Question

1) Benzene is present in soil-water at a particular site where poplar trees are grown. Assume that equilibrium condition has been established between the plant roots and soil water, and the equilibrium concentration in soil-water is 0.02 g/l. Calculate the equilibrium concentration of benzene in the following:

a. Plant Roots

b. Plant transpiration stream

c. Foliage (leaf) Assume ambient concentration of benzene in air is 0.001g/l. Which of the three components of the plant (roots, transpiration stream and leaves) will retain the highest amount of benzene (when compared on per unit basis i.e. on per Kg roots vs per L TS vs per Kg Leaf) in equilibrium conditions?

Answer 1

The amount of benzene (equilibrium concentration) found in the soil-water is at equilibrium with the amount of benzene in the plant roots which are also present in the soil. Hence the concentration of benzene in soil water would be the same as in the plant roots (i.e: 0.02g/L).

However, the plants transpiration system would show lesser amount of benzene, which would further turn to be negligable in the foliage. (because of the ascent of sap).

The root of the plant would retain highest amount of benzene (because of the closeness of the roots to the soil. This further decreases as we move into the upper (aerial) parts of the plant.