Estimating dermal transfer of copper particles from the surfaces of pressure-treated lumber and implications for exposure

Lumber pressure-treated with micronized copper was examined for the release of copper and copper micro/nanoparticles using a surface wipe method to simulate dermal transfer. In 2003, the wood industry began replacing CCA treated lumber products for residential use with copper based formulations. Micronized copper (nano to micron sized particles) has become the preferred treatment formulation. There is a lack of information on the release of copper, the fate of the particles during dermal contact, and the copper exposure level to children from hand-to-mouth transfer. For the current study, three treated lumber products, two micronized copper and one ionic copper, were purchased from commercial retailers. The boards were left to weather outdoors for approximately 1year. Over the year time period, hand wipe samples were collected periodically to determine copper transfer from the wood surfaces. The two micronized formulations and the ionic formulation released similar levels of total copper. The amount of copper released was high initially, but decreased to a constant level (~1.5mgm(-2)) after the first month of outdoor exposure. Copper particles were identified on the sampling cloths during the first two months of the experiment, after which the levels of copper were insufficient to collect interpretable data. After 1month, the particles exhibited minimal changes in shape and size. At the end of 2-months, significant deterioration of the particles was evident. Based on the wipe sample data, a playground visit may result in a potential exposure to 2.58mg of copper, which is near or exceeds the daily tolerable upper intake limits for children under the age of 8, if completely ingested through hand-to-mouth transfer. While nanoparticles were found, there is not enough information to estimate the exposure from the released particles due to a lack of published literature on copper carbonate.