PROCEDURES FOR ALUMINUM SPECIATION IN PERCOLATING WATER OF FOREST SOIL

Speciation of aluminium in forest soil solution, is important for stud ying damage of forest ecosystems. In the present work procedures were developed for the speciation of aluminium by online coupling of chomat ographic separation methods to an element selective and sensitive ICP- MS detection system (Elan 5000).While the inorganic aluminium species were retained on a cation exchange column, the aluminium complexed to organic components passed through the column and could be measured. Po lymeric aluminium hydroxides were determined in the effluent after pyr ocatechol violet was added to the sample prior to the ion exchange pro cedure. A size fractionation procedure of the organic aluminum species was suggested using SEC-ICP-MS. In spring and summer 1997 these speci ation procedures were applied to percolating waters of two different p lots of the Zierenberg project (nothern Hessen, Germany). The plots re present different phases in the process of humus disintegration and sh ould show different contents of low molecular weight aluminium species . Because of the very low concentrations of inorganic aluminium specie s and especially of polymeric aluminium hydroxides direct phytotoxic e ffects may be excluded. Both, the difference between the two parts of varying humus disintegration and the temporal rise of the aluminium co ncentration based on the high molecular organic aluminium species (46. 000 Dalton). In contrast to the present theoretical assumptions, the l ow molecular organic aluminium species (3.500 - 15.000 Dalton) showed neither a trend in time nor a variability between the two plots of dif ferent humus disintegration. The procedures developed in this work app eared to be efficient for the speciation of aluminium in percolating w aters of forest soil. Therefore they should be useful to provide new i nsight into the role of aluminium in the disintegration of humus in fo rest soils.