Environmental concentrations of copper nanoparticles affect vital functions in Ankistrodesmus densus.

Nanoparticles (NPs) have unique properties, leading to their widespread application in industry, consequently increasing their concentration in aquatic ecosystems. Although environmentally significant concentrations are still low, they tend to increase because of the intense use, posing into risk microalgae communities. Microalgae are primary producers that support food chains in aquatic ecosystems; thus factors that interfere with their physiology can be propagated throughout the food web. The present research investigated the effects of copper nanoparticles (Cu-NPs) in the physiology of a cosmopolitan green microalgae, Ankistrodesmus densus. Here, we focused on environmental NPs levels, so an ample Cu-NPs range was used, 0.3-635 µg L-1. Considering that NPs dissolve into the medium releasing their constituent material, free Cu2+ ions were determined and considered as surrogate for NPs concentration, which varied from 2.1 × 10-9 to 8.4 × 10-9 mol L-1. The experiment was based in 72 h Cu-NPs exposure, and to access the physiology of A. densus, we monitored population growth, photochemistry of photosynthesis and the content of cell biomolecules (total proteins, carbohydrates and lipids). The results showed that 2.1 × 10-9 mol L-1 free Cu2+ was enough to decrease growth rate, but 2.5x higher Cu was necessary to affect the photosynthetic parameters. Inorganic carbon fixation rate calculated by absolute electron transport rates was affected. Considering cell biomolecules, total proteins accumulated at 6.5 × 10-9 and kept increasing up to 8.4 × 10-9 mol L-1 free Cu2+. Because this was not related to biomass formation, we suggest a possible association with cell detoxification mechanisms. The most clear finding that emerged from this study is that environmental Cu-NPs concentrations affect vital functions in the green microalgae A. densus. An implication of this is the possibility of facing problems related to a increase of NPs in aquatic ecosystems in the near future.

Physiological responses of Chlorella sorokiniana to copper nanoparticles.

Copper (Cu) nanomaterials have been increasingly researched and produced for many different consumer products. They have high reactivity and bactericidal properties, making them important in antifouling paints, which are thus directly introduced into aquatic ecosystems. However, studies are scarce on the behavior of Cu nanoparticles (Cu-NPs) in natural aquatic systems and their interactions with primary producers such as microalgae. We investigated the effects of NPs on some physiological responses of the freshwater phytoplankton Chlorella sorokiniana. The cells were exposed to nominal concentrations ranging from 2.50 to 635.00 µg L-1 Cu-NPs for 96 h under laboratory-controlled conditions. The cultures were monitored daily for population growth and maximum photosynthetic quantum yield. Total lipids, proteins, and carbohydrates were quantified at 72 h of Cu-NP exposure. The results showed a positive correlation between nominal Cu-NPs and Cu in the biomass (0.97 correlation coefficient) and that this was inversely proportional to total carbohydrates, with a -0.64 correlation coefficient. At the higher end of the Cu-NP concentrations tested, higher total proteins and reduced growth rates were obtained in comparison with controls; we suggest that metal-binding proteins/antioxidants and nonstructural proteins were preferentially produced under these conditions. Our results contribute to an understanding of the interaction between Cu-NPs and a cosmopolitan phytoplankton, C. sorokiniana, and we emphasize that the disposal and use of Cu-NPs requires monitoring because even at environmentally relevant concentrations, the composition of the algae was affected. Environ Toxicol Chem 2019;38:387-395. © 2018 SETAC.

Copper and cadmium complexation by Cylindrospermopsis raciborskii exudates.

Cylindrospermopsis raciborskii is a potentially toxic cyanobacterium that excretes organic materials which act as ligands for metals. Metal ligands may be characterized for their strength of association, e.g., stability constants, which can be either thermodynamic (K) or conditional (K'). In this research we examined K and K' for Cu and Cd complexes with three molecular weight fractions (>30 kDa; 30-10 kDa; 10-3 kDa) of the cyanobacteria EOM. Complexation capacities of the excreted organic materials (EOM) for metals were determined at several ionic strengths (1.0 × 10(-2), 5.0 × 10(-2), 1.0 × 10(-1), and 5.0 × 10(-1) mol L(-1)) at pH 6.6 ± 0.1, with ligands for which no data for their acidity constants are available; these constants are thus conditional for this specific pH. Bayesian statistics showed that with a probability of 95-100% the EOM have two different ligands for Cu but only one for Cd, that ligands for Cu were stronger than for Cd (94-100% probability), and that the smallest EOM fraction had the highest strength of association for Cu (logKCuL 13.5). The lowest affinity was obtained for Cd (logKCdL 8.6) complexed to any molecular weight fraction. The present findings have important ecological implications, since the metal-ligand association is dynamic, and together with a diversity of ligands it can act as an environmental metal buffer. As a result, higher metal loads may be necessary for the detection of toxicity.

