Phytoremediation

A study using plants to pull lead from slag-contaminated soil in Atlanta found that in their pots, 10% of the lead could wind up in the plants. The soil had over 500mg/kg of lead. The paper deals with a number of the technical details, but for now just assume that the whole plant is removed and processed (maybe oxidizing it with H2O2 instead of burning) to retrieve the lead someplace either safe or usable.

If one harvest gets rid of 10%, and you want the concentration to be below 5mg/kg, that's about 44 harvests to clean up that dirt. 37 if you're OK with 10mg/kg, 22 if you're OK with 50mg/kg (and you probably shouldn't be).

The urgency of the problem is because people live there now. Some garden, and some of those eat what's in the garden. 40 years is a long time to maintain a program as people come and go, buildings wear out and get replaced, and political priorities churn.

You'd think that something like this would remain a priority, but experience of fighting wars, especially existential ones, says that even important projects get back-burnered or canned. Losing them is even more disruptive. And 44 years is a long time.