preservative leaching from weathered cca-treated wood
TRANSCRIPT
Preservative leaching from weathered CCA-treated wood
Timothy Townsenda,*, Brajesh Dubeya, Thabet Tolaymata,1, Helena Solo-Gabrieleb
aDepartment of Environmental Engineering Sciences, University of Florida, 218 Black Hall, P.O. Box 116450, Gainesville, FL 32611-6450, USAbDepartment of Civil Architectural and Environmental Engineering, University of Miami, Coral Gables, FL 33124, USA
Received 11 May 2004; revised 18 September 2004; accepted 8 November 2004
Abstract
Disposal of discarded chromated copper arsenate (CCA)-treated wood in landfills raises concerns with respect to leaching of preservative
compounds. When unweathered CCA-treated wood is leached using the toxicity characteristic leaching procedure (TCLP), arsenic
concentrations exceed the toxicity characteristic (TC) limit of 5 mg/L in most cases. The majority of discarded CCA-treated wood, however,
results from demolition activities, where the wood has typically been subjected to weathering. Since preservatives do migrate from the wood
during its normal use, leaching characteristics of weathered and aged CCA-treated wood may differ from unweathered wood. To evaluate
this, CCA-treated wood removed from service after various degrees of weathering was collected from multiple sources and leached with the
TCLP, the synthetic precipitation leaching procedure (SPLP) and California’s waste extraction test (WET). Five to seven individual pieces of
wood were analyzed from each source. The average TCLP arsenic concentration for the 14 sources ranged from 3.2 to 13 mg/L. The average
TCLP concentrations of the 100 wood pieces tested were 6.4, 5.9 and 3.2 mg/L for arsenic, copper and chromium, respectively. Overall, in 60
out of 100 samples tested by the TCLP, arsenic concentrations exceeded 5 mg/L (the TC regulatory value). SPLP leachate concentrations
were similar to TCLP concentrations, although copper leached somewhat more with the TCLP. WET leachate concentrations were
approximately a factor of 10 higher than TCLP concentrations. Discarded CCA-treated wood, even after exposure to years of weathering,
often exceeds the TC limit for arsenic and without the current regulatory exemption would possibly require management as a TC hazardous
waste in the US.
q 2005 Elsevier Ltd. All rights reserved.
Keywords: CCA; Discarded treated wood; Arsenic; Chromium; TCLP; WET; SPLP
1. Introduction
Chromated copper arsenate (CCA) has been the most
common waterborne wood preservative in North America in
recent decades (Solo-Gabriele and Tounsend 1999). In the
CCA treatment process, wood products such as dimensional
lumber, plywood, and poles are preserved by impregnating
the wood with an aqueous solution containing CrO3, CuO,
and As2O5. The amount of CCA added to the wood (referred
to as the retention value, RV) is a function of the intended
use of the wood. CCA-treated wood used for above ground
purposes requires at least 4.0 kg of CCA/m3 of wood
(0.25 lb/ft3), while wood products intended for ground
0301-4797/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jenvman.2004.11.009
* Corresponding author. Tel.: C1 352 392 0846; fax: C1 352 392 3076.
E-mail address: [email protected] (T. Townsend).1 Current address: US Environmental Protection Agency, Office of
Research and Development, Cincinnati, OH 45211, USA.
contact require a minimum RV of 6.0 kg/m3 (0.4 lb/ft3).
Higher RVs are sometimes encountered, with a maximum
of 40 kg/m3 (2.5 lb/ft3) being used for wood submerged in
marine environments.
