Environmental Engineering Reference
In-Depth Information
Other studies have shown that CCA concentrations in above-ground wood
samples are not signifi cantly different from concentrations in new poles, while wood
samples from below-ground contain lower CCA concentrations, suggesting that
leaching is evidently occurring (Morrell and Huffman
2004
). In situations where
the groundwater table is close to the surface, concentrations of these elements are
expected to be spread further from the poles when compared to unsaturated soil
situations (Hingston et al.
2001
; Lebow et al.
2003
).
Leaching tests showed that arsenic and chromium can be controlled by pH levels
(Townsend et al.
2004
). Metal leachability from CCA-treated wood is the highest at
extreme pH values and lowest around pH-7, and increases with increased contact
time. Although copper and chromium leaching from wood reached an equilibrium
within 7 days, arsenic continued to increase throughout the test.
Soil type also plays an important role in the mobility of CCA. It has been found
that the greatest absorption occurs in soils where organic content is moderate to
high, resulting in decreased mobility, while lowest absorption rates are in sandy
clays with a low organic content, allowing for greater mobility (Read
2003
).
In order to investigate the impact on groundwater from tsunami debris, leaching
tests were performed. Research was conducted to examine the possible environ-
mental impacts of using CCA-treated wood for purposes such as landscape mulch.
Two pathways, leaching to groundwater and direct human exposure, were examined
(Townsend et al.
2004
). To examine contamination of groundwater, samples of C&D
(construction & demolition) wood debris mulch were tested to determine the pres-
ence of CCA-treated wood using the synthetic precipitation leaching procedure
(Townsend et al.
2003b
). Arsenic presented the biggest problem when results were
compared to risk-based target concentrations for groundwater. Since contamination
of groundwater depends on many factors, such as underlying soil type, rate of mulch
application, extent of application, and depth of groundwater, the results do not
directly indicate that groundwater contamination will occur.
Townsend et al. (
2003a
) reported that copper, rather than arsenic, was most
toxic to the aquatic environment. However, when copper was present in the CCA
combination, it appears to be have been more toxic than on its own, raising concerns
about the synergistic effects of the combination of copper, arsenic and chromium.
Weis and Weis (
2004
) showed that all the active elements were accumulating in
the aquatic environment (particularly in locations with reduced water fl ow), sediments
and organisms, to the point of reaching the trophic chain. Furthermore, cells and
tissues have also shown to be affected, impinging on growth and increasing mortality.
Chirenje et al. (
2004
) found that fi ne-textured soils and soil with high amounts of
organic matter had larger retention capabilities of copper, chromium and arsenic,
presenting potential contamination problems. This fi nding became important for
riverine and estuarine environments as well as wetlands, since organic matter can be
found in sediment, although these types of ecosystems can also act as metal sinks
which further reduces their availability.
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