ECOTOXICOLOGIA DE IMIDACLOPRIDO E CROMO EM FOLSOMIA CANDIDA EM SOLOS DO BIOMA CERRADO

Abstract

Pesticide residues have been frequently detected in soils around the world, posing potential risks to soil organisms and soil quality, as well as human health. The city of Rio Verde, located in the state of Goiás, Brazil, stands out in the production of grains, where there is an intensive and recurrent use of pesticides, such as herbicides, as well as insecticides, especially neonicotinoids. In addition, there is evidence that agricultural soils in the region are contaminated by chromium (Cr). Depending on the conditions of use, their physicochemical characteristics and environmental conditions, pesticide residues may be present in the soil in concentrations close to or higher than concentrations that cause adverse effects to soil organisms (earthworms, springtails, enchitreids, mites, among others). Understanding the toxicity of pesticides to soil organisms, especially in scenarios involving the presence of other contaminants such as heavy metals, is of fundamental importance so that there is no underestimation of ecological risks to soil organisms. Therefore, the objectives of this work were to perform a literature review on the dissipation of pesticides in Brazilian soils and to evaluate, by means of ecotoxicological assays, the effects of the pesticide imidacloprido, associated or not with Cr, the springtail Folsomia candida, in natural soil samples collected in the region of Rio Verde, Goiás, Brazil and to propagate environmental education by performing a pedagogical intervention presenting soil organisms and their environmental roles in a school. The literature review was conducted using the keywords "dissipation" AND "pesticides" AND "Brazil" in the national and international databases: Scielo, Web of Science and Scopus. A total of 47 articles were included in the discussions, which provided information on the half-life of mineralization and dissipation of 35 active ingredients. The active ingredient with the most papers was atrazine included in 10 studies. The low number of studies involving each active ingredient and the great diversity of soils in Brazil did not allow us to determine pesticide dissipation patterns in Brazilian soils, however, compared to temperate regions, generally the dissipation in tropical climates is faster. Factors such as the physicochemical properties of the active ingredient and the soil, microbial diversity, and the history of applications also interfere with dissipation. Dissipation interferes with the bioavailability of pesticides or metabolites, which will interfere with toxicity to soil organisms, the longer the half-life period, the greater the bioavailability and the greater the possibility of the residues causing effects to these organisms. Toxicity to organisms can be evaluated through survival and reproduction tests regulated by ISO. The test with springtails was carried out with 10 organisms between 10 and 12 days of age, in 6 replicates, for 28 days, with humidity and food replaced weekly. Samples of 5 natural soils, collected in Rio Verde - GO, with varying natural concentrations of Cr were used in two tests. In the first test, without pesticide, there was no effect observed in reproduction and survivor of Folsomia candida. In the second test, with addition of Evidence® 700 WG (70% of imidacloprid), the non-observed effect concentration (NOEC) was 0,32 mg/kg and the lowest observed concentration (LOEC) was 0,64 mg/kg. The concentration of effect on reproduction in 50% of organisms (EC50) was 0.62 mg/kg [0.4693-0.7846] and mortality LC50 = 1.026 mg/kg [0.90 - 1.15]. Although the first test did not show an effect related to the metal chromium, the addition of the pesticide to this soil showed a slight reduction in the expected value of EC50 compared to the values present in the literature (approximately 0.80 mg/kg in a soil with the same classification – oxisol). The pedagogical intervention was carried out in partnership with the “Criar” project of SESC in Palmas – TO, divided into moments: the first moment was a conversation circle followed by the elaboration of drawings of soil organisms, to understand the students' previous knowledge; the second moment was composed of a presentation of soil organisms and their environmental roles; the third moment was the manufacture of a composter; the fourth moment was a technical visit of the students of the project to the Laboratory of Ecotoxicology and Environmental Risks of the Federal University of Tocantins and to close, a new conversation circle was held with the elaboration of drawings of soil organisms. The project sparked the curiosity and sense of responsibility of the students in relation to the environmental protection of the habitat of the "soil bugs" that were previously unknown. Conversation circles and production of drawings were held by the students in stage 1 and in the final stage to observe the evolution of previous and acquired knowledge. Ecotoxicology is a crucial area for environmental protection, as it involves the risks inherent to each chemical compound and its availability, thus, knowing more about the environmental dissipation behavior of various pesticide active ingredients, and their interaction with other chemicals, as well as the monitoring of pesticide residues in agricultural areas and in water. It is important to determine the exposure of organisms to these contaminants. In addition, the determination of concentrations of deleterious effects in non-target organisms is a means of protection for other organisms, since ensuring that the most sensitive organisms are not at risk guarantees protection for the entire trophic chain. In environmental education, which should begin from an early age, ecotoxicology helps to make students aware of the role of each organism in the edaphic fauna, even the smallest ones, and helps to recognize that it is the duty of each individual to protect the environment in which we live.