Single and Combined Effects of Zinc and Manganese on the Bivalve Anodontites trapesialis: Complementary Endpoints to Support the Hypothesis of Manganese Promoting Metabolic Suppression in Gills

Manganese (Mn) might stimulate the valve closure reflex in the freshwater bivalve Anodontites trapesialis, leading to metabolic suppression, whereas zinc (Zn) is not able to modify this behavior. To investigate this particular response, we exposed A. trapesialis specimens to Mn (0.5 mg L-1 ) and Zn (1.0 mg L-1 ) alone, and to their mixture, to measure further endpoints in different clam tissues: glycogen level in gills, and calcium (Ca2+ ), sodium (Na+ ), and chloride (Cl- ) concentrations in the hemolymph. Furthermore, we used cutting-edge technology, proteomics, to evaluate modifications in protein patterns under the 3 exposure tests. The main results highlighted that only Mn caused a clear drop in glycogen levels in gills, an increase in Ca2+ and Na+ , and a simultaneous decrease in Cl- concentration in the hemolymph. The proteomic analysis confirmed that Mn promoted more effects in A. trapesialis than the other tested conditions, because the number of proteins modulated was higher than the results obtained after exposure to Zn and the mixture. Moreover, 11 of the 12 modulated proteins were down-expressed. These results consolidate the hypothesis that Mn might suppress gill metabolic rate in A. trapesialis. Environ Toxicol Chem 2019;38:2480-2485. © 2019 SETAC.