I am no chemist but I have made it my winter project to learn some basics. My understanding (please someone correct me if I am wrong) is the chelating agents are like a vehicle to transport an element esp. metals. They protect that element from too easily reacting with other elements, say oxygen. Exactly how plants or microbes can free the element from EDTA I don’t understand exactly (some kind of exchange?). But I think the EDTA remains intact and can pick up other elements, e.g. lead. I have read that these can’t be removed by normal water treatment plants. Certainly cobalt EDTA is a problem in the residue from bio-gas plants (where it is used to aid fermentation). So it’s not the release that’s the problem, but the agent itself.

EDTA is also being abandoned by some fertilizer companies (e.g. Lebosol) because it can hold metals too tightly. Natural chelating agents like citric acid seem better and safer.