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Dr. David Stilwell, one of the world's leading authorities on pressure treated wood is a researcher with the Department of Analytical Chemistry at the Connecticut Agricultural Experiment Station in New Haven, Connecticut. Dr. Stilwell and his research partner, Katja D. Gorny, crawled under decks in 1996 to find out if arsenic was leaching from them. Their findings8 challenged the belief that arsenic was locked into pressure treated wood. The EPA has requested their studies and these studies have raised concerns around the world about the safety of pressure treated wood.
They studied the soil under seven decks built from pressure treated lumber ranging in ages from 4 months to 15 years. Since decks are horizontal they found them to be a good indicator of the effects of rain and solar radiation as all leached arsenic would fall beneath such structures. Soil samples were collected in a grid like fashion and a total of 85 soil samples were taken. These samples included control samples, which were taken at a minimum of 5 meters from the decks and at least 4 meters apart. The soils in all areas were considered of a sandy loam type. Samples averaged 100 g and came from the upper 5 cm of soil after all debris such as twigs and leaves were removed. The soil samples were tested and the results are shown in the following charts.
The soil samples were consistent with leaching rather than from left over sawdust, as sawdust would have shown the same proportions to the quantities of the chemicals in the wood.
| Table 3 Average Contents in Soils (mg/kg) Compared to Statutory Limits 8 | ||||
|
Element
|
||||
| Location/Limit | Cu | Cr | Cr+6 | As |
| Beneath Decks | 75 | 43 | ND | 76 |
| Control Soils | 17 | 20 | ND | 4 |
| EPA 503 (1993) | 1500 | 1200 | - | 41 |
| State of CT (1996) | 2500 | 3900 | 100 | 10 |
ND - not determined.
*EPA 503 (1993). **State of Connecticut (1996)
Table 4 Range, Average and Standard Deviations (SD) in the Amount (mg/kg) of
Cu, CR, and As in Soil Samples8
|
Deck |
Soil Beneath Deck |
Control Soil |
||||
|
Range |
Avg. |
SD |
Range |
Avg. |
SD |
|
|
Copper |
||||||
|
1 |
22-63 |
34 |
12 |
13-20 |
16 |
3 |
|
2 |
23-65 |
48 |
14 |
12-17 |
14 |
2 |
|
3 |
38-145 |
76 |
25 |
18-30 |
22 |
4 |
|
4 |
41-140 |
75 |
27 |
18-30 |
22 |
4 |
|
5 |
26-273 |
104 |
74 |
10-12 |
11 |
1 |
|
6 |
60-410 |
154 |
87 |
15-27 |
20 |
5 |
|
7 |
17-46 |
31 |
10 |
10-14 |
13 |
2 |
|
Overall |
17-410 |
75 |
10-30 |
17 |
||
|
Chromium |
||||||
|
1 |
20-31 |
26 |
4 |
17-24 |
20 |
3 |
|
2 |
16-73 |
26 |
17 |
13-19 |
16 |
2 |
|
3 |
27-68 |
42 |
11 |
25-30 |
27 |
3 |
|
4 |
34-95 |
58 |
17 |
25-30 |
27 |
3 |
|
5 |
26-138 |
64 |
35 |
17-18 |
18 |
1 |
|
6 |
31-154 |
59 |
33 |
19-23 |
21 |
2 |
|
7 |
16-33 |
23 |
5 |
11-19 |
14 |
3 |
|
Overall |
16-154 |
43 |
11-30 |
20 |
||
|
Arsenic |
||||||
|
1 |
3-19 |
9 |
5 |
2.2-3.5 |
2.6 |
0.4 |
|
2 |
7-91 |
34 |
23 |
3.6-5.2 |
4.2 |
0.6 |
|
3 |
34-99 |
61 |
20 |
2.5-8.3 |
4.9 |
2.2 |
|
4 |
44-333 |
139 |
66 |
2.5-8.3 |
4.9 |
2.2 |
|
5 |
57-215 |
113 |
60 |
2.2-3.9 |
2.7 |
0.7 |
|
6 |
50-350 |
138 |
77 |
3.5-5.3 |
4.4 |
0.7 |
|
7 |
6-80 |
40 |
21 |
1.3-2.4 |
1.9 |
0.4 |
|
Overall |
3-350 |
76 |
1.3-8.3 |
3.7 |
||
This study showed an average arsenic level that far exceeds the State level whereby clean- up standards would have to be met to meet guidelines for residential areas. It also showed that coated decks can retard the leaching of arsenic.
The conclusion from this experiment showed clearly that decks made from pressure treated wood do pose a serious threat to the environment.
Dr. Stilwell continued his research and wrote about it in a publication in the fall of 1998. This time David Stilwell used test coupons made from a variety of pressure treated wood surfaces. Wipe samples were taken from these samples. Some of the coupons were coated with different types of treatments. Although the results would not be indicative of wear and tear with the various coatings, it showed a remarkable decrease in the level of arsenic leaching compared to the uncoated wood.
The result of this experiment proved coating pressure treated wood will eliminate much of the leaching of heavy metals.23
Two charts follow from testing done by Consumer Reports in June of 1998 and
June of 1999. More recent results might be found at your local Library.
Table5 Exterior Deck Treatemnt 9
NOTE: we are in the process of coding Tables 5 and 6. Please refer to the Word or PDF versions of this document.
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