Selectivity of metal bioaccumulation and its relationship with glutathione S-transferase levels in gonadal and gill tissues of Mytilus galloprovincialis exposed to Ni (II), Cu (II) and Cd (II)

In order to identify a metal bioaccumulation marker usable in monitoring programs, we analyzed the metal content in Mytilus galloprovincialis gill and gonadal tissues and its relationship with pi-gst expression levels after a laboratory exposure for 24 h to individual chlorides of Ni, Cu, 5, 15, 35 mu M and Cd 1,5; 5, 10 mu M in artificial sea water. Inductively coupled plasma-mass spectrometry showed that metal content increased in both tissues in an exposure dose-dependent fashion except for Ni in gonadal tissues, where a low value at the highest exposure was observed. Metal bioaccumulation was higher in gill than gonadal tissues as was pi-gst expression level, measured by RT-qPCR, except for the highest Cu exposure. In the gonadal tissue, Ni induced the highest pi-gst increase resulting in 2.5- and 4-fold at 5 and 35 mu M, respectively, while only about twofold for some Cu and Cd dose exposure. In gill tissue, instead Cd produced pi-gst dosedependent increase being 2.3- and 9.6-fold at 5 and 10 mu M, respectively. Ni and Cu meanwhile produced 12 -and 5-fold expression levels only at the highest concentration used. Mytilus galloprovincialis shows also a selectivity to accumulate the investigated metals, since metal concentration reduction in ASW, after exposure, was 96-97 %; 85.1-90 % and 4.5-10 % for Cd, Cu and Ni, respectively. Finally, pi-gst expression levels correlated particularly with the amount of bioaccumulated Cd in gill tissue, indicating pi-gst as a potential marker, even if not univocally, of significative cadmium bioaccumulation usable in environmental monitoring programs.