Arsenic in Treated Wood

plastic benchWhat comes to mind when you think of arsenic?  Inheritance powder?  The possible murder of Napoleon?  Poisoned wells in Bangladesh?  Well, how about playgrounds, decks or picnic tables? 

Concern has been raised that children cavorting around playground equipment made of treated wood may be exposed to dangerous amounts of arsenic.  Decks and picnic tables have also been accused of compromising our health by attacking us with arsenic.  The culprit at the center of the accusations is “chromated copper arsenate,” commonly abbreviated as CCA. Until 2004, this chemical was commonly blasted into wood under pressure to increase its longevity.

Wood is susceptible to attack by fungi and insects and usually rots in a couple of years if untreated but treated wood can last up to ten times as long.  Copper is an effective fungicide, arsenic is lethal to insects and chromium fixes the concoction in place to minimize leaching.  Still, when the preserved wood contacts soil, water, or even skin, some of the arsenic does escape.  Nobody contests the fact that arsenic is extremely toxic or that it may trigger cancer.  The question, as always with exposure to toxins, is dosage.
Without a doubt there are instances in which treated wood has caused poisonings.  Or more appropriately stated, there are cases in which people have poisoned themselves by working with treated wood carelessly.  A U.S. Forest Service worker became extremely ill after sawing treated wood to build picnic tables.  This really was no great surprise since arsenic can attack the nervous system, kidneys, lungs, stomach and liver.  He wore no mask, so he inhaled and ingested the fine sawdust leading to dramatically high levels of arsenic in his blood.  But this situation is not comparable to children playing in a park around pressure treated wood structures.  The playground scenario has, however, been studied.  To mimic a “worst possible case,” a weighted wooden block covered with a moist cloth was repeatedly dragged back and forth over treated wood to estimate the amount of arsenic a hand would pick up.  Then making a reasonable guess about hand to mouth contact, because arsenic does not go through the skin, the researchers calculated a maximum ingestion of 5 micrograms.  What does this mean?  Well we consume about 4-12 micrograms of arsenic naturally every day in our food supply and such amounts have not been linked with problems.  Indeed associations with cancer, and even these are tenuous, only become apparent when drinking water has an arsenic concentration of several hundred micrograms per liter, as is unfortunately the case in some areas in Asia.
So I really don’t think that our children are being poisoned by arsenic in playgrounds.  It goes without saying that treated wood should not be burned and that proper precautions should be taken when working with the substance.  In any case though, chromated copper arsenate has been replaced for non-industrial purposes by two safer materials, Ammoniacal Copper Quaternary (ACQ) and Copper Boron Azole.  But if you are still worried about your decks or picnic tables, you can always use cedar wood which naturally resists insects and fungi.  Or if you really want to be avant-garde, you can use synthetic lumber made from recycled plastic soft drink bottles.  You see, there is some value to soft drinks.
Joe Schwarcz

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