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By
Gregory W. Lemley, adapted by the Ecology Center
November 3, 2000
Pressure Treated Wood: Should I or Shouldn't I Use It?
Of course, no one can answer this question but you, but it might help to look at the facts.
ALTERNATIVES
There
are alternatives. They fall into 4 general categories
1. Other types of wood preservatives
2. Naturally resistant woods
3. Synthetic and composite wood products.
4. Reused lumber.
MORE
INFORMATION
Should I or shouldn't I use pressure treated wood? As the above information
shows, about the only plus for CCA treated wood is cost and it would
seem that, as responsible citizens, we should also count the cost of
the impact on the Earth, not the just the dollars.
If you are reading this you have already decided that there are other factors such as health and environmental degradation that need to be considered and it seems clear that these issues are serious enough that at the very least you should vigorously investigate the other options that are available to you. If you still need more information, read on.
One recent survey in Connecticut, shows that 24 board feet of PT CCA cost $33 and was expected to last more than 40 years while the ACQ treated wood cost $38 with the same longevity. An equal amount of redwood cost $62 and was expected to last for 15 to 25 years while the composite product Trex cost $88 and would last about 30 years.1 More recently, I called Truitt and White Lumber, a major supplier in Berkeley, CA and was told that PT ACQ (the only pressure treated wood they carry) cost $1.17/foot of 2x6. Redwood was quoted as $1.70/foot, Trex as $1.99/foot and Nexwood as $1.89/foot. Clearly the cost and longevity contest goes to the pressure treated woods with redwood and the composites coming in a distant second. And as the wood preservative industry points out, this increased service life does conserve trees. But if you've come this far, you are obviously concerned so keep reading. The picture gets uglier from here on.
Remember that pressure treated wood is poisonous to insects, fungus, and bacteria. It is not surprising that it is also poisonous to larger animals as well. A study in New Zealand found that a 220-pound calf would have to eat 1.5 pounds of CCA-treated wood to die from acute toxicity. That's the equivalent of eating an 18-inch piece of 2x4.2 If you've ever owned horses, you know that that is not an unlikely occurrence. In another study, three scientists from Rutgers University found that several common marine organisms were negatively affected or killed when placed in seawater with small samples of CCA-treated wood.3
Modern Carpentry warns "Before eating any food, carefully wash any skin that has come into contact with pressure-treated wood. Clothing soiled by contact with the wood should laundered before reuse and washed separately from other clothing."4 The American Institute of Timber Construction states that pressure treated woods should not be used where they will come into contact with food or drinking water.5 As you can see, pressure treated wood is definitely not good for you!
By far the most common type of pressure treated wood is designated PT CCA (Pressure Treated Chromated Copper Arsenate). The basic elements involved are copper, chromium, and arsenic. In CCA treated wood, the chromium acts as the bactericide, copper as the fungicide, and arsenic as the insecticide. Even though all three are toxic, the chromium and copper don't raise many concerns (although maybe they should). If we don't inhale it, chromium is not particularly harmful, and copper is not very toxic to mammals, although it is to aquatic life. It's the arsenic that is worrisome.6 All of these compounds are stable and do not break down into other, less harmful substances in the environment.
