Aplicación de solarización y ozonización para la eliminación de residuos de plaguicidas en suelos agrícolas

Résumé

Soil is a dynamic medium in which animal and plant life develops, and which acts as a regulator of water flow. It is also one of the most vulnerable and sensitive environments to pollution. Among all the anthropogenic causes responsible for the appearance of pollutants in the soil, agriculture is the most important source, as the soil is treated directly with chemical substances. The use of pesticides has made it possible to increase agricultural production worldwide, as they reduce crop losses due to different pests and diseases. However, their continuous and uncontrolled use can cause contamination of different parts of the environment (soil, water and air) and affect human health due to their high toxicity and persistence. Sustainable soil management for agricultural activity requires avoiding contamination derived from the use of pesticides, and recovering soils that are already contaminated. To this end, new soil remediation methods are currently being developed. The effectiveness of these decontamination processes depends on the selection of the appropriate technique, and it is necessary to evaluate the agricultural, environmental, social and economic implications. Among these remediation techniques, solarization and ozonation have arisen great interest within the scientific community. Solarization is a hydrothermal technique in which the previously moistened soil is covered with an impermeable plastic that is transparent to solar radiation. It is carried out mainly during the summer months, when temperature and solar radiation are more intense. Ozonation degrades any type of organic molecule to CO2, water and mineral salts, either directly (due to the high oxidizing power of ozone) or indirectly (due to the formation of OH● radicals, which are much less selective). The objective of this Thesis work is to evaluate the efficacy of a combination of solarization and ozonation to eliminate or decrease the concentration of pesticide residues in soils. In this work, the degradation of fifteen active substances belonging to four families of pesticides (neonicotinoids, triazoles, strobilurins and anilinopyrimidines), widely used for the cultivation of horticultural species in the Region of Murcia, was studied. Trials were performed at different scales (laboratory, experimental greenhouse and commercial greenhouse) with soils with diverse physicochemical properties. Ozonation tests were carried out using ozone generators with different capacities and, in all cases, an ozone detector and a residual ozone destructor to avoid possible leakages. Pesticide residues in soil were determined by liquid chromatography coupled to a triple quadrupole mass spectrometer detector (HPLC/MS/MS). The experimental variables were optimized under controlled conditions in order to subsequently realise the treatment in a commercial greenhouse. Thus, the remediation treatments combined solarization and the application of ozone gas in different ways to achieve an increase in the degradation rate of the pesticides studied in the soil. The results obtained showed that the dose and mode of ozone application (surface or subsurface), together with the increase in temperature and the greater number of accumulated hours at high temperatures, were the main factors influencing the efficiency of pesticide degradation. On the other hand, longer residence time of pesticides in the soil caused a higher adsorption of pesticides, decreasing their availability for degradation. The results obtained in the trial conducted in a commercial greenhouse showed an average pesticide degradation of 53% after forty days of treatment. Finally, the main transformation products (TP) generated during the degradation process were identified and monitored, as well as the costs associated with the treatments carried out at different scales of work. In conclusion, the combination of solarization and ozonation techniques was able to degrade pesticide residues present in agricultural soils, in a variable percentage depending on the active material studied, affecting only slightly the soil quality, and can be applied in commercial greenhouses with a not very high economic cost and which depends on the surface or mass treated.