Acute toxicity estimation by calculation— Tubifex assay and quantitative structure‐activity relationships

A quantitative structure–activity relationship (QSAR) model dependent on log P ( n — octanol/water), or log P OW , was developed with acute toxicity index EC50, the median effective concentration measured as inhibition of movement of the oligochaeta Tubifex tubifex with 3 min exposure, EC50( Tt ) (mol/L): log EC50( Tt ) = −0.809 (±0.035) log P OW — 0.495 (±0.060), n = 82, r = 0.931, r 2 = 0.867, residual standard deviation of the estimate = 0.315. A learning series for the QSAR model with the oligochaete contained alkanols, alkenols, and alkynols; saturated and unsaturated aldehydes; aniline and chlorinated anilines; phenol and chlorinated phenols; and esters. Three cross‐validation procedures proved the robustness and stability of QSAR models with respect to the chemical structure of compounds tested within a series of compounds used in the learning series. Predictive ability was described by q 2 = 0.801 (cross‐validated r 2 ; predicted variation estimated with cross‐validation) in LSO (leave‐a structurally series‐out) cross‐validation.