First insight in trace element distribution in the intestinal cytosol of two freshwater fish species challenged with moderate environmental contamination.

Cytosolic distribution of six essential elements and nonessential Cd among biomolecules of different molecular masses was investigated in the intestine of brown trout (Salmo trutta) from the karst Krka River and Prussian carp (Carassius gibelio) from the lowland Ilova River. Fish were sampled at two locations (reference and contaminated) and in two seasons (autumn and spring). Analyses were conducted by size exclusion high performance liquid chromatography and high resolution inductively coupled plasma mass spectrometry. Although studied salmonid and cyprinid fish have different biological characteristics, obtained profiles often showed mostly similar patterns in both species. Specifically, Cd and Cu were dominantly bound to metallothioneins in both species, but the same association was not observed for Zn, whereas Mo distribution was similar in the intestine of both fish species with two well shaped and clear peaks in HMM (100-400 kDa) and VLMM (2-8 kDa) range. In brown trout, Se was mostly associated with biomolecules of very low molecular masses (VLMM, <10 kDa), whereas significant additional elution in HMM region (30-303 kDa) was observed only in Prussian carp. Iron binding to VLMM biomolecules (1.8-14 kDa) was observed only in brown trouts, and of Zn in Prussian carps. Cobalt was mostly bound to HMM biomolecules (85-235 kDa) in brown trout and to VLMM biomolecules (0.7-18 kDa) in Prussian carp. Comparison of intestinal profiles with previously published data on liver and gills revealed some similarities in distribution, but also organ-specific differences due to the different function and composition of each organ. As so far there is no published data on intestinal trace metal distribution, the obtained results represent the novel findings, and the key point for the exact identification of specific metal-binding biomolecules which could eventually be used as biomarkers of metal exposure or effects.