Studiu ecotoxicologic privind toxicitatea substanţei Teflutrin asupra lumbricidelor (Oligochaeta: Lumbricidae)

Abstract

The purpose of the study was to assess through laboratory experiments the acute toxicity manifested by the insecticide Force 1.5 G (acting against the western corn rootworm Diabrotica virgifera virgifera and produced by Syngenta Crop Protection AG, Switzerland) in terms of the content of active substance (tefluthrin 1.5%) on the species Eisenia fetida (red worm). Also, we studied the dynamics of lumbricides in soil (chernozem, FAO System) cultivated with maize (Zea mays L.) and treated with the insecticide Force 1.5 G, on an 454 experimental field, to see the influence of this substance on the number and biomass of earthworms. The study objectives were: to determine the average living biomass and the number of live earthworms/treatment at the beginning and end of the tests; to describe the physical (weight loss) and pathological (lesions, ulcerations of the tegument) symptoms observable in organisms examined during the test; to establish the mortality rate in controls; to establish the mortality rate in test versions; to establish the LD50 value; to specify the highest concentration that did not cause mortality; to specify the lowest concentration that caused 100% mortality; to highlight changes occurred in the dynamics of earthworms (abundance, biomass) due to the impact of the insecticide Force 1.5 G applied on a maize crop (Zea mays L.), in a cambic chernozem soil (FAO System). To achieve the purpose and objectives of the study, there was used the OECD (Organisation for Economic Co-operation and Development) methodology to test the acute toxicity of some chemicals on lumbricides: OECD Guidelines for testing of chemicals: Earthworm acute toxicity tests, no. 207/1984, as well as the 2% formaldehyde method for extracting earthworms from the soil. The study was conducted in the Laboratory of Ecology and Environment Protection of the University of Agricultural Sciences and Veterinary Medicine of Banat, Timişoara, Romania. Based on the study conducted, we were able to draw the following conclusions: 1). The results achieved by conducting the ecotoxicity test in laboratory on the earthworms Eisenia fetida is an another confirmation that these organisms living in soil, with a major role in maintaining its fertility, are sometimes extremely sensitive to substances that reach the soil (pesticides), leading to the idea that their use should be undertaken with caution and responsibility so as not to affect on the long-term or even irreversibly the life of earthworms found in soil and thus their activity which is important in maintaining the fertility of agricultural lands. 2). The tests conducted on an experimental field on the influence of the insecticide Force 1.5 G on lumbricides have shown that this insecticide applied at a dose of 15 kg/ha (or 6 g/4m2 ) exerted a negative effect on the abundance (number of individuals/m2 ) and biomass (g individuals/m2 ) of earthworms in the experimental versions studied.