| Summary: | Abstract Biologically secreted carbonates are archives of environmental conditions, as shell and skeletal element minerals record chemical and physical signals of the ambient environment. We report the impact of Cd2+ and Pb2+ on foraminiferal shell crystal structural and organizational characteristics, such as microstructure, texture, crystal co-orientation strength and crystal twin formation for the rotaliid foraminifera Amphistegina lessonii and Amphistegina lobifera. The investigated species lived first in Cd2+- and Pb2+-free and, at a later growth stage, in Cd2+- and Pb2+-containing water. Enrichment in Cd2+ was increased 4 times relative to the ecological criteria maximum concentration (CMC) for both species. For Pb2+, it was increased 5 times for A. lobifera and 6 times for A. lessonii. Crystal organization was measured with Electron-Backscattered-Diffraction (EBSD), shell structure was imaged with FE-SEM. We detect that the Cd2+ and Pb2+ concentrations influence the degree of shell calcite twin formation. For A. lessonii the addition of Cd2+ to the water prevents crystal twin generation, Pb2+ induces decreased twinned calcite secretion. For A. lobifera, both Cd2+ and Pb2+ significantly decrease crystal twin formation. Our study indicates that crystal twin generation by Rotaliida can be developed as a structural indicator for environmental pollution with heavy toxic elements.
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