ENVIRONMENTAL IMPACT AND SAFETY OF AGROPROTECTIVE CHEMICAL BASED ON THIAMETHOXAM
Authors: Bulatova K. A. , Mallyabaeva M. I. , Tyumkina T. V. , Zainutdinova E. M. , Bаlакirеvа S. V. 
Published: September 2023

The article is devoted to the aspects of environmental safety of the use of Aktara insecticide, widely used in the agro-protective sector, with the active substance thiamethoxam from the class of neonicotinoids. Studies have been carried out on the impact of insecticide on test organisms of soil and aquatic ecosystems, and its transformation in the process of laboratory biodegradation has been studied on the basis of chromato-mass-spectral analysis.

In order to identify the anthropogenic load of soil and water ecosystems during the application of the Aktara preparation containing thiamethoxam, and to assess the toxicity of the insecticide, test objects were studied: earthworms (Lumbricus terrestris L.), shoe ciliates (Paramecium caudatum). The phytotoxicity of the drug was analyzed using test objects - seeds: corn (Zea mays), pea (Pisum sativum), tomato (Solanum lycopersicum), cucumber (Cucumis sativus), carrot (Daucus carota) and cabbage (Brassica oleracea), it was evaluated germination state. The biodegradation of thiamethoxam with the help of soil degrading microorganisms was studied.

The material for the experiments was Aktara, in which the active ingredient is thiamethoxam. Fertile chernozem, selected from the ecologically clean territory of the Iglinsky district of the Republic of Bashkortostan.

In the presented work, experiments were carried out on the effect of the drug on earthworms (Lumbricus terrestris L.), taking into account their behavior, the condition of contact of the test object with the insecticide was modeled.

Studies on phytotoxicity were carried out, vegetables (cucumber, carrot, tomato, cabbage), cereals (corn) and legumes (peas) were used as test objects.

Biotesting on infusoria-shoes (Paramecium caudatum) was carried out by an experimental method using the 2M-BIOTESTER device. Obtaining destructive material - microorganisms-destructors was carried out by the method of «imprints» in Petri dishes on meat-peptone agar, isolating them from fertile chernozem, selected in the Iglinsky district of Bashkortostan.

The change in the destructive material of the active substance of the insecticide was determined using a thin layer chromatogram (TLC), Silufol UV-254 plates were used, the eluent was acetone, the developer was phosphomolybdic acid. Chromato-mass-spectral analysis was performed on a Shimadzu GC-9A instrument.

The results of the analysis of the effect of the insecticide based on thiamethoxam on earthworms showed that this substance has a moderately toxic effect.

In uncontaminated soil, in microbiota-rich chernozem, a large species spectrum and numerical composition of microorganisms were observed: Pseudomonas sp., Bacillus sp., Arthrobacter sp., Azotobacter sp., Flavobacterium sp. The introduction of an insecticide (IC) into the agrosystem leads to a decrease in biomass, inhibition of the microbiota, and a negative impact is noted at the working concentration declared by the manufacturer. When using a dose of insecticide 2 IC in the soil, a further decrease in biomass was recorded and species resistant to toxicity were Pseudomonas sp. and Bacillus sp. With significant soil contamination, at a dose of insecticide 5 IC, the growth of the microenvironment was suppressed.

Biodegradation of thiamethoxam – [5-methyl-3-(2-chlorothiazol-5-ylmethyl)-1,3,5-oxadiazinan-4-ylidene-N-nitroamine], C8H10NO3SCl – was carried out for 170 days.

According to the results of chromato-mass spectral analysis, intermediate products of biodegradation were determined – bis (2-methylpropyl) ester of 1,2-benzenedicarboxylic acid, diisooctyl adipate.

In experiments on the study of phytotoxicity after treatment with the Aktara preparation of various concentrations: IC, 2 IC, 5 IC, the analysis showed a different result in comparison with the control sample.

It has been established that at the right concentration, thiamethoxam can have a positive effect on seed germination. Therefore, thiamethoxam is not toxic to plants if the instructions are followed.

The results of biotesting revealed that the toxicity index of samples with IC preparation and 2 IC corresponds to a moderate degree of toxicity (0,565 and 0,671, respectively) and 5 IC (0,797) corresponds to a high degree of toxicity.