Effects of cadmium exposure on volume regulation in the lugworm, Arenicola marina

Effects of hypo-osmotic stress and Cd (cadmium) exposure, applied singly or in combination, on volume regulation were investigated in Arenicola marina, the common European lugworm. In short-term experiments, the combined exposure to Cd and hypo-osmotic stress mainly affected the worm's capacity for regulating the coelomic fluid volume without significantly affecting the regulation of intracellular fluid volume. Exposure to Cd increased the worm's sensitivity to hypo-osmotic stress noted as increased mortality compared to the mortality in groups exposed only to Cd or hypo-osmotic stress. In long-term Cd exposure experiments, the capacity for coelomic fluid volume regulation was affected even at constant external osmolarity and the tissue water concentration decreased slightly. The results could not be explained by changes in Apparent Water Permeability (AWP) as Cd did not significantly affect this. The glycogen content of the chloragogenous tissue did, however, increase during long-term Cd exposure suggesting a metabolic effect. The results demonstrate that two stressors, each without serious effects when applied alone, may have fatal effects when applied in combination. The kind of osmotic stress applied in these experiments is common in many biotopes inhabited by the lugworm. The severe effects of the combination with Cd exposure indicate that classical ecotoxicology testing could conceivably underestimate the toxicity of chemical compounds due to not considering combined effects of natural and anthropogenic stressors.