Toxicidade de metais: uma avaliação em níveis molecular, individual e riscos para os ecossistemas aquáticos da Amazônia

Abstract

The continuous entry of metals into aquatic ecosystems is a global reality, exacerbated in developing countries. In Brazil, especially in the North region, where most of the Legal Amazon is located, multiple pollution sources have multiplied for decades, posing risks to the aquatic biota. In this perspective, ecotoxicological studies, including the use of biomarkers, and ecological risk assessment protocols, can provide relevant information about the environmental conditions of aquatic ecosystems in this biome. Thus, the main objective of this study was to describe a new species of ostracode and assess its acute sensitivity to metallic salts (CuSO4, CdCl2, HgCl2, ZnCl2), both individually and in combination, as well as to evaluate if environmentally relevant concentrations induce oxidative stress. Finally, an ecological risk assessment protocol was conducted to examine the risks associated with exposure to these metals. Individuals of the species Strandesia rondoniensis used in this study were collected in the Natural Park of Porto Velho, in the Amazon region (state of Rondônia, Brazil), acclimatized, and cultured in laboratory. The growth and reproduction rates of eleven adult individuals of S. rondoniensis were analyzed. The ecotoxicological evaluation involved the simultaneous exposure to each metal individually and in a mixture, through a factorial design for toxicity with 25 different combinations over 48 hours. For the ecological risk assessment, concentrations of metals measured in the waters of various aquatic environments in the Amazon basin were considered based on the risk quotient values. Furthermore, investigations into the responses of biomarkers (Reduced Glutathione – GSH, Lipoperoxides – LPO, Metallothionein – MT, Superoxide Dismutase – SOD, and DNA Strandbreak) were conducted for all metals. The results of taxonomic identification of the species showed a high morphological resemblance to Neostrandesia striata and Bradleytriebella lineata, even though the new species belongs to Strandesia genus, indicating evolutionary convergence. Life cycle analysis showed that individuals of S. rondoniensis exhibit rapid growth and high reproductive rates, favoring their use in laboratory studies. The ecotoxicological results indicated that the toxicity gradient of metals was Cd > Hg > Cu > Zn. Toxicity in the mixture showed that the combination of Cu-Cd and Cu-Zn fit the model better (CA), indicating primarily synergism when copper predominated in the mixture. Meanwhile, the Cu-Hg interaction fit the model better (IA), again indicating synergism when copper was at a higher concentration. The survey conducted in this study shows that, although metal concentrations in the water were generally low, these values were well above the limits established by current national legislation in many areas, showing higher concentrations for the metals Co, Pb, Cr, Cu, and Ni. Concentrations of Mn, Cu, Ba, Pb, Co, Ni, Cr, Zn, Cd, and As were particularly high in sediment for various evaluated environments. Ecological risk assessment for the water compartment revealed that 56% of the studied areas presented a high risk (RQ>1) for aquatic biota. In sediment, 66% of the locations showed high risk and 40% medium risk (RQ = 0.1-1). The contamination factor indicated that 49% of the sampling points showed high contamination, and only 24% showed low contamination. Furthermore, sublethal exposures showed that the antioxidant and detoxification system (SOD, GSH and MT) were activated by exposure to metals; however, not enough to contain oxidative damage; thus, increasing LPO levels, resulting in DNA breakage. Therefore, the continuous contamination of aquatic ecosystems in the Amazon region represents a concerning threat to aquatic biota, as the concentrations found in our study are considerably above tolerance limits for many species, especially for the ostracode S. rondoniensis used in this study.