Study of Sulfate Reduction
255
the samples by filtration and washing off the remains of labeled sulfate by
rinsing in the funnel with the carrier solution. This procedure is rapid, but gives
less reproducible data, and (2) the more complicated one, which includes the
distillation of HzS from the above-mentioned ZnS precipitates to avoid the
background of 35S04 remaining on the ZnS filters. The latter procedure is
longer but more precise. With bUlh procedures, first the supernatant water
from the fixed sample is discharged with the aid of a syphon, the end of which,
inserted into the sample, has 1-cm-high capillary hook at its end. If the direct
filtration procedure is preferred, the ZnS precipitate, together with some 10-15
ml of water remained in the bottle, is transferred into the funnel with the membrane or GF filter, presoaked in 20% NaZS04 solution, and filtered. The
remains of precipitate in the bottle are washed out with 10-20ml of NaZS04
carrier solution into the same funnel. The precipitate is washed off the remains
of labeled sulfate with the same carrier solution containing 1 % of NaZS04 by
passing three subsequent 5-ml portions. The filter is placed into the scintillation vial and radio assayed in Instagel cocktail after resuspending the precipitate. The radioactivity thus measured (Ri) is corrected for zero time control
(Ro). Distillation is carried out as follows. The precipitate from the bottle is
resuspended with 10-15 ml of water and transferred into the reaction tube of
the apparatus (Fig. 5.9.) into which 3ml of 5% NaZC03 has been added. The
subsequent distillation procedure is the same as described above for the
bottom sediments, only 3% HCI instead of the sulfuric acid is used to decompose the ZnS.
The inverse specific radioactivity of labeled sulfate is estimated in the
same way as in the case of the slurry sediment method. First, the cpm radioactivity of 35sol- is measured after corresponding dilution of the working solution (for example, for seawater: dilute 0.2ml in 1000mi and take O.2ml for
radio assay under the same counting conditions as for measuring Ri). The value
thus measured is calculated as cpm per sample (Rs). Similarly, the absolute
content of S04-S is estimated or calculated as IlgS (Ks) per volume of one
sample. Their ratio (KsIRs) will be equal to the value of the inverse specific
radioactivity of labeled sulfate in the experimental vessels (Sr). The rate of
R.xS x24
sulfate reduction As is calculated as following: A = '
r
Ilg S 1-1 day-I,
s
V xt
where Ri is the radioactivity of HzS corrected per zero time counts, cpm in
whole sample; Sr the specific radioactivity of label sulfate, Ilg S cpm- 1 , V the
volume of the sample 1-1, and t the incubation time, h. Examples of As estimations in water columns of meromictic basins are shown in Fig. 5.12.
5.6.4 Location Active Populations of Sulfate-Reduction Bacteria
Instead of a rather tedious colony count, the potential intensity of sulfate
reduction can be applied for this purpose. It is much more simple, rapid, and
255
the samples by filtration and washing off the remains of labeled sulfate by
rinsing in the funnel with the carrier solution. This procedure is rapid, but gives
less reproducible data, and (2) the more complicated one, which includes the
distillation of HzS from the above-mentioned ZnS precipitates to avoid the
background of 35S04 remaining on the ZnS filters. The latter procedure is
longer but more precise. With bUlh procedures, first the supernatant water
from the fixed sample is discharged with the aid of a syphon, the end of which,
inserted into the sample, has 1-cm-high capillary hook at its end. If the direct
filtration procedure is preferred, the ZnS precipitate, together with some 10-15
ml of water remained in the bottle, is transferred into the funnel with the membrane or GF filter, presoaked in 20% NaZS04 solution, and filtered. The
remains of precipitate in the bottle are washed out with 10-20ml of NaZS04
carrier solution into the same funnel. The precipitate is washed off the remains
of labeled sulfate with the same carrier solution containing 1 % of NaZS04 by
passing three subsequent 5-ml portions. The filter is placed into the scintillation vial and radio assayed in Instagel cocktail after resuspending the precipitate. The radioactivity thus measured (Ri) is corrected for zero time control
(Ro). Distillation is carried out as follows. The precipitate from the bottle is
resuspended with 10-15 ml of water and transferred into the reaction tube of
the apparatus (Fig. 5.9.) into which 3ml of 5% NaZC03 has been added. The
subsequent distillation procedure is the same as described above for the
bottom sediments, only 3% HCI instead of the sulfuric acid is used to decompose the ZnS.
The inverse specific radioactivity of labeled sulfate is estimated in the
same way as in the case of the slurry sediment method. First, the cpm radioactivity of 35sol- is measured after corresponding dilution of the working solution (for example, for seawater: dilute 0.2ml in 1000mi and take O.2ml for
radio assay under the same counting conditions as for measuring Ri). The value
thus measured is calculated as cpm per sample (Rs). Similarly, the absolute
content of S04-S is estimated or calculated as IlgS (Ks) per volume of one
sample. Their ratio (KsIRs) will be equal to the value of the inverse specific
radioactivity of labeled sulfate in the experimental vessels (Sr). The rate of
R.xS x24
sulfate reduction As is calculated as following: A = '
r
Ilg S 1-1 day-I,
s
V xt
where Ri is the radioactivity of HzS corrected per zero time counts, cpm in
whole sample; Sr the specific radioactivity of label sulfate, Ilg S cpm- 1 , V the
volume of the sample 1-1, and t the incubation time, h. Examples of As estimations in water columns of meromictic basins are shown in Fig. 5.12.
5.6.4 Location Active Populations of Sulfate-Reduction Bacteria
Instead of a rather tedious colony count, the potential intensity of sulfate
reduction can be applied for this purpose. It is much more simple, rapid, and