There has been considerable discussion in recent weeks about the residential soil standard of 90 parts per trillion (ppt), which was established in 2002 by the Michigan Department of Environmental Quality (MDEQ).
MDEQ adopted the 90 ppt level as part of a large package of administrative regulations that, among other things, made soil standards environmental regulations. Formerly, soil standards existed only as guidance and were not enforceable regulations. When the soil standards were first proposed for public comment, MDEQ did not propose the 90 ppt standard.
Dow participated actively in the development of these regulations before they were proposed, including the development of revised dioxin criteria, which took place over a two to three year period.
As a member of the Michigan Chemical Council, Dow was a Program Advisory Group member, and in that capacity submitted comments on, among other things, proposed changes to the Part 201 direct contact criteria for soils. Dow also submitted its own comments on the proposed regulations. During the development of the regulations, Dow also had meetings with MDEQ officials to provide data and discuss the Company's recommendations, which were based on research and science.
The level of 90 ppt was only approved in the final regulation after the end of the public comment period. MDEQ had publicly proposed 150 ppt.
How was 90 ppt Calculated?
MDEQ uses a mathematical equation, called an algorithm, to establish soil cleanup criteria. It is Dow's understanding that MDEQ used its standard algorithm to calculate the 90 ppt, but deviated from its standard approach on the exposure and toxicity assumptions that are used to calculate this particular standard. In fact, the dioxin standard is footnoted by MDEQ in its final regulations because MDEQ did not follow its standard calculation practice.
The equation considers several factors. A change in any one of these factors could significantly increase or decrease the 90 ppt standard. The equation includes:
- Amount of dirt eaten
- Amount of dirt on skin
- Days per year eating dirt
- Days per year with dirt on skin
- Ability of dioxin to travel from dirt to bloodstream
MDEQ Assumptions
Dow believes many of the state's general assumptions used for setting soil criteria as well as particular assumptions used in the calculation of the dioxin criteria unrealistically overstate potential exposure and risk because they assume:
- Michigan residents wear shorts and T-shirts for 245 days per year, with no consideration for changes in weather.
- Soil is in contact with skin 24 hours per day.
- All skin contact and soil ingestion come from the same location for 30 years.
- The amount of soil estimated to be eaten on a daily basis is twice as much as the US EPA reports in their Exposure Factors Handbook.
- The amount of dioxin that may absorb through the skin is nearly twice as much as the MDEQ's own toxicologists believe could be absorbed.
- Children from birth to age 6 eat soil and have the average weight of a 3 year old.
A 90 ppt standard and seeks to have MDEQ re-propose the standard so that the public can comment on the standard and on the MDEQ assumptions that went into the calculation of the standard.
What's Wrong with Low Standards?
Dioxin background levels reported by MDEQ are as high as 35 ppt in the Upper Peninsula and 34.7 ppt in the Lower Peninsula. MDEQ director Steven Chester indicated that this standard could actually go lower, to 12 ppt. If such a low standard were to be set for Michigan, a major portion of the state could be considered a facility by the MDEQ.
Lawmakers Respond with Legislation
In response to community concerns about soil testing in Midland, Sen. Tony Stamas and Rep. John A. Moolenaar introduced bills to establish 1,000 ppt as the residential action standard for soil, the current national standard most often used by the federal EPA.
Senate Bill 1276 and House Bill 5963 were introduced May 27, 2004, but have since been withdrawn. The legislation would have allowed the higher level until science demonstrates a reason to lower the level in the event of health or safety concerns.
Contact your local legislators for additional information or to offer your input.
