Arsenic Still Leaching from Old Decks

ccabnrIn January of 2004, Canada and the United States started to phase out the manufacture and sale of wood treated with copper, chromium and arsenic (CCA). CCA is used in pressure-treated wood to reduce rotting from insects and microbial
agents. The Healthy Building Network had lobbied government agencies, basing their position partly on sound research by David Stilwell of the Connecticut Agricultural Experimental Station. His work had demonstrated that after leaching out of CCA-treated wood decks, arsenic, a known carcinogen (group 1), was consequently accumulating in nearby garden soil and plants. The toxin can also transfer to skin and become ingested if children play on such decks.

As I explained in a letter this morning to my local member of parliament, the issue is still relevant because many neighbourhoods have CCA-treated decks built before 2004. Many of these have not been well-maintained and stained regularly, and acidic precipitation causes arsenic to be released from treated wood. ( It’s long been known that arsenic is a problem, so I wonder if the original tests, on what was then a newly treated wood-product, were carried out with tap water. At a higher pH, far less arsenic would have leached out. But as David Stillwell indicated, outside of the laboratory, decks are subjected to acidified precipitation, which is capable of dissolving more of the carcinogen.)

Many residents are still not aware of this problem, and I hope our mp will use her influence to help enlighten the public. She is a former colleague, so I hope that it will make a difference. The previous member of parliament did not carry out a much needed and recommended information campaign.

Thanks to a bank sponsor, a water-testing kit was freely distributed to Canadian high schools in 2008, and I used it to get a taste of Stilwell’s work. My report was published in University of Waterloo’s newsletter for chemistry educators.  If teachers obtained class sets of the kit, they too could have easily create meaningful labs like the one that I’m about to describe.

Since the kit is designed to test the amount of arsenic (other tests include manganese, sulphate, chloride, etc.) in water samples, I took about 5 grams of a 5-year old unstained sample of treated wood. Using pliers I cut it into several 1-cm to 2-cm pieces and let soak for 5 minutes in about 100 mL of tap water. After decanting the water into a thin bottle, I successively applied the three reagents of the modified Gutzeit test, which I will describe in detail later.
I also repeated the procedure using 1 mL of vinegar diluted a hundredfold to simulate the approximate average pH of rain samples in Eastern Canada. Of course, to make sure that the arsenic was not coming from the tap water itself, I ran a blank by applying the arsenic test to tap water that had not come into contact with treated wood.
The  results are summarised in the following table.


Admittedly, chopping the treated wood exaggerated the surface area actually exposed in the field, but a mere 5 minutes of soaking greatly underestimated the actual amount of leaching and physical displacement that occurs over the lifetime of a wooden deck or Hydro pole. For instance, David Stilwell found, next to 8 utility poles in Canada, an average of 262 mg of arsenic per kg of soil.

Here’s the chemistry behind the analysis, the so-called modified Gutzeit test.
The first reagent that’s added to 100 mL of sample contains tartaric acid with enhancers. In step 3 it will be evident why the acid is needed. Reagent #2, an oxidizer, is then added to remove hydrogen sulfide interference. Finally, with the addition of pure zinc powder reagent, inorganic arsenic ions (As3+ and As5+) are reduced to As3-, which, in the presence of acid, forms arsine (AsH3) gas:
(in the presence of As3+)
As2O3 + 6 Zn + 12 HCl → 2 AsH3 + 6 ZnCl2 + 3 H2O
(in the presence of As5+)
H3AsO4 + 4 Zn + 8 HCl → AsH3 + 4 ZnCl2 + 4 H2O
The arsine gas comes out of solution and reacts with a test strip
containing mercury (II) bromide (HgBr2), forming mixed arsenic
mercury halogenides:
x AsH3 + y HgBr2 → AsH2HgBr + As(HgBr)3 + other variants
Colours ranging from white to shades of yellow or brown depend on the amount of halogenides formed, which are proportional to the amount of arsenic ions in the sample.
Once the reaction is completed, the test strip is removed and matched to a colour chart to obtain the exact number of ppm (mg/L) of arsenic in the tested sample.
Safety Tips
The reactions should be carried out in a fume hood in case any arsine escapes and the reagent on the mercury strips should not be touched with bare hands. Any readers who are concerned about exposure to arsenic from decks constructed prior to the CCA ban should be relieved to learn that leaching can be greatly diminished by oil-based, semi-transparent wood stains, the kind that soak into the wood. In fact, Stilwell found significantly lower concentrations of arsenic in the soil next to CCA decks that were well maintained.