Pressure treated wood has been in common use for about forty years and much of that is coming out of service and becoming a waste product. The companies that produce this product claim that the compounds are chemically locked to the wood itself and therefore not a hazard to human health and the environment. This statement is mostly true as far as it goes. What they don't tell us is that leaching does occur and that leaching is accelerated by acidic conditions such as is produced by acid rain or occurs during the composting process. A study by the Connecticut Agricultural Experiment Station found an average arsenic concentration of 76 ppm under old CCA treated decks. The state limit is 10 ppm.7 In another East-coast study, soil under an 8-year old deck was found to have 7.7 times the copper concentration, 3 times the chromium concentration, and 31.4 times the arsenic concentration as samples taken at least 15 feet away. It is clear that leaching does occur, at least in areas with high levels of acid rain.8
The EPA has developed the Toxic Characteristic Leaching Procedure (TCLP) to set threshold levels for the toxicity of 39 different chemicals, including chromium and arsenic. If the measured leaching from a waste product exceeds these limits it is considered a toxic waste and regulated accordingly. Arsenic-treated wood such as CCA does not have to pass this test. "Why not?" you ask. It turns out that this obviously questionable product enjoys a special exemption from the TCLP rule in 40 C.F.R. 261.4(b)(9). This is likely the result of strong lobbying pressure from the manufactures of these products.9 Because the point is legally moot, actual data is hard to come by, but results of one test obtained by EBN show that CCA-treated wood actually fails the test for arsenic and only barely passes it for chromium.10
There is evidence of leaching from PT CCA structures into the surrounding environment, but the disposal of this product is by far the more serious environmental problem. It should never, ever be burned! The chemical companies don't tell us is that these compounds, and particularly the arsenic, are released when the wood is burned. Some of these compounds are released directly into the air where the can be inhaled and some remain in the ash where they are highly leachable.11
John Gird at the University of Maryland describes a 1982 Wisconsin case in which a father of six burned CCA-treated scraps to heat his home. The family suffered severe arsenic poisoning by inhaling poisoned dust, by skin contact with the ash, and by ingesting the ash. They suffered blackouts, seizures, hair loss, nosebleeds, skin rashes, and extreme fatigue. The youngest children, who played on the floor, had the most severe problems. Plants and fish in the house died from copper toxicity. The problems continued long after the wood was no longer burned.12 In another case, a farmer in Minnesota spread fireplace ashes from CCA-treated wood in a field where 22 cows were grazing. All 22 cows died from ingesting the ash.13 Just one tablespoon of ash from a CCA wood fire contains a lethal dose of arsenic.14
Pressure treated wood should be placed in lined landfills (itself not a great solution) but construction waste is often too bulky and not allowed in these special landfills. The fact is that it often ends up in unlined landfills where it is subject to eventual leakage into the environment at large. It is known that garden-composting produces elevated acid levels and it seems reasonable to assume that the same is true for decomposing landfills. Much of the eastern shore of San Francisco Bay is landfill and it seems likely that, through years of decomposing and leaching, these compounds might find their way into the Bay. Yet another environmental mess in our future?
It is these sorts of concerns that have prompted the publication Environmental Building News (March 1997) to called for a phase-out of PT CCA. They feel that a timetable should be established to provide a smooth transition to a new generation of safer products. Since each of the 3 producers of pressure-treated wood has already developed these products, this should be able to happen fairly rapidly. One way to spur this phase-out would be to remove the exemption to the TCLP rule that CCA-treated woods currently enjoy. EBN also suggests that the cost of safe disposal should be factored into the purchase price of CCA-treated woods. This "disposal deposit" could then be used to insure proper disposal of treated woods. This extra charge would also more accurately reflect the true cost of pressure-treated woods and create a more realistically competitive market. It seems likely that if some such action is not taken, we as taxpayers, will be burdened with yet another toxic mess to clean up.
It is not only the disposal of this wood though that has raised concerns. The industry claim that these chemicals are stable and safe depends on ideal conditions. Once the wood is treated, a chemical reaction between the preservatives and the wood must occur to lock these compounds to the wood fibers. At 70F this process takes 3 to 4 days. When the temperature drops to 50F, this process takes a couple of weeks. Once the temperature reaches freezing, this reaction does not occur.15 The fact is that CCA-treated wood is often loaded directly from the treatment vats onto the delivery trucks for delivery to the building supply yards. At the lumberyard, the wood is almost never stored in heated buildings, so if you buy the wood in the wintertime (even in temperate climates) the CCA may not be totally fixed and the CCA would still be very leachable. It is a good idea to let the wood sit for a few weeks if you have the time. Unless you are sure that the fixing process is complete, anyone handling this stuff should be very careful. Even if you feel that the process is complete, if the wood is wet extra care should be taken. CCA absorption through the skin is much greater if the wood is wet. Even perspiration from your hands can increase absorption of the CCA.
