Importance of Iodine? - Chemistry Science Fiction

taricha

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Just for fun, here's a made-up argument for why maintaining iodine levels might be useful in reef tank water even for keeping organisms with no known need for iodine directly. In short, iodine might be important as a redox-active element that can influence the form (oxidized or reduced) of other biologically important traces.
I'm out of my depth to know how far the argument makes sense and where it doesn't. So I'm not sure how much of the science fiction is science and how much is fiction. :) So don't take this as me advocating Iodine dosing, I don't know if I believe my story or not.

Iodine in the surface ocean water is often in the ballpark of 0.060 ppm, with 20-30% of that as the more reduced form, iodide or I- and the other 70-80% as the more oxidized form, iodate or IO3-. There are other things that can exist in oxidized and reduced forms, Nitrogen, Sulfur, Fe, Mn, Cu species for instance, but in oxygenic surface water those are usually overwhelmingly in the most oxidized stable form - NO3, SO4, Fe3+ etc. And the metals exist in much lower quantities than iodine. Also, iodine is quite reactive - the two forms I- and IO3- are quite redox-active with a few other important seawater components - namely the trace metals themselves.

So iodine occupies an important (?) (unique ??) niche - it is the highest concentration element that has a significant portion in two different oxidation states and those two states are quite reactive with other biologically required trace elements.

My first interpretation of this was by Redox to pH analogy. Buffers exist as a mix of two forms to react with excess acids or bases and keep the pH stable. So the analogy goes that iodine acts as a reservoir of oxidized and reduced forms in oxygenic surface water to react with excess oxidizers and reducers to "buffer" the ORP of the water, and thus keep other stuff from getting totally oxidized or totally reduced.
There isn't much evidence of that mechanism - I don't find much discussion of I- reducing say Fe3+ to Fe2+ in seawater. But the other half seems well established.
Review on the physical chemistry of iodine transformations in the oceans

This paper is dense, but Fig 4 shows that reduced Fe or Mn, would react with oxidized IO3- and get oxidized. Fig 3 shows that NO2 similarly would get oxidized by IO3- as well.

"Comparing Figures 3, 4 indicates that the Mn2+ and NO−2 reactions with iodine species have a similar range of ΔlogK reaction values [favorable at seawater pH] whereas the Fe2+ reactions with iodine species are more favorable (higher ΔlogK reaction values)."

"Thus, there is no thermodynamic inhibition to IO3- reduction to I- by Fe2+, and this abiotic reaction at a pH of 7 was reported to be 92% complete after 2 hours using initial concentrations of 2 mM Fe2+ and 0.1 mM IO3-"

So rather than "buffering" oxidized and reduced species, it looks like IO3- might act as a reservoir of oxidizer capable of oxidizing biologically important trace metals (and maybe nitrite too - if the amounts are small).

I wonder if this is part of why Fauna Marin's ICP database finds strong correlation (say it with me - "...is not causation") between low iodine and nuisance algae (dino) issues.
 

Randy Holmes-Farley

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That’s an interesting idea. I do not know how plausible it might be, but I don’t think anyone can prove it isn’t important without some sort of complicated experiments.

The redox speciation of trace elements in a reef tank is a totally unknown frontier of knowledge, both from the standpoint of knowing what balance of all the redox species is in any given aquarium, and what impact any of those differences have on the organisms we keep. The best one can do is analogize to the ocean, which has many similar but also many different aspects to redox processes. We have no way to measure it outside a major laboratory endeavor.

For this reason, when folks report an effect of some additive it is worth knowing the redox effects of that additive, which may play a role in impacts it has in the aquarium (or maybe it doesn’t). Lugols for iodine, vitamin C for organic carbon dosing, hydrogen peroxide and ozone use, etc.
 

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This also brings up the interesting possibility that this or other trace elements may impact the bioavailability of other trace elements in ways that we do not understand, and thus the “need” for element X at all may actually depend on the levels of other trace elements.

For example, making up a random example, suppose iodine impacted the bioavailability of manganese. If manganese is high enough, iodine might not be needed at all. But when manganese is lower, perhaps iodine makes it sufficiently bioavailable. That way, a trace element (iodine) may be useful in one tank and not in another for the same organism (a user of manganese).

The reverse could also be true, with one element making another less bioavailable.
 

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This also brings up the interesting possibility that this or other trace elements may impact the bioavailability of other trace elements in ways that we do not understand, and thus the “need” for element X at all may actually depend on the levels of other trace elements.

For example, making up a random example, suppose iodine impacted the bioavailability of manganese. If manganese is high enough, iodine might not be needed at all. But when manganese is lower, perhaps iodine makes it sufficiently bioavailable. That way, a trace element (iodine) may be useful in one tank and not in another for the same organism (a user of manganese).

The reverse could also be true, with one element making another less bioavailable.

