An insight into sediment fractionation analysis: from sampling to visualisation of results

This review is focused on the importance of operational conditions for metal fractionation and their influence on the results obtained, using both sequential and single step extractions. The discussion is about the different pathways by which metals are incorporated into aquatic systems and the relationship between the nature of sediments and their interaction with metals. In addition, the relevance of the so-called metal extraction methods, either sequential or single-step extractions, to obtain information about the bioavailability and mobility of metals in sediments is considered. Several aspects, such as sampling and sample storage, sediment processing (drying and sieving), sediment mass/extractant volume ratio and operational time, are reviewed since they can significantly affect the recoveries of metals associated with each geochemical phase. Finally, chemometric techniques are addressed as useful tools to visualise and interpret the data obtained and transform them into relevant information. Although a variety of reagents and operating conditions have been used with satisfactory results, there are no standardised protocols, with the exception of the BCR, which has undergone successive modifications. This shows that even the best combination of extractants can have advantages and limitations, and the use of one protocol or another will depend on the type of information required. In this sense, the experimental conditions play a relevant role in obtaining reliable information on the mobility and availability of metals.