Distribution, Bioavailability and Speciation of Mercury
189
places where sublimate solution could directly penetrate into the ground, i.e. dip
basins, storage areas and sublimate production.
Within the centres of contamination, Hg concentrations in the g/kg range
were encountered. The contents gradually decrease with increasing depth. The
retention capacity of the several-metres-thick loess layer was, however, not
sufficient to prevent the gravel aquifer in 6-10 m depth from being contaminated. The insufficient adsorption capacity results from the fact that in alkaline
subsoil horizons, which are low in organic C, the adsorption behaviour of Hg is
mainly controlled by its direct interaction with an inorganic surface. The low
clay mineral contents made translocations within the profile even more probable
(Schuster 1991). Beneath the source areas, the unsaturated layer above the
aquifer still contained contaminant concentrations of 10 to some 100 mg Hg/kg
(Fig. 4).
5
Bioavailability
5.1
Introduction
In addition to the food chain, the direct oral intake of soil particles can play an
important role, if dust from polluted soil is whirled up and inhaled or swallowed
during games and sports. Experience has shown that the main part of dust
particles is moistened in the pharynx and then swallowed. Furthermore, direct
oral ingestion of soil particles from hand-to-mouth contact of playing infants can
be a crucial exposure path. Hg may be absorbed within the human body after oral
ingestion provided that Hg fixed on mineral surfaces is mobilized and dissolved
in digestive juices in the gastrointestinal system. These Hg compounds, however,
normally show limited dissolution.
The elution of Hg from soil samples with hydrochloric acid (HCI) is used as an
economical method to simulate the mobilization of heavy metals by gastric acid.
This method does not, however, take into consideration the influence of organic
components, such as enzymes, lipids or mucins. The low absorption of dissolved
heavy metals in the gastric tract, which is, in comparison, much higher in the
intestinal tract, e.g. duodenum and ileum, is also not taken into account. The
passage of dissolved heavy metals from the stomach into the duodenum
represents a change into a different medium with respect to pH value and
electrolyte concentrations. Thus, dissolved heavy metals may be precipitated as
hydroxides and subsequently adsorbed to soil particles or indigestible parts of
nutriments.
To simulate the mobilization of organic pollutants or heavy metals from soil
particles in the gastrointestinal system, several in-vitro models have been
developed in recent years (Ruby et al. 1993, 1996; Hack and Selenka 1996). For
our investigation the in-vitro model according to Rotard was used (Fig. 1).
189
places where sublimate solution could directly penetrate into the ground, i.e. dip
basins, storage areas and sublimate production.
Within the centres of contamination, Hg concentrations in the g/kg range
were encountered. The contents gradually decrease with increasing depth. The
retention capacity of the several-metres-thick loess layer was, however, not
sufficient to prevent the gravel aquifer in 6-10 m depth from being contaminated. The insufficient adsorption capacity results from the fact that in alkaline
subsoil horizons, which are low in organic C, the adsorption behaviour of Hg is
mainly controlled by its direct interaction with an inorganic surface. The low
clay mineral contents made translocations within the profile even more probable
(Schuster 1991). Beneath the source areas, the unsaturated layer above the
aquifer still contained contaminant concentrations of 10 to some 100 mg Hg/kg
(Fig. 4).
5
Bioavailability
5.1
Introduction
In addition to the food chain, the direct oral intake of soil particles can play an
important role, if dust from polluted soil is whirled up and inhaled or swallowed
during games and sports. Experience has shown that the main part of dust
particles is moistened in the pharynx and then swallowed. Furthermore, direct
oral ingestion of soil particles from hand-to-mouth contact of playing infants can
be a crucial exposure path. Hg may be absorbed within the human body after oral
ingestion provided that Hg fixed on mineral surfaces is mobilized and dissolved
in digestive juices in the gastrointestinal system. These Hg compounds, however,
normally show limited dissolution.
The elution of Hg from soil samples with hydrochloric acid (HCI) is used as an
economical method to simulate the mobilization of heavy metals by gastric acid.
This method does not, however, take into consideration the influence of organic
components, such as enzymes, lipids or mucins. The low absorption of dissolved
heavy metals in the gastric tract, which is, in comparison, much higher in the
intestinal tract, e.g. duodenum and ileum, is also not taken into account. The
passage of dissolved heavy metals from the stomach into the duodenum
represents a change into a different medium with respect to pH value and
electrolyte concentrations. Thus, dissolved heavy metals may be precipitated as
hydroxides and subsequently adsorbed to soil particles or indigestible parts of
nutriments.
To simulate the mobilization of organic pollutants or heavy metals from soil
particles in the gastrointestinal system, several in-vitro models have been
developed in recent years (Ruby et al. 1993, 1996; Hack and Selenka 1996). For
our investigation the in-vitro model according to Rotard was used (Fig. 1).