I could be one of those that saw an improvement upon adding iodine. In fact I am so convinced that it impacted my tank positively I also did the DIY Iron and Manganese soon after. The difference between dosing these and tropic Marin A + K, is day and night to me. These almost immediate improvements also confounded my "bag of sand" test, as such improvement was unexpected, ie Alk uptake increase, growth tips sprouting.
 

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I could be one of those that saw an improvement upon adding iodine. In fact I am so convinced that it impacted my tank positively I also did the DIY Iron and Manganese soon after. The difference between dosing these and tropic Marin A + K, is day and night to me. These almost immediate improvements also confounded my "bag of sand" test, as such improvement was unexpected, ie Alk uptake increase, growth tips sprouting.

Tropic Marin A and K has all of those. Do you know if you were adding a different amount or different forms?
 

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Tropic Marin A and K has all of those. Do you know if you were adding a different amount or different forms?
200 litre tank; Started with reacting 1 drop of Lugol's in a litre of tank water for an hour or 2, then dripping that in. Soon got fed up with that so now just putting 1 drop into into the plume of air bubbles from my air pump, in the sump

Manganese, using your DIY, 0.5mls a week, a few drops daily.

Iron 5 iron fumarate tabs (14mg tabs) in 250mls water, 0.5mls a week, a few drops daily.

I was adding 2mls of each A and K daily.

1.5% daily waterchanges, Tropic Marin Classic.
 

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Just for fun, here's a made-up argument for why maintaining iodine levels might be useful in reef tank water even for keeping organisms with no known need for iodine directly. In short, iodine might be important as a redox-active element that can influence the form (oxidized or reduced) of other biologically important traces.
I'm out of my depth to know how far the argument makes sense and where it doesn't. So I'm not sure how much of the science fiction is science and how much is fiction. :) So don't take this as me advocating Iodine dosing, I don't know if I believe my story or not.

Iodine in the surface ocean water is often in the ballpark of 0.060 ppm, with 20-30% of that as the more reduced form, iodide or I- and the other 70-80% as the more oxidized form, iodate or IO3-. There are other things that can exist in oxidized and reduced forms, Nitrogen, Sulfur, Fe, Mn, Cu species for instance, but in oxygenic surface water those are usually overwhelmingly in the most oxidized stable form - NO3, SO4, Fe3+ etc. And the metals exist in much lower quantities than iodine. Also, iodine is quite reactive - the two forms I- and IO3- are quite redox-active with a few other important seawater components - namely the trace metals themselves.

So iodine occupies an important (?) (unique ??) niche - it is the highest concentration element that has a significant portion in two different oxidation states and those two states are quite reactive with other biologically required trace elements.

My first interpretation of this was by Redox to pH analogy. Buffers exist as a mix of two forms to react with excess acids or bases and keep the pH stable. So the analogy goes that iodine acts as a reservoir of oxidized and reduced forms in oxygenic surface water to react with excess oxidizers and reducers to "buffer" the ORP of the water, and thus keep other stuff from getting totally oxidized or totally reduced.
There isn't much evidence of that mechanism - I don't find much discussion of I- reducing say Fe3+ to Fe2+ in seawater. But the other half seems well established.
Review on the physical chemistry of iodine transformations in the oceans

This paper is dense, but Fig 4 shows that reduced Fe or Mn, would react with oxidized IO3- and get oxidized. Fig 3 shows that NO2 similarly would get oxidized by IO3- as well.

"Comparing Figures 3, 4 indicates that the Mn2+ and NO−2 reactions with iodine species have a similar range of ΔlogK reaction values [favorable at seawater pH] whereas the Fe2+ reactions with iodine species are more favorable (higher ΔlogK reaction values)."

"Thus, there is no thermodynamic inhibition to IO3- reduction to I- by Fe2+, and this abiotic reaction at a pH of 7 was reported to be 92% complete after 2 hours using initial concentrations of 2 mM Fe2+ and 0.1 mM IO3-"

So rather than "buffering" oxidized and reduced species, it looks like IO3- might act as a reservoir of oxidizer capable of oxidizing biologically important trace metals (and maybe nitrite too - if the amounts are small).

I wonder if this is part of why Fauna Marin's ICP database finds strong correlation (say it with me - "...is not causation") between low iodine and nuisance algae (dino) issues.
My question is what happens if it’s too high? I heard coral booster with flatworm stop can make acros healthier even without flatworms so I thought I’d give it a try.

I’ve been dosing the recommend amount for like 2 months or so and I had an ICP done. It is known flatworm stop has a lot of it in it, but dang. My iodine 163.9 micrograms/liter
 

Randy Holmes-Farley

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My question is what happens if it’s too high? I heard coral booster with flatworm stop can make acros healthier even without flatworms so I thought I’d give it a try.

