Ecotoxic Effects of the Vehicle Solvent Dimethyl Sulfoxide on Aquatic Model Organisms

Dimethyl sulfoxide (DMSO) is widely used as a vehicle solvent in ecotoxicity bioassays. However, despite its frequent use, itcould be toxic for organisms at some concentrations. Hence, the aim of this study was to investigate the effectsof DMSO on the population growth rate of the microalgaeRaphidocelis subcapitata, the mobility of the microcrustacean Daphnia magna,and the reproduction of the rotiferBrachionus calyciflorus. DMSO was applied to the organisms in concentrations ranging from 0.031–4%. For R. subcapitata significant effects in growth inhibitionafter 72 h of exposure was 0.125% DMSO,being the lowest observed effectconcentration (LOEC). The 50% effective concentration (EC50) was2.138 ± 0.372%. In D. magna,significant differences in the mobility after 24 h or 48 h of exposure was 1% DMSO being 1.712± 0.207% and 1.167± 0.220%DMSO the EC50 observed for 24 h and 48 h exposure, respectively. For B. calyciflorus,it was not possible to validate the tests performed, as there were insufficient animals alive in the control conditions at the end of the exposure period. Therefore, we recommended avoiding DMSO as a vehicle in assays using B. calyciflorus,and to use final DMSO concentrationsin experimental solution not exceeding 0.125% forR. subcapitata and 0.5% for D. magna.

Isolated and combined effects of a submerged macrophyte and a cladoceran on the interactions between Microcystis aeruginosa (Cyanobacteria) and Raphidocelis subcapitata (Chlorophyta)

Introduction: Cyanobacterial blooms in tropical water bodies are increasingly common, because of eutrophication and rising temperatures. Consequently, many freshwater systems are affected, by reducing water quality, biodiversity, and ecosystem services. With the increased frequency of harmful algal blooms, the development of biological tools to improve water quality is an urgent issue. Objective: To evaluate the effects of a submerged macrophyte and a cladoceran on the microcystin-producing cyanobacteria Microcystis aeruginosa (NPLJ-4) and the chlorophyte Raphidocelis subcapitata (BMIUFRPE-02) in mixed cultures. Methods: Two parallel experiments were carried out for ten days to evaluate the effects of the submerged macrophyte Ceratophyllum demersum and the cladoceran Moina micrura on microalgal interactions. Microalgal strains were cultivated in the ASM1 culture medium, under controlled laboratory conditions. The first experiment presented four treatments: M (C. demersum), Z (M. micrura), MZ (C. demersum and M. micrura), and C (control). Meanwhile, the second experiment consisted of five treatments, in which the microalgae were cultivated together at different Microcystis:Raphidocelis ratios: 1:0, 3:1, 1:1, 1:3, and 0:1. Biomass and growth rates of the strains were evaluated every two days, which were statistically treated with three-way or two-way repeated-measures ANOVA. Results: In the first experiment, M. aeruginosa was significantly inhibited in M and MZ treatments from the second day, and Z from the fourth, while R. subcapitata showed no reduction in its biomass in any treatment. On the other hand, R. subcapitata was stimulated from the eighth and tenth days in M treatment and only on the eighth day in Z treatment. In the second experiment, M. aeruginosa was significantly inhibited when cultivated with R. subcapitata in low ratios (Microcystis:Raphidocelis ratio of 1:3) throughout the experiment, while the chlorophyte was stimulated in that treatment. Conclusions: The coexistence of a cyanobacterium with a green alga did not alter the main negative response of M. aeruginosa to the submerged macrophyte and zooplankton but stimulated the green alga. Accordingly, the introduction of submerged macrophytes and cladocerans already adapted to eutrophic conditions, both isolated and combined, proved to be a good method to control cyanobacterial blooms without negatively affecting other coexisting phytoplankton species.

Alteration of acute toxicity of inorganic and methyl mercury to Daphnia magna by dietary addition

Acute toxicity of inorganic mercury [Hg(II)] and methylmercury (MeHg) to Daphnia magna was characterized using a 48-h static, non-renewal acute toxicity test, in which we compared the toxicity of Hg(II) and MeHg in the absence (water-only) and presence of diet [green alga (Raphidocelis subcapitata), yeast, Cerophyll, and trout chow (YCT), or both]. Overall, Hg(II) is more toxic to D. magna than MeHg, with 48-h median lethal concentrations (LC50s) being 4.3 µg/L (95% confidence interval: 4.1–4.5 µg/L) for Hg(II) and 14.3 µg/L (13.2–15.3 µg/L) for MeHg. For Hg(II), the addition of any diet would significantly increase its 48-h LC50, but the 48-h LC50 for MeHg decreased significantly to 7.1 µg/L (6.4–7.8 µg/L) with the algal addition. We also show that the addition of diets significantly influenced the levels and speciation (dissolved vs. particulate) of both Hg forms in the test solution. The bioaccumulation of Hg(II) and MeHg was impacted by the dietary addition, and it appears that the body residue level triggering mortality varied widely among treatments. The results suggest that standard short-term toxicity tests (water-only) should be supplemented with extra tests with dietary addition to provide a more environmentally relevant estimation of short-term toxicity of chemical compounds.

Toxicidade e possível interação celular do Óxido de Grafeno Reduzido com Raphidoceles subcapitata: Análise ultraestrutural

O óxido de grafeno reduzido (rGO) é um nanomaterial formado por carbono, apresentado como um derivado do óxido de grafeno e, devido às suas propriedades, é utilizado em áreas como microeletrônica, mecânica e biomedicina. Apesar da grande quantidade de testes realizados com esse nanomaterial, ainda não há consenso sobre sua toxicidade, quando no meio ambiente. O meio aquático costuma ser o destino final desses compostos e, por isso, as algas verdes costumam ser utilizadas como bioindicador. Este estudo teve como objetivo determinar a ecotoxicidade e possíveis interações da nanopartícula de rGO com a célula de algas verdes de Raphidocelis subcapitata. As alterações estruturais nas algas, expostas a diferentes concentrações a rGO, foram analisadas através de microscopia eletrônica de transmissão (TEM) e espectroscopia Raman, a toxicidade foi avaliada por meio da medida de inibição da biomassa algal. Os resultados indicam que não houve efeito tóxico no organismo estudado, exceto na maior concentração (100 mg.L-1). A análise de TEM demonstrou uma interação das nanopartículas com a célula algal, pela observação da internalização das nanopartículas, bem como pela deposição de rGO na membrana celular. Apesar da ausência de toxicidade em baixas concentrações, os organismos mostraram sensibilidade à presença do rGO. Esses resultados contribuem com a literatura no esclarecimento do comportamento das nanopartículas à base de carbono no ambiente aquático e podem permitir um melhor cuidado com a produção e liberação dessas nanopartículas no meio ambiente.

New Models to Predict the Acute and Chronic Toxicities of Representative Species of the Main Trophic Levels of Aquatic Environments

To assess the impact of chemicals on an aquatic environment, toxicological data for three trophic levels are needed to address the chronic and acute toxicities. The use of non-testing methods, such as predictive computational models, was proposed to avoid or reduce the need for animal models and speed up the process when there are many substances to be tested. We developed predictive models for Raphidocelis subcapitata, Daphnia magna, and fish for acute and chronic toxicities. The random forest machine learning approach gave the best results. The models gave good statistical quality for all endpoints. These models are freely available for use as individual models in the VEGA platform and for prioritization in JANUS software.