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Re: Oxidation of trace elements
- To: Aquatic-Plants at actwin_com
- Subject: Re: Oxidation of trace elements
- From: Paul Sears <psears at nrn1_NRCan.gc.ca>
- Date: Mon, 24 Nov 1997 10:34:41 -0500 (EST)
- In-Reply-To: <199711240848.DAA24292 at acme_actwin.com> from "Aquatic Plants Digest" at Nov 24, 97 03:48:08 am
I have noticed many times in the APD concerns about oxidation
of trace elements for plants, and a few recent posts have brought the
subject up again. For almost all of the things plants need, oxidation
cannot be a problem. I'll go through the list:
K+, Ca++, Mg++, PO4---, NO3-
Not really "trace" elements, and fully oxidised in the forms above.
Cannot be oxidised further.
No higher oxidation states available, (Cu+++ does exist, but will not
be generated in an aquarium).
Present as molybdates and borates, i.e., already fully oxidised.
Can easily be oxidised to Fe+++ in solution, because the Fe(III)oxo-
hydroxide has very low solubility. The solution is to chelate the
stuff, but I suspect the chelate used is the Fe+++ one. The problem
to be dealt with is insolubility, not the oxidation state. Dave Huebert
mentioned that there was no evidence that Fe+++ was useless to plants,
and I'm not surprised. That was a question that I asked a while ago,
and that was not answered - I'm glad it has come up now.
Generally present as Mn++. There are higher oxidation states (e.g.,
permanganate), but the only one that could be of interest to us is Mn(IV),
which _could_ form as MnO2, because that has very low solubility. It
is a pretty strong oxidising agent in acidic solutions, and I don't
think we have to worry about it forming anywhere there is organic
I have drawn a distinction between the ion M++ and the oxidation state
M(II), say, because in a lot of cases the metals aren't there as ions,
there are covalent bonds to other atoms (borates are a good example
definitely B(III), but not B+++).
Quit worrying about it!
Paul Sears Ottawa, Canada