Distribution, Bioavailability and Speciation
of Mercury in Contaminated Soil and Groundwater
of a Former Wood Impregnation Plant
T. SCHC)NDORI', M. EGLI, H. BIESTER, w. MAILAIIN, and W. ROTARD
During five decades of wood impregnation by HgCI2> several tons of mercury had been released into
the environment. About 4-5 tons of emitted mercury (Hg) penetrated through thick loess layers down
to the gravel aquifer. Today, a plume persisting for at least 700 m downgradient is detectable in the
groundwater. Later construction activities resulted in redistribution of soil. The upper soil layer (030 em), toxicologically relevant for human health, became therefore spatially contaminated with 10 to
1500 mg Hg/kg.
The risk assessment with regard to residents and down gradient groundwater abstraction for
drinking water, as well as remediation strategies, is based on the following studies on Hg compounds,
mobility and turnover characteristics.
In order to receive quantitative estimates of mercury, intestinal uptake after oral ingestion of
contaminated soil, extractions with model mixtures of the saliva-gastra-intestinal milieu were carried
out. The results indicate that on the one hand, the amount of available Hg for intestinal uptake
increased above proportion with increasing total Hg « 1-18% of total Hg). On the other, the results of
this comprehensive simulation of the gastra-intestinal-solution were similar to those of the
comparably simple 0.o7n-HCI-extraction.
With regard to the vertical water-soluble Hg transfer, a lower retention capacity exits in deeper
soils due to the stratigraphic sequence (top soil! anthroprogenic fill, loess, and gravel, respectively).
Soil gas measurements show that Hg is also transformed into metallic mercury (HgO), which
propagates through the subsoil in the gaseous phase. Apart from Hgo, mainly matrix-bond Hg forms
in the soil were detected by means of a method of temperature-controlled pyrolysis. In order to
examine the form in which Hg is transported by percolation and groundwater, various operationally
defined Hg fractions (Hg"·', Hgllh) were determined. Thermodynamic equilibrium calculations
confirm that under the existing hydrochemical conditions a high percentage of the inorganic mercury
exists as Hgo besides Hg(OH), even in the groundwater.
1
Introduction and Case History
On the site of a former wood impregnation plant, covering an area of almost
90000 m>, wooden telegraph poles, vine sticks and sleepers for railway tracks
were treated with mercury chloride (HgCU solution (so-called sublimate) and
tar oil to prevent the wood from decay. The facility was operated from early
1900 until 1965. Tar oil (i.e. carbolineum) was used for soaking the bottom
part of the poles only, as this part has to be particularly protected against the
natural rotting power of the soil. Prior to this treatment, the timber was
soaked in sublimate contained in several concrete basins, which together
comprised a volume of almost 1000 m 3 • The antiseptic effect of HgCl2 has been
Environmental Science
Mercury Contaminated Sites (ed. by R. Ebinghaus et al.l
© Springer-Verlag Berlin Heidelberg 1999
of Mercury in Contaminated Soil and Groundwater
of a Former Wood Impregnation Plant
T. SCHC)NDORI', M. EGLI, H. BIESTER, w. MAILAIIN, and W. ROTARD
During five decades of wood impregnation by HgCI2> several tons of mercury had been released into
the environment. About 4-5 tons of emitted mercury (Hg) penetrated through thick loess layers down
to the gravel aquifer. Today, a plume persisting for at least 700 m downgradient is detectable in the
groundwater. Later construction activities resulted in redistribution of soil. The upper soil layer (030 em), toxicologically relevant for human health, became therefore spatially contaminated with 10 to
1500 mg Hg/kg.
The risk assessment with regard to residents and down gradient groundwater abstraction for
drinking water, as well as remediation strategies, is based on the following studies on Hg compounds,
mobility and turnover characteristics.
In order to receive quantitative estimates of mercury, intestinal uptake after oral ingestion of
contaminated soil, extractions with model mixtures of the saliva-gastra-intestinal milieu were carried
out. The results indicate that on the one hand, the amount of available Hg for intestinal uptake
increased above proportion with increasing total Hg « 1-18% of total Hg). On the other, the results of
this comprehensive simulation of the gastra-intestinal-solution were similar to those of the
comparably simple 0.o7n-HCI-extraction.
With regard to the vertical water-soluble Hg transfer, a lower retention capacity exits in deeper
soils due to the stratigraphic sequence (top soil! anthroprogenic fill, loess, and gravel, respectively).
Soil gas measurements show that Hg is also transformed into metallic mercury (HgO), which
propagates through the subsoil in the gaseous phase. Apart from Hgo, mainly matrix-bond Hg forms
in the soil were detected by means of a method of temperature-controlled pyrolysis. In order to
examine the form in which Hg is transported by percolation and groundwater, various operationally
defined Hg fractions (Hg"·', Hgllh) were determined. Thermodynamic equilibrium calculations
confirm that under the existing hydrochemical conditions a high percentage of the inorganic mercury
exists as Hgo besides Hg(OH), even in the groundwater.
1
Introduction and Case History
On the site of a former wood impregnation plant, covering an area of almost
90000 m>, wooden telegraph poles, vine sticks and sleepers for railway tracks
were treated with mercury chloride (HgCU solution (so-called sublimate) and
tar oil to prevent the wood from decay. The facility was operated from early
1900 until 1965. Tar oil (i.e. carbolineum) was used for soaking the bottom
part of the poles only, as this part has to be particularly protected against the
natural rotting power of the soil. Prior to this treatment, the timber was
soaked in sublimate contained in several concrete basins, which together
comprised a volume of almost 1000 m 3 • The antiseptic effect of HgCl2 has been
Environmental Science
Mercury Contaminated Sites (ed. by R. Ebinghaus et al.l
© Springer-Verlag Berlin Heidelberg 1999