Monday, November 21, 2011

Tacoma Smelter Plume: Questions about arsenic and lead in soil

By Amy Hargrove, Soil Safety Program Coordinator, Toxics Cleanup Program

At all three of our recent public meetings — Tacoma, Vashon Island, and University Place — we heard similar questions about arsenic and lead in soil. This blog goes through a little of the science of the Tacoma Smelter Plume...

Will the arsenic and lead in soil leach out or decrease over time?

In general, no. Arsenic and lead bind strongly to “soil organics” — mostly decomposed plant matter. This prevents them from immediately washing away with rain or seeping deeper into the ground. Over a long span of time, like hundreds of years, arsenic and lead may move into deeper soil. For now, Tacoma Smelter Plume contamination is sticking around.

Arsenic and lead don’t break down, either. They are both elements, which means there is no simpler form they can break down into.

If that’s the case, how do you get rid of the contamination?

The best way to permanently get rid of Tacoma Smelter Plume contamination is to dig it up and take it to a landfill. For lower arsenic levels (under 40 parts per million), you can mix contaminated soil with clean soil to dilute out the arsenic and lead.

Another method is to cover contaminated soil with a thick fabric and a layer of clean soil on top. This keeps people from coming in contact with the arsenic and lead below.

h3certain plants take arsenic out of the soil?

Yes, but... Ecology did a study a few years ago using the Chinese brake fern to clean up soil. Unfortunately our climate was too harsh for the ferns. Also, when you use plants to clean up soil, the plants themselves become dangerous waste!

Learn more about Ecology’s cleanup plans.

The photo? A chunk of pure arsenic.

No comments: