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Release of Micronized Copper Particles from Pressure Treated Wood Products.
Citation:
Rogers, K., T. Luxton, J. Griggs, AND K. Bradham. Release of Micronized Copper Particles from Pressure Treated Wood Products. SETAC, Salt Lake City, UT, Salt Lake City, UT, November 01 - 05, 2015.
Impact/Purpose:
The National Exposure Research Laboratory (NERL) Human Exposure and Atmospheric Sciences Division (HEASD) conducts research in support of EPA mission to protect human health and the environment. HEASD research program supports Goal 1 (Clean Air) and Goal 4 (Healthy People) of EPA strategic plan. More specifically, our division conducts research to characterize the movement of pollutants from the source to contact with humans. Our multidisciplinary research program produces Methods, Measurements, and Models to identify relationships between and characterize processes that link source emissions, environmental concentrations, human exposures, and target-tissue dose. The impact of these tools is improved regulatory programs and policies for EPA.
Description:
Micronized copper pressure treated lumber (PTL) has recently been introduced to the consumer market as a replacement for ionized copper PTL. The presence of particulate rather than aqueous copper raises concerns about possible human or environmental exposure. Two common pathways of exposure, leaching during contact with water and transfer during physical contact, were investigated to determine potential risk during intended use of the product. Characterization, leaching tests, and wipe tests were conducted on two representative formulations of micronized copper PTL (micronized copper azole or MCA) to quantify the levels of copper present in the treated material and the amount of copper released during use as well as to determine the form (particle or ion) of the copper after it was released. Additionally, an ionized copper pressure treated wood (alkaline copper azole or ACA) was tested for comparison. The characterization showed that copper carbonate is the primary particle form in the MCA treated wood, however, organically complexed copper is also present. Electron microscopy showed the presence of Nanoscale to microscale particles in the PTL. The leaching results indicate that mostly (> ~95%) ionic copper is released from the MCA wood and that the particulate copper that was released is attached to cellulose and not free in solution. MCA released significantly less copper than the ACA, suggesting a lower potential impact on the environment. The wipe tests, developed by the Consumer Product Safety were used as a surrogate for transfer of copper through hand contact. The results show that the MCA and ACA wood release approximately the same amount of copper with each contact and that the amount of copper released is high initially, but decreases to a constant level after being wiped 2-3times. Weathered PTL (both MCA and ACA) showed a higher residual copper transfer, suggesting that weathering may result in higher surface concentrations after the initial transfer.
