Chromated copper arsenate (CCA) has been
widely used for > 60 years as a wood preservative
to extend the lifetime of wood as a building
material (Bull 2001; Nico et al. 2004). The
wood is treated by impregnation with CCA
under high pressure, resulting in deposition
of copper, chromium, and arsenic oxides in
the wood (Lebow et al. 2003). The most common
formulation of CCA in North America is CCA-C,
consisting of 18.5% copper oxide, 47.5% chromium
oxide, and 34% arsenic oxide (Hingston et
al. 2001). In both Canada and the United
States, manufacturers of wood-treatment chemicals
voluntarily agreed to cease use of CCA on
lumber for nonindustrial purposes as of December
31, 2003 [Health Canada Pest Management Regulatory
Agency (HCPMR) 2002; U.S. Environmental Protection
Agency (EPA) 2002a). However, many residential
structures built from CCA are still in place,
including playground equipment and decks.
In the United States, 14% of public playgrounds
contain CCA-treated wood (U.S. EPA 2004).
In Edmonton, Alberta, Canada, as of August
2003, 222 of 316 public playgrounds owned
and operated by the city contained CCA-treated
wood.
Because of the toxicity of Cr(III) and
inorganic As species [Agency for Toxic Substances
and Disease Registry (ATSDR) 2000; National
Research Council 1999], children’s
exposure to Cr or As from CCA-treated playground
structures and decks is of potential health
concern (Hemond and Solo-Gabrielle 2004).
CCA component leaching increases with weathering
of treated wood (Lebow et al. 2003, 2004a).
Many studies have determined As and Cr in
soil and sand, often with a primary objective
of understanding the leaching of As and/or
Cr into sand and soil (Balasoiu et al. 2001;
Cooper et al. 2001; Hingston et al. 2001
for review; Lebow et al. 2004a; Stilwell
and Gorny 1997; Townsend et al. 2003; Zagury
et al. 2003). Previous analyses of risk and
exposure, therefore, relied on indirect data,
including the concentration of As and/or
Cr in the soil and sand, projections of the
amount of CCA material that ends up on children’s
hands based on average child hand surface
area, adherence factors for soil, and child
behavioral patterns (U.S. EPA 2002b, 2003a,
2003b). No previous study has directly measured
Cr levels on the hands of children after
playing in CCA playgrounds. The purpose of
this study is to fill this gap.
Recently, Kwon et al. (2004) quantified
the amount of As on children’s hands
after playing in playgrounds built from CCA-treated
wood. The procedure involved taking hand-washing
samples of 66 children from eight CCA playgrounds
and 64 children from eight non-CCA playgrounds.
After play, the hands of each child were
rinsed with water and the amount of As in
the rinsate was measured, thus allowing comparison
between CCA and non-CCA playgrounds. Children
from CCA playgrounds had a maximum of approximately
4 µg As on their hands, which is five
times greater, on average, than in non-CCA
playgrounds. To determine Cr on children’s
hands, the samples from the Kwon et al. study
(2004) were re-examined by undergoing an
inductively coupled plasma mass spectrometry
(ICPMS) analysis of 20 elements, including
Cr, As, and Cu. The analysis provided the
first direct measurements of Cr on children’s
hands, eliminating the uncertainties associated
with estimating the levels of Cr on children’s
hands. The data allowed for correlation analyses
of Cr, As, and Cu levels. Principal-component
analysis (PCA) of the multi-element data
from both CCA and non-CCA playgrounds may
provide further information on the characteristic
grouping of As, Cr, and Cu, as well as the
dislodging of these elements from CCA-treated
wood.
Playground selection and sample collection. Playgrounds
were designated as either CCA or non-CCA,
with CCA signifying those either totally
or partially constructed from CCA-treated
wood. A total of 16 playgrounds from the
city of Edmonton--eight CCA and eight
non-CCA--were used in the study and
were chosen to represent the distribution
of site characteristics found across the
city. Both CCA and non-CCA playgrounds were
similar in age, location, and manufacturer.
