Migration of Pesticides in Soil and the Importance of Preferential Flows: Observation, Study, and Mathematical Modeling

Le résumé fourni par la source

Abstract— Pesticide residues were determined in soil and water in several regions (Tula oblast, Krasnodar region, and Uzbekistan). Components of modern pesticides were not detected, but trace concentrations of obsolete organochlorine pesticides were found. The non-obvious patterns of concentration of these residues in soil and water sources indicate their long-term migration potential and the existence of active pathways for their removal into the groundwater zone. A study of transport pathways in soil pore space was conducted using Haplic Chernozem in the Tula oblast as an example. A laboratory lysimetric experiment was conducted with a soil monolith from the upper part of the profile, and scenario-based migration calculations were performed using the PEARL model. The lysimetric experiment revealed extremely uneven flow and removal of the nonsorbable KBr tracer and the pesticide imazamox (Koc = 11 L/kg, DT50 = 200 days) along the base of the monolith. More than 80% of the bromide ion and a significant portion of the pesticide were transported through only three of the five eluate collection sectors, while runoff was minimal in the remaining area of the monolith’s lower boundary. It is possible to quantitatively link the profile structure to vertical preferential flow using the mixing step parameter. The mixing step is defined as the characteristic vertical scale at which the effective flow mixing occurs between the transit and storage zones of the profile. Varying its value from units to tens of centimeters in the PEARL model changes the peak times of calculated concentrations for pesticides characterized by different combinations of mobility and persistence. This allows the mixing step to be be considered a significant parameter when incorporating preferential transport into worst-case risk assessment scenarios.

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