Safety Tips for Using Pressure-Treated Wood
Yes, pressure-treated wood can be painted, but you must wait until the wood is completely dry before doing so. Making sure the wood absorbs all water on the surface before painting can take weeks or months. You should also use a water-based paint and a latex primer.
Chromated Copper Arsenate and Arsenic Poisoning
Chromated copper arsenate slowly seeps out of wood and into the surrounding soil, where it can contaminate groundwater and possibly expose people to toxic chemicals. Additionally, individuals who work with treated wood, such as carpenters and construction workers, may be exposed to high levels of CCA. If chromated copper arsenate exposure is extremely high, it can cause death from arsenic poisoning.
Symptoms of arsenic poisoning include:
In addition to the aforementioned signs and symptoms, arsenic is also linked to a number of cancer types, including:
The treated wood industry voluntarily agreed to take CCA treated wood off the market in response to consumer concerns. By January 2004, the U. S. The Environmental Protection Agency forbade CCA-treated wood for use in residential construction.
Testing for arsenic leaching and migration
I sent soil samples from a CCA-framed bed that was three years old to a lab for analysis. I collected three samples from the wood at three different distances: right next to it, a few inches away, and in the middle of the bed. I sent soil from a bed that has never come into contact with pressure-treated wood as a control. Only the soil very near the treated wood exhibits a level of arsenic higher than the background.
There have been many studies looking at the first two issues, so how much arsenic leaches into the soil from CCA lumber, and more importantly, how much gets taken up by vegetables, and how much ends up in the mouths of children? However, in trying to organize the facts into meaningful information, I discovered definitive answers can be elusive. I am unable to advise you whether or not to use pressure-treated wood. What I can do is explain relevant study findings and provide you with the details you need to make an informed decision.
Although CCA-treated wood has good leaching resistance, some chemical loss does occur. Paul Cooper, a wood scientist at the University of New Brunswick in Canada, discovered uniformly high CCA retention in a study of utility poles of various ages, proving conclusively that significant amounts of preservative had not leached out of the wood. During the first rainy season, there seems to be an initial surge of leaching, after which the wood slows to a slow release of small amounts that gradually gets smaller over time.
When the pH is 3 or lower, all three CCA elements are more likely to leach, which is far too acidic for vegetable cultivation. At levels of 4 and up, pH has no effect.
Cooper has also studied compost bins made of CCA wood, and he discovered that leaching is increased by organic acids created during the composting process. This compromises the stability of the lumber in addition to adding more contaminants to the soil or compost. Cooper does not think pressure-treated wood is appropriate for making compost bins because both outcomes are undesirable, but he is not against using it in gardens. Because finished compost has a pH that is almost neutral, adding compost to CCA-framed beds is not problematic.
Once arsenic is in the ground, it doesn’t migrate much. When there is leaching, arsenic levels rapidly decrease with increasing distance from the wood, typically reaching background levels in raised beds within a few inches.
Although some have expressed concern that leached arsenic will end up in groundwater, Cooper’s utility pole study found no evidence to back up these worries. CCA components were present in very small amounts in groundwater samples collected from close to the poles. Stan Lebow, a wood scientist at the USDA’s Forest Products Laboratory in Madison, Wisconsin, asserts that there is almost no chance of any CCA chemicals contaminating groundwater as a result of use in gardens. They just don’t move that far. ”.
You should handle pressure-treated wood with the same care as you would any potentially hazardous material because the chemicals in the lumber are pesticides.
Protect yourself while working with CCA wood. Always put on a dust mask, gloves, and eye protection. Long sleeves are a good idea, too. Wash yourself and your clothes afterward. The best way to remove all sawdust is with a shop vacuum, so do that last. Dust collection is facilitated by drilling and sawing over paved surfaces. Put wood chips and sawdust in bags and dispose of them in the landfill. Don’t consider these steps optional.
Never, ever, burn CCA-treated wood. Some of the arsenic is released as smoke during combustion, which can be inhaled. The ash, too, contains high concentrations of arsenic.
You can take steps with CCA-treated wood to reduce leaching or migration. Surface residue can be removed by power washing the wood or scrubbing the wood with detergent. After the boards have been cut and drilled, weather them for several months before assembling, if at all possible. According to studies, the first rainy season sees the most leaching. Always drill holes in advance for screws to avoid wood cracking. Cracks are places where preservative can leach. Before filling the bed, line the interior with heavy-duty plastic to create a physical barrier that will stop any CCA compounds from entering your soil. If you lean or kneel on the sides, coating exposed wood surfaces with water-repellent finish, paint, or stain will safeguard your skin. Additionally, it will stop CCA compounds from passing from small hands to small mouths if you have young children.
Finally, you can benefit from the fact that arsenic tends not to move very far in soil. Avoid combining soil from the outer few inches of the bed with soil from further in to keep the arsenic in place. Avoid growing spinach and root crops near CCA-treated wood, especially carrots and radishes. Think about putting a band of dense flowers along the bed’s edge.