Metais pesados em água, sedimentos e peixes no rio Maranguapinho, Região Metropolitana de Fortaleza, Ceará

Abstract

Aquatic ecosystems are considered receivers of contaminants released into the environment, being susceptible the actions of domestic and industrial effluents which are released directly into this ecosystem. Among the environmental contaminants are heavy metals which are highly resistant to degradation. They can occur in different chemical forms in nature and therefore may increase or reduce its toxic characteristics toward several organisms and their biological characteristics, according to their concentration in the ecosystem. The Maranguapinho river presents environmental problems, such as pollution, deforestation of its margins, among others. The river bed is silted up due to the replacement of riparian vegetation and receives several channels in the region, clandestine pipes of domestic sewages. A two-year study was carried out in three reaches located in this river: RMA-A (high basin), RMA-B (middle basin) and RMA-C (low basin). A total of 93 fishes were collected, distributed in four orders, seven families, nine genera and 11 species. The species richness was highest in RMA-B, with five species. Although above the maximum allowed value, the concentrations of Al, Fe and Mn found in the water were not considered contaminants, indicating that these elements are the result of lithological composition of the region. The geoaccumulation index indicated that all the sediment samples of Maranguapinho are classified into Class 1 due to the small variation in the intensity of pollution, revealing that the elements are natural constituents of the basin. The sample size used was 21 individuals for further toxicological representation of fishes captured. Hypostomus jaguribensis and Loricariichthys nudirostris species showed the highest amounts of the metals studied (Al = 44,34 ppm, Fe = 460,15 ppm and Sr = 1,38 ppm), trending to accumulate high amounts of metals in the body and can be considered good bioindicators. The ANOVA revealed a statistically significant difference between the concentrations of Cd and Zn in the viscera of fish and the maximum values allowed by the law, showing that these elements can cause contamination risks to fish and humans and allowed the distinction of marginal influences between the average of Fe and Mn in the viscera of fish and water stations, being the water the factor of entry of the elements in the animal organism. The Maranguapinho river is a natural environment potentially fragile. Several kinds of anthropogenic interferences, such as discharge of effluents, contributes for the its environmental degradation.