The effect of concentration of the toxic substrates: phenol, oNph, mNph, pNph on their microbiological degradation was studied. The dependence was investigated at biocenotic and population levels. The aryl-catabolic properties of 55 biodegrading cultures were studied at an increasing gradient of phenol substrates. The degradation dynamics has been studied at different initial phenol concentrations on 3 bacterial and one yeast strains.