Changes in the chemical speciation of As, Sb and Ge were studied in two Czech reservoirs used as drinking water sources at monthly intervals over the course of a year. The analytical method was based on hydride generation with cryotrapping (HG-CT) and ICP MS/MS, with compromise conditions for simultaneous speciation analysis of these elements. Limits of detection in the low ng/l range for iAs and iSb and sub ng/l for iGe and all methylated species allowed speciation at naturally occurring levels. Both oxidation state and methylation speciation were determined, based on selective HG and CT, respectively.

Vrchlice in Central Bohemia is a eutrophic lake that becomes anoxic in summer, while the oligotrophic or mesotrophic Souš reservoir in the mountainous area of North Bohemia remains well oxygenated. Inorganic Ge in Vrchlice showed nutrient behavior with decreased concentrations in the productivity period in spring and summer due to consumption by diatoms, and conservative presence of MGe throughout the year. Arsenic in Vrchlice in winter time was mainly present as iAs(V), which was partly converted into iAs(III) in the productivity period, while in Sous iAs was always present as iAs(III). A major presence of methylated species was observed during the productivity period. This is contrasting with Sb present as iSb(V), with a fairly constant fraction of MSb of approx. 15–20% and traces of DMSb and TMSb in all months

A significant fraction As and Sb was present in a form not available for HG, manifesting itself as a difference between the sum of As/Sb species determined by HG-CT-ICP MS/MS and As/Sb totals by ICP MS/MS. This “dark” fraction accounted for up to approximately 40–60% regardless of the season. This fraction can be converted to the HG-active form by UV irradiation, producing both inorganic and methylated species.