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Background Lumber treated with chromated copper arsenate (CCA) compounds has been used in residential outdoor wood structures and public playgrounds. The U.S. Environmental Protection Agency (EPA) has conducted a probabilistic assessment of children’s exposure to arsenic using the Stochastic Human Exposure and Dose Simulation model for the wood preservative scenario (SHEDS-Wood). The assessment relied on data derived from an experimental study conducted using adult volunteers and designed to result in maximum hand and wipe loadings to estimate the residue–skin transfer efficiency. Recent analyses of arsenic hand-loading data generated by studies of children actively involved in playing on CCA-treated structures indicate that the transfer efficiency coefficient and hand-loading estimates derived from the experimental study significantly overestimate the amount that occurs during actual play. Objectives Our goal was to assess the feasibility of using child hand-loading data in the SHEDS-Wood model and their impact on exposure estimates. Methods We used data generated by the larger of the studies of children in SHEDS-Wood, instead of the distributions used by U.S. EPA. We compared our estimates of the lifetime average daily dose (LADD) and average daily dose (ADD) with those derived by the U.S. EPA. Results Our analysis indicates that data from observational studies of children can be used in SHEDS-Wood. Our estimates of the mean (and 95th percentile) LADD and ADD were 27% (10%) and 29% (15%) of the estimates derived by U.S. EPA. Conclusion We recommend that the SHEDS-Woods model use data from studies of children actively playing on playsets to more accurately estimate children’s actual exposures to CCA.

Kwon et al. (2004) reported significantly elevated dislodgeable soluble arsenic loads on (one or both?) hands of children following play on structures treated with chromated copper arsenate (CCA) but then concluded that the observed difference is unimportant: With a safe conservative assumption that all the arsenic on children’s hands is ingested, the measured value is below the estimated average daily intake of inorganic arsenic from water and food …. However, Kwon et al.’s analysis is not conservative for at least two reasons. First, it is likely that they substantially underestimated arsenic on hands. Kwon et al. reported, but apparently did not actually measure, total arsenic on hands. They washed hands, filtered the wash water, and measured soluble arsenic in the filtrate. Insoluble residue was measured as dry mass gain on the filters. They then estimated insoluble arsenic on hands as the product of the average arsenic concentration in playground sand samples (not solids recovered from hands) and filter dry weight gain. I did not arrive at this conclusion because the procedures are clearly described in the paper but because a) there is no discussion of extraction of filters and b) the ratios of minimum, mean, median, and maximum “sand arsenic” on hands to minimum, mean, median, and maximum sand mass recovered from hands are nearly constant and equivalent (in all cases but one) to the mean concentration reported for each playground. This procedure could easily give a very poor estimate of insoluble arsenic on hands because unfractionated 0- to 6-in sand samples are likely to be a poor surrogate for adherent particles. The filter residue from the hand-wash water probably contained at least some wood particles with much higher arsenic concentrations and lower densities than the playground sand. Hemond and Solo-Gabriele (2004) reviewed studies in which (typically adult) human hands were used to deliberately wipe CCA-treated lumber and reported much higher arsenic residues on hands than found by Kwon et al. (2004). One obvious potential explanation is that the arsenic concentration in material dislodged from CCA-treated wood (Nico et al. 2004) can easily be 1,000-fold higher than the 2–3 ppm found by Kwon et al. in playground sand. Second, the observed loads that Kwon et al. (2004) reported may be greatly influenced by the very activity they wish to assess. That is, mass recoverable at any given time reflects net accumulation and does not include material already ingested. Consider the following simplified model of mass accumulation on hands: where A = area (in square centimeters), L = load (in milligrams per square centimeter), G = net gain in the absence of ingestion (addition minus losses other than ingestion; in milligrams per hour), and king = a first order rate constant describing ingestion (per hour). At steady state, and Assuming reasonable efficiency of washing, Kwon et al. (2004) provided a measure of the product of the two variables on the left hand side (for soluble arsenic). They have not measured either of the variables on the right hand side. In the absence of knowledge of king, they guessed. Because an infinite number of paired values of G and king can be selected to match the available data, large values of king are not excluded. Hence any reassuring conclusion based on this work is a reflection of the assumed rate at which hand residues are orally harvested and not of the reported measurements. Kwon et al. (2004) further concluded that Most of the arsenic on children’s hands is water soluble and is readily washed off with water. We recommend that children wash their hands after playing to reduce their potential exposure to arsenic. Again, this conclusion is not supported by evidence presented in the article. To evaluate efficiency of washing, some measure of the initial mass present is required. Kwon et al. measured removable soluble arsenic and estimated removable insoluble arsenic. They did not measure or estimate either soluble or insoluble arsenic remaining on the hands. Because insoluble arsenic bound to soil or wood is likely to be at least partially removed mechanically by washing regardless of solubilization, washing is probably a good strategy. However, that argument is merely logical rather than empirical and could have been made in the absence of Kwon et al.’s experiments. Kwon et al. (2004) stated that the purpose of their study was to provide “direct measurement of arsenic levels on the hands of children in contact with … CCA-treated wood ….” Given that arsenic is amenable to biomonitoring via urine, comparable urine samples from children who do and do not play on CCA-treated structures are what is most needed. Then perhaps we would be able to stop guessing about ingestion rates.

Increasing concerns over the use of wood treated with chromated copper arsenate (CCA) in playground structures arise from potential exposure to arsenic of children playing in these playgrounds. Limited data from previous studies analyzing arsenic levels in sand samples collected from CCA playgrounds are inconsistent and cannot be directly translated to the amount of children's exposure to arsenic. The objective of this study was to determine the quantitative amounts of arsenic on the hands of children in contact with CCA-treated wood structures or sand in playgrounds. We compared arsenic levels on the hands of 66 children playing in eight CCA playgrounds with levels of arsenic found on the hands of 64 children playing in another eight playgrounds not constructed with CCA-treated wood. The children's age and duration of playtime were recorded at each playground. After play, children's hands were washed in a bag containing 150 mL of deionized water. Arsenic levels in the hand-washing water were quantified by inductively coupled plasma mass spectrometry. Our results show that the ages of the children sampled and the duration of play in the playgrounds were similar between the groups of CCA and non-CCA playgrounds. The mean amount of water-soluble arsenic on children's hands from CCA playgrounds was 0.50 microg (range, 0.0078-3.5 microg). This was significantly higher (p0.001) than the mean amount of water-soluble arsenic on children's hands from non-CCA playgrounds, which was 0.095 microg (range, 0.011-0.41 microg). There was no significant difference in the amount of sand on the children's hands and the concentration of arsenic in the sand between the CCA and non-CCA groups. The higher values of arsenic on the hands of children playing in the CCA playgrounds are probably due to direct contact with CCA-treated wood. Washing hands after play would reduce the levels of potential exposure because most of the arsenic on children's hands was washed off with water. The maximum amount of arsenic on children's hands from the entire group of study participants was4 microg, which is lower than the average daily intake of arsenic from water and food.

We appreciate the comments of Zagury and Pouschat and their support of our overall conclusions presented in our article (Kwon et al. 2004). In response to their thoughtful comments, we would like to offer the following clarifications. In the introduction of our article (Kwon et al. 2004), we cited Balasoiu et al. (2001), Zagury et al. (2003), and others (Stilwell and Gorny 1997; Townsend et al. 2003), who examined arsenic in soil and sand samples from the field or from the laboratory. These references provide the readers with useful background information on the sources and levels of potential arsenic exposure. Examining the distribution, partitioning, and concentration of arsenic in the environmental media (e.g., soil, sand, water, and wood surface) appeared to be the primary objectives of these studies. Arsenic levels had not been directly measured on the hands of children after contact with either chromated copper arsenate (CCA)-treated wood or soil in playgrounds until our study (Kwon et al. 2004). Because the primary objective of our study was to determine the amount of arsenic on the hands of children after playing in playgrounds, we did not focus on the characterization of arsenic in the soil. Although we determined the levels of arsenic in the composite soil samples from the playgrounds, a detailed characterization of the spatial distribution of arsenic was outside the scope of our study. We agree that the concentration of arsenic in the soil samples varies greatly with the sampling protocols and the location of the samples with respect to the CCA-treated wood structures (Chirenje et al. 2003; Stilwell and Gorny 1997; Zagury et al. 2003; Ursitti et al. 2004). Our composite soil samples could not provide any information on the spatial distribution of arsenic concentration in soil samples collected from the playgrounds. These composite samples were obtained from areas under decks and away from any wood structures. We did not collect soil/sand samples from areas immediately adjacent to the CCA-treated wood. Further studies to understand the distribution of arsenic in playgrounds would benefit from extensive collection and analysis of soil samples from different locations in the playgrounds. We clearly stated that “children playing in playgrounds constructed with CCA-treated wood have approximately five times more arsenic on their hands than do those playing in playgrounds that do not have CCA-treated wood structures.” We also feel that “it is important to point out to the general public that arsenic is naturally present in the soil and sand regardless whether the playgrounds contain CCA-treated wood structures.” During our study, we found that many of the parents of the participating children did not