Avaliação de metais pesados na bacia do Rio Amapari, Amapá e uma perspectiva da toxicologia para o ensino de química

Abstract

Heavy metals are non-biodegradable toxic pollutants that can bioaccumulate in organisms, posing risk to the environment and living beings. Ecotoxicology can be assigned to the teaching of chemistry because it is an interdisciplinary science. The objectives of this work are a) To determine the concentration of zinc, copper, iron, manganese, chromium and cadmium in the water of the Amapari River, b) To evaluate mutagenic and genotoxic effects caused by contaminants present in the water through bioassays with Danio rerio and c) To present toxicology in the teaching of chemistry as an interdisciplinary subject and a didactic proposal with an experiment to detect metals in water. To achieve these objectives water samples were collected from eleven sites in the Amapari River basin using 1 L and 20 L polyethylene containers. In each 1 L sample 1 mL of nitric acid was added, while the 20 L samples were not preserved with acid. An Atomic Absorption Spectrophotometer was used to determine the metals. For the toxicity bioassays, 20 L water samples were added in an aquarium per point, totaling eleven samples. In addition, an aquarium with water from the animal house system was used as a control. The bioassay lasted 96 hours. A total of 108 adult animals were used, fasted for 24 hours from exposure to water, and fed twice a day. For histopathological analysis of the gills, liver, and kidneys, the animals were fixed in Bouin's solution for 24 hours, and then decalcified in 7% EDTA solution for 48 hours. The samples were dehydrated in a series of alcohols, diaphinized in xylene, embedded in paraffin, sectioned at 5 μm, stained with hematoxylin and eosin and analyzed under an Olympus BX41 -Micron Microscope and photographed with a MDCE-5C USB 2.0 camera. The analyses of the water samples showed that Cd (0.018 ml/L), Cr (0.048 ml/L), Cu (0.024), Fe (0.701 ml/L), Mn (0.273) and Zn (0.140ml/L) were detected in the water above the limit established by CONAMA (357/2005) and WHO (2017) at the following sampling points P2, P7, P11. P1, P2, P3, P5, P6, P8, P9 and P10. P1, P2, P3, P4, P6, P7, P8, P10 and P11, respectively. Fe and Mn were higher at all points. In the reading of the blood slides, 276 nuclear alterations were found in total, emphasizing micronucleus (68%), nuclear budding (67%) and nuclear invagination (50%). P1 stood out for presenting the highest percentage values of abnormalities (51%). Histological analysis showed changes in gill tissue in all groups, except in the control group, being more significant in P7, P8 and P9. In the liver and kidneys only mild alterations were observed, the AHI was less than 10, which classifies this organ as normal. In view of this, the toxicological tests carried out in this study emphasize the need to monitor anthropogenic activities carried out in the study area. In addition, the proposal to teach toxicology presented here reminds us of the importance of environmental education at school, especially when it comes to our region