Mercury and selenium poisoning

http://www.pwrc.usgs.gov/products/factsheets/15mersel.pdf

The more I think about it, the more I want to be careful about how much selenium I take in. I was thinking about getting some Brazil nuts, however I am now leery of doing that, considering the radium they may have, and this article of how selenium might interact with mercury. There is probably enough selenium in the foods I eat anyway. Taking a selenium supplement, even a small one may be overdoing it.