In the environment, organic compounds undergo transformation processes that, in rare cases, may lead to transformation products (TPs) that are more toxic than the parent compound (P).  Toxic TPs in effluent pose environmental and human health hazards, but with more than 100,000 organic compounds in daily use it is impractical to fully characterize the TPs for every P.  It is therefore necessary to prioritize for testing those compounds that are likely to lead to toxic TPs.  The toxicity can be split up into to contributions, one related to the hydrophobicity and thus bioaccumulation potential/baseline toxicity and the other one related to the mode of toxic action. Structural alerts (SA, functional groups related to specific or reactive toxicity) are indicators of higher than baseline toxicity. TPs that contribute significantly to the toxic hazard of P retain the SAs from P, carry newly formed SAs, and/or are more hydrophobic than P. In the proposed scheme to prioritize for testing those P that are most likely to lead to toxic TPs, candidate TPs are first predicted based on known transformations, using computational chemistry for abiotic processes and/or software such as the University of Minnesota Pathway Prediction System for biotransformation.  To estimate changes in specific and reactive toxicity, SAs on P and candidate TPs are then identified based on a library of 340 SAs that was constructed from published modeling and experimental results.  The parent compounds are then ranked using an index based on the average number of parent SAs retained on the candidate TPs and the average number of new SAs formed on the candidate TPs.  Finally, to estimate changes in baseline toxicity for P that are highly ranked using the SA index, bioaccumulation of candidate TPs is estimated based on calculated octanol-water partition coefficients.

Prioritizing organic micropollutants to screen for toxic transformation products

246th National Meeting (2013)

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