An electrochemical study of Ni, Sb, Se, Sn, U and V in the estuary of the Tamar

Abstract

Cathodic stripping voltammetry (CSV) was used to investigate the behaviour of several dissolved trace elements (Ni, Sb, Se, Sn, U and V) in the Tamar estuary (south-west England). An attempt was made to differentiate between the labile and non-labile (organically or colloidally bound) metal fractions in the estuary by utilizing ligand competition between an added electroactive ligand and the natural complexing material. Surface-active organic material was found to interfere with the CSV determinations and prohibited the determination of low concentrations of labile Sn, Sb, V and Se occurring in the Tamar estuary, but the total dissolved concentrations of these elements could be determined after UV photolysis. Both labile and total dissolved concentrations of Ni could be determined and these were used to establish the speciation of this element. It was found that the non-labile and labile Ni fractions were not in equilibrium throughout the estuary and that these two fractions behaved independently, the organically complexed fraction behaving conservatively and the labile fraction non-conservatively. Total dissolved selenium and vanadium were found to behave largely conservatively; variation in the concentration of vanadium at very low salinities (below 0·2) could be due to variations in the freshwater input or to removal processes. Uranium was found to show partial removal at low to intermediate salinities. Antimony was found to be scavenged from solution in the low-salinity region (S<5). The concentrations varied in accordance with mid-estuarine release from interstitial waters (antimony), and with scavenging and uptake by anoxic sediments (uranium). Adsorption experiments confirmed that adsorption on iron hydroxide particles could account for some of the variations seen for uranium and vanadium. The tin concentration in the estuary was considerably enhanced by tin pollution at the mouth of the estuary presumably due to inputs of organotin (as tributyltin). This tin was found to behave conservatively.