A MODEL OF ORGANIC-CHEMICAL UPTAKE BY PLANTS FROM SOIL AND THE ATMOSPHERE

A three-compartment mass balance model of a plant is developed to quantify the uptake of organic chemicals from soil and the atmosphere. The compartments are as follows: root, stem, and foliage. The processes involved are diffusion and bulk flow of chemical between soil and root; transport within the plant in the phloem and transpiration streams between root, stem, and foliage; exchange between foliage and air and between soil and air; metabolism and growth. The model is applied to the uptake of Bromacil by the soybean from hydroponic solution, yielding results which compare favorably with experimental data. Illustrative applications to three other chemicals (2,4-D, dichlorobenzonitrile, and hexachlorobiphenyl) from soil are described showing that chemicals present in soil may reach foliage by evaporation from soil with subsequent foliar absorption and by transpiration, the proportions being determined by the chemical's Henry's law constant and octanol-water partition coefficient. The intent is to provide a method by which chemical concentrations in various plant tissues can be estimated from information on chemical properties, concentrations in soil and air, and plant physiology. Applications and data requirements for validation are discussed.