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 quan tify the uptake of organic chemicals from soil and the atmosphere. The compartments are as follows: root, stem, and foliage. The processes i nvolved are diffusion and bulk flow of chemical between soil and root; transport within the plant in the phloem and transpiration streams be tween root, stem, and foliage; exchange between foliage and air and be tween 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 a pplications to three other chemicals (2,4-D, dichlorobenzonitrile, and hexachlorobiphenyl) from soil are described showing that chemicals pr esent in soil may reach foliage by evaporation from soil with subseque nt foliar absorption and by transpiration, the proportions being deter mined by the chemical's Henry's law constant and octanol-water partiti on coefficient. The intent is to provide a method by which chemical co ncentrations in various plant tissues can be estimated from informatio n on chemical properties, concentrations in soil and air, and plant ph ysiology. Applications and data requirements for validation are discus sed.