Chemical Listed Effective December 4, 2015 as Known to the State of California to Cause Reproductive Toxicity: 2,5-Hexanedione and Addition of a Reproductive Toxicity Endpoint (Developmental) for Methyl-N-Butyl Ketone

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Effective December 4, 2015, the Office of Environmental Health Hazard Assessment (OEHHA) is adding 2,5-hexanedione (CAS No. 110-13-4) to the list of chemicals known to the state to cause reproductive toxicity for purposes of the Safe Drinking Water and Toxic Enforcement Act of 1986 (Proposition 651). 2,5-Hexanedione was considered by the Developmental and Reproductive Toxicant Identification Committee (DARTIC) in its official capacity as the “state’s qualified experts” (SQE) at a public meeting held on November 9, 2015. The DARTIC determined that 2,5-hexanedione was clearly shown through scientifically valid testing according to generally accepted principles to cause reproductive toxicity, based on the male reproductive endpoint. Regulations for the listing of chemicals by the DARTIC are set out in Title 27, California Code of Regulations, section 25305(b)(1). At their November 9, 2015 meeting, the DARTIC reaffirmed the listing of methyl-n-butyl ketone (CAS No. 591-78-6) as a chemical known to the state to cause reproductive toxicity on the basis of male reproductive toxicity2 and determined that an additional endpoint, developmental toxicity, be added for methyl-n-butyl ketone.

A complete, updated chemical list is available on the OEHHA website and will be published elsewhere in this issue of the California Regulatory Notice Register.

In summary, as indicated in the table below, 2,5-hexanedione is listed under Proposition 65 as known to the state to cause reproductive toxicity (male reproductive endpoint), and an additional endpoint (developmental toxicity) is added for methyl-n-butyl ketone, effective December 4, 2015.



Toxicological Endpoints

Listing Mechanism*

Effective Date




Male Reproductive Toxicity


December 4, 2015

Methyl-n-Butyl Ketone


Male Reproductive Toxicity



August 7, 2009

Developmental toxicity

December 4, 2015

* Listing mechanism: SQE – “State’s Qualified Expert” mechanism (Health and Safety Code section 25249.8(b) and Title 27, Cal. Code of Regs., section 25305(b)(1)).

Footnotes and References

1 The Safe Drinking Water and Toxic Enforcement Act of 1986, Health and Safety Code section 25249.5 et seq.

2 Methyl-n-butyl ketone was originally listed as a chemical known to the State to cause reproductive toxicity (male endpoint) on August 7, 2009, under the Labor Code mechanism (Health and Safety Code section 25249.8(a)).