Using the Western blot immunochemical analysis method, the heat shock prote
in, GroEL, was found to be either induced or repressed in activated sludge
microorganisms exposed to a range of xenobiotics. At the EC,, concentration
, pentachlorophenol (PCP), cadmium, nickel, 2,4-dichloroaniline, benzoquino
ne, 2,4-dinitrophenol, and 1,1,1 -trichlorcethane all rapidly induced measu
rable GroEL expression, even though the time-dependent response for each of
these compounds was somewhat varied. Toluene and hydroquinone resulted in
repression of GroEL expression to levels below that measured in the control
mixed liquor. For PCP concentrations at or exceeding the EC25' there was a
significant and consistent increase in effluent volatile suspended solids
from activated sludge sequencing batch reactors relative to unstressed cont
rols. These preliminary results indicate that stress proteins may serve as
sensitive and rapid indicators of toxicity which can adversely impact treat
ment process performance in activated sludge systems.