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Thorium Exposure Drives Fatty Acid and Metal Transfer From Biofilms to the Grazer Lymnaea sp.

Aquatic ecotoxicological risks associated with tetravalent metallic elements such as thorium (Th) are still poorly understood. Periphytic biofilm represents an important food source in aquatic environments, thus such risks could severely affect nutrient and energy cycling in these ecosystems. The present study investigated the potential for Th to change fatty acid compositions of biofilm communities. Thorium bioaccumulation and fatty acids (FAs) were measured after 4 weeks to two exposure conditions: a control (C0) and Th (C10). Some major FAs such as C16:1n-7 and the docosahexaenoic acid C22:6n-3 differed significantly between control and C10 conditions. To determine if the Th can be trophically transferred and to investigate the impacts of nutritional quality changes on primary consumers, common pond snails (Lymnaea sp.) were fed for 4 weeks with control and Th-exposed biofilm. Thorium appeared to be trophically transferable to the grazers although we cannot exclude that part of the Th accumulated by the snails may have been taken from the water through release from the biofilms. The composition of major FAs observed in the grazers was also significantly affected, notably by a decrease of total polyunsaturated FAs. These results indicate that very low Th concentrations can decrease the nutritional quality of organisms at the base of the food chain. This article is protected by copyright. All rights reserved.