Synergistic physiological effects of low copper and various oxygen concentrations on Macoma balthica

The negative effects of copper on Macoma balthica are significantly increased when this bivalve is simultaneously exposed to low oxygen concentrations. This might be explained by the fact that low oxygen concentrations (oxygen deficiency) are combined with a slightly lower pH and thus with a different copper speciation, resulting in a higher bio-availability of copper and, consequently, in a higher copper uptake by M. balthica. Symptomatic for the increased negative effects of copper on M. balthica at low oxygen concentrations is an increased oxygen demand, which in turn reflects an increased consumption of energy. Consequently, at low oxygen levels, low copper concentrations (8–15 μg dm^-3) greatly affect the glycogen content of the tissues, and finally (at 15 μg Cu dm^-3) result in a heavy loss of dry weight and a drastic reduction of the adenylate energy charge (AEC). Generally, it might be concluded that dry weight, glycogen content and AEC are more affected by a combination of oxygen deficiency and a low copper concentration (2.5 cm³ O₂ dm^-3, 15 μg Cu dm^-3) than by higher copper concentrations (up to 86 μg dm^-3) at high oxygen levels (5.0 cm³ dm^-3).