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In vitro bioaccessibility of copper azole following simulated dermal transfer from pressure-treated wood
Citation:
Griggs, J., K. Rogers, C. Nelson, T. Luxton, W. Platten, AND K. Bradham. In vitro bioaccessibility of copper azole following simulated dermal transfer from pressure-treated wood. SCIENCE OF THE TOTAL ENVIRONMENT. Elsevier BV, AMSTERDAM, Netherlands, 598:413–420, (2017).
Impact/Purpose:
Investigating the release and dissolution processes for micronized copper treated wood products allows better prediction of long-term behavior. This study characterizes how the physicochemical properties of these preservatives may influence long term exposure to particles and ions under real-world scenarios. Our findings indicate that 1032 µg of Cu for MCA-1 and about 2580 µg of Cu for MCA-2 may be released from surface wipes and would be solubilized upon oral ingestion. In context of current literature reported for these products our findings suggest that for children between 1 and 8 years old, rubbing micronized copper-treated wood boards and subsequently putting contaminated hands in their mouths may expose children to Cu amounts that meet or exceed the daily Tolerable Upper Intake Limit (TUIL), exclusive of the Cu typically ingested from their normal diet and habits (e.g. taking vitamins). While this study does not examine the toxicological implications of children’s exposure to levels of Cu above the TUIL, future studies should be conducted to address the negative effects of short and intermediate exposures to these environmentally relevant Cu levels.
Description:
Micronized copper azole (MCA) and micronized copper quaternary are the latest wood preservatives to replace the liquid lkaline copper and chromated copper arsenate preservatives due to concerns over the toxicity or lack of effectiveness of the earlier formulations. Today, the use of MCA has become abundant in the wood preservative industry with approximately 38 million pounds of copper carbonate being used to treat lumber each year. Despite this widespread usage, little information is available on the bioaccessibility of this preservative upon gastrointestinal exposure. Using a simulated hand-to-mouth/gastric system exposure study we investigated several types of commercially available copper-treated lumber products as purchased and after exposure to outdoor weathering conditions. Soluble and particulate fractions of copper were measured after transfer to and release from surface wipes passed along copper-treated lumber and exposed to synthetic stomach fluid (SSF, pH 1.5) or DI water. Wipes passed along new boards contained greater amounts of copper than wipes from weathered boards. The total copper recovered from the wipes after microwave extraction varied among the different wood types. For all wood types the copper released into SSF was more soluble than what was soluble in DI water. The data suggest that copper from treated wood is highly bioaccessible in SSF regardless of wood type and weathering condition.
