Uptake kinetics and accumulation of pesticides in wheat (Triticum aestivum L.): Impact of chemical and plant properties.

Abstract

Plant uptake is an important process in determining the transfer of pesticides through a food chain. Understanding how crops take up and translocate pesticides is critical in developing powerful models to predict pesticide accumulation in agricultural produce and potential human exposure. Herein, wheat was selected as a model plant species to investigate the uptake and distribution of eleven widely used pesticides in a hydroponic system as a function of time for 144h. The time-dependent uptake kinetics of these pesticides were fitted with a first-order 1-compartment kinetic model. During 144h, flusilazole and difenoconazole, with relative high log Kow (3.87 and 4.36, respectively), displayed higher root uptake rate constants (k). To clarify the role of root lipid content (flip) in plant accumulation of pesticides, we conducted a lipid normalization meta-analysis using data from this and previous studies, and found that the flip value was an important factor in predicting the root concentration factor (RCF) of pesticides. An improved correlation was observed between log RCF and log flipKow (R2=0.748, N=26, P<0.001), compared with the correlation between log RCF and log Kow (R2=0.686, N=26, P<0.001). Furthermore, the hydrophilic pesticides (e.g. log Kow < 2) were found to reach partition equilibrium faster than lipophilic pesticides (e.g. log Kow > 3) during the uptake process. The quasi-equilibrium factor (αpt) was inversely related to log Kow (R2=0.773, N=11, P<0.001) suggesting a hydrophobicity-regulated uptake equilibrium. Findings from this study could facilitate crop-uptake model optimization.