2. Stilwell’s Research, D. Stilwell and K.D. Gorny, Contamination of
Soil with Copper, Chromium, and Arsenic Under Decks Built From
Pressure Treated Wood. Bull. Environ. Contam. Toxicol., 58, 22-29

3. Legal Issues,,
(accessed July 23, 2008).
4. Health and Welfare Canada’s fact sheet on CCA:
(accessed July 23, 2008).
5. Chemistry of modified Gutzeit Test,
(accessed July 23, 2008).


Gluten-free Diet Exposes People to More Arsenic

Fear rarely leads to rational discussions. If not driven by fear, we often adopt unusual diets, perhaps out of an attempt to control our lives in a confusing world. Regardless of the root cause, our world has people who take advantage of either case. Consumer Reports’ January 2015 article The Truth About Gluten does a good job exposing those who profit from some unfounded suspicions about gluten.

Gluten is a protein composite found in wheat, barley and rye. It’s what makes dough elastic; it can trap carbon dioxide and make dough rise; when absorbing the right amount of hot water, a gluten network also traps swelling starch granules, creating the al dente texture of perfectly cooked pasta.

But to the 1% of the population who suffer from caeliac disease, gluten must genuinely be avoided at all costs. An enzyme modifies gluten components or similar molecules found in foods and then the immune system attacks the villi of the small intestine, interfering with nutrient absorption.CeliacMechanism

It’s unlikely that gluten is fully tolerated by the other 99% of the population, but because gluten-free diets have become a fad and ripe for commercial exploitation, it’s extremely likely that many non-caeliacs avoiding gluten are being deceived. For example, even beauty products carry non-gluten labels, and just as 7up fed on a caffeine-fear decades ago—promoting itself as caffeine-free when it never contained the compound—sales of potato-chips disingenuously glutenFreelabelled as “gluten-free” (they have always been naturally free of gluten) have soared by 456% between 2012 and 2014. Compared to new cereals for people, twice as many gluten-free pet foods were launched in 2014.

Here are more Consumer Reports findings:

(1) Gluten does add pleasant texture and taste to foods. To compensate, manufacturers add more sugar and even fat to gluten-free foods.

(2) Gluten-free foods are more expensive than their counterparts.

(3) According to an EPA 2009-10 study, on average 17% of a person’s dietary exposure to inorganic arsenic, a carcinogen, comes from rice (brown rice from Texas being the most contaminated). Gluten-free foods often use rice as a substitute for wheat. As a result gluten-free diets unnecessarily expose many people to more arsenic. How much? Well, most rice is in the 2 to 9 micrograms per 45 g serving ( 2 to 9ug/0.045 kg = 44 to 200 ppb or parts per billion) which is a much higher concentration than the legal limit of arsenic in drinking water at 10 ppb). The rice industry of course plays the “safe-level” card, acting as if arsenic is the only carcinogen in the environment.

There are other environmental sources of arsenic aside from water and rice. Garden vegetables can contain elevated levels of arsenic if they’re grown next to CCA-treated wood, which was sold before 2004. A key study leading to the ban of such wood treatment was conducted by David Stillwell. What I find interesting from a chemical point of view is that it seemed initially that CCA would not leach out when the product was first introduced into the market. The wood had originally been tested with tap water. But in the field, the treated wood was exposed to acidic precipitation, and at a lower pH, the arsenic compounds were more soluble. As I revealed in a University of Waterloo publication,  I used a modified Gutzeit test to convince myself that this is indeed true. How much arsenic was found in food also depended on the part of the plant. Roots and tubers concentrated the most, so carrots generally contained more than tomatoes, all other variables being equal. Of course, other soil components also played a role along with how much stain was applied to the treated wood. Quality stains helped prevent leaching of arsenic.

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