238
Use of Radioisotopes to Study Biogeochemical Cycling of Elements
Ks
800
600
400
200
12
24
36
48
60
Fig. 5.8. Time course of H 2S oxidation in a water sample taken from the redox zone
of the meromictic lake Gek Gel at 26 m depth; the initial H 2S content in the sample
(K,) was 0.8 mg S2-1-\ t is time, hours. The curve depicts the disappearance rate of H 2S
tectable. The incubation of experimental vessels also is concluded by the injection of the same carrier solution.
The scheme of further processing of the samples depends upon the goal
of the researcher. Only the rate of sulfide oxidative transformation in water
and the disappearance of dissolved H 2S from the experimental samples during
their incubation are needed to be measured, these samples can be processed
as follows (a simplified procedure):
A 100-ml subsample is taken from all the samples (including the
zero time sample) after their fixation with the carrier solution and filtered
through the 0.45-~m pore size membrane filter covered with a fine film
of MgC03 sediment by filtration (0.5 ml of suspension containing 10%
of MgC03 is added to 10mi of water, which is then filtered). The filter retains the molecular sulfur So. It may be radio assayed if needed by the
researcher, or discharged. The filtrate is separated into two 20-ml portions in
50-ml beakers and the sulfide sulfur is sedimented in them as ZnS by addition
of lml5% ZnClz. The ZnS precipitates thus formed l-2h later are separated
by filtration through the membrane filters, and the filters (together with the
Zn precipitates) are radioassayed, being resuspended in the scintillation cocktail. For the radioassay of filters with precipitates of ZnS or BaS04 the Instagel
cocktail is used. The zero time sample is processed in the same way as the
experimental ones to know the initial radioactivity of sulfide (Ro). Then the
rate of sulfide oxidation (disappearance) As can be calculated as following
(R - R.)x (K + K )x24
A . = 0
I
S
C
~g S 1-1 day-I, where Ro and R; are the mean
,
Ro XI
radioactivity of ZnS precipitates measured at filters from the zero time and
Use of Radioisotopes to Study Biogeochemical Cycling of Elements
Ks
800
600
400
200
12
24
36
48
60
Fig. 5.8. Time course of H 2S oxidation in a water sample taken from the redox zone
of the meromictic lake Gek Gel at 26 m depth; the initial H 2S content in the sample
(K,) was 0.8 mg S2-1-\ t is time, hours. The curve depicts the disappearance rate of H 2S
tectable. The incubation of experimental vessels also is concluded by the injection of the same carrier solution.
The scheme of further processing of the samples depends upon the goal
of the researcher. Only the rate of sulfide oxidative transformation in water
and the disappearance of dissolved H 2S from the experimental samples during
their incubation are needed to be measured, these samples can be processed
as follows (a simplified procedure):
A 100-ml subsample is taken from all the samples (including the
zero time sample) after their fixation with the carrier solution and filtered
through the 0.45-~m pore size membrane filter covered with a fine film
of MgC03 sediment by filtration (0.5 ml of suspension containing 10%
of MgC03 is added to 10mi of water, which is then filtered). The filter retains the molecular sulfur So. It may be radio assayed if needed by the
researcher, or discharged. The filtrate is separated into two 20-ml portions in
50-ml beakers and the sulfide sulfur is sedimented in them as ZnS by addition
of lml5% ZnClz. The ZnS precipitates thus formed l-2h later are separated
by filtration through the membrane filters, and the filters (together with the
Zn precipitates) are radioassayed, being resuspended in the scintillation cocktail. For the radioassay of filters with precipitates of ZnS or BaS04 the Instagel
cocktail is used. The zero time sample is processed in the same way as the
experimental ones to know the initial radioactivity of sulfide (Ro). Then the
rate of sulfide oxidation (disappearance) As can be calculated as following
(R - R.)x (K + K )x24
A . = 0
I
S
C
~g S 1-1 day-I, where Ro and R; are the mean
,
Ro XI
radioactivity of ZnS precipitates measured at filters from the zero time and