Efeitos isolados e combinados dos metais zinco e alumínio sobre representantes de três níveis tróficos de organismos aquáticos dulcícolas

Abstract

Metals are widely distributed throughout the Biosphere, and the increase in their concentration in aquatic ecosystems may cause concern. Although environmental legislation utilizes the isolated metal toxicity in normative about maximum allowed concentrations in the environment, it is known that the metals cooccur; therefore, studies dealing with the toxicity of metals’ mixtures are of great importance. The aim of our study is to analyze the individual and combined effects of mixtures of zinc (Zn) and aluminum (Al) on the green microalga Raphidocelis subcapitata and on the Neotropical cladoceran Ceriodaphnia silvestrii and, besides that, we also evaluated the isolated effects of Zn on initial stages of zebrafish (Danio rerio). Results indicate that both metals inhibited the growth of R. subcapitata, with IC50-96h: 0.026 mg Zn L-1 and 0.74 mg Al L-1. Regarding the photosynthetic parameters, we observed decay in the efficiency of O2 evolving-complex (F0/Fv) and efficiency of photosystem II (PSII) and the increase of non-photochemical quenchings. Analyzing the growth of R. subcapitata after 96 h, Zn and Al mixtures exerted synergic effects at low concentrations and antagonistic effects at high concentrations. Observing F0/Fv e ΦM, we found antagonistic effects at high Al concentrations. By plotting species sensitivity distributions (SSD), the hazard concentrations to 5% of the species were calculated, HC5: 0.062 mg Zn L-1 and 0.15 mg Al L-1; according to SSD, R. subcapitata was the most sensitive organism to Zn, and it was one of the most sensitive to Al. Regarding the cladoceran C. silvestrii, we observed immobility on acute toxicity tests, 48 h-EC50: 0.22 mg Zn L-1 and 0.52 mg Al L-1; and reduction on the reproduction during chronic toxicity tests,7d-EC50: 0.11 mg Zn L-1 and 0.37 mg Al L-1. Mixtures of Zn and Al on C. silvestrii exert synergism to mobility. Preliminary risk assessments (RA) of C. silvestrii show a higher ecological risk of metal mixtures than the isolated metals’ effects. To zebrafish, we obtained 96h-LC50: 24.18 mg Zn L-1; we also observed that Zn altered the uptake of some essential elements, and altered behavior of zebrafish. Analyzing the RA of Zn on organisms from 3 trophic levels, Zn exerts high ecological risk to R. subcapitata and C. silvestrii, and moderate risk to zebrafish. Therefore, observing mixture data, we can infer that the toxicity of mixtures is often unpredictable since the responses are not always additive. Thus, based on results from this study we reinforce the importance of including ecotoxicological tests of mixtures in risk assessments.