Mechanistic modeling of pesticide uptake with a 3D plant architecture model

Helena Jorda,Andrea Schnepf,Christoph Oberdörster,Jan Vanderborght,Klaus Hammel,Asta Kunkel,Mathieu Javaux,Katrin Huber

doi:10.1007/s11356-021-14878-3

Abstract

Meaningful assessment of pesticide fate in soils and plants is based on fate models that represent all relevant processes. With mechanistic models, these processes can be simulated based on soil, substance, and plant properties. We present a mechanistic model that simulates pesticide uptake from soil and investigate how it is influenced, depending on the governing uptake process, by root and substance properties and by distributions of the substance and water in the soil profile. A new root solute uptake model based on a lumped version of the Trapp model (Trapp, 2000) was implemented in a coupled version of R-SWMS-ParTrace models for 3-D water flow and solute transport in soil and root systems. Solute uptake was modeled as two individual processes: advection with the transpiration stream and diffusion through the root membrane. We set up the model for a FOCUS scenario used in the European Union (EU) for pesticide registration. Considering a single vertical root and advective uptake only, the root hydraulic properties could be defined so that water and substance uptake and substance fate in soil showed a good agreement with the results of the 1D PEARL model, one of the reference models used in the EU for pesticide registration. Simulations with a complex root system and using root hydraulic parameters reported in the literature predicted larger water uptake from the upper root zone, leading to larger pesticide uptake when pesticides are concentrated in the upper root zone. Dilution of root water concentrations at the top root zone with water with low pesticide concentration taken up from the bottom of the root zone leads to larger uptake of solute when uptake was simulated as a diffusive process. This illustrates the importance of modeling uptake mechanistically and considering root and solute physical and chemical properties, especially when root-zone pesticide concentrations are non-uniform.

Highlights

Leaching of plant protection products and their metabolites into the groundwater presents a major risk to the environment and to public health
[cm] and pesticide concentration [g cm-3] in the soil 90 days after planting (DAP), together with the 2D distribution of water [d-1] and pesticide [g cm-3] sinks at − 20, − 40, and − 60 cm depth for a simulation performed with a complex root system architecture
Root solute uptake was modeled as an advective mechanism with ε = 0.5

Summary

Introduction

Leaching of plant protection products and their metabolites into the groundwater presents a major risk to the environment and to public health. Different risk assessment studies are required when new products are placed into markets. A framework by the FOCUS (forum for the coordination of pesticide fate models and their use) group provides four 1D models (e.g., PEARL model (Leistra et al, 2000)) and standard model scenarios, which are used to assess the risk for pesticide enrichment in ground and surface water Environ Sci Pollut Res (2021) 28:55678–55689 et al, 2000). These models describe all relevant processes that determine the fate of pesticides in soils, including the uptake of pesticides by plant roots. All four EU models describe pesticide uptake by plants as a passive advective process (see Table 1), i.e., pesticides are taken up proportionally to water uptake flux. The solute fraction that is taken up is determined by a constant factor, defined as the plant uptake factor (PUF) or the transpiration stream concentration factor (TSCF): Ru 1⁄4 Ru;L*1⁄2TSCF or PUF*CS;l; ð1Þ where Ru [M L-3 T-1] is the mass rate of pesticide uptake per bulk volume of soil, Ru,L [L3 L-3 T-1] the water uptake rate, and CS,l [M L-3] the dissolved solute concentration in the soil

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Conclusion