What to do with old treated lumber in yard

I bought a house a year and a half ago. In the front to separate between lawn and flower bed previous owners put in 40 ft of treated 2 X 4 s. I don't know how long they have been there, but they are well on their way to decomposition now. I am starting a food forest in the front yard and have already planted some semi-dwarf fruit trees. The lumber is a few feet from a cherry tree that was planted last year and is only five feet tall, and hasn't had time for it's roots to get real close, but I don't know how wide an area the arsnic leaches to.

Questions:
Should I, and how would I treat the soil to remove the arsenic? I know that there are plants that collect heavy metals.

Is the arsenic all leached out of the lumber by now or should I take it to the haz mat depot at the dump?

Beth Tumbaco wrote:I bought a house a year and a half ago. In the front to separate between lawn and flower bed previous owners put in 40 ft of treated 2 X 4 s. I don't know how long they have been there, but they are well on their way to decomposition now. I am starting a food forest in the front yard and have already planted some semi-dwarf fruit trees. The lumber is a few feet from a cherry tree that was planted last year and is only five feet tall, and hasn't had time for it's roots to get real close, but I don't know how wide an area the arsnic leaches to.

Questions:
Should I, and how would I treat the soil to remove the arsenic? I know that there are plants that collect heavy metals.

Is the arsenic all leached out of the lumber by now or should I take it to the haz mat depot at the dump?

If the lumber is well on its way to decomposition, I think most of the arsenic has already leached out. I don't think the relatively small amount of arsenic will accumulate in your fruit trees, especially if you keep the soil from being extremely acidic.
If it was my yard, I would just mulch about and let the timbers continue to decay.

I wouldn't feel good about the arsenic having leached away. It's not just me, this study found arsenic accumulation in carrots and lettuce grown in soil that had elevated arsenic levels from treated lumber.

Whatever pieces you can pick up, send them off to the landfill. As far as an accumulator crop, how about some mustard? This reference gives a little bit of the chemistry involved in arsenic accumulation by India mustard. However, note that they say that the arsenic stays mostly in the roots unless there is dimercapto-succinate that can chelate it and allow it to be transported to the leaves. What tat means in practice is that you should amend your soil with sulfur so that the level of sulfur containing chelating molecules in the soil is high. My standard way of doing that is to work some crumbled drywall into the soil.

So my recommendation:

(1) Remove as many intact pieces as you can and send then to the landfill.

(2) Till in some drywall. If you cover the area in question with scraps of half-inch drywall and water it good, the paper will be ready to peel off in a couple of days and then you can use a hoe or shovel to break it up and turn it under.

(3) After you have turned your drywall under and raked the bed for planting, broadcast seed whatever type of mustard you can find. If there is a Korean grocery store around you, get some of that Korean red mustard seed. I think it is sharper tasting than that Florida broadleaf variety, and sharpness is a measure of how much sulfur it has. More sulfur = more efficient arsenic removal.

(4) Just when your mustard starts to bolt, it's time to yank it up by the roots and send it off to the landfill as well.

I may be overly cautious, but at least it gives me peace of mind that I did something positive to address a potential problem.