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Richard Judson,¹ Ann Richard,¹ David J. Dix,¹ Keith Houck,¹ Matthew Martin,¹ Robert Kavlock,¹ Vicki Dellarco,² Tala Henry,³ Todd Holderman,³ Philip Sayre,³ Shirlee Tan,⁴ Thomas Carpenter,⁵ and Edwin Smith⁶

¹National Center for Computational Toxicology, Office of Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA; ²Office of Pesticide Programs, Office of Prevention, Pesticides, and Toxic Substances, U.S. Environmental Protection Agency, Arlington, Virginia, USA; ³Office of Pollution Prevention and Toxics and ⁴Office of Science Coordination and Policy, Office of Prevention, Pesticides, and Toxic Substances, U.S. Environmental Protection Agency, Washington, DC, USA; ⁵Office of Water, Office of Ground Water and Drinking Water, U.S. Environmental Protection Agency, Washington, DC, USA; ⁶Great Lakes National Program Office, U.S. Environmental Protection Agency, Chicago, Illinois, USA

Abstract
Objective: Thousands of chemicals are in common use, but only a portion of them have undergone significant toxicologic evaluation, leading to the need to prioritize the remainder for targeted testing. To address this issue, the U.S. Environmental Protection Agency (EPA) and other organizations are developing chemical screening and prioritization programs. As part of these efforts, it is important to catalog, from widely dispersed sources, the toxicology information that is available. The main objective of this analysis is to define a list of environmental chemicals that are candidates for the U.S. EPA screening and prioritization process, and to catalog the available toxicology information.

Data sources: We are developing ACToR (Aggregated Computational Toxicology Resource) , which combines information for hundreds of thousands of chemicals from > 200 public sources, including the U.S. EPA, National Institutes of Health, Food and Drug Administration, corresponding agencies in Canada, Europe, and Japan, and academic sources.

Data extraction: ACToR contains chemical structure information ; physical–chemical properties ; in vitro assay data ; tabular in vivo data ; summary toxicology calls (e.g., a statement that a chemical is considered to be a human carcinogen) ; and links to online toxicology summaries. Here, we use data from ACToR to assess the toxicity data landscape for environmental chemicals.

Data synthesis: We show results for a set of 9,912 environmental chemicals being considered for analysis as part of the U.S. EPA ToxCast screening and prioritization program. These include high- and medium-production-volume chemicals, pesticide active and inert ingredients, and drinking water contaminants.

Conclusions: Approximately two-thirds of these chemicals have at least limited toxicity summaries available. About one-quarter have been assessed in at least one highly curated toxicology evaluation database such as the U.S. EPA Toxicology Reference Database, U.S. EPA Integrated Risk Information System, and the National Toxicology Program.

Key words: ACToR, carcinogenicity, database, developmental, hazard, HPV, MPV, pesticide, reproductive, toxicity. Environ Health Perspect 117:685–695 (2009) . doi:10.1289/ehp.0800168 available via http://dx.doi.org/ [Online 22 December 2008]

Address correspondence to R. Judson, U.S. Environmental Protection Agency, 109 T.W. Alexander Dr. (B205-01) , Research Triangle Park, NC 27711 USA. Telephone: (919) 541-3085. Fax: (919) 541-1194. E-mail: judson.richard@epa.gov

We acknowledge significant contributions from members of the U.S. EPA Aggregated Computational Toxicology Resource (ACToR) development team: T. Cathey, T. Transue, and R. Spencer of Lockheed Martin, and F. Elloumi, D. Smith, J. Vail, and K. Daniel. We also acknowledge the significant contribution of M. Wolf (Lockheed Martin) in relation to the U.S. EPA’s Distributed Structure-Searchable Toxicity Data Network structure inventory incorporated into ACToR.

This article has been reviewed by the U.S. EPA and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the agency, nor does mention of trade names or commercial products constitute endorsement or recommendation for use.

The authors declare they have no competing financial interests.

Received 8 September 2008 ; accepted 22 December 2008.