EPA’s non-targeted analysis collaborative trial (ENTACT): genesis, design, and initial findings
In August 2015, the US Environmental Protection Agency (EPA) convened a workshop entitled “Advancing non-targeted analyses of xenobiotic chemicals in environmental and biological media.” The purpose of the workshop was to bring together the foremost experts in non-targeted analysis (NTA) to discuss the state-of-the-science for generating, interpreting, and exchanging NTA measurement data. During the workshop, participants discussed potential designs for a collaborative project that would use EPA resources, including the ToxCast library of chemical substances, the DSSTox database, and the CompTox Chemicals Dashboard, to evaluate cutting-edge NTA methods. That discussion was the genesis of EPA’s Non-Targeted Analysis Collaborative Trial (ENTACT). Nearly 30 laboratories have enrolled in ENTACT and used a variety of chromatography, mass spectrometry, and data processing approaches to characterize ten synthetic chemical mixtures, three standardized media (human serum, house dust, and silicone band) extracts, and thousands of individual substances. Initial results show that nearly all participants have detected and reported more compounds in the mixtures than were intentionally added, with large inter-lab variability in the number of reported compounds. A comparison of gas and liquid chromatography results shows that the majority (45.3%) of correctly identified compounds were detected by only one method and 15.4% of compounds were not identified. Finally, a limited set of true positive identifications indicates substantial differences in observable chemical space when employing disparate separation and ionization techniques as part of NTA workflows. This article describes the genesis of ENTACT, all study methods and materials, and an analysis of results submitted to date.
KeywordsToxCast Ring-trial Exposome High-resolution mass spectrometry CompTox chemicals dashboard
The authors wish to thank ICF staff (EPA Contract # EP-C-14-001, work assignment 1-63) for their management of the logistics for the first workshop and completion of the workshop report; Evotec staff (EPA Contract #EP-D-12-034) for their management of the ToxCast chemical library and creation of ENTACT resources; and Oregon State University staff (EPA Contract # EP-16-W-000115) for creating silicone band reference materials. We also thank Annette Guiseppi-Elie, Tina Bahadori, Jennifer Orme-Zavaleta and EPA managers for their support and for understanding the vision for the work. We recognize the Chemical Safety for Sustainability team and John Wambaugh and Kristin Isaacs for their scientific leadership for the Rapid Exposure and Dosimetry project, and all team members for their thoughtful conversations. We greatly appreciate the support of Cameron Clark and Monica Linnenbrink on the EPA FTP site, Andrew McEachran and the Dashboard development team for their efforts to expand mass spectrometry functionality to the Dashboard, and Kathy Coutros for support with the Evotec chemical management contract. Portions of this work were supported by EPA Stage 1-3 Pathfinder Innovation Project “Building a Network to Measure the Totality of Chemical Exposures.”
Compliance with ethical standards
Human serum was used in this study. Consent was obtained at the time of original collection. However, its use in the current project is considered exempt human subjects research under 40 CRF 26.101(b)(4) because the source is “publicly available” (purchased from vendor) and the subjects cannot be identified (samples were both pooled and coded). In accordance with federal regulations, IRB approval for this secondary use was not required by either EPA or NIST.
Conflict of interest
The authors declare that they have no conflict of interest.
The views expressed in this manuscript are those of the authors and do not necessarily represent the views or policies of the US Environmental Protection Agency. Any mention of trade names, products, or services does not imply an endorsement by the US Government or the US Environmental Protection Agency. The EPA does not endorse any commercial products, services, or enterprises.
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