Implications of natural organic matter binding heterogeneity on understanding lead(II) complexation in aquatic systems

Organochlorines (HCH isomers, DDX and individual PCBs) were determined in pine needle litter and upper soil layers of three forest test areas in central Germany. The contents accumulating over a number of years or even decades in the organic surface layer are compared with the levels of new inputs from needle fall as well as with the levels of older inputs in the upper mineral soil layer. Differences in behaviour between the soil horizons are discussed, especially concerning the DDX and HCH groups. With approximately comparable Corg values (approx. 21-24%) the pH value in the range of 4.24-2.90 in the O-horizon of the forest soils exerts a large influence. Hence the A-horizon represents--for p,p'-DDT and gamma-HCH in particular--at pH values of 2.90 a pollutant reservoir which should not be underestimated and which could endanger the rhizosphere and the groundwater. According to PCBs, in the more acidic soils with a pH value <4.0 the lipophilic higher polychlorinated biphenyls were found to be more highly enriched in the humus layer.