**3. Framework for chemical compound interaction with the environment and living organisms**

The ability of numerical models to accurately predict concentrations of target chemical compounds in any living organism depends on the model's ability to mimic the processes involved in their uptake, and this must be assessed before they can be confidently applied [10]. After that it is necessary to consider all of these processes in order to include them in the numerical model that wants to be developed [11].

*Soil-root transport*: The uptake of chemicals by the root from the soil is mediated in high percentage by soil water content through the plant transpiration process [12]. A large number of organic chemicals also can be sorbed or bound to the components in soil (clay, iron oxides, organic matter), those often found in the rhizosphere in significant amounts [13, 14]. Also, lipophilic organic chemicals possess a greater tendency to partition into plant roots than hydrophilic chemicals. Although chemicals properties are important predictors of the uptake potential, the physiology and composition of the plant root itself is also a significant influence, with differences in the uptake potential explained by the varying types and amounts of lipids in root cells [15]. Uptake from the external media is often expressed as a root concentration factor (RCF), which is the ratio of chemical concentration in the root to the concentration found in external media [13, 16].

*Transfer from roots to other anatomical compartments of plants*: The major factor that illustrates the amount of a chemical compound that was transferred from the plant root part to other anatomical compartments is the transpiration stream concentration factor (TSCF) which is the ratio of chemical concentration in transpiration to the concentration found in the external part. TSCF could be predicted from knowledge of the chemical compound lipophilicity, with maximum uptake, a *logKOW* about 1 [17]. Once the chemical is transported to the stem, plant water and solutes take it and continue to transport these chemicals to the rest of the anatomical compartments through vascular systems and cell tissues [18].

*Vapor or gas uptake from ambient air*: Another exposure route with chemicals in case of plant materials could be the ambient air that contains a large number of contaminants. This exposure route is governed by gaseous exchange and facilitates the transport and uptake of chemicals that are volatiles and which are more easily partitioned in air than in water. This has been shown to be the main uptake pathway in the above-ground plant parts for a variety of chemical compounds (e.g. PCBs, tetra- and hexa-chlorinated PCDD/Fs) [19]. Previous studies have reported a good correlation between shoot uptake and chemical properties of compounds (KOW, Henry's Law constant, octanol-air partition coefficient, etc.). In studies presented by [20], it was evidenced that gaseous uptake is the primary pathway for chemicals with an octanol-air partition coefficient (logKOA) less than 11 [20].

*Particulate deposition on plant surfaces*: Pesticides as well as other chemical contaminants are bound to soil particles which may be transported by wind and/or rain and deposited on the above-ground anatomical compartments of plants. Studies presented by [5, 21], evidenced that dry deposition onto the leaf of suspended particles that contain PCCD/Fs is the major route of uptake due to PCCD/Fs permeation through the cuticle. Similarly, in their studies, wet deposition was shown which could also be the dominant deposition mechanism for organic chemicals with Henry's Law constant of less than 1 × 10<sup>−</sup><sup>6</sup> [5, 21].

To date, a number of mathematical models have been developed to facilitate the exposure assessment of chemical contaminants, with important results in the modeling of pollutants' multimedia fate and the modeling of pollutants' linkage with transformation products, especially in water environmental compartments [4].
