Immunological effects of microplastics and an associated metal contaminant (palladium) in the marine bivalve Mytilusgalloprovincialis.

Supervisors: Marina Albentosa, Elena Chaves (IEO, Murcia)
Microplastics (MPs) are widely distributed in marine environments and have been reported to cause harmfulphysiological effects in marine bivalves including immune modulation. While Mytilusgalloprovincialisisa model species in environmental monitoring studies, little is known regarding the effects of MPs andpalladium (Pd) metal on the immune functioning of this species. In this study, gills and gland samples ofspecimens of Mytilusgalloprovincialiswhich were exposed to virgin and palladium-loaded microplasticswere collected for the study of several innate immune functions (lysozymes, peroxidase, protease,antiprotease, and bactericidal activities). The exposure was performed adding the same particleconcentration (2.5 x 106 μm3/mL) to all the particle treatments of Control (microalgae), MP (virginmicroplastics), MP-Pd (spiked microplastics) or dissolved Pd to the waterborne treatment (WB-Pd), eachtank once an hour during 4 hours. Thus, mussels were exposed to 6095 ng of Pd/mussel in each tank whenthe Pd was adsorbed to MP and 2300 ng of Pd/mussels when dissolved in water. Samples analysed werecollected after 4 and 24 hours of exposure (4 and 24 hoe) and after 24 hours of depuration (24 hod). Our data demonstrate that MP reduced lysozymes and peroxidase activity levels in the gills but incombination with Pd, these parameters were not reduced or even increased relative to the control levels.However, these activities levels were increased by MP in the digestive gland but not when MPs were spikedwith Pd. Protease and anti-protease activity levels were not detected in the gills. In the digestive gland,however, the protease activity levels were increased by MP but not with MP-Pd that kept at control levels.Further, MP increased the bactericidal activity levels against V. anguillarumsimilar to MP-Pd in gills butreduced the bactericidal activity levels against V. anguillarumin the digestive gland as did MP-Pd relativeto control levels. Also, MP did not affect bactericidal activity levels against Vibrio harveyiinitially but,reduced activity levels were recorded upon 24 hours of depuration, a limitation recorded for MP-Pd as wellrelative to control. On the other hand, WB-Pd reduced lysozymes activity levels in the gills but had no effectin the digestive glands nor did it affect peroxidase and antiprotease activity levels in either tissue. However,WB-Pd reduced protease activity levels in the digestive gland. Further, WB-Pd decreases bactericidalactivity levels against V. anguillarum, V. harveyiin gills, and against V. anguillarumin the digestive gland.Therefore, our data point to the fact that Pd induces immunosuppression and hence we recommend a timeevolution study to check for the dynamics of its associated immune responses in marine animals.