Growth inhibition of activated sludge microorganisms by chlorophenols and structure-activity relationships and its relation with microbial degradation.

Abstract

The growth inhibition test method was studied for the hazard evaluation of chemicals to microorganisms which play an important role in an aquatic ecosystem. As a source of microorganisms, standard activated sludge which is distributed from Chemical Inspection and Testing Institute, in Tokyo was used and the degree of growth was measured by a turbidity. On eleven chlorophenols tested, 24 h-EC50 values were correlated with 3 physico-chemical parameters, i.e., n-octanol/water partition coefficient (log Pow), dissociation constant (pKa) and Hammett constant (Σσ). Though the toxicity increases from monochlorophenols to trichlorophenol except for chlorophenols substituted at 2, 6-positions, 2, 3, 4, 6-tetra-and penta-chlorophenol were less toxic than 2, 3-, 3, 5-dichloro-and 2, 3, 4-trichlorophenol. Quantitative structure-activity relationship (QSAR) studies show that partition coefficient, a parameter of lipophilicity, gives the best correlation with 24 h-EC50 values by using square of log Pow. Among the isomers of chlorophenols having the same numbers of chlorine atom, ortho isomer appears to be less toxic than meta and para isomers. With regard to several chlorophenols, 24 h-EC50 values were determined by the respiration inhibition method and ATP measurement method, and compared with 24 h-EC50 values by the growth inhibition method shown above. It is suggested that the respiration inhibition method is less sensitive than the growth inhibition method. Furthermore, a relation ship between toxicity and biodegradability was studied by the performance of microbial degradation test at low concentration where the test chemical did not inhibit the growth of microorganismsand it is suggested a few chlorophenols which are persistent at concentration of 100 mg/l can be degraded at a level of 10 mg/l.