First Observation of Unicellular Organisms Concentrating Arsenic in ACC Intracellular Inclusions in Lake Waters

In unicellular organisms, intracellular inclusions of amorphous calcium carbonate (ACC) were initially described in cyanobacteria and, later, eukaryotes from Lake Geneva (Switzerland/France). Inclusions eukaryotes, named micropearls, consist hydrated ACCs, frequently enriched Sr or Ba, and displaying internal oscillatory zonations, due to variations the Ba:Ca Sr:Ca ratios. An analysis our database, consisting 1597 micropearl analyses 34 Titicaca (Bolivia/Peru), showed that a certain number Sr- Ba-enriched micropearls these lakes contain As amounts measurable by EDXS. A Q-mode statistical confirmed existence five chemically distinct morpho-chemical groups As-bearing among which was new category identified Geneva, where is often associated with Mg. This type possibly produced small (7–12 μm size) bi-flagellated organism. Micropearls Titicaca, Sr, found an organism very similar Tetraselmis cordiformis, observed earlier Geneva. larger amounts, can be explained high concentration water this lake. The ubiquity biomineralization process points need for better understanding role crystalline carbonates cycling surface waters.