Upon impregnation, the wood treatment preservatives
undergo a chemical reaction within the wood in which the
preservative elements become bound, or fixed, to the wood
fibers. While arsenic, copper and chromium are considered
fixed from a wood preservation efficacy standpoint,
laboratory research has shown that they do leach from
CCA-treated wood over time when exposed to water
(Cooper, 1991, 1994; Hingston et al., 2001; Lebow et al.,
2003). Several researchers have investigated the impli-
cations of metals leaching from CCA-treated wood
(Rahman and Hughes, 1994; Weis and Weis, 1993, 1999;
FR, 2001). The majority of studies have focused on impacts
to aquatic ecosystems (Weis and Weis, 1993, 1999; Lebow,
1996) and contamination of underlying soil (Stillwell and
Journal of Environmental Management 75 (2005) 105–113
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T. Townsend et al. / Journal of Environmental Management 75 (2005) 105–113106
Gorny, 1997; Townsend et al., 2003a). Concerns over
possible human health impacts, primarily from arsenic,
prompted the wood treatment industry in the US to phase
out the production of CCA-treated wood for most residential
applications beginning in 2004 (68 FR 17366; April 9,
2003). CCA-treated wood will continue to be used for
several non-residential applications such as utility poles and
marine structures.
Despite the reduction in CCA-treated wood production,
the disposal of this material at the end of its useful life
remains a concern. A majority of the CCA-treated wood
ever produced remains in service and will enter the waste
stream in the coming decades (up to 8.0 million metric
tons/year; Solo-Gabriele and Townsend, 1999). Manage-
ment practices for CCA-treated wood include disposal in
landfills and combustion in waste-to-energy facilities.
Management in traditional combustion systems poses a
concern with respect to air emissions and ash quality
(Solo-Gabriele et al., 2002). Recent research has found that
some CCA-treated wood inadvertently becomes included as
part of landscape mulch from construction and demolition
(C&D) debris wood (Townsend et al., 2003b), although the
USEPA has sought to prevent this practice (Springer and
Jones, 2004). While several promising treatment and
remediation technologies have been proposed (Clausen,
2000; Clausen and Kenealy, 2004; Ottosen et al., 2004),
difficulties in identifying and removing CCA-treated wood
from the waste stream and relatively low land disposal costs
have resulted in landfilling being the most practiced
management method in many instances. Landfill disposal
of discarded CCA-treated wood poses its own set of
potential problems. Groundwater contamination is a con-
cern for unlined landfills, and at lined facilities elevated
concentrations of preservative elements in the leachate can
pose leachate management problems.
One method used to assess whether landfill disposal of a
solid waste might impact leachate or groundwater quality is
to conduct a leaching test. The toxicity characteristic
leaching procedure (TCLP) was developed by the US
Environmental Protection Agency (EPA) to simulate
plausible worst-case leaching conditions that might occur
in a landfill containing biodegradable organic wastes
(Francis et al., 1984; Francis and Maskarinec, 1986).
Since organic acids (e.g. volatile fatty acids) are produced
during the anaerobic decomposition of biodegradable waste
in municipal landfills, the TCLP uses acetic acid as an
extraction solution. When the concentration of any of eight
inorganic elements and 25 organic compounds in the TCLP
leachate for a tested solid waste exceeds the defined
regulatory limit, the waste is characterized as a toxicity
characteristic (TC) hazardous waste (40 CFR 261.24). Most
discarded CCA-treated wood, however, is excluded from
the definition of hazardous waste at the US federal level
(40 CFR 261.4(b)(9)).
TCLP data for CCA-treated wood can prove valuable for
several reasons. At least two states (Minnesota and
California) have not adopted the hazardous waste exclusion
for CCA-treated wood. In recent years, the US EPA has
been petitioned to remove the exclusion for CCA-treated
wood. Thus, TCLP leaching results for CCA-treated wood
are important in the event that future policies and
regulations change. Even if a solid waste is exempt from
classification as a hazardous waste, leaching data may help
assess potential impact on landfill leachate quality. TCLP
data for new CCA-treated wood (wood that has not been
exposed to environmental weathering) show that arsenic
frequently leaches at concentrations above the 5 mg/L TC
limit (Townsend et al., 2004). The majority of CCA-treated
wood disposed, however, is not new wood (e.g. construction
scrap), but is wood that has been removed from service after
exposure to environmental weathering (e.g. demolition
debris). Since CCA-treated wood leaches when exposed to
water, especially upon first contact with water (Breslin and
Adler-Ivanbrook, 1998; Lebow et al., 1999; Townsend
et al., 2004), it is plausible that leaching characteristics of
weathered wood will differ from unweathered wood.
