Interactive effects of n-TiO2 and 2,3,7,8-TCDD on the marine bivalve Mytilus galloprovincialis

Despite the growing concern over the potential biological impact of nanoparticles (NPs) in the aquaticenvironment, little is known about their interactions with other pollutants. The bivalve Mytilus sp, largelyutilized as a sentinel for marine contamination, has been shown to represent a significant target fordifferent types of NP, including n-TiO2, one of the most widespread in use. In this work, the possibleinteractive effects of n-TiO2and 2,3,7,8-TCDD, chosen as models of NP and organic contaminant, respec-tively, were investigated in Mytilus galloprovincialis. In vitro experiments with n-TiO2and TCDD, aloneand in combination, were carried out in different conditions (concentrations and times of exposure),depending on the target (hemocytes, gill cells and biopsies) and the endpoint measured. Mussels werealso exposed in vivo to n-TiO2(100 g L−1) or to TCDD (0.25 g L−1), alone and in combination, for 96 h. Awide range of biomarkers, from molecular to tissue level, were measured: lysosomal membrane stabil-ity and phagocytosis in hemocytes, ATP-binding cassette efflux transporters in gills (gene transcriptionand efflux activity), several biomarkers of genotoxicity in gill and digestive cells (DNA damage, randomamplified polymorphic DNA-RAPD changes), lysosomal biomarkers and transcription of selected genes inthe digestive gland. The results demonstrate that n-TiO2and TCDD can exert synergistic or antagonisticeffects, depending on experimental condition, cell/tissue and type of measured response. Some of theseinteractions may result from a significant increase in TCDD accumulation in whole mussel organisms inthe presence of n-TiO2, indicating a Trojan horse effect. The results represent the most extensive dataobtained so far on the sub-lethal effects of NPs and organic contaminants in aquatic organisms. Moreover,these data extend the knowledge on the molecular and cellular targets of NPs in bivalves.