Single extractions versus sequential extraction for the estimation of heavy metal fractions in reduced and oxidised dredged sediments

Sequential extraction is applied to estimate the chemical association of tr ace elements in soils and sediments. An approach where the same information is gained from single extractions would be advantageous: sample preservati on is critical only before and during one extraction, there is no risk for sample losses during consecutive steps and results can be obtained faster. The drawbacks are that more sample is needed and that sample heterogeneity may introduce errors. Five soil or sediment samples were subjected to seque ntial extraction according to Tessier et al. and to single extractions, usi ng the reacting conditions of the sequential steps. Estimates of the acid e xtractable, reducible and residual fractions from single extractions genera lly agreed with these determined by sequential extraction. The oxidisable f raction should be determined by extraction of the residue of a hydroxylamin e-hydrochloride extraction. The differences observed between determined and estimated fractionation would not seriously affect interpretation of the r esults. To estimate metal fractions in soils and sediments, the use of sing le extractions rather than sequential extraction according to Tessier et al . could be justified for practical purposes.