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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.

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Abstract-The multimedia equilibrium criterion model, which can be used to evaluate the environmental fate of a variety of chemicals, is described. The model treats chemicals that fall into three categories. In the first the chemicals may partition into all environmental media, in the second they are involatile, and in the third they are insoluble in water. The structure of the model, the process equations, and the required input data for each chemical type are described. By undertaking a sequence of level I, II, and III calculations, increasing information is obtained about the chemical's partitioning, its susceptibility to transformation and transport, and the environmental process and the chemical characteristics that most influence chemical fate. Output data, consisting of tables and charts, give a complete picture of the chemical's fate in an evaluative or generic environment. The model is illustrated by applying it to two chemicals, pyrene, which is a chemical of the first type, and lead, which is of a second type. The role of this model as a tool for assessing the fate of new and existing chemicals is discussed.