The objective of the research presented in this paper was
to perform TCLP on weathered CCA-treated wood and to
assess the degree to which it leaches arsenic, copper and
chromium. The TC regulatory limits for arsenic and
chromium were used as a benchmark. The CCA-treated
wood characterized was collected from demolition sites or
from disposal facilities, and represented primarily terrestrial
applications such as decks and fences. Additional regulatory
leaching tests, the SPLP and California’s WET, were also
performed on a smaller subset of samples to provide
additional information useful for assessing management
options and consequences.
2. Materials and methods
2.1. Sample collection and preparation
Samples of weathered CCA-treated wood were collected
from 14 different sources. The term ‘source’ represents
either a structure that was demolished or a distinct load of
debris dropped off at C&D debris recycling facility.
Samples consisted of pieces of dimensional lumber and in
some cases round poles. In most cases, seven individual
wood pieces were collected from each source. A total of 100
wood pieces was collected from the 14 different sources.
The sources are identified in Table 1 as sites A–N. The age
of the wood was estimated from information provided by
owners of the structure or from characteristics of the wood
and its accompanying waste (e.g. apparent degree of
weathering, condition of other materials in the load).
The samples were processed to meet the size reduction
requirements of the TCLP, SPLP and WET (less than
0.95 cm). Size-reduced samples were generated using an
electric power drill equipped with a 0.62-cm (0.25-in.) drill
bit. The wood pieces were drilled in multiple locations and
Table 1
CCA-treated wood source description
Source Number of
individual
samples
Composite
sample
Estimated
age
(years)
Description
A 5 Yes 1.5 Ramps and walkways
for portable buildings
B 7 Yes 10 Childern’s
playstructure
C 7 No 20 Components of a
bridge
D 7 No 10 Residential fence
E 7 No 5–15 Highway guardrail
spacer blocks
F 10 Yes 10–15 Residential garden
border fence
G 7 Yes 20 Residental deck
H 7 Yes 10 Non-residential
privacy fence
I 7 Yes 10–15 Structures in park
J 7 Yes 10–15 Structures in park
K 7 No 10–15 Structures in park
L 7 No 10–15 Structures in park
M 7 No 10–15 Structures in park
N 7 No 10–20 Residential dock
T. Townsend et al. / Journal of Environmental Management 75 (2005) 105–113 107
the drill cuttings were collected. An effort was made to drill
through the entire wood piece or at least deep enough into
the wood to collect a sample representative of the entire
piece as required by the TC regulation. Samples from only
the outer fraction of the wood were avoided because the
concentration of preservative is often greatest in the outer
perimeter (Hingston et al., 2001). The drill bit was cleaned
between each sample by rinsing with diluted nitric acid and
de-ionized water. Two-hundred-gram composite samples
were created by mixing approximately 30–40 g of CCA-
treated wood drill shavings from each of the individual
CCA-treated wood pieces from a source together in a
stainless steel bowl.
2.2. Retention value (RV) measurements
RV measurements of the different wood pieces were
made using the X-ray fluorescence (XRF) technique that is
used by the manufactures of CCA-treated wood (performed
using an Asoma model 100 XRF). The RV measurements
collected corresponded to the entire cross-section of the
wood samples; this differs from the industry RV that is
based upon measurement of the outer 1.5 cm (0.6 in.) of the
wood surface. Since the original RVs of the wood products
tested were not known, no evaluation of preservative loss
over time was made.
2.3. Leaching tests
The TCLP was performed on every sample collected
following EPA method 1311 (US EPA, 1996). The TCLP
extraction fluid was prepared by diluting 11.4 mL of glacial
acetic acid and 126.8 mL of 1 N sodium hydroxide with de-
ionized water (DI) to achieve a final volume of 2 L and a pH
of 4.93G0.05. Drill bit shavings (100 g) were weighed and
placed in a polyethylene extraction vessel and 2 L of the
extraction solution was added. The slurry was mixed on a
rotary extractor for 18G2 h after which it was filtered using
a 0.7-mm borosilicate glass fiber filter (Environmental
Express TCLP filter). The filtrates were collected in 1-L
plastic bottles, acidified to a pH of less than 2 and stored at
4 8C until digestion and analysis.
