Aqua regia digestion is a reliable method of extracting elements present in sediments from adsorbed positions, from solution in the interstitial water, and from precipitated oxides, hydroxides, and sulphides. The aqua regia method, when used in combination with the HF–HNO3–HClO4 method for total element extraction from the sediments, provides valuable information on the relative amounts of Fe, Mn, Ni, Cu, Co, Cr, and Zn which are able to migrate in the upper part of the sedimentary sequence. The distribution of Fe and Mn are strongly controlled by pH and Eh. Ni, Cu, Ci, Cr, and Zn are controlled by adsorption to Fe hydroxides, organic matter, and MnO2 as well as Eh and pH with Cu, Co, and Zn showing a stronger correlation with MnO2 than with organic matter and Fe hydroxides.

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