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 (K_ow) as predictors of BCRs from the soil matrix into above- or below-ground vegetation tissues. Calculated octanol/air partition coefficient (K_oa) values are compared with calculated K_ow 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 K_ow and MCI approaches have a similar level of precision for predicting BCRs from soil solution into roots and, among MCI, K_oa and K_ow; K_oa is somewhat more precise and valid than MCI and K_ow for estimating uptake, but all have limited accuracy as bioconcentration predictors. These latter results are derived mainly from the paucity of both reliable K_oa values and measured air-to-plant BCRs and indicate a need for more experimental measurements from which more accurate models may be developed.