Plants and animals need low levels of copper and chromium metals for proper metabolic functions. This process is termed “exposure pathway”.Ĭopper, chromium, and arsenic naturally occur in plants, water, soil, and animals in low amounts. These leached materials have the potential to be taken up by garden plants roots and incorporated into edible food products. Weathering is the potential cause for older landscape wood to release copper, arsenic, and chromium as well as current CA and ACQ components from newer lumber into soils. However, landscapes still have treated lumber from the days of copper, arsenic, and chromium use. Building supply stores may have Safety Data Sheets (SDS) available for treated wood by request.Ĭoncerns about the leaching of wood preserving materials into soils helped initiate the move from Cu, As, and Cr based preservatives to CA and ACQ for use in today’s residential landscape lumber. Lumber is labeled for ground contact use when wood preservative retention standards are met. AWPA provides a Category Infographic for “determining the appropriate preserved wood for a particular project”. The reverse side of the label provides details about proper use information along with the DO NOT BURN TREATED WOOD warning. Lumber with an American Wood Protection Association (AWPA) label on the end of the board will have information regarding ground contact information. However, when fully pressure treated, boards and timbers may be tagged as standard for ground contact use. When dipped, treated wood is not usually recommended for contact with the ground. Treatment is done by dipping (cosmetic surface treatment) or by pressure (preservatives are distributed uniformly throughout the product). The appearance of copper azole treated lumber is similar to that of CCA treated wood, but has a green tint giving it the common name “green wood”. Newer residential wood products are no longer treated with arsenic and chromium wood preservatives.Ĭurrently, wood purchased at lumber outlets for residential landscapes is treated with micronized copper azole (CA) or alkaline copper quaternary ammonium (ACQ). These residential products commonly consist of landscape timbers, porch and patio decking, picnic tables, playground structures, fencing, and walkway materials purchased at local lumber outlets. By 2004, the Environmental Protection Agency (EPA) moved for limited use of CCA (classifying CCA as a restricted-use pesticide for use by certified applicators) in products for residential use. Arsenic containing preservatives have continued to be used for treatment of industrial wood products. In 2002, the wood preserving industry made a voluntary decision to phase out use of arsenic and chromium containing preservatives in wood products for the general consumer’s use. Potential leaching of these preservative components into soils has continually been a cause for concern. Copper (Cu) provided fungicidal activity, arsenic (As) provided insecticidal activity, and chromium (Cr) bound the preservatives to the wood’s structure. In the past, consumer wood products were dipped or pressure treated with inorganic (waterborne) preservatives, which include chromated copper arsenate (CCA), ammoniacal copper arsenate (ACA), and acid copper chromate (ACC). The purpose for treating wood with chemical preservatives is to make it more resistant to decay and effectively longer lasting when used for construction of various types. LayLa Burgess, ©2017 HGIC, Clemson Extension Older Wood Treatments Treated wood is widely available and often the most economical.Īll wood begins to break down in the landscape over time, regardless whether treated or untreated. As an alternative, treated wood has become a widely used option in place of natural decay resistant woods. Premade raised beds may provide a more cost efficient option when considering untreated, naturally decay resistant woods. Natural woods that are slow to decay include redwood, cypress, cedar, and oak however, these woods can be expensive. When considering wood materials for construction outdoors, it is common to think in terms of using the most decay resistant material with the longest life expectancy for the most reasonable cost. What types of wood treatments are safe when growing vegetables? The Purpose of Treatmentsĭecay, caused by exposure to bacteria, fungi, and insects, becomes an important factor when boards and timbers are placed in contact with soil and moisture in the landscape. What types of woods are more resistant to rot, decay, and insect damage? Many questions arise when considering the type of wood to purchase and use in the landscape. LayLa Burgess, ©2017 HGIC, Clemson Extension Wood has a variety of functions in the landscape, raised beds for flowers and vegetables is just one option.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |