Potential arsenic exposures to children associated with in-service … · 2014-05-15 · Potential arsenic exposures to children associated with in-service and recycled CCA-treated

Potential arsenic exposures to children associated with in-service and recycled CCA-treated wood in tropical environments

T. Shibata1, H. M. Solo-Gabriele1, L. E. Fleming1, S. L. Shalat2, Y. Cai3 & T. Townsend4 1University of Miami, Coral Gables, Florida, USA 2Robert Wood Johnson Medical School, Piscataway, NJ, USA 3Florida International Universities, Florida, USA 4University of Florida, Gainesville, Florida, USA

Abstract

CCA-treated wood, which has been a widely used preservative for treating outdoor wood structures, e.g. playsets, has been reported to release arsenic. The objectives of the study were to estimate the potential levels of arsenic exposure to children at CCA-treated wood equipped playgrounds and to evaluate factors that affect the magnitude arsenic releases for pathways which may result in the exposures. Two types of releasable arsenic were evaluated: dislodgeable arsenic released by rubbing the wood and leachable arsenic released by rainfall. Dislodgeable arsenic was tested using synthetic wipes and leachable arsenic was assessed by monitoring outdoor decks and recycled wood mulch. The potential level of arsenic on a child’s hand after individual contact with in-service CCA-treated wood playsets was 2.9 µg/(100 cm2·hand-est) based on the synthetic wipe method. However, such an exposure level can be affected by physical factors such as age of wood, frequency of rubbing, amount of arsenic in the wood, and climate. Arsenic concentration in the surface sand below a CCA-treated deck after 6 and 24 months of arsenic leaching was 4.5 mg/kg and 13.4 mg/kg respectively. Based on these contamination levels, the potential level of arsenic on a child’s hand after contact with sand under the CCA-treated wood structure was computed as 0.05 µg/(100 cm2·hand-est) after 6 months of the installation and increased to 0.15 µg/(100 cm2·hand-est) after 24 month of the installation. Exposure levels from soil can be influenced by soil type and characteristics of the wood structure and rainfall. Overall, this study showed that arsenic releases from CCA-treated playgrounds can be available for potential arsenic exposures to children and the levels are influenced by many environmental factors. In most cases the releases exceeded the risk-based regulatory guidelines. Keywords: arsenic exposure, children, CCA-treated wood, playgrounds, tropical environments.

Environmental Exposure and Health 349

© 2005 WIT Press www.witpress.com, ISSN 1743-3541 (on-line) WIT Transactions on Ecology and the Environment, Vol 85,

1 Introduction

CCA, a chemical preservative containing arsenic, chromium, and copper, has been the most widely used preservative chemical for treating outdoor wood structures, such as playsets, decks, fences, utilities poles, and marine docks in spite of the fact that arsenic and chromium are known to be human carcinogens. Arsenic is more toxic than chromium through oral route of exposures [1–4]. Arsenic has not been mined in the U.S since 1985 and all domestic needs are satisfied by imported arsenic. Approximately from 20,000 to 30,000 metric tons of arsenic have been consumed annually in the U.S since 1985 through 2003 [5]. In those periods, more than 90% of the domestic arsenic has been used for production of CCA [6]. In 2003 domestic manufactures of CCA began a voluntary transition from CCA to alternative wood preservatives in most house hold uses after consultation with U.S. Environmental Protection Agency (U.S. EPA) which resulted in a drop in the estimated domestic consumption to 5,000 tons [7]. As of January 1, 2004, CCA was not allowed to be used for treating wood intended for most residential uses in the U.S. [8]. CCA-treated wood has been phased-down for residential applications. However, many CCA-treated structures currently exist in the U.S. as well as in the world. Recently questions have been raised concerning non-occupational arsenic exposures to individuals, e.g. children who frequently spend some time at CCA-treated wood equipped playgrounds. The potential inhalation of arsenic during play is considered negligible because neither arsenic residue is volatile on the surface of treated wood, or readily available as respirable airborne particulate concentrations under normal conditions [9]. Arsenic can be absorbed through the skin but the level of absorption is comparatively smaller than the amount of arsenic that can be ingested from the oral route. Therefore, the main route of potential arsenic exposures to children at the CCA-treated wood equipped playgrounds is considered to be non-dietary ingestion due to hand-to-mouth behaviors. Significant correlations between the levels of pesticides in the environments, on the hands of young children, especially infants and toddlers, and in urine have been reported [10]. The total urinary arsenic excretion has been reported to be increased in children living in a community with high levels of arsenic in soil compared with a community with low levels in soil [11]. Therefore, it can be hypothesized that children will probably ingest arsenic from playgrounds if arsenic is found on their hands. Earlier studies showed that CCA-treated wood releases arsenic. Arsenic can be removed from CCA-treated wood by touching or rubbing the surface wood with bare hands or synthetic wipes [12–18]. Amounts of arsenic collected on synthetic wipes at playgrounds have been reported as 37.9 µg (per wipe device area) in Washington DC [14], 2.5 µg/cm2 (wood surface area) in Pennsylvania and 1.8 µg/cm2 in Florida, USA [17]. A significant portion of the CCA chemicals could be leached into the environment during the service life of the treated wood products when exposed to rainfall and low pH solutions [19, 20]. A field test in Queensland Australia showed that 4.4% of arsenic was depleted during 300 days monitoring [21]. Consequently, the surface soil below CCA-

350 Environmental Exposure and Health


treated wood structures can become contaminated with arsenic [22, 23, 18]. For example, an average of 76 mg/kg (3 ~ 305 mg/kg) of arsenic in soil was observed in Connecticut [22] and 28.5 mg/kg (1 ~ 217 mg/kg) in Florida USA [23]. Mulch is often applied at playgrounds, parks, and gardens. It can be made from leaves, straw, peat, or wood including recycled construction and demolition (C&D) wood. Wood waste at recycling facilities has been documented to contain up to 30% CCA-treated wood [24]. Such recycled mulch has been found at public playgrounds [25]. Synthetic precipitation leaching procedure (SPLP) showed that concentrations of arsenic released from C&D wood debris ranged from below detection limits of 10 µg/L to 558 µg/L [24]. Therefore, these three, CCA-treated structures, soil under the CCA-treated wood, and mulch containing CCA-treated wood, can be potential sources of arsenic exposure to children at playgrounds. However, studies focusing on these three sources have not been integrated for evaluation of potential arsenic exposure to children until now. The objectives of the study were to estimate the potential levels of arsenic exposure to children at CCA-treated wood equipped playgrounds based on environmental assessments and to evaluate factors that affect the magnitude of such arsenic releases for pathways which may result in the exposures.

2 Materials and methods

The study involved the collection of two different types of arsenic releases from CCA-treated wood;1) arsenic removed by touching or rubbing the surface of CCA-treated wood, named “dislodgeable arsenic” and 2) arsenic released into environment by rainfall resulting in soil and runoff contamination, named “leachable arsenic”. Collected samples were used to estimate the potential arsenic exposures to children after contact with such arsenic releases and to characterize the dislodgeable and leachable arsenic that influence the potential exposure levels. All samples were analyzed for total arsenic at the environmental engineering laboratory, University of Miami.

2.1 Collection and evaluation of dislodgeable arsenic

Synthetic wipes were used to collect dislodgeable arsenic. The purposes of dislodgeable arsenic collection using the wipe method was to obtain information on how much children may collect arsenic on their hands from directly contacting the surface of CCA-treated wood without using actual hands. The potential arsenic exposures to children due to contact with in-service CCA-treated wood structures and environmental factors that influence dislodgeable arsenic were evaluated.

2.1.1 Collection of dislodgeable arsenic Collection of synthetic wipes followed the standard procedure developed by the U.S. Consumer Product and Safety Commission (U.S. CPSC) [14]. Wipes were collected from the surface of wood by pulling a 50 cm2 (diameter = 8cm) polyester cloth attached to the bottom of a 1.1 kg weight. The cloth was stroked



10 times over a 400 cm2 (8 x 50 cm) of wood. One stroke corresponds to back and forth. Three different sets of wood boards were used for the dislodgeable arsenic study. Wipe samples were collected from three different sets of wood boards. These sets included a set that consisted of CCA-treated wood structures throughout Miami-Dade County, Florida, e.g. playsets, benches, and another set consisting of preselected boards from weathered constructed decks (i.e. untreated and the 3.5 kg/m3 confirmed CCA-treated deck). The last set was kept inside the laboratory (untreated, 4 kg/m3 and 40 kg/m3 as indicated upon purchase of the wood (Table 1).

Table 1: Descriptions of sample wood for synthetic wiping study.

Type Retention (kg/m3)

Sample size

Evaluation

ID

Pres

erva

tive,

co

nditi

on

Rat

ed

Mea

sure

d

# of

boa

rds

# of

wip

e se

quen

ces

Tota

l w

ipes

(n)

Age

of w

ood

Usa

ge/ru

bbin

g

Ret

entio

n

Clim

ate

PA ~ PJ

CCA, playground

4.0 ~6.4 -- 100 1 100

D0 None, weathered 0.0 0.0 1 4 4

DA ~ DC

CCA, weathered 4.0 3.5 3 3 x 4 36

L0 None, new lab-kept 0.0 0.0 1 3 3

LA4 ~ LF4 6 3 18

LG4 ~ LL4 6 1 6

LM4~ LP4

CCA, new lab-kept 4.0 3.8

4 10 40

LA40~ LF40 6 1 6

LG40~ LJ40

CCA, new lab-kept 40 39

4 10 40

2.1.2 Evaluation of dislodgeable arsenic All collected dislodgeable arsenic using the synthetic wipe device was converted to the estimated arsenic on a human hand based on the equation [1] [26].

)(2 CFDAsDAs deviceesthand ×=− (1)



where DAshand-est is the estimated amount of dislodgeable arsenic on a human hand as a result of contacting with CCA-treated wood (µg/(100 cm2·hand-est)), DAsdevice is the amount of dislodgeable arsenic collected on the wipe using the device (µg/(50 cm2·device)), CF is the conversion factor (hand-est/device) for the dada from the synthetic wipe value to human hand, 2 is normalizing the hand surface area to 100 cm2. For this study the CF of 0.07 was used for this calculation because dry wipes were used. A more detailed explanation of the data used to develop the value of CF is provided by Shibata et al. 2005 [26]. Wipes collected from the in-service playgrounds (PA ~ PJ) were particularly used to estimate potential exposure levels. All collected wipes were used to evaluate factors which affect the levels of dislodgeable arsenic (Table 1). These factors included 1) CCA retentions, 2) age of wood, 3) frequency of usage or rubbing, and 4) climate. The effects of climate on dislodgeable arsenic were evaluated using wipes collected from playgrounds (PA ~ PJ), a region characterized by an average annual rainfall of 1,487 mm [21]. Data from other locations (including Washington DC [14], Pittsburgh Pennsylvania [17], and Gainesville Florida [17]) were compiled from the literature. It should be noted that these wipe data modified based upon a normalization factor [26] in order to be comparable since their original units were different. Dislodgeable arsenic data along with annual rainfall data [27] are summarized in the Table 2.

Table 2: Rainfall and levels of estimated dislodgeable arsenic on hands in different locations.

Playground Location

Arsenic on hand [µg/(100 cm2·hand-

est)]

Average annual rainfall (mm)

Study

Washington, DC 5.3 (± 2.0) 1,031 U.S. CPSC 2003 Pittsburgh, PA 4.9 (± 3.1) 961 ACC 2003 Gainesville, FL 3.6 (± 2.5) 1,228 ACC 2003

2.2 Collection and evaluation of leachable arsenic

Soil under a weathered CCA-treated wood deck was used to assess the levels of arsenic released during in-service use. The potential levels of arsenic on a child’s hand after contacting soil contaminated with leachable arsenic were estimated based on the soil data. It was important to evaluate leachable arsenic because of its impacts on contamination levels. For this evaluation leachate was collected from two types of CCA-treated wood. One type of leachate was runoff rainfall water from wood boards, called “runoff leachate” and the other was from demolished wood (mulch) type, called “mulch leachate”.

2.2.1 Collection of leachable arsenic Two different monitoring stations were constructed in Miami-Dade County, Florida to evaluate leachable arsenic. One station consisted of a weathered deck from which soil samples found under the deck and runoff leachate samples were collected [18]. The second station consisted of mulch located within an



observation box, from which mulch leachate could be collected [25]. Two decks (with a 3 m2 top surface area standing upon four legs on a 6 m2 surface area of soil base) were installed. The top surface boards of one deck was constructed with 4 kg/m3 rated retention of CCA-treated wood and the top surface boards of the other deck was constructed with untreated wood as a control. The soil was from local rock mining activities in Miami-Dade County, Florida which is formed during the excavation of the local limerock. The total bulk volume of soil below each deck was 4.2 m3 soil (soil particle density of 2,690 kg/m3), resulting in a depth of 0.7 m of soil. Soil samples below the decks were collected using a 28.6 mm diameter unslotted stainless probe fitted with a pre-acid washed plastic liner (Forestry Supplier, Inc., Jackson, MS, USA). Soil samples were collected after 6, 13, 18 and 24 months from the installation date of the decks. The collected sand samples were divided into 2.5 cm depth intervals, and kept in a Ziploc bags until analysis. A rainfall gauge and a leachate collection system were installed at each deck. The leachate collection system consisted of a gutter that drained the lowermost board from each deck. The gutter was covered with a polyethylene liner to prevent rainfall from entering the gutter. Water from the gutter was collected in a plastic reservoir located below each deck. The rainfall and runoff leachate samples from each deck were collected in 120 ml plastic bottles everyday for the first month and twice a week for 13 months, and then once a week for the last eight months. The CCA-treated and untreated decks had been monitored for a 21 month period since September 14, 2002 through June 9, 2004 for a total of 641 days. Six different mulch samples were prepared for collection of mulch leachate from mulch made from recycled C&D wood. Recycled C&D wood was collected at a wood recycling center located in Miami-Dade County, Florida to make handmade mulch. Mulch samples included three types: a) untreated wood mulch (referenced as “000”), b) a combination of 5% treated wood mulch with 95% untreated wood mulch (referenced as “005”), and c) 100% treated wood mulch (referenced as “100”). All types were duplicated. Each mulch sample (000, 005, and 100), originally weighed at 800g, was then placed in the observation box. Each observation box consisted of the following materials : a) top reservoir consisting of a 7 L plastic container (23.5 x 34 cm top opening area), which held 5 cm layer of mulch sample and which had an opening at the bottom for leachate to pass to the bottom reservoir, b) a bottom reservoir consisting of 65 L plastic container; an opening was cut in the lid to allow leachate to collect at the bottom, c) three layers of geotextile (Mirafi 1160N, Pendergrass, GA) with a nominal opening of 0.150 mm wrapped around the top reservoir; this geotextile, which is used in the construction of septic tank drain fields, was assumed to simulate the physical straining associated with a soil layer which would underlie mulch in the field and, d) a plastic net which was placed in the opening between the top and bottom reservoir to provide support for the geotextile. Rainfall data was obtained from the rain gauge connected to the untreated wood deck. Mulch leachate samples were collected after each storm event after 10 storms and then once a week until the end of the monitoring



period. The mulch observation boxes had been monitored from January 11, 2004 through January 20, 2005 for a year.

2.2.2 Evaluation of leachable arsenic The levels of potential arsenic exposure to a child when in contact with soils under the CCA-treated wood structures at playgrounds were evaluated based on the levels of arsenic measured in the soil with time. Collected soil data was used to calculate the estimated arsenic on a human hand based on the equation [2].

)(10 3 HSSAsLAs soilesthand ××= −− (2)

Where LAshand-est is the amount of arsenic (leachable arsenic) on a hand as a result of contact with contaminated soil (µg/(100 cm2·hand-est)), SS is the soil-skin adherence factor (mg/cm2); soil adherence to surface of the skin is a required parameter for calculating dermal dose when the exposure scenario involves dermal contact with a chemical in soil [28], H is the normalized hand surface area (100 cm2·hand-est), Assoil is the arsenic concentration in soil (mg/kg = ng/mg), 10-3 is the conversion factor from ng to µg. For SS, the wide ranges SS values, such as 0.2 ~ 2.2 mg/cm2, were reported [29]. In this study, SS of 0.11 mg/kg, which is a geometric mean with lognormal distribution calculated [30] based on established data [31, 32]. Collected soil, runoff leachate, and mulch leachate were used to evaluate factors that affect the levels of leachable arsenic. These factors included 1) soil, 2) CCA retentions, 3) wood shapes and 4) climate,. For the evaluation of CCA retentions, sawdust samples from boards of the deck were collected in order to identify the initial arsenic mass in the decks. For the initial arsenic mass in the mulch, untreated wood mulch and treated wood mulch were ashed for the analysis.

2.3 Analyses of arsenic

Sample matrices analyzed in this study included polyester wipe for the evaluation of dislodgeable arsenic and water (rainfall and leachate from the decks and mulch), sawdust, ash, and soil for the evaluation of leachable arsenic. All samples were prepared differently prior to the analyses. Wipe samples were processed with a diluted acid extraction method based upon the use of a 10% solution of HNO3 heated to 60 oC [14]. Rainfall, runoff leachate, and mulch leachate were measured for pH (525A, Orion Research Inc., Beverly, MA, USA) immediately after sample collection and acidified by adding 1 ml of 1:1 nitric acid (HNO3) and stored in a refrigerator until sample analysis. Additionally, mulch leachate was digested (U.S. EPA Method 7060A [33]) using HNO3 and hydrogen peroxide (H2O2). Sawdust and soil samples were digested in hydrogen peroxide and hot acid according to U.S. EPA Method 3050B [34]. All prepared samples were then analyzed for total arsenic using an atomic absorption spectrometer (AA) (Perkin Elmer Model AA800, Wellesley, MA, USA). Graphite furnace atomization (GFAA) method was used for analyses of wipe, rainfall, runoff leachate, and mulch leachate. Flame atomization (FLAA) was use for analysis of sawdust samples. Each sub-sample was analyzed in duplicate with GFAA and triplicate with FLAA analyses. All data analyses including



graphical and statistical analyses e.g. mean, standard deviation, correlation, t-tests, and regression analysis were computed using Microsoft Excel 2003.

3 Results and discussion

The potential exposures to children after contact with dislodgeable arsenic and contaminated soil are separately discussed in the section; 3.1 dislodgeable arsenic exposures and 3.2 leachable arsenic exposures.

3.1 Dislodgeable arsenic exposures

The amounts of dislodgeable arsenic ranged from 0.2 to 131 µg per wipes with an average of 21 (± 27) µg/wipe at the playgrounds (PA ~ PJ). Based on the results using equation [1], the level of potential arsenic on a child’s hand at CCA-treated wood equipped playgrounds was estimated to range from less than 0.1 to 18 µg/(100 cm2·hand-est) with an average of 2.9 (± 3.8) µg/(100 cm2·hand-est). This value was similar to other studies which documented 5.3 µg/(100 cm2·hand-est) [14] and 4.9 and 3.6 µg/(100 cm2·hand-est) [17] values (Table 2). The current study supports earlier studies that showed that dislodgeable arsenic was available for potential arsenic exposures to children at CCA-treated wood equipped playgrounds. Although the potential exposure levels were estimated, it is important to recognize that environmental factors will affect exposure levels. The characteristics of dislodgeable arsenic that affect the potential exposure levels are discussed in the following section.

3.1.1 Effects of CCA retentions The levels of dislodgeable arsenic were less than detection limit of 0.1 µg/(100 cm2·hand-est) from untreated wood (L0 and D0). The average levels of dislodgeable arsenic from treated wood; 4 kg/m3 (LG4 ~ LL4) and 40 kg/m3 (LA40 ~ LF40), were 11 (± 4.3) and 195 (± 123) µg /(100 cm2·hand-est) respectively and these values were significantly different (p < 0.001). The levels of dislodgeable arsenic were 20 times different although the difference in the measured retention between two sets of boards was 10 times. Outdoor structures above ground and in ground contact, such as playsets and decks, are in general treated at retention levels between 4 to 6.4 kg/m3 of CCA preservative and the retention level of wood used for marine submersion applications, e.g. pilings for a marine dock, is 40 kg/m3. The study showed that the levels of CCA residues are greatly influenced by the CCA retention levels. For that reason, children may be exposed to significantly larger levels of arsenic when they come in contact with CCA-treated wood of higher retention levels.

3.1.2 Effects of age of the wood The average amount of dislodgeable arsenic from three consecutive wipes on three weathered boards (DA ~ DC), which had been exposed to outdoor for 6, 12, 18, and 24 months, were 7.2 (± 6.1), 5.7 (± 3.6), 6.0 (± 3.1), and 8.7 (± 5.2) µg/(100 cm2·hand-est) respectively with no significant decrease in dislodgeable levels for short periods (Figure 1). The levels of dislodgeable arsenic collected



from the playgrounds (PA ~ PJ) were not correlated with age of the playgrounds (3 ~15 years old). Re-organized data from new lab-kept wood (LG4 ~ LP4), weathered wood (DA ~ DC), and playgrounds (PA ~ PJ) in order of the age of the wood (Figure 2) showed that the levels of dislodgeable arsenic decreased as they were weathered for long periods (r = -0.686). The study showed that children may be exposed to larger levels of arsenic on new CCA-treated playgrounds. The differences in exposure may not be relevant over the short-term (a few months) but may be significant over the course of many years.

