Environmental Issues on the use of CCA treated wood

AC001 (12/98)

Environmental Issues On The Use Of CCA Treated Wood

David E. Stilwell
Department of Analytical Chemistry
The Connecticut Agricultural Experiment Station
123 Huntington Street
P. O. Box 1106
New Haven, CT 06504-1106

Telephone: (203) 974-8457 Fax:(203) 974-8502
E-mail:  David.Stillwell@ct.gov

The most widely used wood preservative in current use is chromated copper arsenate (CCA), due to its excellent fungicidal and insecticidal properties. In the pressure treatment process CCA is applied to the wood, resulting in copper (Cu), chromium (Cr), and arsenic (As) concentrations in the range of 1000 - 5000 mg/ kg. Treated wood is used in the construction of decks, picnic tables, highway sound-barriers, telephone poles, and docks.

Due to the massive amounts of CCA treated wood sold each year, dispersal of these additives from the wood could impact the environment. We have identified potential environmental concerns associated with the use of CCA wood:

• Arsenic translocated to soil and water via: leaching from wood; runoff from lumber yards; and sawdust and physical wearing of the wood.
• Human exposure to arsenic; dislodged from CCA wood surfaces (hand to mouth); during construction (sawdust, and hand to mouth); by plant uptake
• Impact on beneficial marine organisms near docks built with CCA wood
• Disposal of CCA wood

We present a summary of our findings on the amounts of Cu, Cr, and As in soils located under CCA treated wood structures, and on the determination of the amounts of arsenic dislodged from CCA treated wood surfaces.

Copper, Chromium, And Arsenic In Soils Under Decks Built From Pressure Treated Wood.

We conducted a field study to determine if there was any evidence that the CCA preservative could leach from the wood. For this field study the Cu, Cr, and As content in soils under decks built with CCA treated wood was determined. The decks ranged in age from 4 months to 15 years. Decks are ideal for the study of the effects of weathering due to rain and solar radiation on the wood. The wood is above ground and there are large amounts of horizontal surfaces so that any preservative leachate tends to flow directly to the soil below.

A total of 85 soil samples were collected from under a total of seven decks built with CCA pressure treated lumber. Only one of the decks had been coated with paint since construction. Control soils were acquired at a minimum distance of 5 meters from the decks. The samples were analyzed for Cu, Cr, and As by atomic spectroscopy.

The overall range and average for Cu, Cr, and As are given below. At each site, the average Cu, Cr, As content in the soil samples taken beneath the deck was elevated with respect to the average in the control soils. The amounts of analyte in the soil tend to increase with deck age with the exception of samples under a deck that was painted 1 year after construction and then repainted about 8 years later, suggesting that any leaching of CCA may be retarded if the decks are coated soon after construction.

• The overall average Cu, Cr, As content in the soil samples, as well as those from each individual site, was elevated with respect to the averages in the control soils.
• The proportions of Cu, Cr, and As found in the soil were consistent with the results of simulated leaching studies.
• The amounts of analyte in the soil tended to increase with deck age.

These findings suggest that leaching of the preservatives from the wood is a major pathway leading to the observed elevated contents of Cu, Cr, and As in the soils under the decks.

Arsenic Dislodged From CCA Treated Wood Surfaces

A controversy exists on the extent of arsenic exposure due to physical contact with CCA wood surfaces, such as playground equipment, decks and picnic tables, built using CCA treated wood. Studies have shown that virtually no inorganic arsenic is absorbed through the skin, but is readily taken up by ingestion. The potential exposure is hand to mouth, and therefore, children are considered the most vulnerable to this potential risk. Our ongoing study attempts to investigate this vulnerability by analyzing the Cu, Cr, and As in wipe samples taken on a variety of CCA treated wood surfaces.

