The field moves very slowly forward.Proving essentiality has proven more difficult with each new inclusion. The first two papers are not limnological, not even ecological. (Then again - maybe they are.) However, you draw the barriers, each is written by a legitimate leader in the field of trace element nutrition. It "gets me where I live" to acknowledge that most ecologists (that encompasses my fellow travelers in limnology) do not appreciate the significance of trace elements. They tend to mumble that most of them are around in the soil if they are terrestrial ecologists, and that most of them are around in the water if they are limnologists. It was a great comfort to note that in the chapter from his 1991 book, you read a selection from it (under eutrophication), Edmondson acknowledged that Se and Zn might be in short supply in some waters. But, even there, I have a feeling from conversations that that was, at the time, a tentative acceptance. He seemed comfortable concerning their actual influence in fw community structure only after I found a reasonable reference in a National Academy Report (he later sponsored a paper about our Zn/Se work to the academy - but he wanted to be convinced!).

The only influential ecologist whom I know who really felt strongly about the significance of trace elements was Hutchinson. Dr. Patrick, who has written about the trace elements on several occasions, does not think the time has yet come for emphasis. But she has published a new book (1996) and maybe (just maybe) she will try once again to get the limnological community to admit they cannot be ignored. She mentioned that intent just prior to publication. Unfortunately, Hutchinson (and Patrick, I suspect) felt that only time would make colleagues recognize their enormous omission. Hutchinson gave some of the trace elements their "due" in the Treatise on Limnology Vol. 1 (that was written in 1957 !!). But, there was then, and is now, an amazing lack of solid information concerning the trace element needs of any organisms, especially of any aquatic organisms. (You really should read the Treatise - but --- just come visit it some day.) The basic problem is that it is extraordinarily difficult to control trace elements in any test system.

Provasoli, usually identified as a "biological oceanographer interested in plankton nutrition", was absolutely sold on the notion that the trace elements are a critical force in plankton community structure. He lamented at length that the state of the art in chemical preparation made it almost impossible to properly test this hypothesis. At least everyone in the field of phycology is convinced that the trace elements limit growth in the open ocean. [Nitrogen limits in coastal {COASTAL} waters; phosphate is in relativel abundance]. But, Provasoli was continually frustrated in his efforts to prove that by the state-of-the-art of chemical purification. That same state-of-the-art today is, finally, about ready to support such work. (That is what we do in my lab.) Provasoli (who clearly thought as an ecologist) always referred to ecologists as "other", whereas Hutchinson considered them "self". BTW - the identification and quantification of trace elements (or anything) is not the same thing as determining what is actually available to a creature.

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Schrauzer, G. 1984. Introduction to Chapter 2. Biochemistry of the Essential Ultratrace Elements. (Series: Biochemistry of the Elements, Vol. 3):17-31. Plenum Press, N.Y. A leader in the field, offering a state-of-the-art overview. He, Mertz, and Forest Nielson are (I am fairly sure) the "grand old men" of the trace element business - all are active today (1999).

Mertz, W. 1981. The essential trace elements. Science 213:1332-1338. Just what constitutes proof of essentiality? For some organism other than a human? For a human? Some newly published "proof" is often hailed as THE proof of essentiality, even though some earlier "proof" was also hailed as THE proof. What is Mertz's concept of the "total dose-response range"? It should remind you of Parasalsus ("As the dose, so is the poison"). The Eskew, et al., paper from 1983, infra, is THE latest (that’s how slow progress has become, as of 2003) addition to the proofs of essentiality - it only covers plants (microbes, plants, animals are the needed categories) and it does not really offer a "kill". In 1998, the Nat. Acad. Food and Nutrition Board decided to count nickel as an essential for humans - even though hard "kill" proof has never emerged for plants or animals (only for Prokaryotes). Still, it comes closer than anything else in the last several DECADES (>40 yrs)to having been proved essential in the classical sense. The problem is dirt (contamination). There are a fair number of elements still suspected of being essential. A couple more than you might find in the Schrauzer paper - even though Schrauzer, himself, might well agree that they exist. He would avoid listing all the "possibles" because folks often misunderstand.

Eskew, D.; Welch, R., and Cary, E. 1983. Nickel: An essential micronutrient for legumes and possibly all higher plants. Science 222:621-623. A good example of the detailed proof offered when a scientist claims proof of essentiality. Think about the date. Do you realize how little we know "for sure"? Vide supra for the reason this paper is here.

Dr. Bartha (an emeritus member of this grad. program) is credited with identifying nickel as an essential nutrient. He did it with a bacterium. By the way Bartha killed the bacterium in conjunction with his proof. The best they could do for the plant-proof was to damage the leaves. No animal proof has yet been published. Strong suggestions abound concerning the need for nickel in animal metabolism, but no one has yet reported cleaning the contaminating nickel sufficiently out of a system to kill an animal. The reported damages are somewhat theoretical. How would you clean out the nickel in mouse feed? You will be regaled (oppressed) in class with a discussion of our nickel work to date. Especially, as it regards Fe. We managed to kill daphnids by clearing their world of nickel. That work is not yet published. The reason is important to your appreciation of the literature you encounter. Rest assured, you will hear it (and, probably many laments about controlling the test system.)