Copper (Cu
2+
) is an essential micronutrient for cyanobacteria, but it has a toxic effect above a certain threshold. The presence of Cu
2+
in water is usually related to human activity due to it ...being used in pesticides, fertilizer, and algaecides. Previous studies observed that high Cu
2+
concentrations stimulated toxin synthesis in cyanobacteria and microalgae. Furthermore, saxitoxins (STXs) can bind to Cu
2+
transporters in microorganisms, decreasing the Cu
2+
uptake and consequently reducing Cu toxicity. Therefore, considering the invasive capacity of the cyanobacterium
Raphidiopsis raciborskii
and its potential for STXs production, this study aimed to evaluate the effects of different Cu
2+
concentrations in the production of STXs and growth of
R. raciborskii
. In acclimatized growth conditions, cultures of
R. raciborskii
strain (ITUC01) were exposed to four different copper concentrations for 20 days (0.8, 8, 80, and 800 × 10
−3
μmol L
−1
of CuCl
2
).
Raphidiopsis raciborskii
growth and physiological responses were evaluated measuring the cell concentration, cell volume, biovolume, chlorophyll
a
levels, and STXs concentration. Comparing the lowest and highest Cu
2+
concentration (0.8 and 800 × 10
−3
μmol L
−1
), it was observed that the increment of Cu
2+
in the medium led to a reduced maximum growth rate (
μ
max
), cell concentration, biovolume, and chlorophyll
a
levels, while the cell volume increased. Despite the low cell concentration and biovolume in the highest Cu
2+
condition, it was observed that the STXs volumetric concentration was significantly high on day 5, which is indicative of the fact that increased Cu
2+
concentration might induce STXs production in early growth. In addition, our results revealed that STXs production was uncoupled with growth and a reduction of
R. raciborskii
toxicity from day 5 to 20 was observed. Therefore, the present study identified some of the survival responses of
R. raciborskii
in Cu-stressed condition and suggested that Cu
2+
might be one of the factors that can affect
R. raciborskii
bloom toxicity.
•Copper ions released from nanoparticles caused biochemical changes in microalgae.•Photosynthetic processes in microalgae were damaged by copper nanoparticles.•Copper nanoparticles can induce changes ...in carbon fixation by microalgae.
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.
This work describes methodologies for speciation analysis of the metals copper and zinc as total, total dissolved, labile, as well as complexation capacity (conditional stability constants and ...available ligand concentration), using the same technique, differential pulse anodic stripping voltammetry (DPASV). Several supporting electrolytes were tested, and the results showed that KNO3 and HNO3 resulted in voltamograms without interferences as well as excellent resolution for the total and labile fractions. The methodology using the DPASV technique allows a simple and low cost analysis of copper and zinc speciation, with high precision and sensitivity, with limits of quantification (LOQ) of 1.8 nmol L-1 for copper and 2.1 nmol L-1 for zinc.
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 super(+) 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 Cd super(2+) and Cr super(6+). IC50 for P. subcapitata were 0.60 mu mol L super(-1) free Cd super(2+) and 20 mu mol L super(-1) free Cr super(6+), while the IC50 values for M. aeruginosa were 0.01 mu mol L super(-1) Cd super(2+) and 11.07 mu mol L super(-1) Cr super(6+) times P. subcapitata accumulated higher metal concentrations (0.001 -0.05 mu mol Cd mg super(-1) dry wt. and 0.001 -0.04 mu mol Cr mg super(-1) dry wt) than the cyanobacteria (0.001 -0.01 mu mol Cd mg super(-1) dry wt and 0.001 -0.02 mu mol Cr mg super(-1) dry wt). Cadmium was more toxic than chromium to both the microorganisms.
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.
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.
Nanoparticles (NPs) are highly reactive particles that find a broad array of applications in society; as a result, they may accumulate in aquatic environments. Microalgae are the base of foodwebs and ...serve as surfaces for NPs, interacting and transporting them to higher trophic levels. We aimed at understanding the effects of environmentally significant and higher copper nanoparticles (Cu-NPs) concentrations on the photosynthetic performance of Chlorella sorokiniana, which included determining effective quantum yield (F'
v
/F'
m
), photochemical (Q
p
) and non-photochemical (NPQ) quenching, rapid light curves (RLC), light use efficiency (α), minimum saturation irradiance (E
k
) and the maximum relative electron transport rate (ETRr
max
), in addition to chlorophyll a content and cell viability. Dissolved Cu and free ionic Cu concentrations were determined, and dissolved Cu values were used as surrogate for nominal Cu-NPs concentrations. The experiments lasted 72 h and were carried out under controlled conditions. The results showed that cell viability and chlorophyll a decreased as Cu-NPs increased, but the opposite was obtained for the RLC parameters. Light saturation (E
k
) and ETR increased as Cu-NPs concentrations increased in culture medium, but not the efficiency with which C. sorokiniana used the light. By showing that environmentally relevant Cu-NPs influenced C. sorokiniana metabolism, we add to the knowledge on the interactions between environmentally realistic Cu-NPs levels and phytoplankton cells.
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 (log
K
′
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.
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