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ToxCast Chemicals

EPA’s ToxCast research effort has a chemical library of approximately 4,400 unique chemicals (as of December 2017). The library includes a broad range of chemicals with potential for human and ecosystem exposure which have heightened regulatory concern yet are lacking data on potential health effects of these chemicals.

The chemicals in the library have been screened in hundreds of high-throughput screening assays to generate biological activity data. The chemical library is organized into three phases.

In 2007, Phase I was launched, screening 310 chemicals (mostly pesticides) across hundreds of assay endpoints. Phase II data increased the chemical inventory to about 1,800 chemicals. In 2014, Phase III was initiated, increasing the library to over 4,500 chemicals.

Below are links to information about the various ToxCast chemical lists and the workflow EPA follows to select chemicals, procure chemicals, register chemicals, conduct a quality review of the chemicals, and prepare the chemicals for high-throughput screening.


ToxCast Phases, Timing, and Chemical and Assay Endpoint Counts

ToxCast Endpoint Counts