Lead’s low natural bioavailability is the single biggest obstacle to phytoextraction. Chelating agents were proposed as a way around that obstacle, and early results were striking. Leštan, Luo & Li (2008) reviewed the field and concluded that the chemistry is effective but the environmental trade-offs are serious.
How chelators work
Aminopolycarboxylic acids such as EDTA form strong, soluble complexes with Pb²⁺. These complexes desorb lead from soil particles and are taken up by plant roots along with water. In pot trials, chelator addition can increase shoot lead concentrations by one to two orders of magnitude, transforming a low-uptake species into a plausible extractor.
Persistence and leaching
EDTA is not readily biodegradable. Residual chelator continues to mobilise lead and other metals, increasing the risk of groundwater contamination and off-site transport. The review argues that this persistence makes EDTA unsuitable for most in-situ applications, especially where leachate cannot be collected.
The search for cleaner alternatives
Biodegradable chelators such as EDDS, citric acid, and nitrilotriacetic acid degrade faster and therefore pose less long-term leaching risk, though they are generally less effective than EDTA. The practical path forward appears to be combining mild chelators with plants selected for high biomass and rhizosphere activity, applied under controlled conditions where leachate can be managed.
This analysis is grounded in the cited review source. See our methodology for how assisted-phytoremediation evidence is evaluated.