On May 9, 2009 EPA Administrator Lisa Jackson directed her staff to reassess the human health effects due to exposure to dioxin, which included the development of preliminary remediation goals (PRGs) for dioxin in soil. The EPA Office of Solid Waste and Emergency Response (OSWER) prepared a public review document titled “Draft Recommended Interim Preliminary Remediation Goals For Dioxin In Soil At CERCLA and RCRA Sites” dated December 2009. EPA followed up the draft PRGs document with notice of the proposed interim PRGs in the Federal Register1. Public comments regarding the proposed dioxin standards were accepted until February 26, 2010.
Both the U.S. Chamber of Commerce and the U.S. Department of Defense (DOD) have concern that many of the studies used to develop the Interim PRGs do not represent the most current science and urge the EPA to wait for completion of EPA’s dioxin reassessment before proposing revised dioxin limits. The issuance of Interim PRGs in June 2010 is scheduled to be superseded with final dioxin limits in December 2010. The U.S. Chamber of Commerce and the DOD express concerns regarding lowering dioxin limits in residential and commercial/industrial soil to concentrations below ambient levels in rural soils. DOD points out the urban concentrations of dioxins would be higher that ambient concentrations in rural soils.
The Interim PRGs have the potential to cause confusion with the regulators and the regulated community alike. Providing interim standards may result in reopening closed sites and include the possibility of revising those standards twice within the same year, depending on the findings for the final dioxin standards.
EPA’s current recommended PRG for CERCLA and RCRA sites, issued April 13, 1998, are 1 part per billion (ppb = 1,000 parts per trillion (ppt)) for dioxin toxicity equivalents (TEQs) in soils at residential sites. The recommended PRGs for dioxin in soil at commercial/industrial sites are 5 ppb and 20 ppb, respectively, where exposure is due to direct contact. The revised proposed dioxin levels provided in the January 7, 2010 Federal Register would be lowered to 72 ppt for residential soils and 950 ppt for commercial/industrial soil. These proposed PRG concentrations are reportedly intended to protect against cancer effects at a risk level of affecting approximately 1 in 100,000 individuals, according to the EPA. The EPA also is considering a second alternative set of dioxin TEQ limits; 3.7 parts per ppt in residential soil and 17 ppt in commercial/industrial soil. This second set of PRGs reportedly is intended to protect against cancer effects at a risk level of affecting approximately 1 in 1,000,000 individuals, according to the EPA. EPA acknowledges that these lower concentrations may be below the average concentration of dioxin in rural U.S. soils.
The Interim PRGs are to be finalized in June of 2010. The limits are identified as Interim limits because EPA has yet to fully complete their reassessment of dioxin and plan to issue final remedial goals for dioxin in soil at the end of 2010. According to the U.S. Chamber of Commerce, the National Academy of Science (NAS) has been critical of “a number of key science and risk assessment positions taken by the EPA with respect to dioxin’s risk to humans”, based upon the last dioxin assessment issued by EPA in 2003. The NAS comments, and other comments, are to be addressed in the final dioxin assessment to be completed later this year.
This article was authored by William Chambers, Acacia Environmental Group LLC. For more information on the author see here.
1 Federal Register/Volume 75, No. 4/Thursday, January 7, 2010/page 984