Effects of lipid-water partitioning and volatilization on the uptake, translocation, and release of organic contaminants by grasses

While the interaction of organic compounds with plants has been the subject of numerous studies, there remains a need for research on the mechanisms involved in solute uptake, storage, and release. This work consisted of three primary investigations: the measurement of lipid-water partition coefficients, monitoring the transient uptake behavior of solutes by annual rye grass, and the development of a model to describe this uptake behavior.; The first phase of this research focused on the influence of plant lipids on equilibrium sorption. The plant-water sorption isotherms of benzene, 1,2-dichlorobenzene, and phenanthrene were measured over a large range of solute concentrations. The plant materials studied included the shoots of annual rye, tall fescue, red fescue, and spinach as well as the roots of annual rye. For the compounds studied, partitioning into the lipids is believed to be the primary sorption mechanism. The estimated lipid-water partition coefficients of individual solutes were found to be significantly, greater than the corresponding octanol-water partition coefficients.; In the next segment of this study, the uptake of benzene and 1,2-dichlorobenzene by living annual rye plant was studied. The solutes were detected in the plants, with the concentration declining exponentially with vertical position within the plant. The accumulation levels of solute in the plant correlated well with the measured transpiration rate. Values of the quasi-equilibrium factor, alpha, for the lowest portions of the plant shoots did not approach values of unity in experiments lasting up to 4 weeks. These data suggest that volatilization of the solutes is a key process affecting the accumulation levels of the solute in the plant.; Finally, a model was developed to simulate the movement of conservative organic solutes in grass plants. Close agreement of the model output with the experimental data indicates that a relatively simple, one-dimensional advection-dispersion model with a volatilization loss term is capable of describing the transient uptake behavior of benzene by annual rye grass. The importance of the volatilization loss term in fitting the experimental data further supports the hypothesis that volatilization is a key process affecting benzene accumulation in the shoots of annual rye grass.