I’ve been dosing the recommend amount for like 2 months or so and I had an ICP done. It is known flatworm stop has a lot of it in it, but dang. My iodine 163.9 micrograms/liter

Without knowing the form, it’s hard to know much, but if that is iodide and iodate, I doubt it does much harmful.

I once dosed iodate for a while, not realizing then that the kit I was using did not detect that form. IIRC, I eventually saw some browning of corals as it accumulated.
 
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taricha

taricha

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For this reason, when folks report an effect of some additive it is worth knowing the redox effects of that additive, which may play a role in impacts it has in the aquarium (or maybe it doesn’t). Lugols for iodine, vitamin C for organic carbon dosing, hydrogen peroxide and ozone use, etc.
Speaking of peroxide, check out what it does with iodine (from the paper)...

"Wong and Zhang (2008) showed that H2O2 oxidizes I- in artificial seawater from pH 7-9, which is consistent with Figure 7B. However, I- oxidation does not lead to iodate. In fact, I- reforms. They proposed that I2 formed and was reduced back to I-, but they did not provide a mechanism."

File this underthe recurring theme: peroxide does some unanticipated things in seawater.
 

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File this underthe recurring theme: peroxide does some unanticipated things in seawater.

Adding something to your file. :)

Interestingly, when looking into some papers on this topic, I ran across a reference of another situation where hydrogen peroxide acts as a reducing agent (like with copper) rather than as an oxidant that most people expect. it once again should remind us that folks using hydrogen peroxide for various purposes are impacting the speciation and bioavailability of trace elements in their systems (which few users recognize).


"hydrogen peroxide acted as a net reductant for manganese oxides and completely masked oxidation of Mn by the superoxide free radical"
 
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taricha

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Actually, I shouldn't have called this unanticipated...
H2O2 oxidizes I- in artificial seawater from pH 7-9, which is consistent with Figure 7B. However, I- oxidation does not lead to iodate. In fact, I- reforms. They proposed that I2 formed and was reduced back to I-
What's described here is basically iodide acting as a catalyst to decompose hydrogen peroxide. Which is the classic "elephant toothpaste" demo.

The fuzzy prediction we might make from this is that we could expect tanks with higher iodine levels to have a shorter dwell time for peroxide in the water. And tanks that are depleted in iodine may keep peroxide in the water much longer.
 
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taricha

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The redox speciation of trace elements in a reef tank is a totally unknown frontier of knowledge, both from the standpoint of knowing what balance of all the redox species is in any given aquarium, and what impact any of those differences have on the organisms we keep. The best one can do is analogize to the ocean, which has many similar but also many different aspects to redox processes. We have no way to measure it outside a major laboratory endeavor.
It's totally true that quantifying the Fe2+ vs Fe3+ or similar for Mn etc is way beyond hobby abilities.
But it might be doable for iodine.
Seachem test kit detects iodide, and Red sea kit does iodide+iodate. Both are plenty sensitive and easily quantifiable, @Rick Mathew and I have worked with both of them (unfortunately not both kits at the same time). In theory, using both of them simultaneously would allow us to check if our tanks have a split between the reduced iodide and oxidized iodate like in sea surface water, where maybe 20-30% stays as the iodide form.
Rick and I checked that Red sea measured Iodide and iodate the same, but I never bothered to verify that seachem can measure only iodide and not iodate.
 

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It's totally true that quantifying the Fe2+ vs Fe3+ or similar for Mn etc is way beyond hobby abilities.
But it might be doable for iodine.
Seachem test kit detects iodide, and Red sea kit does iodide+iodate. Both are plenty sensitive and easily quantifiable, @Rick Mathew and I have worked with both of them (unfortunately not both kits at the same time). In theory, using both of them simultaneously would allow us to check if our tanks have a split between the reduced iodide and oxidized iodate like in sea surface water, where maybe 20-30% stays as the iodide form.
Rick and I checked that Red sea measured Iodide and iodate the same, but I never bothered to verify that seachem can measure only iodide and not iodate.

Yes, it can be done for iodine. I've done that in the past using total iodine and an iodide tests.
 

Kzang

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Yes, it can be done for iodine. I've done that in the past using total iodine and an iodide tests.
I’ve always wondered, but can’t DM you.

So you have a phd in chemistry? What do you do for a living?

Ya been active in chemistry in marine aquaria for ages, so I was just curious.

I wish I was better at chemistry stuff
 

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I’ve always wondered, but can’t DM you.

So you have a phd in chemistry? What do you do for a living?

Ya been active in chemistry in marine aquaria for ages, so I was just curious.

I wish I was better at chemistry stuff

Yes, I have a PhD in chemistry, and a BA in chemistry and biology

If you have linkedin, you can see my professional career here:


I lead discovery at a tiny biotech company called Entrega.

 

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Troylee

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