Environmental Engineering Reference
In-Depth Information
dissolved sulphur species, a range of insoluble iron sulphides, such as iron
monosulphide (FeS), greigite (Fe
3
S
4
), and pyrite (FeS
2
), are formed. Insoluble
iron sulphides have been detected in water columns of the Black Sea and
Framvaren Fjord [14, 58, 88]. Organic sulphur in the suspended phase and
thiols have been measured in several anoxic marine basins [14, 20].
The origin of sulphur intermediate species under anoxic conditions is a con-
troversial issue and the details of their transformations are poorly understood
(for review see Zopfi et al. [111]). The formation of these species occurs via
both chemical and biological reactions. Oxidation of hydrogen sulphide with
oxygen and Fe(Mn) oxyhydroxides and sulfate reduction are the main processes
responsible for sulphur intermediates formation in the euxinic water columns
except of the elemental sulphur, which is formed only during hydrogen sulphide
oxidation. Biological sulphide oxidation is described elsewhere in this volume
(e.g., Overmann and Manske; Pimenov). Chemically mediated reactions of
thiosulphate formation are elemental sulphur(polysulphides) hydrolysis, poly-
thionate disproportionation, and the reaction between elemental sulphur and
sulphite (e.g., [96]).
A number of different analytical techniques including voltammetry, reverse-
phase high pressure liquid chromatography (RP-HPLC), colorimetry, ion chro-
matography have been used to measure concentrations of sulphur intermediates
in euxinic environments (reviewed by Zopfi et al. [112]).
The occurrence of inorganic sulphur species in the oxic water is discussed
elsewhere [99]. Data on sulphur intermediates using colorimetry method were
obtained by Volkov [99] and by Volkov et al. [102]. The precision of the
original method is
3-5% and the detection limit is 0.03µM [100]. The average
concentrations of reduced inorganic sulphur species in the anoxic zone of
the Black Sea are summarized in Table 3. Elemental sulphur data refer to
the sum of elemental sulphur allotropes (zero-valent sulphur) and the zero-
valent sulphur derived from some fraction (n-1) of the original polysulphide
S
n
2
−
. Thiosulphate data in the table represent the total amount of thiosulphate,
sulphite and polythionates.
Elemental sulphur concentrations in the Black Sea anoxic zone varied be-
tween zero and 5.4 µM and increased with depth. At some stations there was
a concentration maximum observed at the oxic/anoxic interface. The latter is
likely to be associated with sulphide oxidation by dissolved oxygen and/or Mn
oxyhydroxides. [97] suggested that concentrations increasing with depth reflect
ongoing process of polysulphide formation by the reaction between zero-valent
sulphur and
±
Σ
H
2
S. The vertical distribution of thiosulphate had similar shape
as that of the elemental sulphur. The concentration range was from 0 to 5.9µM.
In contrast, Luther [50] using a cathodic stripping square wave voltammetry
(CSSWV) method did not detect all, thiosulphate, sulphite and tetrathionate,
in the Black Sea anoxic zone (method's detection limit is 50 nM). Zero-valent
