Treated Lumber FAQ

Question:

I have a vegetable garden in my backyard. The border for this that we put in about ten years ago is pressure treated lumber. I have heard that this can contaminate the soil with arsenic. Is this true? And is there a way to have my soil tested for any contamination? Also, would you recommend changing the border and substituting something else?

Minnesota Master Gardeners say:

 Most treated lumber over the past two decades has been treated with CCA (chromated copper arsenate). Recent research by Prof. Carl Rosen, Department of Soil, Water and Climate at the University of Minnesota, and his colleagues, has shown that CCA treated landscape timber about 10 years old does leach chromium, copper and arsenic into the soil. The levels of all three elements were highest near the timber, and were near normal background levels a foot or so away. Furthermore, Rosen's group also showed that vegetable plants grown in soil taken from within 1 inch of the timber will take up arsenic (though not chromium or copper).

The amount taken up was measurable but substantially less than U.S. Public Health Service standards and also substantially less than Canadian statutory limits. Some argue, however, that these standards are not sufficiently strong and not scientifically based. For further details about this study, see this Yard and Garden Newsletter: http://www.extension.umn.edu/yardandgarden/YGLNews/YGLN-June0101.html#as

The EPA and the lumber industry have agreed to stop sales of CCA treated lumber starting in 2004. One reason for this is that there are now good arsenic-free alternatives. Some of these alternatives are discussed in this Yard and Garden Newsletter: http://www.extension.umn.edu/yardandgarden/YGLNews/YGLN-July0101.html#wood Note that one alternative is to use naturally rot- and insect-resistant woods such as redwood or cedar.

If you incorporate a lot of compost into your soil, the arsenic and other elements will bind to organic matter. Also, most of us do not "live out of our gardens." We get most of our food from other sources, so the exposure to arsenic may be quite small.

If you are uncomfortable with the possible arsenic contamination, I would recommend that vegetables be planted at least 15 inches away from CCA treated timber and that a barrier of 6 mil plastic be used to reduce the arsenic leaching into the soil.

Testing for arsenic in your soil is probably cost prohibitive and not readily available for homeowners. You might contact your county health department to see if a test is possible.

If you decide to remove CCA treated lumber from your house or garden, be sure to dispose of it in a safe manner. It should be treated as toxic material!