Transport of methyl tert-butyl ether through alfalfa plants

Concentrations measured in alfalfa plant stem segments indicated th at plan ts grown in methyl tert-butyl ether (MTBE)-contaminated soil took up the ch emical through their roots. Assuming a cylindrical shape for the plant stem , a mathematical model was developed to describe the transport of MTBE thro ugh the stems. Simulation results from uniform and nonuniform initial conce ntration distributions across the stem radius were compared with steady-sta te experimental data. With known values of plant stem radius, water usage, water content, and the distance over which the concentration decreased by 5 0%, the diffusion coefficient of MTBE radial transport across the plant ste m was estimated with 95% confidence to be in the range of 8.43-16.2 x 10(-8 ) cm(2)/s with a mean of 1.23 x 10(-7) cm(2)/s. When the diffusion coeffici ent was calculated based on transient experimental data, the values with 95 % confidence interval ranged from 4.14 x 10(-7) to 8.00 x 10(-7) cm(2)/s wi th a mean value of 6.07 x 10(-7) cm(2)/s. The difference between these two results can be reduced by more accurate estimation of the water flow veloci ty through plant stems. The model is-applicable to other species including sunflowers and poplars upon substitution of appropriate parameters.