204
T. Schiindorf et al.
The formation of elementary Hgo in the subsoil could be documented and is
hypothesized to be the result of secondary transformation reactions of cationic
Hg(II). This process may be due to microbiall1i\ediation or to reducible reagents
such as humic matter or iron. Therefore, the soil gas measurements for elemental
Hgo provide good guidance in the field as well as for sample selection for
laboratory analysis and during the interpretation of the gathered data, i.e. the
evaluation of horizontal Hg transport in the gaseous phase.
Organically complexed Hg predominates in topsoil leachate, whereas the
proportion of easy reducible inorganic forms is highest in the strongly
contaminated leachate of the anthropogenic fill. This behaviour is obviously
caused by still existing and very soluble HgCl2 salt. Water analysis show that
contaminated groundwater mainly contains inorganic Hg species, of which an
important part is present as Hgo. This could be confirmed by equilibrium
calculations.
Bioavailability tests, using also digestive model juices, give evidence of an
overproportional increase of Hg, which is available for absorption in the human
body after oral intake of contaminated soil, with increasing total Hg concentrations from less than 1 up to 18% of total Hg. Therefore, a worst-case
assumption of 20% bioavailability has been chosen by the public health office to
assess the intervention value for human exposure by topsoil contamination. With
respect to groundwater contamination level and calculated Hg emissions, our
investigations clearly show, furthermore, that the aquifer has to be cleaned up
(cf. Anonymous 1993b).
Consequently, a remediation technique has to be developed on the basis of the
presented study. This technique has to deal with many difficult handicaps such as
the highly heterogeneous distribution of Hg in the topsoil, the contaminated
deeper vadose zone in the areas of the former Hg use, the contaminated saturated
zone (aquifer) as well as the different Hg behaviour - due to varying species -
and the fact that the area has been built over by new family houses, highrise
buildings etc.
References
Andersson A (1979) Mercury in soils. In: Nriagu 0 (ed) The biogeochemistry of mercury in the
environment. Elsevier-North-Holland Biomedical Press, Amsterdam, pp 79-112
Andren AW, Nriagu)O (1979) The global cycle of mercury. In: Nriagu 0 (ed) The biogeochemistry of
mercury in the environment. Elsevier, North-Holland Biomedical Press, Amsterdam, pp 1-21
Anonymus (1993a) Zweite Verwaltungsvorschrift des Umweltministeriums zum Bodenschutzgesetz
iiber die Probennahme und -aufbereitung von Bodenproben vom 24.08.1993, veriiffentlicht in:
Gemeinsames Amtsblatt des Landes Baden-Wiirttemberg (GABL) Nr. 30 vom 29.09.1993
Anonymus (1993b) Orientierungswerte fiir die Bearbeitung von Altlasten und Schadensfiillen, Stand:
12.08.1993, veriiffentlicht in: Gemeinsames Amtsblatt des Landes Baden-Wiirttemberg Nr 33 vom
30.11.1993
ATSDR, Agency for Toxic Substances and Disease Registry, US Department of Health and Human
Services, Public Health Service (1992) Draft toxicological profile for mercury. Atlanta, Georgia
Behra P (1987) Etude du comportement d'un micropollutant metallique - Ie mercure - au cours de sa
migration Ii travers un milieux poreux sature: identification experimentale des mecanismes
T. Schiindorf et al.
The formation of elementary Hgo in the subsoil could be documented and is
hypothesized to be the result of secondary transformation reactions of cationic
Hg(II). This process may be due to microbiall1i\ediation or to reducible reagents
such as humic matter or iron. Therefore, the soil gas measurements for elemental
Hgo provide good guidance in the field as well as for sample selection for
laboratory analysis and during the interpretation of the gathered data, i.e. the
evaluation of horizontal Hg transport in the gaseous phase.
Organically complexed Hg predominates in topsoil leachate, whereas the
proportion of easy reducible inorganic forms is highest in the strongly
contaminated leachate of the anthropogenic fill. This behaviour is obviously
caused by still existing and very soluble HgCl2 salt. Water analysis show that
contaminated groundwater mainly contains inorganic Hg species, of which an
important part is present as Hgo. This could be confirmed by equilibrium
calculations.
Bioavailability tests, using also digestive model juices, give evidence of an
overproportional increase of Hg, which is available for absorption in the human
body after oral intake of contaminated soil, with increasing total Hg concentrations from less than 1 up to 18% of total Hg. Therefore, a worst-case
assumption of 20% bioavailability has been chosen by the public health office to
assess the intervention value for human exposure by topsoil contamination. With
respect to groundwater contamination level and calculated Hg emissions, our
investigations clearly show, furthermore, that the aquifer has to be cleaned up
(cf. Anonymous 1993b).
Consequently, a remediation technique has to be developed on the basis of the
presented study. This technique has to deal with many difficult handicaps such as
the highly heterogeneous distribution of Hg in the topsoil, the contaminated
deeper vadose zone in the areas of the former Hg use, the contaminated saturated
zone (aquifer) as well as the different Hg behaviour - due to varying species -
and the fact that the area has been built over by new family houses, highrise
buildings etc.
References
Andersson A (1979) Mercury in soils. In: Nriagu 0 (ed) The biogeochemistry of mercury in the
environment. Elsevier-North-Holland Biomedical Press, Amsterdam, pp 79-112
Andren AW, Nriagu)O (1979) The global cycle of mercury. In: Nriagu 0 (ed) The biogeochemistry of
mercury in the environment. Elsevier, North-Holland Biomedical Press, Amsterdam, pp 1-21
Anonymus (1993a) Zweite Verwaltungsvorschrift des Umweltministeriums zum Bodenschutzgesetz
iiber die Probennahme und -aufbereitung von Bodenproben vom 24.08.1993, veriiffentlicht in:
Gemeinsames Amtsblatt des Landes Baden-Wiirttemberg (GABL) Nr. 30 vom 29.09.1993
Anonymus (1993b) Orientierungswerte fiir die Bearbeitung von Altlasten und Schadensfiillen, Stand:
12.08.1993, veriiffentlicht in: Gemeinsames Amtsblatt des Landes Baden-Wiirttemberg Nr 33 vom
30.11.1993
ATSDR, Agency for Toxic Substances and Disease Registry, US Department of Health and Human
Services, Public Health Service (1992) Draft toxicological profile for mercury. Atlanta, Georgia
Behra P (1987) Etude du comportement d'un micropollutant metallique - Ie mercure - au cours de sa
migration Ii travers un milieux poreux sature: identification experimentale des mecanismes