DETERMINATION OF METAL ORGANIC ASSOCIATIONS IN SOIL LEACHATES BY INDUCTIVELY COUPLED PLASMA MASS-SPECTROMETRY

The potential effect of acid rain on the mobilization of metals in coniferous humus and deciduous humus soils has been studied. Soil leachates were obtained by passing aliquots of simulated acid rain through soil columns over a period of 536 days. The simulated acid rain consisted of dilute aqueous solutions of nitric and sulphuric acids (molar ratio 1: 2) which were adjusted to one of the following pH-values 2.5, 3.3, 4.0 and 5.7 (the latter being the normal equilibrium pH of water saturated with carbon dioxide). Selected leachate samples were injected onto a size exclusion column, the effluent from which was connected on-line to a UV-visible detector and to the nebulizer of an inductively coupled plasma-mass spectrometer. A mobile phase of 0.2 M ammonium acetate at a flow rate of 0.3 ml min.-1 provided adequate chromatographic resolution. The results indicated that at high pH more organic material was dissolved, whereas the total metal concentration was usually lower. Only inorganic species (Al, Mn, Fe, Ni, Cu, Zn, Cd and La) were detected in leachates from deciduous humus soils. When the pH was > 2.5, leachates from coniferous humus soils also contained Al, Fe and Cu as organically-bound species having shorter retention times than the inorganic species. Metal concentrations found in deciduous leachates were, in general, higher than those in corresponding coniferous leachates.