Home | Previous | Table of Contents | Next


The Canadian Center for Occupational Health and Safety (CCOHS) had this to say about using CCA near food in their publication. "CCA-treated wood should not be used where it is likely to come in contact with food (for example, cutting boards) since some leaching can occur under certain conditions."24 Many researchers have shown that acid rain is one of these conditions.

A Canada Plan Service Publication warns "Wood treated with CCA and ACA does not produce poisonous vapors, but traces of the chemical salts can dissolve in water and then be transferred to the food by contact."17

Health and Welfare Canada's publication says that, "it should not be used indoors or where it could come into contact with water, feed, or food."12

The Connecticut Department of Health's publication tells us, "CCA-treated boards used to frame garden beds can be expected to leach arsenic into the soil next to the boards. The leached arsenic is expected to mix with the remaining soil in the bed as the soil is turned over and prepared for planting. This will decrease the concentration of arsenic in the soil through dilution. This dilution effect combined with the evidence that plant uptake of arsenic is fairly small, suggests that the amount of arsenic in produce grown in such beds will not be a health concern.

The Connecticut Agricultural Experiment Station is planning to further evaluate plant uptake of arsenic. As an added precaution, they suggest lining the inside surface of CCA-treated framing with plastic to minimize the mixing of leached arsenic into the garden bed."6

In a publication by Weather-Bos we learn that Edward Polaski who compiled a review of research on pressure-treated wood for the state department of Conservation and Natural Resources found himself fired from his position four months before his retirement. "Polaski said he was let go because of his work on the reports and the resulting pressure from the wood products industry, a charge the state denies.

Polaski's CCA-treated wood report cited studies showing 20 percent, 30 percent, even more than 50 percent of the chemical can "leach" out of the wood. Much of the problem is caused by impure or improperly applied chemicals used in the wood treatment process, causing incomplete "fixing" of the chemicals within the wood."

"Polaski is not alone in his concerns. "I don't think his conclusions are overstated. It's better to be concerned and conservative before you make the mistake of introducing arsenic into the environment," said Dr. Garn Wallace, a biochemist at Wallace Laboratory, in El Segundo, California. The private lab specializes in plant nutrition, soil composition testing and heavy metal research.

Wallace said liquid oozing from CCA-treated wood could contaminate ground water under porous- sandy soils and produce a host of health problems in humans, from liver and kidney failure to cancers.

Wallace's study show that arsenic from CCA-treated wood stunts plant growth and turns leaves yellow. Vegetables grown in soil with an elevated arsenic level can contain high arsenic levels themselves. "It's obvious from the studies that the growth of herbaceous plants is injured in the presence of CCA-treated wood," he said. "I don't know at what levels injuries to people occur, but there is a plausible risk factor."

Stilwell's research is referred to in this article and he is quoted as saying, "There is always the benefit vs. risk question to be answered in these situations and that got lost in the promotion of CCA-treated wood," Stilwell said. "It's now being promoted for applications beyond its original scope, and some of those are not a good idea."2

In a publication by Exteriorwood (makers of CCA) the question, "Can I use treated wood around food, water, vegetables or other plants." is asked. Their answer "Treated wood should not be used in direct contact with human food or drinking water. Incidental contact with CCA- treated wood, such as in docks or bridges, is acceptable. Unlike some other types of treated wood, Wolmanized wood is suitable for raised flower or vegetable beds, landscaping, mushroom trays, grape and tomato stakes, greenhouse uses and similar applications. The Wolman preservative is highly leach resistant because the chemicals become locked or "fixed" within the wood."20

In an article by ENN we are warned, "Arsenic will collect in the ashes (of burned pressure treated wood), tainting them, so don't spread them in your garden."19

In an article in Kitchen Garden we are given this advise, "There are things you can do to CCA -treated wood to minimize leaching or migration. Scrubbing the wood with detergent or power washing it will remove surface residue. If possible, let the boards weather for several months after they've been cut and drilled before assembling. Studies show the greatest amount of leaching occurs the first rainy season. Always predrill holes for screws, which will prevent cracks in the wood. Cracks are places where preservatives can leach. Lining the inside of the bed with heavy- duty plastic before filling it will create a physical barrier to any CCA compounds moving into your soil. Painting exposed wood surfaces with water-repellant finish, paint, or stain will protect your skin if you kneel or lean on the sides. And if you have small children it will also prevent CCA compounds moving from little hands to little mouths.
Finally, you can take advantage of arsenic's tendency to not travel far in the soil (arsenic in wood ash is highly "leachable"). To keep the arsenic in place, refrain from mixing soil along the perimeter few inches of the bed with soil farther in. Avoid growing spinach and root crops particularly carrots and radishes, close to CCA-treated wood. In general, plants tend to hold what arsenic they accumulate in their roots, typically in their fibrous roots. Consider planting a band of compact flowers along the edge of the bed."15

In an article in This Old House Magazine we are told "Dangling somewhere on each pallet was supposed to be another label with cautions required by the U.S. Environmental Protection Agency. The cautions are vague and mild: "Exposure to inorganic arsenic may present certain hazards. Do not use treated wood under circumstances where the preservative may become a component of food or animal feed." "Nowhere is there a hint of how much pesticide is in each stick of lumber. A single 12-foot long 2 by 6 contains more than an ounce of arsenic- enough to kill 250 adults were they to ingest it."1

Stilwell's research actually began after receiving numerous calls from gardeners concerned about its use in their gardens. His research found significant levels of contamination consistent with leaching not sawdust.

Stilwell in his research grew Romaine lettuce to see its arsenic levels in three mediums, here are his results from his paper.

"Romaine lettuce was container grown in media to which either CCA sawdust or CCA wood blocks were added. After 26 days of growth, the lettuce was harvested, dried and analyzed for arsenic. The lettuce grown alongside the CCA woods blocks contained 1.7± 0.32 mg./kg arsenic (dry weight basis). Lettuce grown in media containing CCA sawdust, at a 32 and 480-mg/kg and arsenic level, contained 0.43 and 4.1 mg/kg arsenic respectively. Lettuce grown in control conditions contained less than 0.4 mg./kg. Converting these to lg arsenic/50g serving yields the following <1(control), 1(grown in media containing 32 mg/kg arsenic), 10 (grown containing 480 mg kg arsenic), and 4 (grown media alongside CCA wood blocks). These values to the dietary intake of inorganic arsenic of 4-12lg/day (all age groups)."

Dr. Stilwell concludes, line interior of raised beds constructed using CCA wood with plastic."3

P. Cooper of the University of New Brunswick states in This Old House Magazine " that he built a compost bin out of pressure-treated wood and discovered that acids in the compost caused doubled leaching from the wood."1

This must lead us to wonder why acidic mulches and compost added to our gardens would not present the same problems if added to pressure treated beds.

Home | Previous | Table of Contents | Next