Assessing the Impact of Copper and Zinc Oxide Nanoparticles on Soil: A Field Study

<div><p>It is not known if the annual production of tonnes of industrial nanoparticles (NPs) has the potential to impact terrestrial microbial communities, which are so necessary for ecosystem functioning. Here, we have examined the consequences of adding zero valent copper and zinc oxide NPs to soil in pots that were then maintained under field conditions. The fate of these NPs, as well as changes in the microbial communities, was monitored over 162 days. Both NP types traveled through the soil matrix, albeit at differential rates, with Cu NPs retained in the soil matrix at a higher rate compared to ZnO NPs. Leaching of Cu and Zn ions from the parent NPs was also observed as a function of time. Analysis of microbial communities using culture-dependent and independent methods clearly indicated that Cu and ZnO NPs altered the microbial community structure. In particular, two orders of organisms found in rhizosphere, <em>Flavobacteriales</em> and <em>Sphingomonadales</em>, appeared to be particularly susceptible to the presence of NPs. Together, the migration of NPs through soil matrix and the ability of these potential pollutants to influence the composition of microbial community in this field study, cannot help but raise some environmental concerns.</p> </div

Microbial community distribution in the soil exposed to copper or zinc oxide nanoparticles under field conditions as measured using FAME analysis and microbial community diversity indicators as measured using community level physiological profile analysis.

*<p>FAME data for top layer zinc 160 days not obtained due to contamination of sample.</p

Cu K-edge powdered X-ray diffraction spectra of soil cores at different depths at the four time points.

<p>All panels (A–D) show spectra for a Cu NP reference (black line) and the untreated, control soil (grey line). Spectral features are indicated by dashed lines:the Cu pre-edge feature associated with zero valent Cu⁰ (black dashed line) and the post edge feature in the untreated soil,a shoulder associated with adsorbed Cu²⁺ (red dashed line).</p

Zinc K-edge powdered X-ray diffraction spectra of soil cores at different depths at the four time points.

<p>All panels (A–D) contain a reference spectrum for ZnO NP (black line) and untreated soil (grey line). Spectral features associated either with the ZnO NPs (black dashed lines) or the untreated soil (red dashed lines) are indicated.</p

Temperature and precipitation over time at the field study location.

<p>Bold and thin lines represent temperature and precipitation, respectively. The parameters were measured using Davis-Vantage Pro2. Day 0 was January 19, 2011.</p

Concentration of Cu and Zn in the extracted soil cores as a function of depth and time.

<p>The break in the X-axis occurs at 35 and 60 mg kg⁻¹ for Cu and Zn, respectively.</p

Relative abundance of bacterial orders (%) determined by pyrosequencingin the top, middle and bottom horizons of unexposed and nanoparticle-exposed soils.

<p>Horizontal colored bars represent different bacterial orders identified in soils from control (Con), Cu NP (Cu) and Zn NP (Zn) experimental pots treated for 160, 30, 7 and 0 days. *Others represents all of the orders in which the percentage was <1.</p

Powdered X-ray diffraction analysis of the Cu NPs, showing the linear combination fit (with R values referring to a general goodness of fit parameter).

<p>Powdered X-ray diffraction analysis of the Cu NPs, showing the linear combination fit (with R values referring to a general goodness of fit parameter).</p

X-ray diffraction patterns for copper (A) and zinc oxide (B) nanoparticles.

<p>Different color arrows indicate specific copper phases. Speciation of the Cu phase was determined by comparison with the International Center for Diffraction data (ICDD) powder diffraction files with experimental data (Cu metal <i>01-085-1326</i>, Cu₂O <i>01-078-2076</i>, CuO <i>00-041-0254</i>). ICDD files for ZnO were <i>01-079-0206</i>.</p

% of Flavobacteriales, Rhizobiales and Sphingomonadales in control soil and that exposed to nanoparticles. (Con, Control; Cu, Cu nanoparticles; Zn, ZnO nanoparticles).

<p>% of Flavobacteriales, Rhizobiales and Sphingomonadales in control soil and that exposed to nanoparticles. (Con, Control; Cu, Cu nanoparticles; Zn, ZnO nanoparticles).</p