Toxicidade subcrônica de lambaris Astyanax aff. bimaculatus expostos ao zinco / Subchronic toxicity in Astyanax aff. bimaculatus exposed to zinc.

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

Many metals occur naturally in aquatic environments and are classified as pollutants only when added by men in sufficient amounts to produce deleterious effects on organisms. Among these metals already existent on the aquatic environment it can be mentioned zinc (Zn) which is an essential element for living beings. In high concentrations, zinc can become toxic to living things by reducing the serum levels of copper, causing an immunity decrease. This study aims to analyze the bioaccumulation and the effects of subchronic exposure to different concentrations of Zn, on the histology of gills, liver and testis of adult individuals of lambaris Astyanax aff. bimaculatus to evaluate the potential of the species asbioindicator of water quality. Sixty five lambaris were used, divided equally into five tanks. A control group was made, kept under the same conditions as the treated ones, nevertheless without the metal. Every day was added 0,16, 0,33, 0,5 and 0,66 μg L-1 of Zn in the water, adding up to 5, 10, 15 and 20 mg L-1 Zn, respectively, at the end of the experimental period, of 30 days. At the end of exposure, animals were anesthetized, euthanized, weighed, measured and the bones, testis, liver, gills, head and muscle were removed. Collected tissue samples were dried and digested for the determination of zinc concentrations over atomic absorption spectrophotometer. The remaining tissue was fixed, included and sectioned in rotative microtome and stained for producing slides. At the groups where the Zn serum in water were 5 and 10 mg L-1, the accumulation of the metal was higher on the testis, followed by gills, bones, head and muscles, and in the treatments where the Zn serum in water were 15 and 20 mg L-1, the accumulation of the metal was higher on the gills, followed by testis, bones, muscle and head. Various histopathologies were classified and quantified on the gills, testicles and liver which were also measured points over the nucleus and cytoplasm of hepatocytes, sinusoidal capillary and leukocyte infiltrated, beyond the determination of the nuclear diameter of hepatocytes and calculated hepatossomatic indexes. On the testicles were morphometrically quantified, the matching points on cyst, intertubule, sperm and seminal fluid. The results show that even in the lowest concentration (considered as the top allowed by environmental regulations) experimental levels of Zn caused irreversible damage in both gills and liver of A. aff. bimaculatus, compromising the function of these tissues. The exposure of A. aff. bimaculatus to Zn caused severe and permanent histopathological changes on the testicles, leading to a reduction on sperm production, which may result, in the natural environment, the decline of fertility rate and the local extinction of the population. The presented results clearly proved the increasing accumulation of Zn on different tissues of animals in study kept down a subchronic exposure (30 days). Thus, A. aff. bimaculatus showed itself a susceptible species even when exposed to 5 mg L-1 Zn, established by CONAMA Resolution No. 357, of 17/03/2005 as the maximum for appropriate water for breeding. Therefore, it is suitable as a bioindicator.

ASSUNTO(S)

metal pesado fígado brânquias testículo toxicologia zoologia heavy metal liver gill testicle toxicology

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