Spot research states that" "The zinc coating of hot-dipped galvanized steel will last in the harshest soil is 35 to 50 years and in less corrosive soil 75 years or more. Although humidity affects corrosion, temperature itself has less of an impact. Galvanized zinc coatings respond well in extreme cold and hot temperatures."

https://www.bucket-outlet.com/Does-Galvanized-Steel-Rust.htm

Below, in wet or soaked environments, it indicates ten years. Other indicators do note that it depends very much on the thickness of the zinc coating, so it's going to vary. I can't validate the reliability of the research as I'm not a metallurgist but other sources tend to back this up.

So the answer is that eventually what you put in there will end up in the soil, and whatever's in that steel and zinc coating (including all contaminants) will end up in your soil. It just may take from 10 to 75 years. Are there problematic contaminants in steel? Yep. Of high enough concentration to be a concern? I can't say.

If it was a serious concern, then there would be a lot of livestock walking around contaminated by heavy metals :-)) Most livestock tanking or troughs are made from galvanized metal. And people as well, as galvanized piping was used to conduct drinking water until just a couple of decades ago!

Seriously, the amount of leaching - primarily zinc but also some cadmium - will be minimal with a galvanized mesh. Zinc is a necessary mineral both for healthy plant growth as well as healthy humans but is present in the soil in very small quantities - far below what the suggested daily intake is for humans. Any leaching will not significantly add to that amount. And it will also not leach very far from the source.

btw, water storage cisterns are often made from galvanized metal as well.....drinkable water storage.

I did want to point out some chemistry issues here, though.

Well, there were reasons we got rid of galvanized pipes: https://americanvintagehome.com/advice-for-older-homes/need-swap-galvanized-pipes/

They rust away. And of course, you're drinking what leaches into the water from that. It can be problematic, as in the case of Flint, Michigan, where the original piping had lead in it, if the pH of the water changes (which was the problem in Flint).

Copper is much better, as is our modern PVC. But of course, copper can have its own impurities if not made well, and it's expensive beyond all belief these days.

I would tend to agree that the zinc leaching is not of concern. It's the steel as it decays. Carbon steel tends to be what's used in most mesh. It's nice and cheap. It also contains the following: chromium, molybdenum and nickel.

Chromium can be...problematic...at some valence charges in very tiny amounts (to phrase that more definitively, don't screw around with any amount of chromium, period). The molybdenum is at high percentage and could be problematic during the leaching process, but fortunately isn't super toxic and the mass of the steel low enough not to be an issue. Nickel won't be a problem.

The zinc here doesn't bother me in the slightest. Zinc does leach in soils at about the same speed as phosphorus (so slowly, but it does leach). It will slowly disperse and become a non-issue, but would be locally toxic if it did build up. As always, it's the dose that makes the poison and zinc will happily block the absorption of other minerals. But that's not going to happen for the above reasons.

And, of course, we do use them in cisterns due to the pH and ions present not being notably hard on steel. Water is not soil so the comparison really shouldn't be made here, as some sources have repeatedly told me on other items. Even so, galvanized tanks often don't look good after only a few decades and have quite a lot of rust apparent. But PVC is hard to cast or seal in that size, so our options are limited.

My opinion is actually fairly neutral on these things; I use metal spikes, but probably wouldn't use a metal mesh on the philosophy that nobody needs a new tetanus shot the next time they put a hand through it and cut themselves. (Sidenote: My doctor recommends that I renew that every eight years since I garden, minimum, so I do it every 6). Even the metal spikes rust through the pretty thick paint jobs, so I figure everything goes eventually and you're going to get everything in it in your soil.

It should be noted that the zinc coating in galvanized steel is pretty stable EXCEPT in highly acid environments. The corrosion rate of the coating rises rapidly below pH of 4.5. So if you happen to have such highly acidic soil, you will get some zinc contamination, but your gopher proofing will also degrade pretty rapidly. Now, that being said, the amount of zinc in galvanized mesh is pretty small.

Zinc occurs naturally in most soil, at about 100ppm. So that means a cubic yard of soil is going to have about a quarter pound of zinc in it. I can't imagine you're going to get anywhere near that much zinc out of a yard of galvanized mesh. It will corrode out as a salt, which is pretty soluble, and will leach away, anyway. So if you want to worry about zinc, I'd worry about your soil first.

Quite--and as noted, the zinc isn't of vast concern for any of us. Although would you happen to have a source for the 100PPM? Most soil tests I read are 20 PPM or less through Logan Labs, which we consider just fine. My two most recent from today came back with 8.8 and 12 PPM respectively and I passed them as perfectly OK; anything over 3 is fine. I'm curious.

I doubt this would push up the overall soil profile by 5 PPM temporarily overall anyway with the thickest coating, which I doubt this has.

The one thing we should note is that every fertilization is going to be with acidic water. Even rainwater normally has a pH of 5.0 to 5.5, with acid rainfall being quite a lot lower.

Thunderstorms here in PA, on hot days, can drop as low as 3.8, but that's quite unusual. Normal rainfall is 4.0 to 4.5.

Location will come into play here as well, would be the short version.

And of course, soil is not water, and the soil solution is not the soil pH, which will vary considerably.

So I'm worried less about the zinc than I am the steel contaminants making their way along.

And I'm actually not much worried about that except for one or two, and not too worried even about those, not enough to bring myself off neutral to negative. :-)

https://www.sciencedirect.com/science/article/pii/S0065211308606355

Good point about rainwater being quite acidic.

Oh, thanks for the zinc article! I'll read that this evening.