0

2

4

6

8

10

12

14

16

6 months 12 months 18 months 24 monthsWeathering time

Ars

enic

[ug/

(100

cm2.

hand

-est

)] Standard deviations

0

2

4

6

8

10

12

14

16

0 5 10 15 20Age of playgrounds (Years)

Ars

enic

[ug/

(100

cm2.

hand

-est

)] new lab-kept woodweathered woodin-service playsets

Figure 1: Dislodgeable arsenic after two years of outdoor exposure for CCA-treated wood coupons.

Figure 2: Dislodgeable arsenic versus age of CCA-treated wood.

1

10

100

1,000

10,000

1 2 3 4 5 6 7 8 9 10# of Repetitive wiping (10 strokes/wipes)

Ars

enic

[ug/

(100

cm

2.ha

nd-e

st)] Standard deviation

40 kg/m3

4 kg/m3

0

5

10

15

20

25

6 months 12 months 18 months 24 monthsWeathering time

Ars

enic

[ug/

(100

cm

2.ha

nd-e

st)] 1st set wipes

2nd set wipes3rd set wipes

Standerd deviations

Figure 3: Dislodgeable arsenic from new laboratory kept wood after repetitive wiping.

Figure 4: Dislodgeable arsenic from a weathered CCA-treated deck.

3.1.3 Effects of frequency of usage or rubbing The dislodgeable arsenic from new lab-kept wood; 4 kg/m3 (LL4 ~ LP4) and 40 kg/m3 (LG40 ~ LJ40), decreased significantly (p = 0.003 and 0.033) from the first set of wipes 11 (± 4.7) and 239 (± 196) µg/(100 cm2·hand-est) to 1.1 (± 0.1) and 19 (± 8.2) µg/(100 cm2·hand-est) by the 10th set of wipes (Figure 3). Wipe data collected from the weathered deck (DA ~ DC) also showed that the levels of dislodgeable arsenic decreased notably with increasing numbers of repetitive



wipes (Figure 4). The study showed that the amount of dislodgeable arsenic decreases as the same surface area on CCA-treated wood is repeatedly rubbed. In other words, the surface areas of CCA-treated playsets frequently contacted by persons could have a smaller amount of dislodgeable arsenic temporarily. Thus, the levels of arsenic exposure to children may vary depend on the popularity, or frequency of usage of the playground.

3.1.4 Effects of climate The average levels of dislodgeable arsenic from in-service playgrounds in the regions were well correlated (R2 = 0.93) with the average annual precipitation in the same regions. The levels of dislodgeable arsenic decrease as the amount of precipitation increases (Figure 5). Perhaps rainfall washes more available dislodgeable arsenic on the wood surface resulting in a smaller buildup of dislodgeable arsenic in regions which have larger rainfall. This effect needs to be future studied. The study showed that children in the tropical environments, e.g. Miami-Dade County, Florida in which there is larger annual rainfall, may be exposed to less dislodgeable arsenic.

Figure 5: The levels of dislodgeable arsenic and average annual precipitation.

3.2 Leachable arsenic exposures

Arsenic concentrations in the soils collected below the CCA-treated deck were highest within the upper 2.5 cm of soil with values of 4.5 mg/kg, 11.5 mg/kg, 12.2 mg/kg, and 13.4 mg/kg after 6, 13, 18 and 24 months, respectively. The arsenic concentrations observed in the surface soils were comparatively smaller than data from earlier studies, which showed an average of 76 mg/kg (3 to 305 mg/kg) in Connecticut [22] and 28.5 mg/kg on average (1 to 217 mg/kg) in Florida [23). The arsenic level in the surface soil under the CCA-treated deck has already exceeded risk-based direct exposure standards of the U.S. EPA soil screening level (SSL) of 0.4 mg/kg [35] and Florida Soil Cleanup Target Levels (SCTLs) of 0.8 mg/kg for residential areas and 3.7 mg/kg for industrial areas [36] after 6 months of the installation. Based on the arsenic levels in the soil using equation [2] the potential levels of arsenic on a child’s hand by touch with soil were less than 0.01 µg/(100 cm2·hand-est) under the non CCA-treated wood deck but with soil under the 6 month old CCA-treated deck was 0.05 µg/(100 cm2·hand-est) and increased to 0.15 µg /(100 cm2·hand-est) for the 24

y = 15.54e-0.0011x

R2 = 0.9259

0

1

2

3

4

5

6

800 1,000 1,200 1,400 1,600Average annual rainfall (mm)

Ars

enic

[ug/

(100

cm2.ha

nd-e

st)]

Pittsburgh, PA

Washington, DC

Gainesville, FL

Miami-Dade, FL



month old deck. The study supported earlier work that showed that soils below CCA-treated decks frequently exceeded guideline levels. Although the potential exposure levels were estimated, it is important that environmental factors can impact exposure.

