This site will post communications directed to the Roane Community Advisory Group (CAG) as they are received in order to keep the community affected by the TVA ash dike failure fully informed.

General information regarding the CAG and relevant public documents are posted at the CAG website.

Tuesday, February 9, 2010

TDH on Selenium

I have reviewed the paper that was a source of concern and some of the literature behind the recommendations in it.

First I have to say that many of the fish from Watts Barr should not be consumed because of the advisories already in place. The advisories for PCB and other contaminants are likely of greater concern than selenium. I understand the concept of not adding to a problem already present, but I can in no way let a largely theoretical discussion of selenium detract from the larger issue of people ignoring fish advisories for much more potent contaminants.

That said, I can find no reference for acute toxicity by selenium at the levels represented in eating even a rather large meal of fish with a selenium level at the Risk Based Screening Level. This theoretical dose would of course be higher than the recommended daily consumption level by several fold, but the averaging out of the dose as presented in EPA’s Selenium Factsheet is how the measure of chronic toxicity was intended to work. One would not eat a selenium meal each day but rather get a dose on an occasional basis. The studies on which the recommendations are based show that people with average daily intakes as high as 850 micrograms of selenium per day showed no signs of ill effects. Of course, some of the days/ meals would have been significantly higher.

The screening level set by EPA should be quite protective. The exposure medium is fish tissue which would not be as effective as a designed capsule that would be used in a clinical trial. The chronic toxicity studies from which FDA tolerance limits are derived use estimates and reconstruct doses in a manner similar to the risk assessment. At two large meals per week the rate of fish consumption is should be an adequate for most fish consumers and represents a reasonable maximum exposure (RME).

RME refers to people who are at the high end of the exposure distribution (approximately the 95th percentile). The RME scenario is intended to assess exposures that are higher than average, but are still within a realistic range of exposure. Screening values are set according to EPA guidance to estimate RME.

As always Tennessee Department of Health will continue to follow the cleanup of the ash spill and will work with TDEC on fish advisories and other environmental public health concerns.


Brad Parman
Environmental Epidemiologist
East TN Regional Health Office
1522 Cherokee Trail
Knoxville, TN 37920
Front Desk: 865-546-9221
Phone: 865-549-5234
Fax: 865-594-5738

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