The SPLP and WET were only performed on a smaller
subset of samples. The individual wood samples from
sources A, B, and E–J were composited into one sample
representing each source; TCLP, SPLP and WET were
performed in triplicate on these composite sources. The
leaching tests on the composite samples were performed on
10 g subsamples, and 200 mL of leaching solution was used
to maintain a liquid-to-solid ratio of 20:1 for SPLP and
TCLP. For the WET, a liquid-to-solid ratio of 10:1 was
used. The SPLP (US EPA method 1312) is similar to the
TCLP, with simulated rainwater being used as the extraction
solution instead of simulated landfill leachate. The simu-
lated rainwater was created by adding 0.4 mL of a sulfuric
acid and nitric acid solution (60 g sulfuric acid and 40 g of
nitric acid) to a 2-L volumetric flask and bringing to volume
with reagent water to achieve a final pH of 4.20G0.05. The
rest of the procedure was conducted in a similar fashion to
the TCLP. The WET utilizes a buffered citric acid solution
as the leaching fluid. The WET extraction solution was
prepared by titrating a 0.2 M citric acid solution with 4.0 N
sodium hydroxide to a pH of 5.0G0.05. The WET requires
that 100 g of sample be leached with 1 L of extraction
solution for 48 h. The procedure performed here deviated
slightly from the method as defined by California in that de-
oxygenation of the extraction solution by bubbling nitrogen
was not carried out (CCR, 1998). Other features of the
experiment were the same as the TCLP. The final pH of the
leaching solutions at the end of the leaching experiments
was recorded.
2.4. Leachate digestion and analysis
Prior to analysis, the leachate samples were digested
following US EPA method 3010 (US EPA, 1996). This
method is an open vessel digestion procedure that requires
the addition of concentrated nitric acid and hydrochloric
acid to a representative 100 mL sample. A Thermo Jarrel
Ash inductively coupled plasma atomic emission spectro-
photometer (ICP-AES, Thermo Jarrel Ash Model 95970,
US EPA method 6010B) was used to analyze arsenic,
copper, and chromium in the digested samples. Detection
limits for the instrument were 0.03, 0.014, and 0.017 mg/L
for arsenic, copper and chromium, respectively. Duplicate
samples, matrix spikes, reagent water spikes, and instrument
calibration checks using standards were performed follow-
ing typical laboratory quality control procedures.
T. Townsend et al. / Journal of Environmental Management 75 (2005) 105–113108
3. Results and discussion
3.1. Wood retention values
The RVs for the weathered CCA-treated wood samples
ranged from 2.7 kg/m3 (source D) to 7.2 kg/m3 (source
N). As presented in Table 2, the range of RVs
encountered for wood pieces from the same source
often varied considerably. Heterogeneity of the wood
and the variation of the original preservative retention
value can lead to observed variability in the XRF analysis
(Lebow et al., 2004). The initial preservative loading is a
function of the intended use of the wood. Several
different types of wood pieces were tested from many
of the sources (e.g. for some sources posts buried in the
soil or submerged in water, as well as dimensional deck
or fence boards, were tested), and since the amount of
preservative added may differ depending on the appli-
cation, some variability is expected. For example, sample
N originated from a dock demolition, and had samples
with both extremely low (0.5 kg/m3) and extremely high
(29.3 kg/m3) RVs. The low RV samples corresponded to
several older planks that were extremely weathered, while
the high RV samples corresponded to poles that were
treated to very high initial RVs and that were added to
the dock in more recent years (they were still in relatively
good condition). As described previously, the RVs
measured in this study correspond to the preservative
content of the entire cross-section of a wood sample, not
the outer 1.5 cm (0.6 in.) of the wood surface that the
wood preservation industry typically reports for treated
wood products. The observation that some measurements
were below the typical minimum RV for CCA-treated
wood products of 4.0 kg/m3 could be the result of the
variability discussed above as well as preservative loss
over time. Since no measurements of initial RV of the
wood samples were available, no definite conclusion was
reached.