The study protocol was reviewed and approved
by the University of Alberta Health Research
Ethics Board.
The samples used were the same as those
used in Kwon et al. (2004). Selected sites
were sampled in random order in August 2003.
As children arrived at a playground, parental
permission was obtained in the form of written
consent to allow the children’s participation
in the study. On average, seven to nine children
were sampled at each site. Upon completing
their play, each child provided hand-washing
samples by washing hands for 1 min in Ziploc
bags (18 20
cm; Johnson and Son Ltd., Brantford, ON,
Canada) filled with 150 mL deionized water.
A blank sample of deionized water was also
prepared for each site and except for hand-washing,
subjected to the same procedures, including
transportation, as the other samples. The
age and length of play time of each child
was recorded, and the hand-washing samples
were poured into polystyrene bottles. Each
bag was rinsed with an additional 80 mL water
and combined with the corresponding 150 mL
rinsate, yielding a 230-mL sample from each
child. Samples were then filtered with Whatman
glass microfiber 1.2-µm filters (Whatman
International Ltd., Maidstone, UK). The filtrate
(soluble fraction) and the residual sand
collected on the filters were separately
stored at 4°C until used. For a more
detailed description of playground selection
and sample collection, please consult Kwon
et al. (2004). Samples from 63 children who
played in CCA playgrounds and 64 children
who played in non-CCA playgrounds were available
for this study.
Determination of soluble chromium
and 20 elements in the soluble fraction
of the hand-washing samples. Ten
milliliters of each filtered sample was
acidified to a final concentration of
1% nitric acid (aq). Concentrations
of total Cr were determined in nanograms
per milliliter (parts per billion) for
each sample. Cr concentration was multiplied
by the volume of each sample (230 mL)
to yield the total amount of Cr (nanograms)
on children’s hands.
The samples were analyzed using an ICPMS
(6100DRC Plus; Perkin-Elmer/Sciex, Concord,
Ontario, Canada). A multielement analysis
was carried out for each sample for the following
elements: As, beryllium, barium, bismuth,
cadmium, cobalt, Cr, Cu, iron, gallium, indium,
magnesium, manganese, nickel, lead, rubidium,
selenium, strontium, thallium, vanadium,
and zinc. The liquid was introduced via a
Meinhard nebulizer coupled with a cyclonic
spray chamber. An ASX-500 autosampler (CETAC
Technologies Inc., Omaha, NE, USA) was used.
The RF power was 1.3 kW. Argon gas flow rate
was 15 L/min (plasma gas), 0.8 L/min (nebulizer
gas), and 1.5 L/min (auxiliary gas). Calibration
of the ICPMS was carried out using six Cr
concentrations (0, 5, 10, 15, 20, and 25
ppb) at the beginning of each run, as well
as after every 10 samples with 15 ppb Cr.
National Institute of Standards and Technology
(NIST) Standard Reference Material (SRM)
1640, Trace Elements in Natural Water (NIST,
Gaithersberg, MD, USA), was analyzed once
during each run as a quality control. This
SRM was diluted 2-fold before analysis. The
average measured value of Cr in the SRM was
34.2 ± 4.1 µg/L from the repeat
analyses over 3 days, which is in agreement
with the certified SRM value of 38.6 ± 1.6 µg/L.
Determination of chromium and 20
elements in the insoluble fraction of
hand-washing samples. Because
the hand-washings contained residual
particles from the children’s hands,
the amount of residue collected on the
filters and the concentrations of Cr
in the residue were determined separately
from those in the solutions of the hand-washings.
Hand-washing samples were filtered using
Whatman glass microfiber filters with
1.2-µm pores. The filter was then
dried at 140ºC and weighed, to determine
the exact amount of sand collected on
the children’s hands.
The sand, along with the filter, was digested
with a mixture of concentrated HNO3/perchloric
acid/hydrofluoric acid (1:1:1 volume ratio).
Initially, the mixture was heated to 40-60ºC
for 1 hr, followed by heating at 100ºC
to completely dissolve all solid material.
It was then boiled for 1 hr to evaporate
the acids to almost dryness, then was redissolved
in 1% HNO3 in preparation for
ICPMS analysis as described previously (Kwon
et al. 2004). Total Cr concentrations in
the sand were then determined via a multi-element
analysis using an ELAN 6000 ICPMS (Perkin-Elmer/Sciex).
The same 21 elements were analyzed as for
the hand-washing solutions.
Playground sand/soil samples. Three
composite sand/soil samples were taken from
each playground site on the same day as the
hand-washing samples. Extensive sand/soil
sampling was done in playgrounds G and R
(24 samples collected in each). Sampling
was carried out as previously described (Kwon
et al. 2004).
Determination of arsenic, chromium,
and copper in sand and soil samples. The
levels of As, Cr, and Cu in the samples
were measured by EnviroTest Laboratories
(Edmonton, Alberta, Canada) according
to U.S. EPA SW-846 method 3050B (U.S
EPA 1996). This procedure is summarized
in Kwon et al. (2004), along with the
results of the As analysis.
Statistical analysis. Statistical
analyses were performed using SPSS 12.0 (SPSS
Inc., Chicago, Illinois, USA) and Microsoft
Excel 2003 (Microsoft Corporation, Redmond,
Washington, USA). Data are expressed as mean ± SD.
Metal concentrations below detection limit
(nondetectable) are expressed as half the
detection limit of the metal unless otherwise
specified in the text. The average concentrations
of Cr, Cu, and As in hand-washings of children
from CCA playgrounds were compared with those
of the children from non-CCA playgrounds
via a two-independent-samples t-test.
The difference in Cr levels between male
and female children were also compared via
separate two-independent-sample t-tests
for both CCA and non-CCA playgrounds. A p-value < 0.05
was considered statistically significant.
Correlation analyses were performed for Cr
levels and As levels, as well as for Cr and
Cu levels and for As and Cu levels. PCAs
were performed for all metal levels analyzed
at each playground, using SPSS 12.0. For
each playground, all components with eigenvalues > 1
were extracted. The results of the Kaiser-Meyer-Olkin
measure of sampling for both CCA (0.7) and
non-CCA (0.6) playgrounds were equal to or
above the minimum recommended value of 0.6.
The correlation matrices in both cases were
proven not to be identity matrices by Bartlett’s
test of sphericity (p < 0.001 in
all cases for both CCA and non-CCA playgrounds).
Therefore, the hand-washing concentration
data meet the minimum standards for PCA.
We analyzed 21 components (elements). The
relationships between all the variables (i.e.,
the hand-washing concentrations of all metals
examined via ICPMS) were reduced to seven
components (components 1-7) for both
CCA and non-CCA playgrounds, when nondetectables
are assumed as half the detection limit.
In this case, in both CCA and non-CCA playgrounds,
component 1 accounts for most (30% and 22%)
of the variance seen in the data, whereas
components 2 and 3 account for approximately
12% (CCA) and 13% (non-CCA), and 11% (CCA)
and 10% (non-CCA) of the variance of the
data, respectively. If nondetectable levels
are assumed as zero, then components 6 and
7, explaining 53% and 45% of the variance
of the data, are extracted for CCA and non-CCA
playgrounds, respectively. In this case,
component 1 accounts for 30% (CCA) and 22%
(non-CCA), component 2 for 12% (CCA) and
13% (non-CCA), and component 3 for 11% (CCA)
and 10% of the variance. The PCA was based
on covariance matrices, as all variables
had the same units (parts per billion).
Demographics of the participating
children. Compared with the previous
study on As (Kwon et al. 2004), three
of the samples analyzed previously for
CCA playgrounds were not analyzed this
time because of spillage from their containers.
