Application of biochar is a good way of filtering soil from accumulated heavy metals by adsorbing them on biochars. There are number of publications on this issue , can be easily browsed through published literature...
yes, the natural organic matter can contact the heavy metals, and some research works were published in EST, especially for the humic acid. you can try to inspired from them.
Organic matter has a natural ability to hold heavy metals and some good papers and reviews are available. You may get some of them using some search machine.