You never want rock metals, so the slenium must be a plant source, something rarely ever sold commercially. I assume some plants may supply more slenium than others, but if the soil does not have it to begin with, then you can never know for sure your getting extra selenium, this is why the vitamin manufactures sales people ROCKS, which are of no value.

I personally take rock selenium and apply to my gardens in the hopes that the plants will use it and then I will get it from the plants.

Second option

Deep Earth Clay
This has most of your minerals in the form of volcanic dust that was put down in layers that most likely killed most animal life in the same process, these layers can be several inches thick or many feet thick and as well be on the surface or very deep in the earth. The deep earth clay has zero pollution and I only use it.

This clay has been eaten upon for many thousands of years by bacteria, all plants due great in clay type soils.

We humans can eat clay and get some value from it, but ideally it is best to eat the plant after it has eaten the clay.

Those lacking minerals may want to become what is called a "dirt eater" which stands for clay. 1 teaspoon in a gallon of water and set in the sun and drink 24 hours later. The larger minerals will pass through the elimination system doing no harm, not like the deadly vitamin rocks that are made so small they enter the blood stream and get trapped.

For this reason, I use a deep earth clay which also comes from a place that is rich in selenium.

You have asked a GOOD QUESTION that few think of.

Blessings,
MH

only 3-4 brazil nuts are needed a day


http://ithyroid.com/selenium.htm