Abstract
Transformation products ought to be an important consideration in chemical alternatives assessment. In this study, a recently established hazard ranking tool for alternatives assessment based on in silico data and multicriteria decision analysis (MCDA) methods was further developed to include chemical transformation products. Decabromodiphenyl ether (decaBDE) and five proposed alternatives were selected as case chemicals; biotic and abiotic transformation reactions were considered using five in silico tools. A workflow was developed to select transformation products with the highest occurrence potential. The most probable transformation products of the alternative chemicals were often similarly persistent but more mobile in aquatic environments, which implies an increasing exposure potential. When persistence (P), bioaccumulation (B), mobility in the aquatic environment (M), and toxicity (T) are considered (via PBT, PMT, or PBMT composite scoring), all six flame retardants have at least one transformation product that can be considered more hazardous, across diverse MCDA. Even when considering transformation products, the considered alternatives remain less hazardous than decaBDE, though the range of hazard of the five alternatives was reduced. The least hazardous of the considered alternatives were melamine and bis(2-ethylhexyl)-tetrabromophthalate. This developed tool could be integrated within holistic alternatives assessments considering use and life cycle impacts or additionally prioritizing transformation products within (bio)monitoring screening studies.
Highlights
Transformation of chemicals is an important but often neglected issue in chemical risk assessment
The toxicological risks associated with chemicals can be underestimated if only parent compounds are considered, as some chemicals can transform into more hazardous compounds
The importance of considering transformation products in risk assessment has been an ongoing topic of discussion for several substances,[5,6] such as for the flame retardant decabromodiphenyl ether.[7,8]
Summary
Transformation of chemicals is an important but often neglected issue in chemical risk assessment. Hazard data were calculated using the same models as in the previous study for both the six flame retardants and their transformation products.[26] In brief, chemical structure information (SMILES) was used to derive data from 55 QSAR models including models from the open-source tools EPISUITE,[27] VEGA,[28] TEST,[29] and OECD QSAR Toolbox;[15] models for endocrine related responses on the OCHEM platform[30] from the USEPA organized Collaborative Estrogen Receptor Activity Prediction Project (CERAPP),[31] Collaborative Modelling Project for Androgen Receptor Activity (CoMPARA),[32] and the literature[33] (Table S2) These models covered 20 hazard criteria for P, B, M, and T (Table S2). CTS QSAR Toolbox BioTransformer transformation pathways phase I and phase II metabolism for mammals (human, dog, and rat) phase I metabolism for human phase I and phase II metabolism for rat phase I and phase II metabolism for mammals stepwise transformation predictions yes, with a limitation of maximum 5000 metabolites yes, up to four steps no only one step at a time probability ranking one classification ranking and two scoring methods classification ranking not provided not provided microbial metabolism
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