Abstract
Copper based nanoparticles (NPs) are used extensively in industrial and commercial products as sensors, catalysts, surfactants, antimicrobials, and for other purposes. The high production volume and increasing use of copper-based NPs make their ecological risk a concern. Commonly used copper-based NPs are composed of metallic copper or copper oxide (Cu and CuO NPs); however, their environmental toxicity can vary dramatically depending on their physico-chemical properties, such as dissolution, aggregation behavior, and the generation of reactive oxygen species. Here, we investigated the NP dissolution, organismal uptake and aquatic toxicity of Cu and CuO NPs at 0, 0.1, 1, 5 or 10 mg Cu/L using a previously developed multi-species microcosm. This 5-day microcosm assay was comprised of C. reinhardtti, E. coli, D. magna, and D. rerio. We hypothesized that Cu and CuO NPs can elicit differential toxicity to the organisms due to alterations in particle dissolution and variations in organismal uptake. The actual concentrations of dissolved Cu released from the NPs were compared to ionic copper controls (CuCl2) at the same concentrations to determine the relative contribution of particulate and dissolved Cu on organism uptake and toxicity. We found that both NPs had higher uptake in D. magna and zebrafish than equivalent ionic exposures, suggesting that both Cu-based NPs are taken up by organisms. Cu NP exposures significantly inhibited algal growth rate, D. magna survival, and zebrafish hatching while exposure to equivalent concentrations of CuCl2 (dissolved Cu fraction) and CuO NPs did not. This indicates that Cu NPs themselves likely elicited a particle-specific mechanism of toxicity to the test organisms, or a combination effect from ionic Cu and the Cu NPs. Overall, this work was the first study to utilize a small-scale rapid assay designed to evaluate the fate and ecotoxicological impacts of Cu and CuO NPs in a mixed aquatic community.
Highlights
Relevant nanomaterial (NM) ecotoxicological assessments are essential to evaluate the risks of engineered NMs; these are difficult to conduct due to the intense financial and labor resources they require, as well as the regulatory requirements for in situ environmental NM exposures
The average Hydrodynamic diameter (HDD) of Cu NPs was 1137.1 ± 123.8 nm, and their corresponding zeta potential (ZP) was −16.1 ± 0.84 mV, whereas CuO NPs had an average HDD of 900.4 ± 100.9 nm with an average ZP of −16.5 ± 0.76
The dissolution rate constants and predicted maximum dissolved Cu released over 120 hour are shown in Table S2.† The rate constants suggest that CuO NPs released ions more rapidly than Cu NPs, with 0.0334 h−1 for CuO NP and 0.0246 h−1 for Cu NP respectively; the final equilibrium dissolved Cu concentration was predicted to be 14.3% higher for the Cu NPs (3.2 mg Cu per L) relative to the CuO NPs (2.8 mg Cu per L)
Summary
Relevant nanomaterial (NM) ecotoxicological assessments are essential to evaluate the risks of engineered NMs; these are difficult to conduct due to the intense financial and labor resources they require, as well as the regulatory requirements for in situ environmental NM exposures. The aquatic environment is at risk for exposure to engineered NMs as is it a natural sink for pollutants and a natural vehicle for pollutant migration.[6] This includes copper-based nanoparticles (NPs) entering wastewater streams following industrial and commercial use.[5,6,7,8] Copper-based NPs are widely used in industrial and commercial products as sensors (49%), catalysts (20%), surfactants (6%), antimicrobials (4%), and other purposes (21%) such antifouling paints.[9,10,11,12] The high production volume and increasing use of copper-based NPs make their ecological risk a concern.[13] Copper-based NP toxicity to individual species has been investigated for multiple aquatic organisms.[11] Toxicity can be caused by ionic Cu released from copper-based NPs, this is considered by many to be the main mechanism of toxicity to a variety of aquatic organisms.[14,15,16,17] Despite this finding, others have suggested that when both ions and NPs are present, non-additive toxicological responses are observed which are indicative of particle-specific mechanismIJs) of toxicity.[18]
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