Effects of crystal structure on the uptake of metals by lake trout (<i>Salvelinus namaycush</i>) otoliths

Abstract

This is the first study to report spectroscopic and elemental analysis of aragonite and vaterite growing simultaneously and separately in both the core and the edges of the same otolith. Our investigations focused on understanding differential trace metal uptake, including the influence of the metal itself (i.e., ionic radii), the crystalline structure, and the development state of the fish. Chemistry and crystal structure of sagittal otoliths from lake trout (Salvelinus namaycush) were studied using laser ablation combined with inductively coupled plasma mass spectrometry (LA-ICP-MS) and Raman spectroscopy, respectively. Analyses of the composition of vaterite and aragonite growing in the same growth ring show that smaller cations like Mg (0.86 Å) (1 Å = 0.1 nm) and Mn (0.81 Å) were more abundant in the vaterite hexagonal crystal structure, whereas larger cations such as Sr (1.32 Å) and Ba (1.49 Å) were preferentially incorporated in aragonite (orthorhombic). Similarly, the coprecipitation of aragonite and vaterite in cores and edges allowed us to demonstrate that the uptake rates (as determined by element-specific partition coefficients) for Sr and Ba were greater in aragonite than vaterite, whereas those of Mg and Mn were higher in vaterite than in aragonite.