Science Inventory

Transformation and release of nanoparticle additives & byproducts from commercially available surface coatings on pressure treated lumber via dermal contact

Citation:

Clar, J., William E. Platten III, E. Baumann, A. Remsen, S. Harmon, K. Rogers, T. Thomas, J. Matheson, AND Todd P. Luxton. Transformation and release of nanoparticle additives & byproducts from commercially available surface coatings on pressure treated lumber via dermal contact. SCIENCE OF THE TOTAL ENVIRONMENT. Elsevier BV, AMSTERDAM, Netherlands, 694:133669, (2019). https://doi.org/10.1016/j.scitotenv.2019.133669

Impact/Purpose:

Current wood treatment processes and commercial stains used for outdoor wood preservation utilize nanotechnology to preserve the wood against fungal and microbial decay and protect the surface from damage caused by Ultraviolet light (UV). For protection against fungal and microbial decay of lumber Copper Carbonate (Cu2CO3(OH)2) is used an antimicrobial agent. For protection against UV degradation Zinc Oxide is added to surface coatings (stains) as a UV absorber. The use of these nanomaterials reflect uses with very high exposure potential and provide a unique opportunity to integrate ORDs scientific niche in the areas of exposure, health and ecological effects, and modeling. This novel product-application-based research will examine nanoscale ZnO, Cu2CO3(OH)2 formulations and their transformed products employed in wood treatment\coating by determining their release, exposure, fate, and transformation as well as their health and ecological effects. Research will critically inform the engineered nanomaterial (ENM) decision tree product and provide information to develop integrated adverse exposure pathways (AEPs) to adverse outcome pathways (AOPs) associated with current wood treatment and surface applications employing ENM ZnO and Cu2CO3(OH)2 commercial products. Unique aspects of this research include the use of commercial nanoscale products, characterization ENM release and transformation associated with a high exposure application, and assessing the effects associated with exposure to mixtures of ZnO, Cu2CO3(OH)2 ENMs and their transformed products. Research findings will inform: i) regulatory uncertainties associated with exposure and effect risks associated with ENM employed in antimicrobial and surface applications with high exposure potential; and ii) newly initiated European Commission LIFE project NanoMONITOR effort that will inform ENM risk assessment under REACH.

Description:

Production and marketing of “nano-enabled” products for consumer purchase has continued to expand. However, many questions remain about the potential release and transformation of these nanoparticle (NP) additives from products throughout their lifecycle. In this work, two surface coating products advertised as containing ZnO NPs as active ingredients, were applied to micronized copper azol (MCA) and aqueous copper azol (ACA) pressure treated lumber. Coated lumber was weathered outdoors for a period of six months and the surface was sampled using a method developed by the Consumer Product Safety Commission (CPSC) to track potential human exposure to ZnO NPs and byproducts through simulated dermal contact. Using this method, the total amount of zinc extracted during a single sampling event was <1 mg/m2 and no evidence of free ZnO NPs was found. Approximately 0.5% of applied zinc was removed via simulated dermal contact over 6-months, with increased weathering periods resulting in increased zinc release. XAFS analysis found that only 27% of the zinc in the as received coating could be described as crystalline ZnO and highlights the transformation of these mineral phases to organically bound zinc complexes during the six-month weathering period. Additionally, SEM images collected after sampling found no evidence of free NP ZnO release during simulated dermal contact. Both simulated dermal contact experiments, and separate leaching studies demonstrate the application of surface coating solutions to either MCA and ACA lumber will reduce the release of copper from the pressure treated lumber. This work provides clear evidence of the transformation of NP additives in consumer products during their use stage.