know that arsenic was naturally present in the environment, albeit with varying concentrations. They thought that if there was any arsenic, it must have been added to the environment by someone. Conversely, if there was no added “synthetic” arsenic, they did not consider arsenic as a potential health concern. This attitude toward toxic substances (natural versus synthetic) can be counterproductive in the effort to achieve the goal of protecting public health. Properly informing the public that arsenic is naturally present in the soil helps people to understand that it is important for children to wash their hands after playing, regardless of whether the playgrounds contain CCA-treated wood structures. The hand–mouth activities of young children can result in the ingestion of arsenic that may be adsorbed on their hands. Children should wash their hands after playing to reduce their potential exposure to arsenic. We agree with Zagury and Pouschat that “potential ingestion of arsenic from soil under CCA-treated structures should not be neglected.” All efforts need to be made to minimize children’s exposure to the toxic species of arsenic.

Several nations today ban or severely restrict the use of wood preserved with chromated copper arsenate (CCA), but many existing structures still remain—for example, about 70% of existing U.S. single-family homes and 14% of public playgrounds incorporate CCA-treated wood. In recent years, scientists have studied how arsenic leaches from CCA-treated wood, but they have only inferred exposure levels from measurements of arsenic concentrations in soil and sand near treated wood structures. In this issue, Elena Kwon of the University of Alberta and colleagues report on direct measurements they made of arsenic on the hands of children playing in playgrounds, some with CCA-treated wood structures and others without [EHP 112:1375–1380]. The team reports that although playing on treated structures increases the amount of arsenic on children’s hands, washing the children’s hands after playing may be enough to avoid the health risks associated with CCA. For several decades, CCA-treated wood was widely used in the United States, Canada, and other countries for playground equipment, fences, and backyard decks. Bans and restrictions on the use of CCA-treated wood have been driven largely by concerns that treated wood could release chromium and arsenic, posing risks to human health. Especially vexing was the possibility that children who contacted CCA-treated wood structures were, because of their propensity for hand-to-mouth contact, especially at risk for ingesting arsenic. Although touching treated wood will not liberate the 70- to 170-milligram dose of arsenic that is fatal to humans, ingesting lower doses of the substance has been linked to several cancers and other ailments. The scientists measured arsenic on the hands of 130 children who visited 16 public playgrounds in Edmonton, Canada, over the period 5–21 August 2003. They tested all children who visited the playgrounds during randomized observation times and whose parents allowed them to participate in the study. The children averaged 4.75 years of age and spent an average of 1.25 hours on the playground. When each child was finished playing, his or her hands were rinsed for 1 minute in a Ziploc bag of deionized water. The water and any soil/sand rinsed from the child’s hands were analyzed separately in the laboratory for arsenic content. The team also collected soil/sand samples from each playground; samples from near the structures provided a measure of the arsenic that had leached from the wood, while those taken far from the structures indicated how much arsenic was present naturally. In comparing playgrounds with and without CCA-treated wood structures, the team found no statistically significant difference in the amount of arsenic in the soil/sand samples or in the soil/sand washed from the children’s hands. However, children who had played in the treated-wood environment had an average of 0.50 micrograms of soluble arsenic rinsed from their hands—more than five times as much as the children who did not play on treated structures. EPA research indicates that ingestion, rather than inhalation or dermal absorption, is the primary route of exposure related to arsenic-related ailments. Children aged 2–6 typically ingest about half of whatever they collect on their hands. But even assuming that the children in the study managed to ingest all of the arsenic on their hands, their average dosage was less than the average Canadian child’s daily dose of arsenic through food and water (about 0.6 micrograms per kilogram body weight). The scientists also found that the first rinsing removed most of the arsenic from the children’s hands. That could be the prescription for parents whose children frequent playgrounds with treated-wood structures—and who want to play it safe.