Studying Sulfur Cycling with the Aid of 35S
239
the experimental vessels correspondingly; Ks the amount of sulfide initially
injected into them together with the working isotope solution, f..lgSI-1; Kc the
same in the ambiental water samples; t the time of incubation, h.
The rate of formation and the ratio of products of oxidation might also
be measured in the same subsamples taken from the experimental bottles. The
sum of sulfate + thiosulfate sulfur could be estimated as described above (see
point 1 on the preparation of working solution) as the radioactivity of BaS04
precipitate obtained after permanganate oxidation of thiosulfate to sulfate.
The sum of sulfide plus sulfane S2-reduced sulfur of thiosulfate may be measured in two different ways. One is the precipitation of sulfate (as BaS04) in
the filtrate left after the separation of ZnS. The BaS04, formed after the addition of 1 ml10% BaCI to the 40-ml portion of this filtrate 1 h later is separated
by filtration. The thiosulfate remains in the filtrate. It is then oxidized with the
acid permanganate solution as described above. The sulfate formed is precipitated as BaS04 and radio assayed at the filter. Exactly one half of its radioactivity (R,) belongs to the sulfane sulfur of thiosulfate (S2-), and its other half
to sulfate of its sulfur (S+6). Thus the total amount of reduced sulfur, having
the S2- sulfide valence (Rc), will be equal to the sum of R; (radioactivity of
sulfide sulfur) + 112 R,.
Another technique to estimate this sum of sulfide and sulfane sulfur (RJ
is the use of silver ions, which hydrolyze the thiosulfate molecules and precipitate both the sulfane and the sulfide sulfur as Ag2S. This can be done as
follows. Subsamples of 30ml (for freshwater) or of 5 ml (for seawater) taken
from the experimental samples fixed with the carrier solution are placed into
50-ml beakers with 2ml of 10% AgN03 solution (freshwater) or with
4ml of the same solution (seawater) + 20ml of distilled water + 0.02ml of the
carrier solution without sulfate (seawater). Two hours later, the Ag2S precipitates thus formed (together with AgCI in the seawater) are separated by filtration through the membrane filters covered with Mg-carbonate (see above).
The filters, together with this precipitate, are placed into the beakers with
10ml of 0.1 % KMn04 + 1 ml1/3 HCI solution. The beakers are left for 1 day.
Then their content is heated to boiling point and discolored with hydrogen
peroxide while still hot. The sulfate formed is precipitated as BaS04, separated
by filtration and radio assayed. The total amount of reduced (S2-)-sulfur thus
oxidized (As) is calculated as As values (see above). Correspondingly, the
radioactivity of the whole amount of S+6 formed during the Hl 5 S oxidation
(e.g., S6+ of thiosulfate and sulfate) could be radioassayed at one filter which
contains the BaS04 precipitated from the filtrate left after Ag2S separation.
The approaches and techniques described above make it possible, if necessary, to measure the rate of formation of all principal products of sulfide oxidation in water basins: So, S2032-, and S04. This methodology appeared to be
applicable for investigation of the mechanisms of in situ hydrogen sulfide oxidation, which might be different in various water bodies, and even in their different biotopes, depending on numerous environmental factors, and especially
upon the degree of participation of native bacterial populations. The problem
239
the experimental vessels correspondingly; Ks the amount of sulfide initially
injected into them together with the working isotope solution, f..lgSI-1; Kc the
same in the ambiental water samples; t the time of incubation, h.
The rate of formation and the ratio of products of oxidation might also
be measured in the same subsamples taken from the experimental bottles. The
sum of sulfate + thiosulfate sulfur could be estimated as described above (see
point 1 on the preparation of working solution) as the radioactivity of BaS04
precipitate obtained after permanganate oxidation of thiosulfate to sulfate.
The sum of sulfide plus sulfane S2-reduced sulfur of thiosulfate may be measured in two different ways. One is the precipitation of sulfate (as BaS04) in
the filtrate left after the separation of ZnS. The BaS04, formed after the addition of 1 ml10% BaCI to the 40-ml portion of this filtrate 1 h later is separated
by filtration. The thiosulfate remains in the filtrate. It is then oxidized with the
acid permanganate solution as described above. The sulfate formed is precipitated as BaS04 and radio assayed at the filter. Exactly one half of its radioactivity (R,) belongs to the sulfane sulfur of thiosulfate (S2-), and its other half
to sulfate of its sulfur (S+6). Thus the total amount of reduced sulfur, having
the S2- sulfide valence (Rc), will be equal to the sum of R; (radioactivity of
sulfide sulfur) + 112 R,.
Another technique to estimate this sum of sulfide and sulfane sulfur (RJ
is the use of silver ions, which hydrolyze the thiosulfate molecules and precipitate both the sulfane and the sulfide sulfur as Ag2S. This can be done as
follows. Subsamples of 30ml (for freshwater) or of 5 ml (for seawater) taken
from the experimental samples fixed with the carrier solution are placed into
50-ml beakers with 2ml of 10% AgN03 solution (freshwater) or with
4ml of the same solution (seawater) + 20ml of distilled water + 0.02ml of the
carrier solution without sulfate (seawater). Two hours later, the Ag2S precipitates thus formed (together with AgCI in the seawater) are separated by filtration through the membrane filters covered with Mg-carbonate (see above).
The filters, together with this precipitate, are placed into the beakers with
10ml of 0.1 % KMn04 + 1 ml1/3 HCI solution. The beakers are left for 1 day.
Then their content is heated to boiling point and discolored with hydrogen
peroxide while still hot. The sulfate formed is precipitated as BaS04, separated
by filtration and radio assayed. The total amount of reduced (S2-)-sulfur thus
oxidized (As) is calculated as As values (see above). Correspondingly, the
radioactivity of the whole amount of S+6 formed during the Hl 5 S oxidation
(e.g., S6+ of thiosulfate and sulfate) could be radioassayed at one filter which
contains the BaS04 precipitated from the filtrate left after Ag2S separation.
The approaches and techniques described above make it possible, if necessary, to measure the rate of formation of all principal products of sulfide oxidation in water basins: So, S2032-, and S04. This methodology appeared to be
applicable for investigation of the mechanisms of in situ hydrogen sulfide oxidation, which might be different in various water bodies, and even in their different biotopes, depending on numerous environmental factors, and especially
upon the degree of participation of native bacterial populations. The problem