Plants can be used to absorb contaminants and convert them into harmless compounds. While rockcress (Arabidopsis) inserted with a variant of cytochrome P450 was able to break down the RDX left behind in the soil of firing ranges, weed roots can only go so deep. Inserting the cytochrome P450 2E1 into an aspen allowed the plant to absorb chloroform, TCE, carbon tetrachloride and even vinyl chloride over a 100 times better than the unaltered plant. The process by which plants remove toxins from soil is called phytoremediation. Trees can absorb as much as 48 pounds of carbon a year. Besides sequestering carbon, tree roots, in collaboration with bacteria and microrhiza, are able to break down carbon chains and make toxins inert. This does take a long time, but is very cost-effective. Full article here.
Keep checking for updates. For now, you might want to use spinach as a cover crop as the roots absorb lead. (Do not eat spinach or compost it in this case).