These samples were for two female children
and one male child, ages 4, 2, and 2.5
years, respectively. Exclusion of the
three samples does not greatly affect
the age distribution of the children
(figure not shown). The average ages
of the participating children were 4.8 ± 2.5
years for the CCA playground (63 children)
and 4.8 ± 2.4 years for the non-CCA
playground (64 children). There was no
significant difference in age between
the two groups (p = 0.98). Thus,
a total of 127 children (63 from CCA
playgrounds and 64 from non-CCA playgrounds)
were accounted for in the hand-washing
analysis. Sixty-nine (54.3%) of the participating
children were boys, and 58 (45.7%) were
girls.
Length of play time. The
mean play time was 76 ± 46 min for
CCA playgrounds and 49 ± 28 min for
non-CCA playgrounds. The difference between
the means is driven by longer play times
(> 120 min) for a few children (n =
8) in the CCA playgrounds. No correlation
was seen between play time and age for children
in CCA (r = 0.27) or non-CCA (r = -0.06)
playgrounds. The play times of the children
whose samples were spilled were 30, 30, and
60 min. These times are not on the high or
low end of the distribution of play time
lengths for CCA playgrounds seen in Kwon
et al. (2004) and affect its shape minimally.
Table
1
|
Table
2
|
Concentration of chromium in the
sand/soil from the playgrounds. Table
1 shows the concentrations of Cr in the
sand/soil samples collected from each
of the 16 playgrounds. Detection limit
was 0.5 mg/kg for Cr and 2.0 mg/kg for
Cu. The mean Cr concentrations are 2.0 ± 0.8
(median, 1.8; range, 0.8-4.6) and
1.3 ± 0.4 (median, 1.3; range,
0.7-2.2) mg/kg for CCA and non-CCA
playgrounds, respectively. The difference
between these concentrations was statistically
significant (
p = 0.003).
The mean concentration of Cu in CCA playgrounds
was 2.7 ± 1.8 mg/kg (median, 2.0;
range, nondetectable to 8.0). In most non-CCA
playgrounds, the concentrations of Cu in
the soil were below the detection limit of
2 mg/kg, resulting in a mean value of Cr
for all non-CCA playgrounds below detection
limit. The difference in Cu concentrations
between the CCA and non-CCA playgrounds was
also statistically significant (p < 0.0005).
Amount of soluble chromium in the
hand-washing samples. Table 2
summarizes the results of analysis of
the hand-washing samples for soluble
Cr, insoluble Cr, and total Cr. To determine
soluble Cr, the hand-washings were filtered
to remove any particulate matter (> 1.2 µm),
including sand. Detection limit was 0.01
ng/mL or 2.3 ng for Cr. The concentration
of soluble Cr (nanograms per milliliter)
is multiplied by the total volume (230
mL) to obtain the number of nanograms
Cr on the child’s hands. The overall
mean value was 759 ± 575 ng (median,
564; range, nondetectable to 4,761) for
CCA playgrounds. For non-CCA playgrounds,
the overall mean value was 304 ± 265
ng (median, 272; range, nondetectable
to 1,035). The difference between the
two means was statistically significant
(p < 0.003).
Amount of chromium in the sand residue
collected in the hand-washing samples. The
amounts of sand collected from the hand-washing
samples, in dry weight, of the sand samples
analyzed were 22.0 ± 19.1 mg (median,
16.4 mg; range, 0.8-95.8 mg) for
CCA playgrounds and 25.2 ± 23.3
mg (median, 16.6; range, 3.7-116.2
mg) for non-CCA playgrounds (p =
0.38). Thus, there was no significant
difference between the mean amounts of
sand on the children’s hands in
CCA and non-CCA playgrounds (Table 2).
The mean values of Cr in the sand washed
from children’s hands were 409 ± 646
ng (median, 228 ng; range, ND-3,144
ng) in CCA playgrounds and 348 ± 509
ng (median, 164 ng; range, 20-3,147
ng) in non-CCA playgrounds. There was
no significant difference between the
two groups in sand Cr levels in hand-washings
(p = 0.56), probably because
of the small amounts of sand collected
on children’s hands from both CCA
and non-CCA playgrounds.
