Figure 1.
Overview of the experimental set-ups for gas trapping experiments in the laboratory and in the field.
(A) Schematic of the experimental set-up for the laboratory gas trapping experiments, with the separate in-situ production of volatile methylated As species in a gas-tight reaction vessel (left) and direct introduction of volatile methylated Se and S species (right), connected to (B), a set of glass impingers filled with concentrated nitric acid and c, schematic of the experimental set-up for the field gas trapping experiments, which consists of a flow-through box equipped with an air pump connected to the set of glass impingers (B). During field application, one impinger was connected to one flow-through box and the flow-through boxes were deployed in triplicate.
Figure 2.
Relationship between the efficiency of chemotrapping in nitric acid and boiling points of the studied volatile compounds.
Error bars indicate the standard deviation of the measurements of triplicate samples.
Table 1.
Studied volatile species, including their structure and boiling points, calculated total trapping efficiencies, and observed reactions products and structures after trapping and transformation in concentrated nitric acid.
Figure 3.
Analysis of trapping liquid samples after gas trapping experiments with volatile, methylated Se, S and As compounds.
Stacked chromatograms of solutions with non-volatile Se (top), S (middle), and As (bottom) standards (dashed lines), and chromatograms of diluted nitric acid trapping liquids (solid lines) produced in the gas trapping experiments with volatile organic Se, S and As compounds. The chromatograms are ten-point moving averages.
Figure 4.
Field study site and speciation analysis of field samples.
(A) Location of the studied minerotrophic peatland, Gola di Lago, in southern Switzerland, (B) Legend depicting the investigated species in both the trapping liquids and the surface waters (the fraction of other species was calculated as the total elemental concentration minus the elemental sum of the identified species), (C) Speciation of Se, As and S in the three trapping liquid samples (elemental basis), (D) Speciation of Se, As and S in the three surface water samples (elemental basis). Error bars indicate the standard deviation of triplicate analysis of the samples.
Figure 5.
Chromatograms of trapping liquid- and surface water samples collected at Gola di Lago.
(A) Stacked chromatogram of the gas trapping liquid sample 1 from Gola di Lago for Se (top), S (middle), and As (bottom) and (B) Stacked chromatogram of the surface water sample 1 from Gola di Lago for Se (top), S (middle), and As (bottom). Chromatograms for blanks are indicated by dashed lines. All chromatograms are five-point moving averages, and the identified compounds and their molar concentrations (on an elemental basis) are indicated at the corresponding peaks. Details of both methods are given in Table S3 in Supporting Information File S1.