Nickel isotope fractionation during laterite Ni ore smelting and refining: implications for tracing the sources of Ni in smelter-affected soils

Nickel isotope ratios were measured in ores, fly ash, slags and FeNi samples from two metallurgical plants located in the Goiás State, Brazil (Barro Alto, Niquelândia). This allowed investigating the mass-dependent fractionation of Ni isotopes during the Ni-laterite ore smelting and refining. Feeding material exhibits a large range of δ60Ni values (from 0.02 ± 0.10 ‰ to 0.20 ± 0.05 ‰, n=7), explained by the diversity of Ni-bearing phases, and the average of δ60Nifeeding materials was found equal to 0.08 ± 0.08‰ (2SD, n=7). Both δ60Ni values of fly ash (δ60Ni = 0.07 ± 0.07‰, n=10) and final FeNi produced (0.05 ± 0.02 ‰, n=2) were not significantly different from the feeding materials ones. These values are consistent with the very high production yield of the factories. However, smelting slags present the heaviest δ60Ni values of all the smelter samples, with δ60Ni ranging from 0.11 ± 0.05 ‰ to 0.27 ± 0.05 ‰ (n=8). Soils were also collected near and far from the Niquelândia metallurgical plant, to evaluate the potential of Ni isotopes for tracing the natural vs anthropogenic Ni in soils. The Ni isotopic composition of the non-impacted topsoils developed on ultramafic rocks ranges from -0.26 ± 0.09 ‰ to -0.04 ± 0.05 ‰ (n=20). On the contrary, the Ni isotopic composition of the non-ultramafic topsoils, collected close to the plant, exhibit a large variation of δ60Ni, ranging from -0.19 ± 0.13 ‰ up to 0.10 ± 0.05 ‰ (n=4). This slight but significant enrichment in heavy isotopes highlight the potential impact of smelting activity in the surrounding area, as well as the potential of Ni isotopes for discerning anthropogenic samples (heavier δ60Ni values) from natural ones (lighter δ60Ni values). However, given the global range of published δ60Ni values (from -1.03 to 2.5 ‰) and more particularly those associated to natural weathering of ultramafic rocks (from -0.61 to 0.32‰), the use of Ni isotopes for tracing environmental contamination from smelters will remain challenging.

Sources de variation intra-populationelle de la morphologie des otolithes: asymétrie directionnelle et régime alimentaire

Otoliths are calcified structures located in Osteichthyes’ inner ear that are involved in audition and balance. Their morphology is used as an indicator of various ecological processes or properties. This application requires identifying the endogenous and exogenous factors that act simultaneously as sources of shape variation. This thesis aims at detecting and quantifying the relative contributions of directional asymmetry and diet to otolith shape variation at the intra-population level. Directional asymmetry between left and right otoliths was found in flat-fishes, the blind-side otolith being always longer and larger, whereas it was negligible in round-fishes. However, asymmetry amplitude never exceeded 18 %, which suggests evolutionary canalization of otolith shape symmetry. A correlation between global diet and otolith was detected in 4 species studied in situ. Diet composition contributed more than food amount to morphological variation and affected otolith shape both globally and locally. An experimental study on sea bass (Dicentrarchus larbrax) showed that diet composition in terms of essential polyunsaturated fatty acids at larval stage affects otolith morphogenesis during juvenile stage without impacting on individuals’ somatic growth. This result suggests a direct effect of diet on otolith shape and not an indirect one through the somatic-otolith growth relationship. This effect disappeared at later stages, morphogenetic trajectories converging back to a similar shape, which suggests ontogenetic canalization of otolith shape.