One series of CCA wood surfaces tested consisted of CCA treated wood purchased at lumber yards. For this study, seven sets of eight foot long CCA pressure treated boards were purchased from 3 lumber yards over a period of one year. Each set consisted of 3-4 boards, and the total number of boards surveyed was 23. Three of the sets (5-7) consisted of pine that was pressure treated with both CCA and a water repellent. These water repellent (WR) CCA boards are commonly used for decking (5/4 x 6 inches). In all cases measurable amounts of arsenic were dislodged from the surfaces of these test coupons. The levels of arsenic dislodged from the wood surfaces, after 1 month of weathering (nominal), ranged from 6-122 µg/100 cm2, and averaged 40 µg/100 cm2. These values are similar to those found by the Consumer Product Safety Commission study on CCA wood purchased from lumber yards.

We also surveyed CCA wood surfaces on wooden playscapes at three municipal parks built using CCA treated wood. A total of 45 wipe samples were taken from horizontal deck plank surfaces. The average amount of arsenic dislodged on the wood surfaces on the playscapes (8.8 µg/100 cm²) was considerably less than the average found on the new wood surfaces surveyed from lumber yards (40 µg/ 100 cm²). The reasons for the lower values on the surfaces of boards actually in use are not clearly understood, but they could be due to differences in the wear and weathering history. In separate experiments, we have shown that repetitive physical contact of the same surface (such as could be expected on the playscape surfaces) will result in significant decreases of arsenic dislodged as a function of repetition. The effects of long term weathering on the amounts of arsenic dislodged from the test coupons are in progress.

In addition to the horizontal surfaces tested at the municipal playscapes, a total of twelve samples were taken from the vertical poles used to support the structures (when testing the vertical pole surfaces a hand was substituted for the block and weight). The amounts of arsenic dislodged from these pole surfaces ranged from 5-632 µg/100cm² and averaged 105 µg/100 cm². Though these values were much higher than those observed on the horizontal surfaces, these results should be taken as indicative, as the testing method for the horizontal and vertical surfaces were not the same.

Coating The Wood Reduces Arsenic Dislodged From The Surface

Finally, the effectiveness of coatings to form a surface barrier for arsenic was tested. For this study , the amounts of arsenic dislodged from CCA wood surfaces was determined before and after coating with a paint or stain. Four coatings were applied to four coupons each. The coatings were polyurethane deck and porch enamel, a latex acrylic solid color stain, a spar varnish, and a semi-transparent oil stain contain alkyl resins. The spar varnish is not recommended for use on foot-traffic areas. The amounts of arsenic dislodged from the surfaces was determined before, after, and up to 1 year after coating.

The application of these coatings effectively eliminated the surface removable arsenic over the one year test period. Compared to the precoat values, there was more than a 95% reduction in the arsenic dislodged from the CCA wood surfaces coated with polyurethane, acrylic, or spar varnish. The percent reduction on surfaces coated with the oil based alkyl resin ranged from 80-97% and averaged 90%.

It should be pointed out, however, that this test did not determine how well these coatings stood up to wear and tear. Information on this has recently appeared in Consumer Reports (Exterior Deck Treatments Test, June 1998, pp. 32-34). We advise consulting with your paint dealer in order to determine which coating would most appropriate for a given use, such as high foot traffic areas.

Suggestions

• Coat CCA wood with paints or stains formulated for such use, and recoat as required.
• Keep children and pets out of under-deck areas.
• Follow safe handling and disposal guidelines when using CCA-wood in building
• Consider use of alternative products on areas that may be contacted by children

More information...

Summary

The most widely used wood preservative in current use is chromated copper arsenate (CCA), due to its excellent fungicidal and insecticidal properties. However, due to the massive amounts of CCA treated wood sold each year, dispersal of these additives from the wood could impact the environment. In this report we have identified potential environmental concerns associated with the use of CCA wood. We also present a summary of our findings on the amounts of Cu, Cr, and As in soils located under CCA treated wood structures, and on our determinations of arsenic dislodged from CCA treated wood surfaces.