Final Report - ICPDR

4.1.3 Inorganic micropollutants in suspended solids, sediment and mussels
IWACO (2000) proposed limit values for heavy metals in sediment of the Danube
river basin:
Metals Unit Limit value in sediment
Zinc mg/kg 200
Copper mg/kg 50
Chromium mg/kg 100
Lead mg/kg 100
Cadmium mg/kg 1
Mercury mg/kg 0.5
Nickel mg/kg 50
Arsenic mg/kg 40
The heavy metal concentrations varied in a wide range depending on the type of the
samples and the type of heavy metal. Figures 4.1.3.1-11 summarize the different
heavy metal concentrations in suspended solids, sediment and different mussel
species collected in the Tisza (yellow) and its tributaries (red), respectively. Figures
are grouped in one page indicating the amounts of the same pollutant measured in
the three different investigated compartments. In case of mussels the use of
logarithmic scale on Y axis is more demonstrative and advisable at the same time,
because the differences in the order of magnitudes are illustrated only by that way.
Altogether the three most frequently found mussel species were selected for the
inorganic and organic micropollutant analysis, depending on which of them was
present in the given sampling location. Data on Unio tumidus, U. pictorum and U.
crassus are available as the results of the ITR program referring to the Tisza and its
tributaries.
Mercury (Hg) limit concentration was exceeded in the suspended solids and bottom
sediment of the tributary Sajó. The amount of 1,3 mg/kg measured in the suspended
solids is almost the double than in the sediment sample (0,75 mg/kg). It is a very
clear phenomenon, which indicates historic (former) mercury pollution. During
flooding the mixing up causes resuspension. Heavy metals could be remobilized from
the deposited sediment layer and transported further downstream along the river at
any time.
There are no important differences among the three commonly occurring mussel
species in terms of the investigated mercury concentrations (Figure 4.1.3.1). It is
interesting that a slight decrease is detected in the upstream direction. The range of
mercury concentration is generally below 0,1 mg/kg. The tributaries represent the
same degree of pollution; the Zagyva contains the lowest mercury value (in Unio
tumidus).
The cadmium (Cd) concentration was dominantly well above the 1 mg/kg limit value
both in the suspended solids and sediments of Tisza River (3-5 mg/kg), a bit higher
values were found in the sediment (Figure 4.1.3.2). The sediment of Szamos has the
maximum Cd value (7 mg/kg). Higher amounts (approaching and exceeding 10
mg/kg) were measured in the different mussels especially in case of mussels
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