Notice of Intent to List S,S,S-Tributyl Phosphorotrithioate (Tribufos, DEF) as Known to the State to Cause Cancer

The California Environmental Protection Agency’s Office of Environmental Health Hazard Assessment (OEHHA) intends to list S,S,S-tributyl phosphorotrithioate as known to the State to cause cancer under the Safe Drinking Water and Toxic Enforcement Act of 1986. This action is being taken under the authoritative bodies listing mechanism.

OEHHA requested information relevant to the possible listing of S,S,S-tributyl phosphorotrithioate in a notice published in the California Regulatory Notice Register on May 21, 2010 (Register 2010, No. 21-Z).  OEHHA received no public comments.

Background on listing via the authoritative bodies mechanism:  A chemical must be listed under the Proposition 65 regulations when two conditions are met:

1. An authoritative body formally identifies the chemical as causing cancer (Section 25306(d)).
2. The evidence considered by the authoritative body meets the sufficiency criteria contained in the regulations (Section 25306(e)). 

However, the chemical is not listed if scientifically valid data which were not considered by the authoritative body clearly establish that the sufficiency of evidence criteria were not met (Section 25306(f)).

The U.S. Environmental Protection Agency (U.S. EPA) is one of several institutions designated as authoritative for the identification of chemicals as causing cancer (Section 25306(m)).

OEHHA is the lead agency for Proposition 65 implementation.  After an authoritative body has made a determination about a chemical, OEHHA evaluates whether listing under Proposition 65 is required using the criteria contained in the regulations.

OEHHA’s determination: S,S,S-Tributyl phosphorotrithioate meets the criteria for listing as known to the State to cause cancer under Proposition 65, based on findings of the U.S. EPA (U.S. EPA, 1997).

Formal identification and sufficiency of evidence for S,S,S-tributyl phosphorotri­thioate:  In 1997, the U.S. EPA published a report on S,S,S-tributyl phosphorotrithioate entitled Memorandum: Carcinogenicity Peer Review (2nd) of Tribufos (DEFTM).  This report concludes that the chemical causes cancer, which satisfies the formal identification and sufficiency of evidence criteria in the Proposition 65 regulations.

OEHHA is relying on the U.S. EPA’s discussion of data and conclusions in the report that S,S,S‑tributyl phosphorotrithioate causes cancer.  The section of the 1997 U.S. EPA report entitled “Classification of Carcinogenic Potential” found that “[t]ribufos should be characterized as ‘likely’ at high doses, based on increases in tumors in both sexes of the CD-1 mouse; the liver of male mice, in the lung of female mice, and in the small intestine (rare tumors) in both sexes of mice.”  The liver tumors in male mice were hemangiosarcomas, the lung tumors in female mice were alveolar/bronchiolar adenomas, and the tumors in the small intestine in male and female mice were adenocarcinomas. 

Thus, the U.S. EPA (1997) has found that S,S,S-tributyl phosphorotrithioate causes increased incidences of malignant liver tumors in male mice and rare malignant tumors of the small intestine in male and female mice.

Request for comments:  OEHHA is committed to public participation in its implementation of Proposition 65.  OEHHA wants to ensure that its regulatory decisions are based on a thorough consideration of all relevant information.  OEHHA is requesting comments concerning whether S,S,S-tributyl phosphorotrithioate meets the criteria set forth in the Proposition 65 regulations for authoritative bodies listings.  In order to be considered, OEHHA must receive comments by 5:00 p.m. on Monday, September 13, 2010.  OEHHA hereby extends the public comment period for Tribufos or DEF to 5 p.m., Wednesday, October 13, 2010. We encourage you to submit comments in electronic form, rather than in paper form.  Comments transmitted by e-mail should be addressed to sam.delson@oehha.ca.gov.  Comments submitted in paper form may be mailed, faxed, or delivered in person to the addresses below:

Mailing Address: Sam Delson
Office of Environmental Health Hazard Assessment
P.O. Box 4010, MS-19B
Sacramento, California 95812-4010

Fax: (916) 323-8803

Street Address: 1001 I Street
Sacramento, California 95814

If you have any questions, please contact Sam Delson at sam.delson@oehha.ca.gov or at (916) 445‑6900.

Comment Period

• Comment Period - Notice of Intent to List S,S,S-Tributyl Phosphorotrithioate (Tribufos, DEF) as Known to the State to Cause Cancer
• Extension of Comment Period - Notice of Intent to List S,S,S-Tributyl Phosphorotrithioate (Tribufos, DEF) as Known to the State to Cause Cancer
• 2nd Extension of Comment Period - Notice of Intent to List S,S,S-Tributyl Phosphorotrithioate (Tribufos, DEF) as Known to the State to Cause Cancer

Chemical Reference

• S,S,S-Tributyl phosphorotrithioate (Tribufos, DEF)

Related Notices

• Request for Relevant Information on a Chemical Being Considered for Listing by the Authoritative Bodies Mechanism: S,S,S-Tributyl Phosphorotrithioate (Tribufos, DEF)

  May 20, 2010
• Chemical Listed Effective February 25, 2011 as Known to the State of California to Cause Cancer S,S,S-Tributyl phosphorotrithioate (Tribufos, DEF)

  Feb 25, 2011

Footnotes and References

U.S. Environmental Protection Agency (U.S. EPA, 1997). Memorandum: Carcinogenicity Peer Review (2nd) of Tribufos (DEFTM).  Office of Prevention, Pesticides and Toxic Substances. May 22, 1997.

All referenced sections are from Title 27 of the Cal. Code of Regulations.