Sugarcane vinasse is one of the main residues generated by the transformation of cane into ethanol. Because of the high organic content (COD), high biochemical oxygen demand (BOD), low pH, the large amount that this residue is generated (15l for every liter of ethanol produced) and their use as fertilizer on the sugarcane crop, this residue is potentially polluting to the soil ecossystem and by percolation to water ecossystem too. Thus, this study aimed to assess the toxicity of vinasse by analyzing Oreochromis niloticus gills exposed to different dilutions (1%, 2.5%, 5% and 10%) in two bioassays. The gills were collected, fixed and analyzed using ultra morphological, histological, and histochemical techniques. After exposure to the vinasse, a statistically significant reduction of the ridges present on the surface of pavimentous cells was observed in one of the bioassays; such structures are responsible for mucus retention, which helps to protect the tissue. In addition, an intumescence of the cells was observed in the treatments with vinasse as well as an increase in the amount of chloridric cells. Some striking tissue changes detected in the treatments were epithelial detachment and loss of integrity of secondary lamellae, causing their rupture and consequent hemorrhage. In the first bioassay, the amount of these changes was statistically significant at the 5% dilution, and the focus of hemorrhage was significant at all dilution ratios. In the second bioassay, the epithelial disorganization was statistically significant only at the 2.5% dilution of vinasse. Moreover, for both bioassays performed, a significant increase in mucous cells was observed when compared with the control. Our results demonstrate the toxic action of sugarcane vinasse, which caused histopathological changes in the exposed animals at all four dilution tested. This highlights the need for caution in the disposal of sugarcane vinasse on the soil, especially due to its capacity for being leached or percolated into water resources, which could seriously damage aquatic fauna.

Water is an essential factor for maintaining the vital functions of living beings. Nickel is the 24th most abundant element on Earth; it is a heavy metal that is genotoxic and mutagenic in its chloride form. Due to industrial use, its concentration in surface sediments increased considerably. Fish develop characteristics that make them excellent experimental models for studying aquatic toxicology. They are particularly useful because they can alert of the potential danger of chemical substances or environmental pollution. Due to water quality impairment and because there are few published studies that relate nickel to tissue alteration, this study aimed to examine the consequences of nickel in an aquatic environment. For this analysis, individuals of Oreochromis niloticus were exposed for 96 h to three different concentrations of nickel dissolved in water according to the standard established by Brazilian law and compared them to a control group. After exposure, the gills were analyzed using X-ray microanalysis, ultramorphology, and histological and histochemical analysis. The results demonstrated that all the concentrations used in the experiment altered the histophysiology of the individuals exposed. In conclusion, the nickel presents a toxic potential to fish, even at the lowest concentration tested, which is equivalent to half of the concentration allowed by law. The CONAMA resolution should be revised for this parameter because of the interference of this metal in the histophysiology of the tested organism.

The indiscriminate use of pesticides has become a serious environmental concern. Insecticide imidacloprid (IMI) is the second most widely used pesticides worldwide. In 2010, 1.934 tons of IMI were sold in Brazil, mostly to be used in sugarcane crops. Several studies have detected its presence in the aquatic environment constituting a risk to non-target organisms. The aquatic animals are organisms used for environmental biomonitoring worldwide. They are considered excellent genetic models to detect environmental mutagens. Among animal species, the fish Oreochromis niloticus, commonly known as Nile tilapia, has been used to evaluate DNA damage. The present study therefore evaluated the effect of IMI on the genetic material of Oreochromis niloticus (Pisces) erythrocytes exposed to different concentration (250; 125 and 62.5 µg/L) of IMI used in growing sugarcane. The effect of the IMI was measured using the comet assay and the micronucleus (MN) test, assays that detected genotoxic damage. The results in the comet assay demonstrated that the concentrations tested induced primary damage to DNA. They also proved the occurrence of MN and nuclear abnormalities at the higher concentration used in the micronuclei and other nuclear abnormalities test. The insecticide IMI induced primary DNA damage at all concentrations and

bic microbial metabolism as well as growth of aquatic plants, which favors the assimilation of nutrients and, consequently, improves the quality of the treated effluent.Conclusions: Therefore, bioremediation with water hyacinth used in sugarcane vinasse showed to be effective in reducing the BOD and is an alternative for the treatment of this waste.

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