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a b s t r a c tMicrosporidia parasites are commonly found in amphipods, where they are often asymptomatic, vertically-transmitted and have several effects on host sexuality and behaviour. As amphipods are often used as models in ecotoxicological studies, we investigated the effect of microsporidian infections on energy reserves and defence capacities of Gammarus roeseli under cadmium stress. Only females were infected by two microsporidia parasites: Dictyocoela roeselum or Dictyocoela muelleri. In physiological conditions, microsporidia had no major effect on energy reserves and defence capacities of G. roeseli, while under cadmium exposure, energy reserves and antioxidant defence were weaker in infected females. Moreover, higher malondialdehyde levels detected in infected females revealed that they suffered more cellular damages. Our results suggest that microsporidia may affect gammarid fitness in stressful conditions, when parasitic stress cannot be compensated by the host. Consequently, microsporidia parasites should be a factor necessary to take into account in ecotoxicology studies involving amphipods.

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In this study, the presence of anthropogenic gadolinium (Gd) was evaluated in rivers, close to wastewater treatment plant outputs. Then, one site was selected for in situ experiments to assess the bioaccumulation of Gd in the digestive gland and in the gills of two bivalves (Dreissena rostriformis bugensis and Corbicula fluminea). For both organisms, the results suggested that the bioaccumulation of Gd can be observed when organisms are exposed in a geogenic and anthropogenic Gd mixture. In order to observe if Gd can bioaccumulate in tissues of bivalves when the ion is only present as the main anthropogenic speciation of Gd, i.e., Gd-contrast agents (Gd-CAs), the gadoteric acid was used for a laboratory experiment. In this case, the presence of Gd was clearly detected in a significant amount in the digestive glands of D. rostriformis bugensis and C. fluminea while low concentrations are measured in the gills. For the first time, these results clearly showed that Gd can bioaccumulate in bivalve tissues even when it is only present as Gd-CAs. Biochemical activities were measured in the digestive gland and in the gills of the bivalves to assess the effects of Gd-CA bioaccumulation. No significant variations were observed in the gills. Concerning the digestive gland, after 7 days of exposure at 10 μg L of Gd as Gd-CA speciation, GST activity in D. rostriformis bugensis and lipid hydroperoxide and mitochondrial electron transfer system in C. fluminea had increased. The results suggest an acclimation of the organisms to the presence of Gd-CAs in the medium within less than 21 days.