The use of size-normalised procedures in the analysis of organic contaminants in estuarine sediments

Sediments are being used increasingly for monitoring the aquatic environment because of their ability to integrate contaminants over time, and because they provide valuable information on source, dispersion and accumulation of toxicants. However, as the majority of contaminants are usually associated with the fine fraction of the sediment, interpretation of spatial distributions is often confounded by variable grain size. The confounding effects of variable grain size can be reduced by separating the fine fraction of the sediment and analysing the contaminant concentration of this material. This approach is commonly used in heavy metal studies, but it is rare in the analysis of organochlorine compounds because of an absence on information on possible contaminant loss to the sieve water during the separating process, and possible removal of contaminants with the coarse fraction. Results from the current study indicate such losses to be minimal and examples are presented to illustrate the superiority of size-normalised data in the identification of source and in the determination of dispersion and accumulation of contaminants.