3.2.1 Effect of soil Total masses of arsenic introduced into the soil increased with time resulting higher concentrations in the soil. In this study, about 50% of arsenic leached from the CCA-treated deck was captured in the surface soil (0 ~ 2.5 cm depth) but still arsenic was observed below surface (Figure 6). Soil used for this study was sandy. It should be noted that the sorption capacity of soil for arsenic was reported to be different in soil types and ranges widely, e.g. 1 to 7.9 mg/kg for fine sand; ~ 28.9 mg/kg for residual soil; ~ 80 mg/kg for brown, clayey sand; 252 mg/kg for silty fine sand with little clay [37]. In the case that the soil under the CCA-treated wood structure has larger sorption capacity for arsenic, larger amount of arsenic leached into the soil can be captured in the surface. The study suggested that children may be exposed to arsenic at higher levels if the soil has a higher sorption capacity for arsenic.

Figure 6: Arsenic concentrations in the soil under the CCA-treated deck.

3.2.2 Effect of CCA retentions The concentrations of arsenic in rainfall were consistently less than detection limit of 1 µg/L during the entire monitoring period. In the runoff leachate from the untreated deck the concentration arsenic was consistently below 1 µg/L. For the mulch leachate (000), the arsenic concentrations were consistently below the detection limit of 3 µg/L except for the beginning of the monitoring that detected small concentrations (3 ~ 13 µg/L) because the sorted untreated wood contained small amount of arsenic, 1 mg/kg, initially. The average arsenic concentration in the runoff leachate from the CCA-treated deck during one year was 1,000 µg/L. The average arsenic concentrations in the mulch leachate were 341 µg/L and 4,940 µg/L from the mulch (005 and 100) during one year monitoring. The arsenic levels were significantly correlated with the amount of arsenic in the mulch (005 and 100) (95% confidence, r = 0.864 ~ 0.962). These results showed that higher CCA retentions release higher concentrations of leachable arsenic. The measured retention of the CCA-treated wood deck used in this study (3.5 kg/m3) was comparatively smaller than the common retention levels

0.00 5.00 10.00 15.00

Cumulative arsenic in soil (mg/kg)

Surface ~ 2.5

5.0 ~ 7.5

10.0 ~ 12.5

15.0 ~ 17.5

20.0 ~ 22.5

Dep

th (c

m) after 6 months

after 13 monthsafter 18 monthsafter 24 months



(4 ~ 6.4 kg/m3) of playsets. Therefore, the estimated potential levels of arsenic previously mentioned might underestimate the true value. The arsenic levels in leachate from the CCA-treated deck and the wood mulch (005 and 100) were significantly higher than the U.S. EPA drinking water standards [38] which includes a Maximum Contaminant Level Goal (MCLG) of 0 mg/L and the Maximum Contaminant Level (MCL) of 0.050 mg/L (0.010 mg/L as of January 23, 2006) [39] and the Florida Criteria for Surface Water Quality Classifications [40], which includes a maximum permissible concentration of 0.050 mg/L for all water classes (I to V). It should be noted that leachates from the wood is not considered to impact children directly. The study showed that high retention of CCA-treated wood structures can impact soils more than lower retentions and as a result, increase the potential levels of arsenic exposures to children through contact with contaminated soil.

3.2.3 Effect of wood shapes The CCA-treated deck released 10% of the initial mass of arsenic into the soil under the deck during 21 months of monitoring. This translates to a leaching rate of 7% per year. The measured rate in the current study was similar to the rates (4% per 300 days) as measured in Brisbane, Queensland, Australia [21]. The treated wood mulch sample (005 and 100) released 13 ~ 22% of the initial mass of arsenic during one year. These rates were about twice and three times faster than the CCA-treated deck. These differences in the arsenic levels were believed to be due to the difference in the surface areas of the wood. The surface area of the mulch was comparatively larger than a board, which was used for the top deck surface. Apparently even though the same amount of rainfall fell on the deck and the mulch, rainfall extracted more arsenic from the mulch than the deck. Consequently soil can be more rapidly contaminated with arsenic by placing CCA-contaminated mulch on the ground compared with the CCA-deck. The study showed that the levels of leachable arsenic, which were introduced into the soil, increases if the CCA-treated wood structure has larger surface areas and thus serve as a more rapid source of soil contamination.

