Environmental Engineering Reference
In-Depth Information
treated still exists in service. Chromated copper arsenate (CCA) is a major wood preserva-
tive that was used in North America for many years for lumber treatment against insects
and microorganisms because (a) it was inexpensive, (b) it left a dry, paintable surface,
and (c) it bonded well, and was thus relatively leach-resistant. Primary utilization was for
decks, playground equipment. Even today, it would not be unusual to ind that outdoor
wooden facilities with CCA treatment. CCA associated with playground equipment is
particularly problematic since children are directly exposed through physical contact
and subsequent oral contact by ingesting food with hands having previously been in
contact with CCA contaminated wood. The U.S. Consumer Product Safety Commission
(CPSC) has stated that this might even cause cancer in children (Green Building News,
2003). There is increasing concern about potential environmental contamination from
leaching of Cu, Cr, and As from treated wood in service and from wood removed from
service and placed in landills and composted material. Open burning of this type of
wood is also potentially hazardous. Proper incineration procedures are necessary. The
life cycle of treated wood is estimated to be about 25 years, and the wood is then dis-
carded as waste. By 1995, more than 90% of 67 million kg of utilized waterborne preser-
vatives were CCA-treated (Solo-Gabriele and Townsend, 1999). The quantity of removed
treated wood from services has been estimated by the Forest Products Laboratory (FPL)
in Madison, Wisconsin, to increase from 6 million to 16 million m
3
by the year 2020
(Cooper, 1993).
Moghaddam and Mulligan (2008) tested CCA-treated gray pine species wood for leach-
ing using a modiied TCLP method to determine the leaching of the three metals under
various conditions. To obtain the results, samples of ground wood were soaked in acetic
acid (0.1 N) at pH values of 3, 4, or 5, temperatures were 15°C, 25°C, or 35°C and leaching
time was 5, 10, and 15 days. The amounts of chromium as chromium oxide (ІІІ) (CrO
3
),
copper as copper oxide (CuO), and arsenic as arsenic oxide (ІІІ) (As
2
O
3
) leached from the
wood were determined to be 49% CrO
3
, 34% As
2
O
3
, and 17% CuO. The study also exam-
ined the effects of pH and temperature on the leaching of the three metals, from the wood,
for a 5-day period, and found that measurable amounts of chromium, copper, and arsenic
in the leachates. Arsenic was found to be the least resistant metal to leaching when the
temperature increased and chromium was the most resistant. In addition, there was more
leaching of all three elements as the pH decreased. The effect is shown for pH 4 in Table
7.5. The results of the study showed that there is the risk of soil, water, and environmental
contamination by chromium, copper, and arsenic, wherever chromated copper arsenate
treated wood is used or disposed of in a landill. Chromium was leached the least despite
being present in the greatest proportion. Disposal must be in a lined landill to avoid con-
tamination of the groundwater.
TABLE 7.5
Results of Leaching Tests with Acetic Acid under Various Conditions
Conditions
Chromium (mg/L)
Copper (mg/L)
Arsenic (mg/L)
TCLP regulatory level
5.0
Not on the list
5.0
Experimental data at 35°C, pH 4
5 days
0.6
4.9
4.5
10 days
1.1
5.9
5.7
15 days
1.4
6.4
5.5
Source:
Adapted from Moghaddam, A.H. and Mulligan, C.N.,
Waste Management
, 28, 628-637, 2008.
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