Unveiling population-specific outcomes: Examining life cycle traits of different strains of Chironomus riparius exposed to microplastics and cadmium questions generality of ecotoxicological results.

Ecotoxicological tests used for risk assessment of toxicants and its mixtures rely both on classical life-cycle endpoints and bioindicator organisms usually derived from long-term laboratory cultures. While these cultures are thought to be comparable among laboratories and more sensitive than field organisms, it is not well investigated whether this assumption is met. Therefore, we aimed to investigate differential life-cycle endpoints response of two different strains of C. riparius, one originally from Spain and the other from Germany, kept under the same laboratory conditions for more than five years. To highlight any possible differences, the two populations were challenged with exposure to cadmium (Cd), polyvinyl chloride (PVC) microplastics and a co-exposure with both. Our results showed that significant differences between the strains became evident with the co-exposure of Cd and PVC MPs. The German strain showed attenuation of the deleterious Cd effects with microplastic co-exposure in survival and developmental time. Contrary to that, the Spanish strain showed no interaction between the substances. In conclusion, the toxicity-effects of contaminants may vary strongly among laboratory populations, which makes a universal risk assessment evaluation challenging.