LAUSR

Abstract A huge variety of organic microcontaminants are presently detected in freshwater ecosystems, but there is still a lack of knowledge about their interactions, either with living organisms or with other contaminants. Actually, carbon nanomaterials like fullerenes (C60) can act as carriers of organic microcontaminants, but their relevance in processes like bioaccumulation and biotransformation of organic microcontaminants by organisms is unknown. In this study, mesocosm experiments were used to assess the bioaccumulation and biotransformation of three organic microcontaminants (venlafaxine, diuron and triclosan) in river biofilms, and to understand how much the concomitant presence of C60 at environmental relevant concentrations could impact these processes. Results indicated that venlafaxine exhibited the highest bioaccumulation (13% of the initial concentration of venlafaxine in water), while biotransformation was more evident for triclosan (5% of the initial concentration of triclosan in water). Furthermore, biotransformation products such as methyl‐triclosan were also present in the biofilm, with levels up to 42% of the concentration of accumulated triclosan. The presence of C60 did not involve relevant changes in the bioaccumulation and biotransformation of microcontaminants in biofilms, which showed similar patterns. Nevertheless, the study shows that a detailed evaluation of the partition of the organic microcontaminants and their transformation products in freshwater systems are important to better understand the impact of the co‐existence of others microcontaminants, like carbon nanomaterials, in their possible routes of bioaccumulation and biotransformation. HighlightsRiver biofilms are a good model to assess the effect of pollutants at a community level.Impact of C60 in bioaccumulation and biotransformation of VLF, DIU and TCS was assessed.Venlafaxine showed the highest potential to accumulate in river biofilms.Biotransformation was more evident for triclosan.Presence of C60 did not alter bioaccumulation and biotransformation of OMC.