Total amount of chromium in the hand-washings. The
total amount of Cr (the sum of soluble and
insoluble) present in the hand-washing samples
is also summarized in Table 2. The mean values
were 1,112 ± 1,089 ng (median, 688
ng; range, 78-5,875 ng) for CCA playgrounds
and 652 ± 586 ng (median, 492 ng;
range, 61-3,377 ng) for non-CCA playgrounds,
respectively. The difference in mean total
Cr levels was statistically significant between
the two types of playgrounds (p =
0.004), driven mainly by the soluble Cr.
To examine if longer play time (> 120
min) of eight children in the CCA playground
could influence the outcome of the comparison,
the data set was reanalyzed after removing
the data from the eight children who played
in the CCA playground for > 120 min. The
difference in mean total Cr between CCA and
non-CCA playgrounds remained statistically
significant (p = 0.007), even
when measurements from the eight children
with long play times were removed from the
CCA group. Three samples, two CCA and one
non-CCA, were missing in the insoluble Cr
analysis because of spillage. The values
for mean total Cr in CCA and non-CCA playgrounds
do not change if nondetectable Cr levels
are taken as zero.
Correlation of total chromium levels
with age, sex, and length of play time. Figure
1 shows the correlation analysis of total
Cr concentrations in hand-washing samples
with children’s age. It appears
that there is some correlation between
the two variables, as the lines have
positive slopes, although they are weak
correlations for both the CCA (
r =
0.24) and non-CCA (
r = 0.35) playgrounds.
There is weak (if any) correlation between
length of play time and soluble Cr levels
in hand-washings of children after playing
in CCA (
r = 0.31) and non-CCA
(
r =
0.32) playgrounds (Figure 2). The conclusions do not change when nondetectable
Cr levels are taken as zero. There is weak (if any) correlation between children’s
age and levels of Cr (CCA:
r = 0.24; non-CCA:
r = 0.35) or between
length of play time and levels of Cr (CCA:
r = 0.31; non-CCA
r =
0.32) in hand-washing samples.
No statistically significant difference
was found between Cr levels in the hand-washings
of male and female children, for CCA or non-CCA
playgrounds, regardless of whether nondetectable
levels of Cr were assumed to be half the
detection limit (CCA: p = 0.45; non-CCA: p =
0.06) or zero (CCA: p = 0.45; non-CCA: p =
0.23).
Correlation analysis of soluble chromium,
copper, and arsenic levels in hand-washing
samples. To better understand
the relationship between Cr, Cu, and
As levels on the hands of children after
contacting CCA-treated wood, we performed
correlation analyses between soluble
Cr and Cu, Cr and As, and Cu and As levels
in the handwash samples.
Figure 3 shows a strong correlation (r =
0.736) between Cr and As levels in samples
collected from children playing in CCA playgrounds
and a weak correlation in samples from non-CCA
children (r = 0.486). Similarly, a
strong correlation (r = 0.782) between
As and Cu levels in hand-washings can be
seen for CCA playgrounds. However, there
is an outlying Cu value (84.2 µg) for
CCA playgrounds. Removal of this outlier
reduces the strength of this correlation
(r = 0.685) slightly (Figure 4). The
correlation is weaker for non-CCA playgrounds
(r = 0.503) (Figure 4).
A strong correlation (r = 0.801)
is also seen between Cr and Cu levels in
hand-washing samples from CCA playgrounds.
Removal of the outlying Cu value (84.2 µg)
slightly reduces the correlation (r =
0.672). The correlation between Cr and Cu
levels in non-CCA samples is much weaker
(r = 0.252) (Figure 5).
