Extração ultrassônica e quantificação de pesticidas (alaclor, atrazina, clorpirifós e trifluralina) por cromatografia á gás e espectrometria de massas: estudo comparativo em amostras de solo de ambientes agroecológicos e convencionais

Abstract

Pesticides, or agrochemicals, are chemical compounds used in plantations as agricultural defensive, allowing plants not to be affected by insects and weeds that compromise their growth. However, the presence of these compounds can harm the health of the fauna, flora, biota and the human, since they can be absorbed by the food as much as they are present in the soil, in the water, in the air and in the sediment. Alachlor, chloroacetamide and herbicide, were banned in Brazil in 2013. Atrazine and trifluralin are herbicides belonging to the triazine and dinitroaniline classes, respectively, and the latter is a compound that is banned in the USA. Chlorpyrifos is an insecticide for which it is of great interest to study because it is an organophosphorus compound. The region to be studied comprises Contest Settlement, located in the city of Lapa - PR, 62 km from the capital Curitiba, where there is food production in an agroecological and conventional way. Although there is evidence of the dangerousness of pesticides, it should be emphasized that there are no Brazilian laws that contemplate concentration values that can be used in agricultural soil. The objective of this study was to evaluate the presence and mobility of pesticides that are possibly present in the agricultural soil of the Contested Settlement, in order to allow a comparison between the two agricultural production means. Three agroecological production sites and three conventional production were selected. The soil samples were collected in two sampling intervals at two months, at two depths: on the surface and at 20 cm, using a Dutch auger. Samples were transferred to previously identified cleaned glass vials and kept at 4ºC in the absence of light during transport. Upon arriving at the laboratory, the samples were kept frozen. For the validation of the analytical method, concentrations of 10, 20, 50 and 90 μg L-1 of the pesticides were added simultaneously in soil samples. The extraction of the pesticides was carried out with of ethyl acetate in ultrasound. Samples were filtered through a glass fiber membrane and florisil cartridge and the solvent was evaporated in a rotary evaporator. The compounds were reconstituted in ethyl acetate and filtered through a PVDF membrane. The obtained extracts were injected in a gas chromatograph, coupled to mass spectrometer of the brand Agilent model 7890/7000, under predetermined conditions. The method was validated with r2 higher than 0.99 for the linear range of 1 to 100 μg L-1. Alachlor, atrazine, chlorpyrifos and trifluralin presented LQ values ranged from 0.2 to 1.5 ng g-1. The results of recoveries for the same compounds ranged from 83.0% to 113%, with RSD less than13%. From the analysis of the samples, only chlorpyrifos presented concentration higher than the LQ at a conventional production point.