On-site analyses as a decision support tool for dredging and sustainable sediment management
Résumé
On-site chemical characterisation technologies are of key importance for sustainable management of sediments in a perspective of circular economy, either in a marine (harbours) or inland (waterways) context. They allow the collection of data on mineral chemistry of sediments, in view of the evaluation of their suitability for a reuse scenario, as well as on their contents in contaminants, in order to provide a first evaluation of their acceptability. Data obtained with on-site technologies cannot be used for compliance, but they are invaluable for decision support. They provide immediate results – usually within minutes – and allow dynamic or adaptive sampling strategies. A laboratory confirmation scheme is still required for validation, but sample selection for laboratory analyses is improved if on-site measurements are available. Data collection can be carried out during detailed sediment mapping prior to dredging. On-site analyses of each sample provide a better data quality than composite analyses and allow refining the dredging strategies. Sediment characterisation during dredging operations allows a better management of each load, according to contamination and reuse suitability. It allows selective storage and processing of sediments stocks on land. Among currently available technologies, portable X-ray fluorescence (pXRF)allowsroutine measurements for most of the major elements (Ca, Fe, K, Ti, Mn, and with less precision, Si, Al, P, S and Cl) and for many inorganic contaminants (or "heavy metals": Pb, Zn, Cu, As, Sb, Cr, V, etc). Some contaminants (Hg, Cd, Ag) cannotbe routinely analysed at low concentrations but may be detected when present at elevated levels. Portable gas chromatography and GC/MS provide routinely field data on light or volatile organic contaminants. Emerging technologies provide promising perspectives for the detection of heavier organic contaminants, the speciation of inorganic contaminants, the measurement of light elements, inaccessible to pXRF, and the identification of mineral phases. These include portable Fourier transform infrared spectroscopy (pFTIR), portable X-ray diffraction (pXRD), laser-induced breakdown spectroscopy (LIBS) and portable microRaman spectroscopy.
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