PCAs on soluble copper, chromium,
and arsenic levels. The
relationships between the various concentrations
of metals and the first three components
are summarized as rotated component loadings
(data not shown), which are basically
correlations between the variables and
the factor patterns (Rummel 1970). A
component loading close to an absolute
value of one signifies that a variable
is highly correlated to a factor pattern,
whereas an absolute value close to zero
indicates that a variable is not involved
in a factor pattern. These loadings are
plotted in 3-dimensional rotated space
to visualize the metal patterns in CCA
and non-CCA hand-washings (figures not
shown).
The pattern of metal concentrations is
similar between playgrounds. In both cases,
there is a main cluster of metals to the
right of the component plots, with magnesium,
barium, bismuth, thallium, and indium removed
from this cluster. As, Cr, and Cu are all
in the main cluster. However, they are closer
to each other in CCA playgrounds than in
non-CCA playgrounds.
None of the metals had consistently high
(≥ 0.5)
component 2 or 3 loadings except for beryllium,
bismuth, indium, thallium, and barium. However,
rotated component 1 loading of Cr in CCA
playgrounds (0.876) was higher than in non-CCA
playgrounds (0.661). Cu component 1 loadings
were higher and As component 1 loadings were
the same between CCA (As: 0.83; Cu: 0.76)
and non-CCA playgrounds (As: 0.78; Cu: 0.48).
The playground sites sampled were matched
on location and manufacturer for both CCA
and non-CCA playgrounds, and weather conditions
during sampling were similar for both types
of playground. Sampling days were alternated
for both CCA and non-CCA sites. Thus, adequate
controls were in place to ensure that any
difference in the levels of Cr on children’s
hands between CCA and non-CCA playgrounds
could be attributed to the type of playground.
The length of play time and the age of the
children were uncontrolled variables, which
maximized the number of children sampled.
The distribution of these variables was similar
for both CCA and non-CCA playgrounds (Kwon
et al. 2004). There was no correlation between
age and play time for either type of playground.
Statistical tests confirmed that Cr levels
found in the handwash samples were independent
of age (Figure 1) and sex.
The total amount of Cr (Table 2), including
both water-soluble Cr in the washing water
and insoluble Cr in the sand of the handwash
samples, was significantly higher for the
CCA group (1,112 ± 1,089 ng) than
for the non-CCA group (652 ± 586 ng).
This difference was due to the soluble Cr
in the handwash water. A statistically significant
difference was found between the CCA and
non-CCA playgrounds with respect to levels
of soluble Cr in the handwash samples (Table
2). The amount of soluble Cr for the CCA
group (759 ± 575 ng) was significantly
higher than that for the non-CCA group (304 ± 265
ng). This represents an approximately 2-fold
difference between the two types of playgrounds.
Children 2-6 years of age have frequent
hand-to-mouth activity [8-10 contacts
per hour, on average (Reed et al. 1999; Tulve
et al. 2002)]. Therefore, soluble Cr on their
hands could be ingested (Tulve et al. 2002).
The increased levels of Cr found on the
hands of the CCA group of children are thought
to be rubbed off the CCA-wood by direct contact.
A small amount of Cr can be dislodged from
CCA-treated wood (Cooper et al. 2001; Hingston
et al. 2001; Lebow et al. 2003). It is this
dislodgeable Cr that is thought to be transferred
to the hands of children when they touch
the wood. Figure 2 shows no correlation between
play time and total handwash Cr for either
CCA (r = 0.31) or non-CCA playgrounds
(r = 0.32). For play times ≤ 30
min, there is weak or no correlation between
play time and total handwash Cr for CCA (r =
0.51) and non-CCA (r = -0.05)
playgrounds. This suggests that Cr loading
either is saturated at a very early time
point or exists in some type of equilibrium
between loading and unloading. An absence
of correlation was also seen between length
of play time and As loading for both CCA
(r = 0.28) and non-CCA (r =
0.33) playgrounds. The results were similar
for Cu (CCA r = 0.18, non-CCA r = -0.28)
(data not shown).
