Stability and mobility of metal-humic complexes isolated from different soils

The contamination of potable water aquifers by heavy metals is one of the m ost severe environmental threats. For the transport of heavy metals from va rious types of contaminated sites into the ground water and also into surfa ce water aquifers, humic substances (HS) are recognized to be of main impor tance. Dissolved in natural waters humic substances are readily complexed w ith a variety of metal ions. Therefore, humic substances are of cardinal im portance for the migration and, consequently, the pollution of ground water s with heavy metals. Our paper presents the results of a comprehensive comp arison of several isolated humic acids of soils of different origin (differ ent geochemical milieu) and their metal complexes. Two polluted sites in Ge rmany, which differ in their geochemical milieu (pH-value) were selected. T he aim of our experiments was to describe the properties of terrestrial hum ic substances depending on their origin and genesis as well as the effects of the transport of humic substance-bound metals into the water-unsaturated soil zone. After determination of heavy metals in the soils by photon acti vation analysis the activated soil was used as an inherent tracer in batch experiments with the isolated humic acid. After adsorption of the loaded hu mic acid on an XAD-8 resin column, the partition of metals mobilized by hum ic acids could be quantified. There are correlations of the formation of me tal-humic complexes with the soil pedogenes, with the pH-value as well as w ith the humic acid concentration.