Distribution, Bioavailability and Speciation of Mercury
185
The inorganic and organic component of each model juice was prepared
separately in concentrations twice as high as shown in Table 1 and subsequently
mixed applying a ratio of 1:1 before treatment of the soil sample.
Five g of the soil sample were shaken at 37°C according to the flow chart (Fig.
1). When the saliva-stomach stage was terminated, 10 ml of the solution were
centrifuged for 1 h at 4600 rpm and 3400 g. The supernatant liquid was analyzed
for heavy metals by plasma mass spectrometry (ICP-MS) and atomic absorption
spectrometry (AAS). Mercury was analyzed by cold vapour AAS and ICP-MS.
To the remaining mixture of saliva, stomach juice and soil sample, duodenum
juice and bile juice was added and shaken for 6 h.
After centrifugation for 1 h at 4600 rpm and 3400 g, the supernatant liquid was
analyzed for heavy metals. For the analysis of mercury by ICP-MS, standards and
samples had to be stabilized with sodium bromide.
2.2.4
Solid-Phase Hg Pyrolysis
This method is used to differentiate between Hg compounds that are fixed to soil.
An electric furnace provided with a thermometer in a sample vessel was
connected to a detection cell located in an AAS-detector (Perkin Elmer 3030).
Sublimating Hg compounds released from the samples were thermally reduced to
Hgo by passing a heated glass tube (800°C) before reaching the detection cell. All
samples were heated continuously to 700°C at a rate of 0.5 aCts in an N2 flow of
0.3 lImin. Related to the physical properties of various Hg compounds, Hg is
released at different temperatures. Results are presented as Hg-release curves,
showing the amount of the released Hg versus the sample temperature (Biester
1997a, b).
2.2.5
Elementary Mercury (HgO) in Soil Gas
During the exploratory borings, soil gas was gained by means of a membrane
pump via a hose in the sampling device at a flow rate of 90 lIh and subsequently
measured by CV AAS (mobile Hg monitor, type HG MAK 1200 of Seefelder
MeBtechnik). Interference by other gaseous substances also absorbing UV light
in the range of 253.7 nm can be compensated for by setting the zero point with
the sample gas by means of an absorption cartridge for Hg. Such disturbing
volatile substances, however, did not occur in the present study.
2.2.6
Water-Extractable Hg Fractions in the Soil
After extraction with deionized water according to DIN 38414 S4, the waterextractable Hg fraction was divided into Hgo aq' by SnC12 easy reducible Hg
(HgIIa) and total soluble Hg (Hg-tot), determined after oxidation of organic or
185
The inorganic and organic component of each model juice was prepared
separately in concentrations twice as high as shown in Table 1 and subsequently
mixed applying a ratio of 1:1 before treatment of the soil sample.
Five g of the soil sample were shaken at 37°C according to the flow chart (Fig.
1). When the saliva-stomach stage was terminated, 10 ml of the solution were
centrifuged for 1 h at 4600 rpm and 3400 g. The supernatant liquid was analyzed
for heavy metals by plasma mass spectrometry (ICP-MS) and atomic absorption
spectrometry (AAS). Mercury was analyzed by cold vapour AAS and ICP-MS.
To the remaining mixture of saliva, stomach juice and soil sample, duodenum
juice and bile juice was added and shaken for 6 h.
After centrifugation for 1 h at 4600 rpm and 3400 g, the supernatant liquid was
analyzed for heavy metals. For the analysis of mercury by ICP-MS, standards and
samples had to be stabilized with sodium bromide.
2.2.4
Solid-Phase Hg Pyrolysis
This method is used to differentiate between Hg compounds that are fixed to soil.
An electric furnace provided with a thermometer in a sample vessel was
connected to a detection cell located in an AAS-detector (Perkin Elmer 3030).
Sublimating Hg compounds released from the samples were thermally reduced to
Hgo by passing a heated glass tube (800°C) before reaching the detection cell. All
samples were heated continuously to 700°C at a rate of 0.5 aCts in an N2 flow of
0.3 lImin. Related to the physical properties of various Hg compounds, Hg is
released at different temperatures. Results are presented as Hg-release curves,
showing the amount of the released Hg versus the sample temperature (Biester
1997a, b).
2.2.5
Elementary Mercury (HgO) in Soil Gas
During the exploratory borings, soil gas was gained by means of a membrane
pump via a hose in the sampling device at a flow rate of 90 lIh and subsequently
measured by CV AAS (mobile Hg monitor, type HG MAK 1200 of Seefelder
MeBtechnik). Interference by other gaseous substances also absorbing UV light
in the range of 253.7 nm can be compensated for by setting the zero point with
the sample gas by means of an absorption cartridge for Hg. Such disturbing
volatile substances, however, did not occur in the present study.
2.2.6
Water-Extractable Hg Fractions in the Soil
After extraction with deionized water according to DIN 38414 S4, the waterextractable Hg fraction was divided into Hgo aq' by SnC12 easy reducible Hg
(HgIIa) and total soluble Hg (Hg-tot), determined after oxidation of organic or