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

The California Environmental Protection Agency’s Office of Environmental Health Hazard Assessment (OEHHA) is requesting information as to whether S,S,S-tributyl phosphorotrithioate meets the criteria for listing under the Safe Drinking Water and Toxic Enforcement Act of 1986. This action is being proposed under the authoritative bodies listing mechanism.

Chemical Being Considered for Listing by the Authoritative Bodies

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 appears to meet 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 appears to satisfy 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.

OEHHA issued a request for relevant information on this chemical in November 2000.  In 2004, following review of public comments received, OEHHA withdrew the chemical from consideration for listing at that time.  In light of the recent Court of Appeal decision in Exxon Mobil Corporation v Office of Environmental Health Hazard Assessment et al. (2009) 169 Cal. App. 4th 1264, OEHHA has determined that it will not consider dose-response issues for this chemical during the listing phase of the process.  Such issues will be addressed as necessary following a listing decision.  Therefore, OEHHA is re-issuing a request for relevant information for this chemical.

Request for relevant information:  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 public comment concerning whether S,S,S-tributyl phosphorotrithioate meets the criteria set forth in the Proposition 65 regulations for authoritative bodies listings.

After reviewing all comments received, OEHHA will determine whether S,S,S-tributyl phosphorotrithioate meets the regulatory criteria for administrative listing.  If it is determined to meet the listing criteria, OEHHA will proceed with the listing process and publish a Notice of Intent to List.

In order to be considered, OEHHA must receive comments by 5:00 p.m. on Tuesday, July 20, 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: 
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

Optional public forum:  Upon request, OEHHA will schedule a public forum to provide individuals an opportunity to present oral comments on the possible listing of S,S,S-tributyl phosphorotrithioate.  At the forum, the public may discuss the scientific data and other relevant information related to whether this chemical meets the criteria for listing in the regulations.

Requests for a public forum must be submitted in writing no later than Friday, June 18, 2010.  The written request must be sent to OEHHA at the mailing address above.  If a public forum is requested, a notice will be posted on the OEHHA web site at least ten days before the forum date.  The notice will provide the date, time, location and subject matter to be heard.  Notices will also be sent to those individuals requesting such notification.

If you have any questions, please contact (916) 445‑6900.

Link to Public Comments

Chemical Reference

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

Related Notices

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

  Aug 12, 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.