Table 2
XRF retention value results
Source Mean XRF (kg-CCA/m3)
A 3.98 (3.84K4.29)a
B 4.96 (4.32K5.43)
C 5.19 (4.32K6.07)
D 2.65 (2.46K2.83)
E 5.62 (5.15K6.04)
F 4.28 (3.26K5.89)
G 3.94 (2.20K6.39)
H 4.05 (3.48K4.56)
I 3.40 (1.17K5.62)
J 2.89 (1.65K5.47)
K 3.17 (1.81K4.40)
L 3.65 (2.87K4.38)
M 4.19 (3.76K4.67)
N 7.24 (0.5K29.4)
a Average (lowestKhighest).
3.2. TCLP results for individual sources
The TCLP was performed on a total of 100 different
samples of weathered CCA-treated wood from the 14
sources outlined in Table 1. The mean concentrations of
arsenic, copper and chromium extracted using the TCLP are
summarized in Table 3. The average TCLP concentrations
for the 14 sources ranged from 3.2–13 mg/L for arsenic,
2.4–15 mg/L for copper, and 0.8–7.1 mg/L for chromium.
The average TCLP concentrations of all 100 wood pieces
tested were 6.4, 5.9, and 3.2 mg/L for arsenic, copper and
chromium, respectively. Fig. 1 illustrates the range of
concentrations among the 100 samples, showing the
distribution of arsenic concentrations encountered. Mean
TCLP concentrations extracted from 13 samples of new,
unweathered CCA-treated wood were 7.0, 9.9 and 2.6 mg/L
for arsenic, copper and chromium, respectively (Townsend
et al., 2004).
When concentrations of the three leached preservative
elements were compared, TCLP arsenic concentrations
were in most cases the highest, followed by those of copper,
and then chromium. This leaching trend was observed
in 63 of the 100 samples. Copper leached more than
arsenic (with chromium leaching least) in 26 of the same
100 samples. Only in one sample did chromium leach the
most. Previous leaching studies conducted on unweathered
CCA-treated wood have observed similar trends, with
arsenic and copper leaching the most in most cases and
chromium leaching the least (Warner and Solomon, 1990;
Cooper, 1991; Townsend et al., 2001; Hingston et al., 2001).
While chromium in the CCA treating solution is initially in
the more mobile hexavalent form, it becomes reduced to the
relatively less mobile trivalent form upon contact and
fixation with the wood (Cooper and Ung, 1993; Hingston et
al., 2001), thus accounting for the relatively lower leaching
typically observed with chromium.
Table 3
TCLP results for the individual sources sampled
Source Na Mean concentration (mg/L)Gstandard deviation
Arsenic Chromium Copper
A 5 9.6G5.3 5.6G2.8 15G4.8
B 7 11G2.5 6.7G3.1 11G5.4
C 7 13G3.8 7.1G3.2 7.8G3.8
D 7 3.2G2.7 2.4G1.6 2.4G3.0
E 7 7.1G2.8 2.9G1.4 6.2G4.3
F 10 8.2G5.0 3.0G2.2 5.1G3.2
G 7 3.5G4.3 2.6G2.4 5.7G2.7
H 7 6.6G1.7 3.8G2.2 5.8G1.9
I 7 4.1G1.4 0.82G0.13 2.4G1.3
J 7 4.5G4.7 1.2G1.1 2.8G2.8
K 7 4.6G2.4 2.3G2.0 5.3G3.7
L 7 6.0G1.5 2.9G1.5 3.6G2.1
M 7 5.3G1.8 2.0G0.96 3.3G1.5
N 7 4.5G3.8 1.9G0.98 8.7G12
a N, number of individual samples.
Fig. 1. Distribution of arsenic TCLP concentrations for individual treated wood samples.