A maximum amount of 4.8 µg soluble
Cr was found on a child’s hands after
play in a CCA playground (Table 2). If an
estimated body weight of 17.8 kg (for a child
2-6 years of age) is used, the maximum
amount of Cr found is equivalent to 0.3 µg/kg
body weight. If it is assumed that all the
Cr on a child’s hands is ingested,
the measured value is below the maximum estimated
average daily intake of total Cr, approximately
1.5 µg/kg and 0.9 µg/kg, for
Canadian children in the age ranges 0.5-4
and 5-11 years, respectively [Canadian
Environmental Protection Act (CEPA) 1999].
The average daily dietary ingestion of total
Cr in Canada is 13.3-16.9 µg
for children ages 0.5-4 years, 18.9-21.6 µg
for children ages 5-11 years, and 27.3 µg
for adults (CEPA 1999). The average daily
dietary ingestion of total Cr for an adult
is 25-224 µg in the United States
(ATSDR 2000), 100 µg in Spain (Garcia
et al. 2001), 59.9 µg in India, and
224 µg in Japan (Iyengar et al. 2002).
A chronic oral reference dose of 3 µg/kg/day
is given for ingestion of Cr(VI) (U.S EPA
1998). The threshold concentration of Cr(VI)
for skin hypersensitivity is 10 mg/kg body
weight (ATSDR 2000; Bagdon and Hazen 1991).
The 2-fold difference in the amount of
soluble Cr on children’s hands between
CCA and non-CCA playgrounds is not as great
as that previously found for As. The difference
in As amounts between CCA and non-CCA playgrounds
was 5-fold (Kwon et al. 2004). This is consistent
with other studies showing that As is more
readily dislodged from CCA wood than Cr (Fahlstrom
et al. 1967; Henshaw 1979; Hingston et al.
2001).
Cr in CCA wood is present primarily in
insoluble Cr(III) forms complexed to the
wood lignin, cellulose, and carbohydrates
(Hingston et al. 2001; Pizzi 1990a,b). Cr-As
complexes can also bind wood components (Bull
2001; Lebow et al. 2004b). Any soluble Cr
[Cr(VI)] present after wood treatment is
fixed (reduced to the trivalent form) with
time (Bull 2000, 2001; Henshaw 1979; Nico
et al. 2004). At 98.2% Cr fixation, a small
fraction (2 µg/cm2) of total
Cr, Cu, or As is leached (Hingston et al.
2001). However, this fixation process is
slow, and Cr(VI) can remain in CCA wood for
over 6 months (Bull 2001). In addition, Cr(III)
is considered leachable when it undergoes
ligand exchange reactions, thus detaching
from the wood components and precipitating
onto the wood surface, where it is weakly
absorbed (Bull 2000, 2001; Nico et al. 2004).
The exact form in which Cr is leached is
unclear, but it has been suggested to be
leachable by itself as Cr(VI) and in the
form of various Cr arsenates (Pizzi 1990a,
1990b). Results of correlation analyses found
a strong correlation between Cr and As levels
on children’s hands after contacting
CCA wood (r = 0.736; Figure 3). This
correlation is absent in non-CCA playgrounds
(r = 0.486; Figure 3).
The form in which Cu is leached from CCA
wood is unknown, but Cu arsenates and some
form of Cu-Cr-As complexes (Hingston
et al. 2001) have been suggested as possible
leachable species (Lebow et al. 2003). Another
possibility is that Cu leaches independently
of Cr and As as a result of binding different
spaces on the wood (Bull 2000, 2001). A strong
correlation was present between Cu and As
levels in hand-washings from CCA (r =
0.685) but not non-CCA (r = 0.503)
playgrounds (Figure 4). Likewise, a strong
correlation was present between Cu and Cr
in CCA (r = 0.672) but not non-CCA
(r = 0.252) playgrounds (Figure
5). Thus, these results (Figures 3-5)
suggest that Cu, Cr, and As co-leach from
CCA-treated wood, either as dislodgeable
complexes/residues or as separate species.
