Technical basis for polar and nonpolar narcotic chemicals and polycyclic aromatic hydrocarbon criteria. III. A polyparameter model for target lipid partitioning.

A method is presented for extending the target lipid model (TLM) of narcotic toxicity to polar narcotic chemicals. The proposed polyparameter TLM extends the applicability of the TLM by including polar compounds and removing explicit chemical class corrections. The validity of the model is tested using a data set of 1,687 acute toxicity tests for 42 aquatic species, including fish, amphibians, arthropods, mollusks, polychaetes, coelenterates, protozoans, and algae, and 398 chemicals. The target lipid-water partition coefficient is computed using the Abraham polyparameter model. This replaces use of the octanol-water partition coefficient so that the partitioning of polar narcotic chemicals can be described correctly. The model predicts the log median lethal concentration with a root mean square error of 0.460 for nonpolar and polar chemicals and 0.501 for only polar chemicals.