Compound-specific recording of gadolinium pollution in coastal waters by great scallops.

Gadolinium-based contrast agents (GBCAs), routinely used in magnetic resonance imaging (MRI), end up directly in coastal seawaters where gadolinium concentrations are now increasing. Because many aquatic species could be sensitive to this new pollution, we have evaluated the possibility of using shellfish to assess its importance. Gadolinium excesses recorded by scallop shells collected in Bay of Brest (Brittany, France) for more than 30 years do not reflect the overall consumption in GBCAs, but are largely controlled by one of them, the gadopentetate dimeglumine. Although its use has been greatly reduced in Europe over the last ten years, gadolinium excesses are still measured in shells. Thus, some gadolinium derived from other GBCAs is bioavailable and could have an impact on marine wildlife.

Understanding otolith biomineralization processes: new insights into microscale spatial distribution of organic and mineral fractions from Raman microspectrometry.

It is generally accepted that the formation of otolith microstructures (L- and D-zones) and in particular the organic and mineral fractions vary on a daily basis. Raman microspectrometry provides a nondestructive technique that can be used to provide structural information on organic and mineral compounds. We applied it to thin otolith sections of hake in order to address the following issues: (1) the simultaneous characterization of variations in the organic and mineral fractions both in the core area and along successive otolith microstructures; (2) elucidation of significant differences between these fractions; (3) quantification of the effects of etching and staining protocols on otolith structures. The primordium appeared as a punctual area depicting higher luminescence and greater concentrations in organic compounds containing CH groups. Sulcus side showed similar composition suggesting that the contact of the otolith with the macula and its orientation in otosac occur rapidly (about 10 days). The characterization of L- and D-zones in the opaque zones indicated that both structures contained organic and aragonitic fractions with cyclic and synchronous variations. Contrary to the results obtained after EDTA etching, L-zones depicted greater concentrations in organic compounds containing CH groups, whereas D-zones appear richer in aragonite. This organic fraction seemed to be revealed by Mutvei's staining and was affected by EDTA etching which suggests that it corresponds to the soluble fraction of organic matrix. Such results indicate that L- and D-zones differ in their respective organic constituents. Raman microspectrometry thus appears as a powerful technique to acquire quantitative information that is required for a better understanding of otolith biomineralization.