Further, PCA was carried out to determine
whether there is a characteristic pattern
of Cu, Cr, and As in CCA hand-washings different
from that in non-CCA hand-washings. When
a nondetectable level of a metal is taken
as half of its ICPMS detection limit, seven
components are extracted, accounting for
approximately 70% (non-CCA) and 77% (CCA)
of total data variation. Components 1, 2,
and 3 are used to create rotated component
plots (figures not shown), which summarize
the data in pattern form. The bulk of the
metals, including As, Cu, and Cr, are grouped
in a main cluster and are correlated primarily
to component 1. Beryllium, bismuth, indium,
thallium, barium, and cadmium are grouped
separately from the other metals, with stronger
correlations to components 2 and 3. Their
presence in the hand-washings is probably
not a result of contact with CCA-treated
wood, but of contact with other substances
in the environment. The correlations of As,
Cr, and Cu levels to component 1 are essentially
higher in CCA and non-CCA playgrounds. Thus,
it seems that hand-washing samples from CCA
playgrounds show grouping patterns of CCA
components absent in non-CCA samples.
Kwon et al. (2004) found no significant
difference in the amount of As in sand between
CCA and non-CCA playgrounds. However, this
is not the case for Cr. Analysis of sand/soil
samples from the playgrounds for Cr levels
shows a statistically significant difference
between CCA and non-CCA playgrounds. Previous
studies have shown Cr leaching into soil
adjacent to CCA-treated poles, decks, and
structures (Balasoiu et al. 2001; Chirenje
et al. 2003; Cooper et al. 2001). However,
the increased levels of soluble Cr seen on
the hands of children in the CCA group, as
well as the stronger correlation of Cr levels
with the CCA playground pattern, are likely
due to increased Cr exposure via direct contact
with CCA-treated wood, because insoluble
Cr levels in the hand-washings are not significantly
different between CCA and non-CCA playgrounds.
The concentrations of soil/sand Cr for each
type of playground (CCA: 2.0 ± 0.8
mg/kg; non-CCA: 1.3 ± 0.4 mg/kg) are
above the Canadian guideline level (0.4 mg/kg)
for hexavalent Cr in all land use (residential/parkland)
in Canada [Canadian Council Ministry of the
Environment (CCME) 1995]. However, soil and
sand Cr is predominantly present in the insoluble
Cr(III) form (for which there is no CCME
guideline level (CCME 1995), and thus is
unlikely to enter the hand-washing samples
(U.S. EPA 1998).
Cr is ubiquitous in the natural environment.
The toxicity of Cr varies dramatically, depending
on its speciation. Although Cr(III) in small
amounts is an essential nutrient, Cr(VI)
is highly toxic. Because Cr(VI) is water
soluble, we recommend that children wash
their hands after playing on CCA-treated
wood.
Children have approximately two times more
Cr on their hands after playing in playgrounds
containing CCA-treated wood structures than
non-CCA playgrounds. This increased level
of Cr is probably due to direct contact with
CCA-treated wood and subsequent transfer
of Cr and Cr complexes onto children’s
hands. It could also be due to direct contact
with sand adjacent to surrounding CCA-treated
structures, which is less likely, as most
Cr in soil/sand is insoluble. Soluble Cr
was washed off the children’s hands
with water and into the hand-washing samples.
The maximum amount of Cr found on children’s
hands was 5.9 µg (4.8 µg soluble),
which is much lower than the average daily
intake of total Cr in the Canadian diet (13-27 µg).
Correlation analyses indicate strong associations
between Cr, Cu, and As levels in CCA hand-washings
that are absent in non-CCA hand-washings.
PCA provides further evidence that Cr, As,
and Cu in hand-washing samples from children
who played in CCA playgrounds are grouped.
These results point to the co-leaching of
these three elements from CCA wood.
Correction |
Some of the values in the section “Amount
of chromium in the sand residue collected
in the hand-washing samples” were
incorrect in the original manuscript
published online. They have been corrected
here. |