In May 2009, during a visit to Midland, Mich. to review the ongoing cleanup of the Dow Midland plant and the Tittabawassee River, Environmental Protection Agency (EPA) Administrator Lisa Jackson committed to proposing new preliminary cleanup goals (PRGs) for dioxin by the end of 2009. Administrator Jackson also announced that she expected the Agency to complete its reassessment of dioxin risks and release it for public review within the same time frame.
On Dec. 30, 2009, EPA fulfilled the Administrator’s commitment to issue new dioxin PRGs, but the Agency has not released a new draft dioxin risk assessment.
Under the National Contingency Plan, EPA generally establishes PRGs on a site-specific basis “based on readily available information, such as chemical-specific ARARs or other reliable information.” PRGs are then modified, as necessary, based on the remedial investigation and feasibility study and final cleanup levels are established when a remedy is selected. 40 CFR 300.430(e)(2)(i).
In the case of dioxin, however, in 1998 EPA’s Office of Solid Waste and Emergency Response (OSWER) established a uniform national PRG of 1 ppb for exposure to dioxin in residential soils. This level was consistent with the cleanup level established for Times Beach, Mo., and other dioxin sites around the country. Based on available science, it represents an upper-bound lifetime excess cancer risk of 2.5 x 10-4, which EPA considered to be within the NCP risk range, although at “the higher end of the range of excess cancer risks that are generally acceptable at Superfund sites.” Approach for Addressing Dioxin in Soil at CERCLA and RCRA Sites, OSWER Directive 9200.4-26, April 13, 1998. In the guidance OSWER noted that EPA was reexamining the toxicity of dioxin and committed to reviewing the PRG when the dioxin reassessment was complete. Specifically, the guidance states: “The Office of Solid Waste and Emergency Response does not believe it is prudent to establish new, and possibly varying, precedents for Superfund or RCRA dioxin levels just prior to the release of this reassessment report.”
Ironically, OSWER now may be doing just that. No reassessment of dioxin was ever released following issuance of the 1998 guidance, but Administrator Jackson has committed to release it shortly.
Notwithstanding the imminent release of a new dioxin risk assessment, EPA is now proposing change the PRG for dioxin in residential soils to 72 parts per trillion (.072 ppb). This corresponds to a 1 x 10-5 excess cancer risk. Public Review Draft, Draft Recommended Interim Preliminary Remediation Goals for Dioxin in Soil and CERCLA and RCRA Sites, OSWER 9200.3- 56 (Dec. 30, 2009) (herein after Draft Dioxin PRGs). This new PRG is not based on any new science or “a new or independent review of dioxin toxicity.” Draft Dioxin PRGs, at 3 (noting that the final dioxin reassessment is still under development). For cancer risks, draft PRG is based on a 1985 oral cancer slope factor derived by EPA’s Office of Health and Environmental Assessment. For noncancer risks, the draft PRG is based on ATSDR’s 1998 minimum risk level of 1 pg/kg-day. Draft Dioxin PRGs, at 9.
To justify changing the PRG in the absence of new science, EPA states that the 1998 PRG for residential soil did not consider non-cancer effects or dermal exposure. Draft PRG, at 6. EPA uses the non-cancer effects to justify not using the full risk range when setting the PRG at a 1 x 1-5 cancer risk level. The non-cancer risk level is based on ATSDR data, even though ATSDR has been very careful to say that “ATSDR does not establish clean-up goals or preliminary remediation goal, but ATSDR believes that health risks associated with dioxins in soil below 1 ppb would be low under most scenarios where the primary exposure pathway is incidental ingestion through direct exposure to soil.” Update to the ATSDR Policy Guideline for Dioxins and Dioxin-Like Compounds in Residential Soil, November 2008, at 3. As a result, EPA’s justification for changing the PRG for dioxin in soil appears to rest entirely on the consideration of dermal exposure.
If EPA changes the PRG for dioxin, that will bring into question a number of CERCLA and RCRA cleanups. At a minimum, when conducting a 5-year review of a dioxin Superfund cleanup, EPA will revisit whether the cleanup is protective, and based on a new PRG guidance, may determine that cleanups of dioxin in residential soil to the 1 ppb level are not protective of human health. Under its standard consent decree reopeners, EPA can then require responsible parties to perform additional cleanup work.
EPA is taking comment on the Draft Dioxin PRGs until Feb. 26, 2010, and plans to issue the final dioxin PRGs in June 2010.