Partition of Volatile Organic Compounds from Air and from Water into Plant Cuticular Matrix:  An LFER Analysis

Abstract

The partitioning of organic compounds between air and foliage and between water and foliage is of considerable environmental interest. The purpose of this work is to show that partitioning into the cuticular matrix of one particular species can be satisfactorily modeled by general equations we have previously developed and, hence, that the same general equations could be used to model partitioning into other plant materials of the same or different species. The general equations are linear free energy relationships that employ descriptors for polarity/polarizability, hydrogen bond acidity and basicity, dispersive effects, and volume. They have been applied to the partition of 62 very varied organic compounds between cuticular matrix of the tomato fruit, Lycopersicon esculentum, and either air (MX a ) or water (MX w ). Values of log MX a covering a range of 12.4 log units are correlated with a standard deviation of 0.232 log unit, and values of log MX w covering a range of 7.6 log unit are correlated with an SD of 0.236 log unit. Possibilities are discussed for the prediction of new air-plant cuticular matrix and water-plant cuticular matrix partition values on the basis of the equations developed.

A review of measured bioaccumulation data on terrestrial plants for organic chemicals: Metrics, variability, and the need for standardized measurement protocols

“…For example, RCFs [8,53], stem or wood concentration factors [30,[54][55][56][57]; and aboveground or shoot concentration factors [33,43,58] have been related to log K OW . Similarly, based on the assumption that the lipophilic cuticle is the major plant component governing air-plant interactions, simple regression models have been developed that relate air-shoot BCFs to K OA [59][60][61][62] or to a combination of K AW (dimensionless) and K OW [63].…”

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“…For example, outlier data points would be identified by large differences between experimental and calculated values. In the case of benzil we can now estimate the blood-brain distribution, (20,21) permeation from water through human skin, (22) nasal pungency threshold, (23,24) eye irritation threshold, (25) aqueous narcosis, (26) and plant cuticle uptake (27) through previously derived correlations. Each estimation requires as input parameters the numerical values of the benzil solute descriptors.…”

Developing Methods to Predict Chemical Fate and Effect Endpoints for Use Within REACH

“…Phase descriptors for numerous bulk phase-water, bulk phase-air and surface-air partitioning systems have been and are currentl y being determined experimentally [12][13][14][15][16][17][18][19][20]. A selection of environmentally relevant partitioning systems with available phase descriptors is given in Table 3.…”

“…Cell permeation [16] Plant cuticle permeation [15] in the system. In the context of REACH, pp-LFERs offer the opportunity to predict various types of partitioning properties and transfer rates based on only five solute descriptors and in a consistent manner.…”