Effect of incubation of bioreactor-treated soil with selected surfactants in the followup PAH biodegradation experiment on (a) toxicity to the parental DT40 cell line, and (b) genotoxicity as determined by relative LC50 values (mutant LC50/parental LC50) using the DNA repair-deficient mutants Rad54−/− and Rev1−/−. Bars represent means and standard deviations of three experiments. An asterisk indicates a significant difference (α=0.05) for a given cell line between a treatment and the initial bioreactor-treated soil. BTS, bioreactor-treated soil; NS, no-surfactant control; P, POESH, B, Brij 30; S, Span 20; L, lower surfactant dose; H, higher surfactant dose.