Determination of half life of the pesticides chlorpyrifos (14C) in an agricultural soil of the VI region by means of the using isotopic techniques

Chlorpyrifos is an organophosphorus insecticide widely used in Chilean agriculture in the control of plagues of insects in soil and several crops. From an environmental point of view, to know the behavior and fate of Chlorpyrifos under different moisture regimes in soil is important because it contributes to optimize its use, assuring that collateral effects do not take place inside or outside the application area and in addition it specifies the optimal conditions of application to obtain better results in the treatment with the land insecticide. In this work it was studied the half life of Chlorpyrifos (14C) in an agricultural soil of VI Region, by means of the use of Isotopic techniques, under two moisture regimes of 50 and 75% of the Field Capacity. The ground samples were fortified with doses of 10 mg/Kg and incubated to 20oC and in absence of light. The dissipation of Chlorpyrifos in soil was determined during 110 days of test, through the quantification of remaining 14CO2 by liquid scintillation counting. Results show temporary differences in the half life for different moisture regimes, with T1/2 of 21 and 28 days for the soil to 75 and 50% of the Field Capacity, respectively. It was studied the factors related to soil and plaguicide that could affect speed of degradation, either accelerating or inhibiting the process of dissipation of Chlorpyrifos, under the described moisture regimes. The results indicated that the fast degradation of the insecticide organophosphorus in the soil to 75% of the CC is product of biotic and abiotic processes. Between the abiotic processes the neutral hydrolysis constituted the principal route of dissipation, mainly due to the moisture content and pH presented in soil (pH 7,2). Nevertheless, factors as the high content of organic matter of the soil, low water solubility, high coefficient of adsorption and bond p=S of the Chlorpyrifos, they suggest the sorption process would inhibit hydrolysis, slowing down the determined times of half life in this work. As far as the biotic processes, the biodegradation was also influenced by the greater moisture content of the soil, where the soil to 75% of the Field Capacity, has shown the greater microbial activity and faster dissipation of Chlorpyrifos with a smaller T1/2, in comparison to the soil with minor moisture contained. Nevertheless, the contribution of the biodegradation is diminished in comparison to hydrolysis process, due to the conditions of incubation of the soil diminish the microbial activity in the time. In both moisture treatments, the dissipation of Chlorpyrifos present a two-phase process, showing a fast initial stage followed by a long term slow phase. The speed of dissipation of Chlorpyrifos was fitted and described suitably by a kinetic model of first order (Γ2 = 0.96), with T1/2 that differs in inferior percentage to 10%. Finally between the advantages presented by this technique, the low variability, the high sensitivity of detection and in addition the possibility to detection and quantification without the necessity of an extraction of analytes from soil samples (au)