196
T. Schondorf et al.
which led to a significant Hg contamination along the soil profile. The Hg
concentration in the eluate exceeds by more than one order of magnitude the
values of the soil profile from the storage area discussed above. Apart from the
sample from the artificial fill, the less reducible, i.e. water-soluble organic Hg
complexes are predominant, presumably with humic matter like fulvic acid.
Their fraction of 65% in the upper part of the loess layer increased to 83% in
deeper soil up to 93% in the sand/gravel sediments. Elementary mercury
decreases to background values with increasing depth in the vertical profiles. In
the case of low contaminated topsoils, mercury is encountered in an organic
complex bound form only. Besides these laboratory results, a perched sample
gained from 0.5 m depth contained 28 pg Hg/l, 27.7 ~lg/l of which in an organic
complex form. Hgo was not determined.
In highly contaminated samples, HgIIa is often predominating, presumably
mainly in the original form of HgCl2 salt which is dissolved in high
concentrations in these samples during the leaching procedure. Inspection
samples of loess analyzed for DOC (here as water-soluble organic carbon)
determined 10-17 mg DOC/I in the eluate. This confirms that there is sufficient
mobilizing organic matter such as fulvic acid to transport most of the soluble Hg
fraction in organic complex form, as observed.
7
General Elution Behaviour
The determination of the water-soluble total Hg fraction according to DIN 38414
S4 may be used as a rough indicator for the leachate behaviour of Hg by in-situ
percolating water and, thus, for assessment of the risk for groundwater
contamination, in case there are no better data available such as leachate
samples recovered from lysimeters.
7.1
Results and Discussion
Figure 8, a double logarithmic diagram, illustrates the large range of the Hg
concentrations in the eluate in relation to the total contents of mercury in the
soil. If the soil samples are subdivided according to origin and geological aspects,
a structure can be realized which illustrates the influence of the sample type:
compared with the total contents, the highest water soluble Hg fraction is
encountered in the gravel/sand sediments recovered from the aquifer underneath
the loess sediments. Additionally, this sample type represents the best correlation
to total Hg for the following three reasons: homogenous, low contents of organic
matter (Corg ca. 0.1%), relatively homogenous mineral composition and
comparably uniform Hg binding forms. Decreasing elution values were, in
general, recorded in loess - artificial fill - topsoil with increasing variation at the
same time. This seems to be due to the fact that the sorption capacity of the soil
T. Schondorf et al.
which led to a significant Hg contamination along the soil profile. The Hg
concentration in the eluate exceeds by more than one order of magnitude the
values of the soil profile from the storage area discussed above. Apart from the
sample from the artificial fill, the less reducible, i.e. water-soluble organic Hg
complexes are predominant, presumably with humic matter like fulvic acid.
Their fraction of 65% in the upper part of the loess layer increased to 83% in
deeper soil up to 93% in the sand/gravel sediments. Elementary mercury
decreases to background values with increasing depth in the vertical profiles. In
the case of low contaminated topsoils, mercury is encountered in an organic
complex bound form only. Besides these laboratory results, a perched sample
gained from 0.5 m depth contained 28 pg Hg/l, 27.7 ~lg/l of which in an organic
complex form. Hgo was not determined.
In highly contaminated samples, HgIIa is often predominating, presumably
mainly in the original form of HgCl2 salt which is dissolved in high
concentrations in these samples during the leaching procedure. Inspection
samples of loess analyzed for DOC (here as water-soluble organic carbon)
determined 10-17 mg DOC/I in the eluate. This confirms that there is sufficient
mobilizing organic matter such as fulvic acid to transport most of the soluble Hg
fraction in organic complex form, as observed.
7
General Elution Behaviour
The determination of the water-soluble total Hg fraction according to DIN 38414
S4 may be used as a rough indicator for the leachate behaviour of Hg by in-situ
percolating water and, thus, for assessment of the risk for groundwater
contamination, in case there are no better data available such as leachate
samples recovered from lysimeters.
7.1
Results and Discussion
Figure 8, a double logarithmic diagram, illustrates the large range of the Hg
concentrations in the eluate in relation to the total contents of mercury in the
soil. If the soil samples are subdivided according to origin and geological aspects,
a structure can be realized which illustrates the influence of the sample type:
compared with the total contents, the highest water soluble Hg fraction is
encountered in the gravel/sand sediments recovered from the aquifer underneath
the loess sediments. Additionally, this sample type represents the best correlation
to total Hg for the following three reasons: homogenous, low contents of organic
matter (Corg ca. 0.1%), relatively homogenous mineral composition and
comparably uniform Hg binding forms. Decreasing elution values were, in
general, recorded in loess - artificial fill - topsoil with increasing variation at the
same time. This seems to be due to the fact that the sorption capacity of the soil