Cadmium bioaccumulation in tubificid oligochaetes in relation to metal vertical distribution in sediment and bioturbation intensity was studied during a 56-day experiment with a constant contamination source in the overlying water (20 microg L(-1)). The indoor microcosms simulate a two-compartment biotope with three experimental treatments based on metal exposure and faunal composition: contaminated water column with or without worms and uncontaminated water column with worms. Cadmium bioaccumulation in worms was studied after 7, 14, 21, 28, and 56 days. Bioturbation was analyzed as a functional parameter representative of organisms' activity and using conservative particulate tracers: luminophores (phi = 63-100 microm and 100-315 microm) and microspheres (phi = 1 microm). The results show no significant effects of cadmium exposure on bioturbation, despite high bioaccumulation levels in worms (50 microg g(-1) dry wt.), suggesting the existence of detoxification/sequestration processes.