids were predicted to be mutagenic. An analysis of the electrotopological values (E-state descriptors) for developmental toxicity demonstrated that the electronegativity of all the halogen descriptors within classes (e.g. mono, di and tri HAAs) were constant and hence shows no demonstrated effect upon this particular health-related endpoint compared to mutagenicity where the magnitude of the E-State values varied within and between classes of these analogues according to the electronegativity of the halogens.
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