AWWA WQTC60578

AWWA WQTC60578 Use of Quantitative Structure Toxicity Relationships (QSTR) to Prioritize Disinfection Byproducts for Research
Conference Proceeding by American Water Works Association, 11/15/2004

Bull, Richard J.; Bull, O. Michael; Reckhow, David

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An approach to identifying high priority areas for research on disinfection byproducts has beenexplored. Chemicals that have been identified as byproducts of chlorination for which there areno primary data available to describe their toxicological properties were subject to quantitativestructure toxicity relationship (QSTR) analysis utilizing TOPKAT, a program that includesmodules for predicting the probability that a chemical is a carcinogen or developmental toxicant.The program also estimates a chronic lowest observed adverse effect level (LOAEL). The latterparameter has been used to estimate the likely potency of a chemical, whether it acts as ageneral toxicant, carcinogen or developmental toxicant. This has allowed comparisons ofdifferent classes of disinfection byproducts (DBPs) and to identify those chemicals within a class thatmay be of most concern. In general, the potency of halogenated DBPs fit within the sameranges as observed with carcinogens in general. Median levels of chronic LOAELs of thehalogenated DBPs fall into the range of 10-100 mg/kg daysup-1/sup. This potency range captures mostof the regulated DBPs, although some are seen to fall above 100 mg/kg daysup-1/sup. However, thereis considerable variation in median potencies of different halogenated DBP classes. Severalclasses of common halogenated DBPs appear to be significantly more potent (e.g. thehalonitriles, haloamides and furanones related to MX). The greater potency predicted for MXand its analogs are not too surprising, but these DBPs typically occur at much lowerconcentrations. It is of interest that limited exploration of non-halogenated byproducts identifiedclasses of DBPs that have median potencies approximately 2 orders of magnitude greater thanhalogenated compounds (e.g. nitrosamines). This analysis suggests that byproducts thatinvolve nitrogenous precursors need to be investigated much more fully than they have to beento date. Includes 19 references, tables, figures.