Predicting the Bioconcentration of Organic Chemicals from Soil or Air into Plants Using Quantitative Structure Activity Relationships
A bioconcentration ratio (BCR) represents the ratio of the concentration of a chemical found in an exposed biological system, such as a plant or fish, to the concentration in the exposure medium (water, soil, or air). A comparison is made of the precision and accuracy of the molecular connectivity index (MCI) and the octanol/water partition coefficient (Kow) as predictors of BCRs from the soil matrix into above- or below-ground vegetation tissues. Calculated octanol/air partition coefficient (Koa) values are compared with calculated Kow and MCI values as predictors of measured air-to-plant BCRs. Based on a statistical evaluation of explained variance, residual error, and cross-validation, this evaluation reveals that the MCI provides higher precision, greater ease of use, and a more cost-effective method for predicting the potential bioconcentration of a chemical from soil into above-ground vegetation. Statistical analyses of the various methods reveal that both the Kow and MCI approaches have a similar level of precision for predicting BCRs from soil solution into roots and, among MCI, Koa and Kow; Koa is somewhat more precise and valid than MCI and Kow for estimating uptake, but all have limited accuracy as bioconcentration predictors. These latter results are derived mainly from the paucity of both reliable Koa values and measured air-to-plant BCRs and indicate a need for more experimental measurements from which more accurate models may be developed.