TOX21SL: Tox21 Screening Library

List Details

Description: TOX21SL is a list of unique DSSTox substances comprising the original screening library for the Tox21 program, a multi-federal agency collaborative among US EPA, the National Institutes of Health (NIH) National Toxicology Program (NTP) and National Center for Advances in Translational Science (NCATS), and the US Food and Drug Administration (FDA). EPA, NTP and NCATS partners contributed approximately equal size inventories to the library, whereas FDA contributed a small set of drugs. EPA’s contribution to the original TOX21SL fully covered its ToxCast inventory, so retains significant overlap with the current ToxCast HTS inventory (TOXCAST). The NTP contribution was drawn from the NTP bioassay and research testing programs of chemicals of interest to environmental toxicology, and the NCATS contribution consisted primarily of marketed drugs. Tox21 compounds were selected based on a wide range of criteria, including, but not limited to: environmental hazard or exposure concern based on production volume (industrial chemicals) or occurrence data, availability of animal toxicity study data, food-additives, fragrances, toxicity reference chemicals, and drugs or known bioactive compounds. Chemicals in the original Tox21 program underwent screening at the intramural NCATS robotics testing facility. All HTS assay data generated in association with the Tox21 program are publicly available through PubChem (, as are the analytical chemistry quality control (QC) summary records generated in association with the Tox21 testing program. Tox21 assay data are also included in EPA’s ToxCast data downloads (

For current information on the Tox21 program, see

Update (Nov 20, 2018):

The following publication coauthored by Tox21 Federal Partner Leads lays out a strategic and operational plan for the Tox21 program from 2018 onward:
The plan articulates areas of focused scientific investment, both in chemical and biological space, to which new Tox21 cross-partner projects will be directed. In keeping with the new strategic plan, the Tox21 testing library moving forward is being consolidated under EPA chemical management and includes the full, currently available EPA ToxCast chemical library as well as approx. 1300 newly added chemicals provided by the NTP that were in the original TOX21SL library. The full chemical library available to the Tox21 cross-partner projects as DMSO solutions currently exceeds 6400 chemicals, of which nearly 6000 were included in the original TOX21SL library. A snapshot of this active plating library list (dated 11/21/2018) can be accessed at EPACHEMINV_AVAIL.

Number of Chemicals: 8947