If the wood is dry but you see a white surface residue you should also beware. This white stuff is probably crystals of the arsenic salt that has not been properly fixed into the wood and is thus more likely to be absorbed through your skin. You should also not breath sawdust from cutting the wood. So if you must use this stuff, use all of the precautions you can.
Yet one more factor that the conscientious consumer must consider is that by using these chemically treated products, you are supporting an industry that uses and transports large quantities of toxic chemicals. We all know that they are never as careful as they claim and apparently minor spills are commonplace. An official at one of the three preservative producers told EBN that in trucking chemicals "there's not anybody that hasn't had a leak, with local environmental officials brought in, and a big stink made,"16 and it seems that often spills at the larger plants aren't even reported so one must wonder what the soil is like at these plants.
By the time these chemicals are used to treat the wood, they are down to about 1% solution, but they are transported in a much more highly concentrated form. Train derailments and overturned big rigs are almost commonplace, so one must wonder how soon a tanker with these concentrated chemicals will crash and rupture-spilling these poisons into our environment. Or, if you're a pessimist like me, you might wonder how often it has happened and we simply haven't heard.
RAISED
GARDEN BEDS
One popular use of PT CCA wood is in the construction of raised garden
beds. When it first appeared, pressure treated wood was considered the
answer to a gardener's prayer, but as the above discussion shows this
is not necessarily the case. There are several issues that the potential
gardener should consider. One is the toxicity of the wood itself. Can
anyone or anything ingest it, chew on it, etc.? Is anyone likely to
have contact with the wood and rub these poisons off onto hands, tongues,
or any other body parts? Can the wood contaminate the surrounding soil
and if so, what are the affects of contact with this soil and what happens
if something eats this soil (like your 6-year old)? And can these poisons
be transmitted to the vegetables you grow in these beds?
Before answering these questions, we should look more closely at arsenic. There are 2 basic types of compounds formed with this element. The first is a class of organic compounds found in nature. They contain carbon as part of their chemical structure. We typically eat 25 to 50 micrograms (a microgram is a millionth of a gram or 0.000001 gm) of arsenic in this form every day. These compounds are excreted before they can do us any harm. It is the other class, inorganic compounds, that causes all the concern. This type accumulates in living tissue where it interacts with cell enzymes and impairs metabolism. It is the inorganic type that is found in pressure treated woods.
In large doses, inorganic arsenic is a strong poison. Ingesting 60 to 100 milligrams (0.06 to 0.1 grams) can be fatal for an average adult. Lesser amounts cause vomiting and diarrhea and lower the production of red and white blood cells. Inorganic arsenic is also carcinogenic. While the effects of these large doses are certainly of concern, it is perhaps the effects of repeated small doses that are of greater concern to the gardener.17 Do the vegetables take up small amounts of these compounds? If so, how much and are they harmful to eat?
The USDA says that background levels of arsenic in the soil (both organic and inorganic) of 0.1 to 10 ppm are normal up to 40 ppm is considered a tolerable. It is to be assumed, although not specifically stated, that this is largely the naturally occurring organic type. Above that level, detectable amounts of arsenic start showing up in children's urine, because kids eat dirt. The Agency for Toxic Substance and Disease Registry (ATSDR) in Atlanta, states that an average adult woman (130 lbs.) can ingest up to 18 micrograms (0.000018 grams) of inorganic arsenic per day without harmful affects.18 However, I found no studies on the long-term effects of exposure to low level doses of these compounds, so my question is, "How do they know?" Aren't these the same people that told us that DDT and asbestos were safe?
The first two questions have been answered above, so we will look at the next question. It is clear that some leaching of arsenic from PT CCA wood does occur but several studies have found it to be limited to about 6". A 1979 paper in the Journal of Environmental Quality reported that CCA leaching from stakes in direct soil contact for 30 years in a wet climate showed that soil within 6" of the stakes showed 10-15 times the arsenic concentration over levels further away from the stakes. In another study, Paul Cooper, a wood scientist from the University of New Brunswick in Canada, tested CCA-migration from utility poles of varying ages. He found that there was an initial surge during the first rainy season but then leaching settled down to a slower release rate that remained fairly constant. He also found that these chemicals "Just didn't migrate that far."
