Toxicologia de anfíbios in situ: levantamento bibliográfico e estudo de caso com girinos de leptodatylus luctator

Abstract

Amphibians play a fundamental role in the functioning of ecosystems, especially in nutrient cycling, energy flow, and pest control. This group shows a massive population decline, with approximately 41% of all species at risk, highlighting pollution from pesticide use as one of the main threats to the loss of anura biodiversity. This is because amphibians have a highly permeable epidermis and a biphasic way of life, where they use both the aquatic and terrestrial environments, allowing exposure and making them susceptible to the chemical agents released into the environment. Amphibians are a group considered a model in ecotoxicological studies. However, due to the greater control of experimental conditions, the vast majority of studies are conducted in the laboratory, thus maintaining a gap in knowledge about the effects of pesticides on amphibians in natural environments. Under natural conditions, where environmental variables are not controlled, experiments must relate all the dynamics of interaction of the substances in the environment, the environmental variables, and the influences they cause on the organisms. To evaluate the studies already carried out under natural conditions, a bibliographical survey was carried out by consulting the Web of Science and SCOPUS databases, considering articles published in the last twenty years, using the terms 'field experimentation' or 'in situ study', associated with 'tadpole' and 'agrochemical' or 'pesticide', using a descriptive methodology. Twenty-one abstracts were found, where they were evaluated and methodologies checked to ensure only the analysis of experiments conducted in the field. Thus, ten papers were selected for the construction of the review. The works related to the theme used native amphibian species, considered generalists, present in the study region and were executed in environments destined to agricultural cultivation with control groups in preserved locations. In these works, different methodologies were used, such as intentional spraying of water bodies, quantification of pesticides in the study sites, and checking the changes caused by the environment on the tadpoles. The main evaluations were based on tadpole survival and morphological changes, and in some cases cytological and biochemical assays. In the second chapter, an insitu test was performed to compare the sensitivity of Leptodactylus luctator tadpoles in lentic environments around and inside the Turvo State Park (PET) conservation unit. Ten lentic environments were evaluated, five inside and five around the PET, analyzing pesticides and physical/chemical parameters of the ponds. To study the tadpoles, one spawning was collected, taken to the laboratory until they reached stage 25 on the Gosner table, and then relocated to the 10 sample environments, with 15 tadpoles in each environment, in triplicate. Each group of tadpoles was placed in a pond, isolated within a trap allowing fluid exchange with the environment, but protected from predators. After 14 days, removed, counted, and taken to the laboratory for determination of length, mass, and subsequent verification of micronuclei and nuclear changes in erythrocytes (ANEs). After the analyses of the slides with cell counts, it was observed in both environments the presence of micronuclei and ANEs in the individuals, mainly showing binucleated, anucleated, notched nucleus, lobed nucleus, nuclear buds, karyolysis, and apoptosis cells. Regarding pesticides, residues of clomazone and chlorpyrifos were found inside the PET, and atrazine was found in the surrounding area. In addition, azoxystrobin (0.022 µg L̵¹) and imidacloprid (0.028 µg L̵¹) were quantified in the area surrounding the park. More studies are needed to verify the possible harmful effects of pesticides on Leptodactylus luctator and even on other species present in the region, as well as at other times of the year.