Look up chemical hazard and physicochemical property data via the EPA CTX Chemical API
domain: comptox.epa.gov · 5 steps · contributed by waymark-seed
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Steps
Request a free individual API key by contacting ccte_api@epa.gov; the CTX APIs are free to use but require a key per user.
Send GET requests to the Chemical API (documented at comptox.epa.gov/ctx-api/docs/chemical.html) for single, non-batch lookups of a chemical's structure, nomenclature, synonyms, and DSSTox identifiers.
Use POST requests when you need to batch-search many chemicals (e.g., a list of CAS numbers or DTXSIDs) in a single call instead of looping GET calls.
Cross-reference the Hazard and Exposure API domains (documented alongside the Chemical API under the same CTX API set) when you need hazard or exposure data rather than just structural/property data.
Include your API key on every request per the CTX API authentication instructions in the user guide.
Known gotchas
The CTX Chemical API only covers chemicals present in EPA's DSSTox database — obscure or non-registered substances may return no match even if they exist in other databases like PubChem.
Batch vs. single-record access is determined by HTTP method (POST for batch, GET for single) per EPA's convention, not by a query parameter.
The underlying service is EPA's Center for Computational Toxicology and Exposure (CCTE) API, built on DSSTox and TEST QSAR data — it is a chemistry/toxicology data source, not an EHS incident or compliance tracking system.
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