In a more specific study of a raised garden bed constructed of pressure treated wood, four samples were taken at specific distances from the wooden sides of the bed. The pressure treated bed had been in use for 3 years prior to these tests.19
1.
Sample #1 was taken in a bed constructed of untreated wood. It showed
a background level of 4.4 ppm arsenic.
2. Sample #2 was taken in the pressure treated bed 2 ft. from the treated
wood sides. It showed a level of 4.2 ppm arsenic.
3. Sample #3 was taken 2 inches from the sides and showed a level of
20 ppm arsenic.
4. Sample #4 was taken 6 inches from the side and showed a level of
4.8 ppm, nearly background level.
It seems certain that the extra 15 ppm in sample #3 is the result of leaching inorganic arsenic from the treated wood. This arsenic seems to be well attached to the soil particles and not likely to travel further. It does means that this 6 inches is permanently contaminated. You should not grow vegetables in that strip nor turn that soil into the rest of your garden. It means that children, dogs, turtles or any other animals you do not want to die cannot ingest this soil.
In a study of composting bins made from CCA-treated wood, Paul Cooper, also found that the organic acids formed during the composting process caused more leaching thus elevating the level of arsenic in the compost. Since finished compost has an almost neutral ph, this is not a problem in the garden, but CCA-treated wood certainly is not suitable for compost bins.20
So the final questions remains. What about the vegetables grown in this soil? There have been at least three major studies done on vegetables grown in arsenic-enhanced soils. Their results all clearly show that arsenic accumulates only in very small amounts in vegetables. For example, crops grown in soil with total available arsenic of 24 ppm had the following arsenic levels in the edible parts: green beans, 0.29 ppm; carrots, 0.11 ppm; and tomatoes, 0.14 ppm. These were total arsenic levels. Carrots, for example, grown in soil with no added arsenic contained 0.05 ppm arsenic.21 So it seems that the arsenic taken up by vegetables grown in contaminated soil is not the major concern. Still, to be on the safe side, you should avoid foods with elevated levels of inorganic arsenic. These compounds are not readily excreted by the body and government agencies who set these levels of safe ingestion of chemicals are often more sympathetic to large industry than to the lowly consumer.
Gregory W. Lemley
1Ruth
Lively, The Kitchen Gardener #15, The Taunton Press, pp. 55-59.
2 Environmental Building News; Jan. 1993, pp. 10
3 Ibid, pp. 9
4 Wagner, Wallace H., and Howard Smith. Modern Carpentry.
Tinley Park, Illinois: Goodheart-Willcox. Pp. 53
5 American Institute of Timber Construction, Timber
Construction Manual. New York: John Wiley and Sons, Pp. 8-789
6 Ruth Lively, The Kitchen Gardener #15, The Taunton
Press, pp. 55-59.
7 Richard Martin of Origen Biomedical, 2525 Hartford
Rd, Austin, TX 78703 or at www.origenbio.net/arsenic.html
8 Environmental Building News; June 1997, pp. 3
9 Environmental Building News; March 1997, pp. 10
10 Ibid; pp. 11
11 Environmental Building News; Jan. 1993, pp. 10
12 Ibid; Jan. 1993, pp. 12
13 Ibid; Jan. 1993, pp. 12
14 Richard Martin of Origen Biomedical, 2525 Hartford
Rd, Austin, TX 78703 or at www.origenbio.net/arsenic.html
15 Environmental Building News; Jan. 1993, pp. 10
16 Ibid; Jan. 1993, pp. 10
17 Ruth Lively, The Kitchen Gardener #15, The Taunton
Press, pp. 55-59.
18 Ibid; pp. 55-59.
19 Ibid; pp. 55-59.
20 Ibid; pp. 55-59.
21 Ibid; pp. 55-59.
22 Richard Martin of Origen Biomedical, 2525 Hartford
Rd, Austin, TX 78703 or at www.origenbio.net/arsenic.html