Uptake of trifluralin and lindane from water by ryegrass

Abstract

Understanding of the plant uptake of organic chemicals is essential to assessing contaminant mobility in the ecosystem, exposure to humans, and phytoremediation technologies. In this study, we measured the uptake of trifluralin and lindane from water by ryegrass as a function of uptake time for periods of 96 and 120 h, respectively. Trifluralin concentration in ryegrass increased sharply at the early stage of uptake and reached the maximum at 10 h, and then decreased with uptake time. 14C-labelled trifluralin uptake displayed a similar trend but a higher 14C-concentration than that of extracted parent compound, indicating metabolism and formation of bound residues following trifluralin uptake. Lindane concentration in ryegrass slowly increased with uptake time and approached a plateau, indicating minimal metabolism and formation of bound residues. The difference in the uptake characteristics of these two chemicals may be related to the differences in their lipophilicity, and chemical and biological reactivities. A two-compartment model accounting for the contributions of transpiration, metabolism and formation of bound residues to overall uptake was developed to assess the uptake kinetics. The model adequately described the uptake of trifluralin and lindane into ryegrass by providing the first-order rate constants of uptake, release, transpiration, and metabolism and formation of bound residues. These rate constants are used in calculating plant concentration factor (PCF). The ratios of trifluralin concentrations in ryegrass to its aqueous concentrations are between the PCF at thermodynamic equilibrium and the PCF at steady state, suggesting the utility of both PCF values.