Evaluation and comparison of two selective extraction procedures for heavymetal speciation in sediments

Two sequential extraction procedures (the former proposed by the Standard, Measurements and Testing-SM&T-program of European Union and the latter deri ved from those of Tessier and Forstner with various modifications) have bee n compared, by analyzing a reference material (CRM 601) certified for the c ontent of heavy metals in the three solutions resulting from the SM&T proce dure. Scanning electron microscopy-energy dispersive X-ray analysis (SEM-ED X) was used to evaluate the composition of the residues after various extra ctions. Reliable results, both in terms of precision and accuracy, were obt ained for the first two steps of the SM&T scheme. As regards the third step , because it was modified during this work, a direct comparison of our resu lts with those certified is not possible. SEM analysis confirmed that the s cheme previously used in the laboratory was more aggressive compared to the SM&T procedure, which has also the advantage that the only CRM available f or metal partitioning in sediments is certified using this method.