T. Townsend et al. / Journal of Environmental Management 75 (2005) 105–113 109
The results of the RV analyses and the TCLP leaching
measurements were used to estimate the percentage of CCA
preservative leached from the wood samples. The mass of
arsenic, copper, and chromium leached from the wood (mg-
metal/kg-wood) was determined using the volume of
leaching fluid used (2 L) and the mass of sample leached
(0.1 kg). These data were then converted to the mass of
CCA leached per volume of wood (kg-CCA/m3 of wood). A
wood density of 514 kg/m3 (32 lb/ft3) was assumed. The
mean fraction of CCA leached was 8.5%, ranging from less
than 1–25%. Ninety percent of the samples leached between
1.5 and 18%. The observed leaching percentages compare
relatively well and fall within the range of other experiments
(Warner and Solomon, 1990; Kennedy and Collins, 2001;
Townsend et al., 2004).
The observation that the preservative elements leached a
similar amount using the TCLP from the weathered CCA-
treated wood reported here in comparison to previous results
for new wood samples may have several causes. While
preservatives do leach from CCA-treated wood when
exposed to weathering, much of this loss will occur from
preservative in the outer layers of the wood. When the
TCLP is performed, the entire wood sample is size-reduced
and tested. The material leached comprises both wood that
is directly exposed to weathering (i.e. the exterior portion)
and wood that has not been directly exposed (i.e. the interior
portion). With the exception of heavily deteriorated
samples, a larger fraction of the wood tested will come
from portions of the wood piece not exposed to weathering.
Changes in preservative element chemistry over time may
also impact leaching. Recent research has found that
leachates from older CCA-treated wood samples (including
some of those tested in this study) contained more trivalent
arsenic than leachates from new CCA-treated wood (Khan
et al., 2004). The original form of arsenic in the treatment
solution is the pentavalent species, and over time it appears
that some arsenic is reduced to the trivalent form, which has
been found to be generally more mobile in the environment
(Squibb and Fowler, 1983).
3.3. Composite sample results
Table 4 presents the average results for the TCLP, SPLP,
and WET performed on the composite samples. The TCLP
results for the composite samples (Table 4) for a given
source were sometimes different than the average of the
individual samples presented earlier (Table 3), a result of
the inherent sample variability encountered with CCA-
treated wood (Hingston et al., 2001) and smaller sizes used
for the composite samples. A dramatic result noted from
Table 4 is the larger extent to which WET leaches the three
metals when compared to TCLP and SPLP. The WET
extracted statistically (pZ0.001) higher concentrations of
all three preservative elements than both the TCLP and the
SPLP. No statistically significant difference (pZ0.001) was
noted between the concentrations extracted by the TCLP
and the SPLP. These relationships are better illustrated in
Fig. 2, which plots element concentrations from the SPLP
and WET as a function of the TCLP concentrations for the
same samples. The solid line presented in each plot
corresponds to the relationship where the WET or SPLP
concentration equals the TCLP concentration.
TCLP and SPLP are conducted at a 20:1 liquid-to-solid
ratio and WET is carried out at 10:1 liquid to solid ratio; the
TCLP and SPLP are twice diluted compared to WET and in
general higher leachate concentrations are observed at lower
Table 4
Comparison of average composite batch tests results
Source Arsenic concentration (mg/L) Chromium concentration (mg/L) Copper concentration (mg/L)
WET TCLP SPLP WET TCLP SPLP WET TCLP SPLP
A 44 5.2 6.9 42 3.4 3.6 73 6.3 5.0
B 52 6.3 8.0 38 3.0 3.1 58 6.3 4.4
E 35 6.4 6.2 21 1.9 1.6 45 4.2 2.3
F 40 8.0 7.0 24 2.7 2.3 44 4.3 2.0
G 23 5.2 4.5 22 2.4 1.8 50 3.7 1.2
H 45 4.8 6.9 31 2.1 2.5 34 4.8 3.0
I 37 3.3 3.6 21 0.58 0.58 58 2.0 0.56
J 28 3.1 3.3 15 0.62 0.58 37 1.6 0.60
T. Townsend et al. / Journal of Environmental Management 75 (2005) 105–113110
liquid-to-solid ratio (Townsend et al., in press). The greater
preservative element concentrations observed in the WET
leachates relative to the TCLP and SPLP leachates most
likely result, however, from citrate’s propensity to chelate the
three CCA elements. Other leaching studies support this
conclusion (Hooper et al., 1998; Townsend et al., 2004). The
acetate in the TCLP solution certainly displays a propensity
to complex with some elements. In a study on lead leaching
from cathode ray tubes, Jang and Townsend (2003) found
lead to be extracted in similar amounts using the TCLP and
the WET. In the case of CCA-treated wood, however, the
arsenic, copper and chromium have a much greater
propensity to leach under the WET relative to the TCLP.
