THE EFFECT OF SEQUENTIAL EXTRACTIONS OF SUSPENDED PARTICULATE MATTER ON TRACE-METAL SORPTION AND MICROBIAL CELL STABILITY

Sequential extractions, according to a modified scheme proposed by Tes sier et al. (Tessier A, Campbell PGC, Bisson M. Sequential extraction procedure for the speciation of trace metals. Anal Chem 1979;51:844-85 1), were performed on suspended particulate material (SPM) from the Ri ver Mersey, North-West England. The resulting solid-phase fractions we re spiked with trace levels of Cd and Cu and their metal-binding prope rties were investigated as a function of pH. The results indicated tha t metal binding decreased as the material was successively extracted, i.e. the unextracted fraction bound the most metal, while the particle s which had undergone all of the extractions bound the least metal. Th is effect was attributed to the loss of particle mass during the extra ctions and to the relative metal affinities of the newly exposed surfa ces. The exposure of new potential binding sites was not an overriding influence on metal binding. The strongest binding of Cd appears to be to the nominal manganese oxyhydroxide phase, with no measurable bindi ng of Cd by the residual mineral fraction. By contrast, the nominal ir on and manganese oxyhydroxides, organic material and the residual mine ral fraction all appear to affect Cu binding significantly. The effect of the extractions on the particles was also investigated by transmis sion electron microscopy. Micrographs indicated that the biological ma terial in the sample had undergone significant alteration after treatm ent with the first and second extractants (acetate and hydroxylamine, respectively), i.e. before removal of the nominal organic fraction. Th ese changes in biological material. may affect metal binding, complica ting the interpretation in terms of simple mineral and organic phases. (C) 1998 Elsevier Science B.V.