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Copper formulations have been used for decades for antimicrobial and antifouling applications. With the development of nanoformulations of copper that are more effective than their ionic and microsized analogues, a key regulatory question is whether these materials should be treated as new or existing materials. To address this issue, here we compare the magnitude and mechanisms of toxicity of a series of Cu species (at concentration ranging from 2 to 250 μg/mL), including nano Cu, nano CuO, nano Cu(OH)2(CuPro and Kocide), micro Cu, micro CuO, ionic Cu2+(CuCl2and CuSO4) in two species of bacteria (Escherichia coliand Lactobacillus brevis). The primary size of the particles studied ranged from 10 nm to 10 μm. Our results reveal that Cu and CuO nanoparticles (NPs) are more toxic than their microsized counterparts at the same Cu concentration, with toxicities approaching those of the ionic Cu species. Strikingly, these NPs showed distinct differences in their mode of toxicity when compared to the ionic and microsized Cu, highlighting the unique toxicity properties of materials at the nanoscale. In vitroDNA damage assays reveal that both nano Cu and microsized Cu are capable of causing complete degradation of plasmid DNA, but electron tomography results show that only nanoformulations of Cu are internalized as intact intracellular particles. These studies suggest that nano Cu at the concentration of 50 μg/mL may have unique genotoxicity in bacteria compared to ionic and microsized Cu.

Silver nanoparticles (Ag NPs) are commonly added to various consumer products and materials to impair bacterial growth. Recent studies suggested that the primary mechanism of antibacterial action of silver nanoparticles is release of silver ion (Ag+) and that particle-specific activity of silver nanoparticles is negligible. Here, we used a genome-wide library of Escherichia coliconsisting of ∼4000 single gene deletion mutants to elucidate which physiological pathways are involved in how E. coliresponds to different Ag NPs. The nanoparticles studied herein varied in both size and surface charge. AgNO3was used as a control for soluble silver ions. Within a series of differently sized citrate-coated Ag NPs, smaller size resulted in higher Ag ion dissolution and toxicity. Nanoparticles functionalized with cationic, branched polyethylene imine (BPEI) exhibited equal toxicity with AgNO3. When we used a genome-wide approach to investigate the pathways involved in the response of E. colito different toxicants, we found that only one of the particles (Ag-cit10) exhibited a pattern of response that was statistically similar to that of silver ion. By contrast, the pathways involved in E. coliresponse to Ag-BPEI particles were more similar to those observed for another cationic nanoparticle that did not contain Ag. Overall, we found that the pathways involved in bacterial responses to Ag nanoparticles are highly dependent on physicochemical properties of the nanoparticles, particularly the surface characteristics. These results have important implications for the regulation and testing of silver nanoparticles.

With the increased use of engineered nanomaterials such as ZnO and CeO2nanoparticles (NPs), these materials will inevitably be released into the environment, with unknown consequences. In addition, the potential storage of these NPs or their biotransformed products in edible/reproductive organs of crop plants can cause them to enter into the food chain and the next plant generation. Few reports thus far have addressed the entire life cycle of plants grown in NP-contaminated soil. Soybean (Glycine max) seeds were germinated and grown to full maturity in organic farm soil amended with either ZnO NPs at 500 mg/kg or CeO2NPs at 1000 mg/kg. At harvest, synchrotron μ-XRF and μ-XANES analyses were performed on soybean tissues, including pods, to determine the forms of Ce and Zn in NP-treated plants. The X-ray absorption spectroscopy studies showed no presence of ZnO NPs within tissues. However, μ-XANES data showed O-bound Zn, in a form resembling Zn-citrate, which could be an important Zn complex in the soybean grains. On the other hand, the synchrotron μ-XANES results showed that Ce remained mostly as CeO2NPs within the plant. The data also showed that a small percentage of Ce(IV), the oxidation state of Ce in CeO2NPs, was biotransformed to Ce(III). To our knowledge, this is the first report on the presence of CeO2and Zn compounds in the reproductive/edible portion of the soybean plant grown in farm soil with CeO2and ZnO NPs.