Hooper et al. (1998) reported that acetic acid failed to
complex oxyanion-forming elements such as arsenic and
chromium. Citric acid has multidentate ligands while acetic
acid has monodentate ligands, and in general, complexes
with monodentate ligands are less stable than those with
multidentate ligands (Stumm and Morgan, 1996). Upon
statistical analysis of the TCLP and SPLP data, no significant
difference was noted for all three elements. Fig. 2, however,
indicates that while arsenic and chromium concentrations
are very similar between SPLP and TCLP, copper concen-
trations are somewhat higher using the TCLP. When
new, unweathered CCA-treated wood samples were tested
(Townsend et al., 2004), a similar trend was observed, with
the TCLP and SPLP extracting similar concentrations of
arsenic and chromium, and copper concentrations being
somewhat greater with the TCLP compared to the SPLP.
4. Regulatory and disposal implications
US hazardous waste regulations exclude most CCA-
treated wood from the definition of hazardous waste. The
federal register notice discussing this decision (45 FR
78530; November 25, 1980) cites the fact that CCA-treated
wood was already reviewed for its environmental and
human health impacts under federal pesticide rules, and was
found to be safe for use. At least two states (Minnesota and
California), however, did not adopt the exclusion as part of
their state hazardous waste regulations. The EPA has
been petitioned to remove this regulatory exclusion for
CCA-treated wood, but had not acted on the petition at the
time this research was conducted.
In the absence of the 40 CFR 261.4(b)(9) RCRA
exclusion, the results indicate that in many cases discarded
CCA-treated wood, even if it has been exposed to weath-
ering and already lost preservative chemical in the
environment, would be a toxicity characteristic (TC)
hazardous waste. The TC threshold for both arsenic and
chromium is 5 mg/L; copper is not a TC element. Of the 100
samples tested using TCLP, 60 exceeded 5 mg/L for arsenic
(Fig. 1) and 20 exceeded 5 mg/L for chromium (Table 5). All
of the samples that exceeded 5 mg/L for chromium also
exceeded for arsenic. TCLP data for new, unweathered
CCA-treated wood (Townsend et al., 2004) found arsenic
concentrations to exceed the TC limit in 11 out of 13 samples
characterized. None of the new, unweathered samples
exceeded the TC-limit of chromium. The US EPA, as well
as many state regulatory agencies, recommends comparing
the 95% upper confidence limit (UCL95) to appropriate
regulatory standards (US EPA, 2000). The UCL95 for the
100 samples evaluated was found to be 7.1 mg/L for arsenic
(greater than the TC threshold) and 3.7 mg/L for chromium
(less than the TC threshold).
US regulations may also exclude solid wastes from the
definition of hazardous waste if they are only characterized
as hazardous because of chromium and the chromium
exclusively or nearly exclusively exists in the trivalent form
(40 CFR 261.4(b)(6)). Generators believing their waste to
meet the 40 CFR 261.4(b)(6) criteria must petition the US
EPA (or a state program authorized to implement RCRA) to
take advantage of the exclusion. The generators must also
demonstrate that the discarded wood will not be managed in
a form where the trivalent chromium will be oxidized to
hexavalent chromium. Since the hexavalent chromium in
the CCA preservative solution is converted to the trivalent
form upon contact with the wood fibers, one would not
expect chromium to cause CCA-treated wood to be
hazardous (unless it were managed in oxidizing conditions,
as might be encountered in some combustion systems). Thus
the primary concern from a hazardous waste management
perspective would be arsenic.
