Perylene, a 5-ring polycyclic aromatic hydrocarbon is common in estuarine sediments and its toxicity in the benthic and planktonic compartments is not yet clarified. The objectives of this work were: (1) to follow the toxicity of high concentrations of perylene (110 mg l(-1)) on benthic bacteria and macrofauna (amphipod Corophium multisetosum); (2) to determine the effects of a low load of perylene (2 microg l(-1)) on the metabolism of suspended bacteriobenthos after 9-day exposure, mimicking the effects of tidal erosion; (3) to contrast the effects of this low perylene load on the particle-free bacterioplankton and on the suspended and particle-adhered bacteriobenthos. No impact was detected in bacterial abundance exposed to 110 mg perylene l(-1) for 9 days. This concentration of perylene evoked no acute effects in C. multisetosum but, chronic toxicity assays revealed statistically significant negative effects on survival, growth and number of pregnant females. The bacterioplankton and the suspended bacteriobenthos, exposed to 2 microg perylene l(-1) during 2 weeks, responded with altered profiles of activity when compared to the control suspension. These values ranged, respectively, for bacterial biomass production from 134 to 210 and from 24 to 184 mug C l(-1) h(-1), for aminopeptidase from 1824 to 11,127 and from 1464 to 15,488 nmol l(-1) h(-1), and for beta-glucosidase from 87 to 400 and from 57 to 1278 nmol l(-1) h(-1). The rate of oxygen consumption in the perylene-exposed suspension (0.04-2.85 mmol O2 kg(-1) dw sed h(-1)) exhibited a clearly distinct profile in relation to the control (0.57-1.60 mmol O2 kg(-1) dw sed h(-1)). The overall reactivity of the bacteriobenthos to perylene was interpreted as the result of toxic pressure followed by evolution of a diverse bacterial community.