Focused Microbiome Shifts in Reconstructed Wetlands Correlated with Elevated Copper Concentrations Orginating from Micronized Copper Azole- Treated Wood

Micronized copper (Cu) azole (MCA) wood preservative formulations include Cu in nano form, and relatively little is known about longer term effects of Cu leached from MCA into wetland ecosystems. We tested the hypothesis that changes in soil microbiomes within reconstructed freshwater wetlands will be associated with exposure to elevated Cu concentrations originating from immersed MCA-treated wood stakes. Eight replicate communities were assembled with Willamette Valley (OR, USA) flood plain soil and clonally propagated wetland plants within mesocosms. Inundated communities were equilibrated for 5 months before installation of MCA or control southern yellow pine stakes (n = 4 communities/experimental group). Soil samples were collected for 16S and internal transcribed spacer amplicon sequencing to quantify responses in prokaryotes and eukaryotes, respectively, at 15 time points, spanning two simulated seasonal dry downs, for up to 678 days. Physiochemical properties of water and soil were monitored at 20 and 12 time points respectively, over the same period. For both taxonomic groups of organisms, phylogenetic diversity increased and was positively correlated with elapsed days. Furthermore, there was significant divergence among eukaryotes during the second year based on experimental group. Although the composition of taxa underwent succession over time, there was significantly reduced relative abundance of sequence variants from Gomphonema diatoms and Scutellinia fungi in communities where MCA wood stakes were present compared with the controls. These focused microbiome shifts were positively correlated with surface water Cu and soil Cu concentrations, which were significantly elevated in treated communities. The reconstructed communities were effective systems for assessing potential impacts to wetland microbiomes after exposure to released copper. The results further inform postcommercialization risk assessments on MCA-treated wood. 

Impact/Purpose

Engineered nanomaterials (ENMs) have been recognized as valuable components of new technologies and are currently being used in a variety of consumer products due to their unique physical, chemical, and electrical properties. The properties that make these particles functionally unique also may influence their toxicity to organisms in ecosystems. One of the challenges scientists face when examining the potential environmental health and safety aspects of ENMs is to understand how organisms are impacted by exposure to compounds that are released into the environment from the use, degradation or weathering of nanoenabled products. EPA scientists investigated how forms of Cu released from wood preserved with micronized copper azole (MCA) might adversely affect wetland microbial communities. Over the course of 2 years, the microbiological and physiochemical characteristics of reconstructed wetland communities were analyzed, and the results indicate that focused impacts to microbial communities were positively correlated with elevated surface water Cu and soil Cu concentrations orginating from MCA treated wood. The results presented here make a point regarding risk assessments of such materials. When studying how organisms are impacted by exposure to compounds that are released from nanoenabled products, it is critical to understand how the ENMs were transformed prior to the release. In the case of MCA treated wood, the risk to sensitive wetland soil microbes is not directly attributable to the properties of the nano copper carbonate in MCA, but rather from the Cu ions released by the dissolution of those particles. The results will be of interest to federal and state agencies that may conduct post-commercialization risk assessments on nanoenabled products.

Citation

Reichman, J., M. Johnson, P. Rygiewicz, B. Smith, M. Bollman, M. Storm, G. King, AND C. Andersen. Focused Microbiome Shifts in Reconstructed Wetlands Correlated with Elevated Copper Concentrations Orginating from Micronized Copper Azole- Treated Wood. Society of Environmental Toxicology and Chemistry, Pensacola, FL, 40(12):3351-3368, (2021). [DOI: 10.1002/etc.5219]

DOI: Focused Microbiome Shifts in Reconstructed Wetlands Correlated with Elevated Copper Concentrations Orginating from Micronized Copper Azole- Treated Wood