The US regulations also exclude household waste from
the definition of hazardous waste and CCA-treated wood
Table 5
Exceedances of TC threshold concentrations
Source N samples
analyzed
N samples exceed-
ing 5 mg-As/L
N samples exceeding
5 mg-Cr/L
A 5 4 3
B 7 7 5
C 7 7 4
D 7 2 1
E 7 6 1
F 10 6 2
G 7 2 1
H 7 5 2
I 7 2 0
J 7 3 0
K 7 3 1
L 7 6 0
M 7 3 0
N 7 4 0
Fig. 2. Metal leachability in SPLP and WET relative to TCLP.
T. Townsend et al. / Journal of Environmental Management 75 (2005) 105–113 111
discarded by the homeowner would not be hazardous,
regardless of the TCLP results (although many municipa-
lities require separate collection and special handling of
household hazardous wastes; see 40 CFR 261.4(b)(1)).
Regulatory interpretation would be required to determine
whether some sources of discarded CCA-treated wood
would be household waste. Examples include discarded
wood from decks, docks, and fencing removed from
residential properties by construction contractors. For the
case of lead-based paint debris, the EPA has interpreted
waste removed from residences by contractors to be
household waste (US EPA, 2003).
In California, a solid waste can be hazardous if the TCLP
concentration exceeds the TC concentration or if the WET
concentration exceeds the California-specific soluble
threshold limit concentration (STLC). The STLC for arsenic
and chromium are 5 mg/L, respectively, and for copper it is
25 mg/L. The weathered wood samples tested here
exceeded the STLC for each of the three metals in every
sample. California does not exclude household hazardous
waste from regulation, although it does allow some utility-
generated waste CCA-treated wood to be managed as non-
hazardous waste in lined landfills.
The leaching test results also provide insight as to
potential impacts on landfills, regardless of whether it is a
regulated hazardous waste. The TCLP was designed to
simulate acid-forming conditions in a municipal waste
landfill. The results thus indicate that weathered CCA-
treated wood might result in elevated pollutant concen-
trations in landfill leachates (and possible groundwater
impact at unlined sites). It is important to recognize that the
TCLP may be limited with respect to assessing actual
leaching of wastes in operating landfills (US EPA, 1991;
Cernuschi et al., 1990; Poon and Lio, 1997). Lead leaching,
for example, was found to be much lower in the presence of
actual landfill leachates compared to TCLP (Jang and
Townsend, 2003). On the other hand, arsenic was found to
leach a greater amount in landfill leachate compared to
TCLP (Hooper et al., 1998). In limited testing on one
sample of new, unweathered CCA-treated wood, TCLP and
MSW landfill leachate extracted similar concentrations of
arsenic and chromium, while copper was higher in the
landfill leachate (Townsend et al., 2004).
5. Conclusion
Landfill operators will be faced with an increasing
amount of CCA-treated wood requiring disposed in coming
T. Townsend et al. / Journal of Environmental Management 75 (2005) 105–113112
years. Laboratory results indicate that leaching of preserva-
tive chemicals from CCA-treated wood, most notably
arsenic, may be a concern. Weathered CCA-treated wood
will be the major contributor to the amount of CCA-treated
wood being disposed, and the results of this study find that
weathered wood does indeed leach preservative elements at
a similar magnitude as new, unweathered wood using
laboratory leach tests. Many lined landfills send their
leachate to off-site wastewater treatment plants for treat-
ment and disposal, and these facilities often impose
pretreatment standards. Elevated concentrations of elements
such as arsenic could result in extra fees and possibly the
denial of service. Several facilities in Florida are already
having problems with elevated arsenic concentrations
impacting leachate disposal, though the source of the
arsenic has not been conclusively identified. Valuable
follow-up studies would be to assess arsenic, copper and
chromium extraction from CCA-treated wood using actual
landfill leachates and in simulated landfills to assess whether
the elements are truly mobile in the landfill environment.
Acknowledgements
This research was sponsored by the Florida Center for
Solid and Hazardous Waste Management. The authors
thank Koppers, Inc. in Gainesville, FL for their help with the
XRF analysis. The assistance of Ajay Seth was greatly
appreciated. The authors would like to acknowledge two
anonymous reviewers for their valuable feedback on the
content of this paper.
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