3.3 Effect of climate

Almost the same patterns of arsenic concentrations in the mulch leachate (005 and 100) were observed (Figure 7). Multiple regression analysis suggested that pH values of rainfall and time since the monitoring had begun controlled these changes in leachable arsenic concentrations. For example, arsenic concentrations may decrease gradually with time as it was also seen in the runoff leachate (Figure 8) while lower pH of rainfall could release higher concentrations of arsenic in the leachate. Although the concentration may decrease with time, the total mass of arsenic leached increased with time because of cumulative effects. It should be note that the observed soil had been receiving runoff (1,595 mm of rainfall) from the CCA-treated deck for less than 2 years and age of studied playgrounds (PA ~ PJ) were 3 ~ 15 years old. These playground soils, which must had received larger amount of arsenic than the monitored soil under the deck, are assumed to have higher soil arsenic



concentration levels. Thus, estimated exposure levels based on the short term observed soil may not represent older playground soil. The study showed that children may be exposed to higher levels of arsenic through touching contaminated soil if the playground is old; there is large rainfall in the location, e.g. tropical environment; and the pH of rainfall is low, e.g. acid rain.

10

100

1,000

10,000

100,000

1/11

/04

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/04

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/04

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/04

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/04

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/05

Date (month/day/year)

Ars

enic

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L)

Mulch 005

Mulch 100

-500

1,0001,5002,0002,5003,0003,5004,0004,5005,000

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Date (month/day/year)A

rsen

ic (u

g/L)

CCA-treated deck

Figure 7: Average leachable arsenic (µg/L) from the mulch (005 and 100).

Figure 8: Leachable arsenic (µg/L) from the CCA-treated wood deck.

4 Conclusions

The study concludes that children at CCA-treated wood equipped playgrounds will probably collect arsenic while playing. The levels of potential arsenic exposure are dependent on a number of environmental factors, such as CCA retentions, the way of usage, age, surface area of playgrounds, soil, and climate, which influence the levels of dislodgeable and leachable arsenic from CCA-treated wood. Larger amounts of both dislodgeable and leachable arsenic are available from structures with higher CCA retentions. The levels of dislodgeable arsenic may be more available at newer playgrounds than old while the levels of soil contamination resulted from leachable arsenic will be larger at older playgrounds. Likewise, the levels of dislodgeable arsenic may be less available in tropical environments than other locations, in which there is less rainfall, while the levels of soil contamination resulting from leachable arsenic may be larger in tropical environments than other locations. The average daily dose (ADD) for arsenic, which is used for risk analysis on non-carcinogen effects, can be roughly estimated using data collected in this study and children’s data. In this study human factors that affect the levels of potential arsenic exposures were not studied. Tropical environments may influence these human factors, such as duration and frequency of playing and moisture levels on hands. Hot temperatures and frequent rainfall may reduce exposure time. On the other hand, hot and humid weather may cause sweaty hands that are capable of removing more arsenic than dry hands [41]. It should be emphasized that there is no safe dose or threshold for arsenic because it is a human carcinogen while the estimation of ADD is important for the risk analysis on non-carcinogen effects.



To date, the U.S. EPA had not yet recommended that consumers should replace or remove existing CCA-treated wood structures, although an interim report has been released concerning the potential use of coatings that can be applied to existing structures to minimize exposures [42]. Contaminated soil and mulch should be covered with new soil or another buffer material as a temporary solution. In the long term, it is suggested that no new CCA-treated wood be used for residential purposes internationally and contaminated soil as well as mulch be removed from residential areas. For recycled wood mulch, it is proposed for the producers to separate CCA-treated wood from C&D wood waste at wood recycling centers prior to the production of mulch made from C&D wood. Finally, it is very important to share scientific information as well as engineering solutions between public, industries, and governments nationally and internationally for safer environments for children.

Acknowledgements

Funding for this project was received from the National Institute of Environmental Health Sciences (NIEHS-P30 ES05022 and NIEHS-P30 ES05705), Florida Center for Solid and Hazardous Waste Management (FCSHWM), Institute of Hazardous Material Management (IHMM). The research team gratefully acknowledges Gary Jacobi, Tara Fishbain, Caitlin Feikle, Geoff Klug, Colleen Block, Yuki Sotome, Alicia Muniz, and Brajesh Dubey for their assistance.

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