It's the Environment!
Cleaning Up Dioxin
15 March 2010
Peter deFur
Dioxin is one of the chemicals commonly found as a contaminant at Superfund and RCRA sites around the country. This chemical is the principal contaminant at such well-known sites as Times Beach, Missouri and Pensacola, Florida where homes were bought by the government and the residents relocated because of the widespread elevated dioxin levels in soil. The Environmental Protection Agency (EPA) is completing its reassessment of dioxin (by the end of 2010, according to administrator Jackson) and will set new clean-up levels. In the meantime, EPA proposed interim soil clean-up standards, referred to as Preliminary Remediation Goals, or PRGs that will update the decades-old PRG and serve as a place holder until the dioxin reassessment is completed and released.
EPA’s effort is laudable for getting rid of a cleanup standard that was so woefully out-of-date that it was never used. The old standard of 1000 parts per trillion, or ppt, did not account for any current information on carcinogenicity, reproductive effects, bioaccumulation or uptake through skin. It is no wonder that the proposed clean-up numbers are more than10 times lower than the old one.
In comments submitted to EPA on the dioxin PRGs (see estewards.com for a copy), I recommended four corrections or changes to the EPA proposal, having the effect of lowering the clean-up numbers even more. First, the EPA guidance does not include inhalation in the quantitative estimates from which the clean-up n umber was derived. While EPA is correct that dioxin is largely absorbed via food, and not inhalation, the inhalation pathway may be significant in some situations and guidance should direct site specific assessment to consider this possibility.
Second, EPA incorrectly refers to “natural background” as the exposures from dioxin in air, water, soil that are not caused by specific sources from human activities. Dioxin is not naturally produced, the only known sources are of human creation and substantial evidence indicates that dioxin levels were immeasurably low prior to the industrial revolution. EPA needs to adopt the correct term “ambient.”
EPA accepts the ambient levels of approximately 0.2 to 11.4 ppt as normal and concludes that clean-up levels in this range could not be applied. If EPA uses current data and sets a clean-up level to protect cancer at a 1 in a million risk, the soil level would be 3.7 ppt. But because this number would present challenges to apply, EPA is willing to accept a higher cancer risk.
EPA should set the cancer PRG at 3.7 ppt because that number is both scientifically sound and based on a health protective policy.
The EPA proposal wisely takes on the problem of non-cancer effects that can occur at quite low exposures and are evaluated via a “reference dose”. The reference dose estimates the total amount of a chemical from all sources of exposure, both on-site and from uncontrollable sources. To protect against effects other than cancer, the soil level would be 72, but only because EPA does not include other sources of dioxin exposure (in our every day lives). Using the reference dose requires assuming that we all get some exposure from our every-day activities not related to the contaminated site, so only part of the reference dose can be considered site-related. If EPA includes the other dioxin exposures, then the soil PRG for non-cancer will have to- and should- be reduced.
The proposed PRGs for dioxin are too high and EPA provided the technical explanation for why they are too high, and for the numbers that should be adopted as interim values.
The problem EPA faces is intense lobbying from companies like Dow and GE that do not want to clean up dioxin contamination to lower levels, despite all we know about the harm from dioxin and related chemicals. Now is the time for EPA to stand up to big companies and set protective standards for the sake of human health and the environment.