Assessing the Dissipation of Pesticides of Different Polarities in Soil Samples

Abstract

A methodology has been developed to assess the presence and dissipation of herbicides of a wide range of polarities in soil using in-tube solid-phase microextraction (IT-SPME) coupled online to capillary liquid chromatography (capLC). The compounds investigated were tritosulfuron (TRT), triflusulfuron-methyl (TRF), aclonifen (ACL), and bifenox (BF), with log octanol-water partition coefficients (log Kow) ranging from 0.62 to 4.48. The method provided suitable linearity at concentration levels of 0.5–4.0 µg/g for TRT and TRF, and 0.2–1.0 µg/g for ACL and BF, and intra- and interday precision (expressed as relative standard deviation) ≤4% and ≤8%, respectively. The mean recoveries ranged from 90% to 101%, and the limits of detection (LODs) and quantification (LOQs) were in the intervals of 0.05–0.1 µg/g and 0.1–0.4 µg/g, respectively. The accuracy of the method was also satisfactory. The proposed approach was successfully applied to assess the degradation of the tested herbicides in different types of soil (agricultural, urban and forest) after being exposed to different laboratory and outdoor conditions. The results obtained showed a greater persistence of the most apolar compounds ACL and BF, with percentages of degraded herbicide ≤31% regardless of the soil characteristics. In contrast, a significant degradation of highly polar herbicides TRT and TRF was observed in soils with the lowest organic matter, even after a few days of exposure. For example, the percentages of remaining TRT and TRF in this kind of soil after 20 days were ≤65%; the half-life time of TRF was only 24.8 days. These results indicate that the proposed approach can be considered as an effective tool for a better understanding of soil pollution.