For those of you who enjoyed my previous blog posts on selenium, here’s a little lagniappe for you on the behavior of selenium in the aquatic environment.  As I mentioned in an earlier post, selenium acts a lot like sulfur in that it combines with other elements and organic matter to form different species. (For an explanation of elemental species, here is a link to another post https://waterblogger.org/contaminants/the-mercury-cycle/). In surface waters with a lot of oxygen, you’ll most often find two mineral species called selenite and selanate, which are the result of the combination of selenium with oxygen. Algae and other floating microorganisms in the water are sucking up this stuff, turning it into organic forms of selenium and accumulating it within their teeny weenie little organic structures.

Down below the water, you’ll find a lot going on in the dynamic chemical environment of sediment. There’s lots of organic material in sediment with which selenium can combine to form organic selenium species. There are also lots of other elements like iron with which selenium species react. And there are all sorts of microorganisms tooling around looking for a snack. Under these varying conditions of chemical and biochemical activity, selenium is being converted from one selenium species to another.

For example, all those microorganisms chowing down on the selenium in sediment frequently methylate it, which forms organic selenium species. (Read the post at the above link, to find out what methylation is). Organic selenium species get processed right into the living structures of the tissues of animals like fish. According to the great compendium of the Toxicological Profile for Selenium published by the Agency for Toxic Substance and Disease Registry (ATSDR), these organic selenium species are similar to the organic sulfur ones used by living organisms in the production of amino acids. In fact, ATSDR says selenium substitutes for sulfur in amino acids. The names for these amino acids are selenocysteine and selenomethionine. Do you remember what amino acids are? They are the building blocks of protein. Protein supports the growth of tissue, muscles, and bones. Neither fish nor we could get along without protein.

So those are the mechanisms by which selenium in the aquatic environment enters the food chain. Basically all the little guys like algae and microorganisms that feed on selenium in the water and the sediment are eaten right up by insect larvae, larval fish, clams and mussels, and similar denizens of the aquatic world, which in turn are then eaten up by fish and birds. Voila, a perfect web for selenium poisoning.