how much iodine?

[Veneer]

Does anybody know the typical iodine levels found in inland freshwater systems? While being instructed in endocrinology, the professor claimed that people living inland who get no seafood or iodine supplementation (eg. iodized salt) are at true risk of iodine deficiency because food sources of iodine inland is so negligible. And I hadn't really questioned it.

In my 412 page "Textbook of Limnology" by Gerald Cole (1994), the index points to a single page in reference to "iodine." On that page, the only information on iodine are afterthoughts at the ends of two paragraphs: That it is a needed inorganic micronutrient in "some (but not all) algae," and that it is among boron, cadmium, rubidium, and poisons lead, arsenic, and mercury in the list of elements that "could" be a minor element in a given lake's water.

Seems like this minimal mention of the element suggests iodine's basic lack of importance in freshwater ecosystems, or, possibly it just reflects still (at least in 1994) poor understanding in the area of study.

At the risk of making a possibly extraneous connection, the tissue of Macrobrachium rosenbergii contains only ~15% of the iodine of comparable marine Penaeids.

[Mustafa]

Does anybody know the typical iodine levels found in inland freshwater systems?

See...the problem with "typical" iodine levels in freshwater systems is that there are really no typical freshwater systems. Whereas the chemical composition of the ocean is pretty much uniform all around the world, freshwater systems, since they are not interconnected all over the world, are very different from each other. I would venture to say that there are no two rivers or lakes that have the same chemical composition. It all depends on how long the river is, what type of soil or mineral rocks it flows through or what type of chemicals from rain runoff enters its waters. Even within the same river there will be differences in chemical composition depending on location. For example, in the upper parts of a river system close to their "spring" a river or creek may be either almost pure rainwater or may be rich in certain minerals due to the rocks that the water flows through. The same river can change in chemical composition dramatically further down the "road" when other little creeks join the river and other types of soil and minerals add to its chemical compostion.

In any case..I don't think that you can find significant amounts of free Iodine in freshwater systems. Whatever little amounts you can find is usually bound up in algae, microorganisms and other animals who eat them. One thing is for sure...there are no uniform Iodine levels in freshwater as in ocean water. And even in the ocean shrimp don't just suck up Iodine...they have to eat it.

A lot of freshwater animals have adapted to these changing conditions described above. Their needs are very different from saltwater animals. That's why it is a fallacy to look at saltwater composition and deduct that freshwater animals need certain elements contained in ocean water for survival. It just makes no sense.

Mustafa