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Re: Iron gluconate

George Slusarczuk <yurko at warwick_net> wrote:

> Iron gluconate is the salt of gluconic acid, which is a product of
> glucose oxidation. Gluconic acid contains one carboxylic acid group and
> 5 hydroxy groups, so it tends to chelate. Because it is a sugar, I would
> imagine that "bugs" love it!
> Gluconic acid does exist in nature, as a byproduct of fungal oxidation
> of corn syrup and from other sources. If it "finds" an available iron
> ion nearby, it may well form a chelate with it. I don't think that in
> nature it lasts for very long.

A wild guess: perhaps iron gluconate (Flourish) might provide ferrous
iron in a form easily used by plants. I don't know if there is any
chemical transformation required for plants to use iron chelated by EDTA
or DTPA. A passage from "The Complete Book of Aquarium Plants" by
Allgayer & Teton - Ward Lock, London 1987 which James Purchase sent me
in excerpt, says that plants ONLY use iron in chelated form. I wondered
about this and I wondered if the iron has to be chelated by a specific
organic acid. The reason I ask this is that "free" iron radicals do
exist in the substrate at cation exchange sites and that Paul Krombholz
(I think) said that plant roots secrete organic acids which exchange
hydrogen cations for the ferrous cations. In this way, the iron would be
transportable into the root hair but I don't know the chemical mechanism

Back to iron gluconate, if the stuff is so labile (easy to decompose),
why would they use it in Flourish? Most every other aquatic fertilizer
that I know of uses EDTA or DTPA and I just assumed that Flourish would
be the same. I can't see that the cost of the chemicals is a factor when
the retail markup, packaging and distribution are the major factors in
the cost of a $10 bottle of the stuff. The typical hobbyist will want to
choose something which is going to last a long time and be cost
effective. If he can get dry chelated trace elements (ala PMDD) that is
pretty cost effective but if that weren't available, he'd probably be
interested in a commercial aquarium product.

Why use iron gluconate in preference to other Fe chelates?

Does iron have to be chelated by a specific organic acid in order to be
absorbed by aquatic plant roots or leaves?

Steve Pushak                              Vancouver, BC, CANADA 

Visit "Steve's Aquatic Page"      http://home.infinet.net/teban/
 for LOTS of pics, tips and links for aquatic gardening!!!