Science Inventory

Release and transformation of nanoparticle additives from surface coatings on pristine & weathered pressure treated lumber

Citation:

Thorton, S., S. Boggins, D. Peloquin, Todd P. Luxton, AND J. Clar. Release and transformation of nanoparticle additives from surface coatings on pristine & weathered pressure treated lumber. SCIENCE OF THE TOTAL ENVIRONMENT. Elsevier BV, AMSTERDAM, Netherlands, 737:139451, (2020). https://doi.org/10.1016/j.scitotenv.2020.139451

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:

As the market for “nano-enabled” products (NEPs) continues to expand in commercial and industrial applications, there is a critical need to understand conditions that promote release of nanomaterials and their degradation products from NEPs. Moreover, these studies must aim to quantify both the abundance and form (aggregates, ions, hybrids, etc.) of material released from NEPs to produce reasonable estimates of human and environmental exposure. In this work ZnO nanoparticles (NPs), a common additive in NEP surface coatings, were dispersed in Milli-Q water and a commercially available wood stain before application to pristine and weathered (outdoor 1 year) micronized copper azole pressure treated lumber (MCA). Coated lumber surfaces were sampled consecutively eight times 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. Surprisingly, the highest total release of Zn was observed from aged lumber coated with ZnO NPs dispersed in wood stain, releasing 233 ± 26 mg Zn/m2 over the course of all sampling events. Alternatively, separate leaching experiments using a synthetic precipitation solution to simulate environmental release found aged lumber released significantly less Zn than pristine lumber when using the same coating formulation. Zinc speciation analysis also demonstrates that transformation of crystalline ZnO to Zn-organic complexes shortly after application to aged lumber. Regardless of experimental treatment, the majority of applied zinc (>75%) remains on the MCA surface. Finally, this work highlights how the nature of the screening technique (dermal contact vs. leaching) may result in different interpretations of exposure and risk.