Chemical behavior of Cu, Zn, Cd, and Pb in a eutrophic reservoir: speciation and complexation capacity.

This research aimed at evaluating cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn) speciation in water samples as well as determining water quality parameters (alkalinity, chlorophyll a, chloride, conductivity, dissolved organic carbon, dissolved oxygen, inorganic carbon, nitrate, pH, total suspended solids, and water temperature) in a eutrophic reservoir. This was performed through calculation of free metal ions using the chemical equilibrium software MINEQL+ 4.61, determination of labile, dissolved, and total metal concentrations via differential pulse anodic stripping voltammetry, and determination of complexed metal by the difference between the total concentration of dissolved and labile metal. Additionally, ligand complexation capacities (CC), such as the strength of the association of metals-ligands (logK'ML) and ligand concentrations (C L) were calculated via Ruzic's linearization method. Water samples were taken in winter and summer, and the results showed that for total and dissolved metals, Zn > Cu > Pb > Cd concentration. In general, higher concentrations of Cu and Zn remained complexed with the dissolved fraction, while Pb was mostly complexed with particulate materials. Chemical equilibrium modeling (MINEQL+) showed that Zn(2+) and Cd(2+) dominated the labile species, while Cu and Pb were complexed with carbonates. Zinc was a unique metal for which a direct relation between dissolved species with labile and complexed forms was obtained. The CC for ligands indicated a higher C L for Cu, followed by Pb, Zn, and Cd in decreasing amounts. Nevertheless, the strength of the association of all metals and their respective ligands was similar. Factor analysis with principal component analysis as the extraction procedure confirmed seasonal effects on water quality parameters and metal speciation. Total, dissolved, and complexed Cu and total, dissolved, complexed, and labile Pb species were all higher in winter, whereas in summer, Zn was mostly present in the complexed form. A high degree of deterioration of the reservoir was confirmed by the results of this study.

Cylindrospermopsis raciborskii (Cyanobacteria) exudates: chemical characterization and complexation capacity for Cu, Zn, Cd and Pb.

Cylindrospermopsis raciborskii is a cosmopolitan and potentially toxic planktonic Cyanobacteria that produces and exudes copious amounts of dissolved organic materials. This organism dominates the eutrophic reservoir Barra Bonita (Brazil), where it normally blooms throughout the year. This investigation focused on the characterization of such exudates analyzing their capacity to complex copper, zinc, lead and cadmium through the determination of ligand concentration (CL) and conditional stability constant (logK'ML), as well as elemental composition (C, H, N and S), the content of carbohydrates, proteins, lipids and dissolved organic carbon (DOC). The dissolved organic material was fractionated into 3 molecular weights (>30 kDa; 30-10 kDa; 10-3 kDa) and each fraction was analyzed. The results showed that in the >30 kDa and 30-10 kDa fractions carbohydrates dominate over proteins and lipids. Different CL and logK'ML were obtained for the different molecular weight fractions of the excreted organic materials, suggesting high diversity of ligands. In the >30 kDa, there were more complexing sites (CL) for Cu, but higher affinity (K') for Zn. In the 30-10 kDa fraction, the higher CL was for Cd, but the greatest affinities were for Cu and Zn. In the 10-3 kDa fraction, higher CL was obtained for Cd and Zn, while Cu and Cd had the highest strengths of association. In the environment, such diversity of ligands and strengths of association can result in a displacement of metals weakly bound to the EOM, and increase metal buffering capacity of the environment, supporting higher metal inputs before toxic effects are detected in the biota.

Cadmium and Chromium Toxicity to Pseudokirchneriella subcapitata and Microcystis aeruginosa

The toxicity of cadmium and chromium to Pseudokirchneriella subcapitata and Microcystis aeruginosa was evaluated through algal growth rate during 96h exposure bioassays. Free metal ion concentrations were obtained using MINEQL+ 4.61 and used for IC50 determination. Metal accumulations by the microorganisms were determined and they were found to be dependent on the concentration of Cd2+ and Cr6+. IC50 for P. subcapitata were 0.60 µmol L-1 free Cd2+ and 20 µmol L-1 free Cr6+, while the IC50 values for M. aeruginosa were 0.01 µmol L-1 Cd2+ and 11.07 µmol L-1 Cr6+ . P. subcapitata accumulated higher metal concentrations (0.001 -0.05 µmol Cd mg-1 dry wt. and 0.001 -0.04 µmol Cr mg-1 dry wt) than the cyanobacteria (0.001 -0.01 µmol Cd mg-1 dry wt and 0.001 -0.02 µmol Cr mg-1 dry wt). Cadmium was more toxic than chromium to both the microorganisms.