Interactive effects of biotic and abiotic environmental stressors on carbamazepine toxicity in the non-biting midge Chironomus riparius

Abstract

The toxicity of contaminants in freshwater ecosystems can increase in combination with environmental stress, leading to a potential underestimation of risk in conventional assessments. The number of multiple-stress experiments in ecotoxicology is growing constantly, but pharmaceuticals have mostly been disregarded. As an omnipresent pharmaceutical in the water cycle, the antiepileptic drug carbamazepine (CBZ) was chosen as test substance for our 28-day binary stress experiments with the non-biting midge Chironomus riparius. Elevated population densities, food limitation, temperature, and a reduction of organic matter (OM) were chosen as relevant environmental stressors. In five stress intensities, they were combined with the 10% lethal concentration (LC10) of CBZ to investigate the joint effect of stress and CBZ exposure. We were able to demonstrate that the toxicity of CBZ increased with higher larval densities and reduced OM. Mortality of the midges exposed to CBZ increased by a factor of 1.69 with 100 larvae per vessel and by a factor of 2.87 at 0.25% OM compared to the conventional test protocol, while the stressors alone did not reduce survival. Conventional low-stress laboratory tests as conducted for the risk assessment of chemicals would have underestimated the toxicity of CBZ. Even though it is necessary that more than binary stressor combinations are included in future experiments, the present results extend our knowledge about the toxicity of pharmaceuticals, such as CBZ, in stressful environments and emphasize the importance of including pharmaceuticals in multiple stress experiments.