Dissolved Ni Concentrations Research Articles

Distribution, speciation and particle-water interactions of nickel in the Mersey Estuary, UK

The speciation and reactivity of Ni have been studied in a highly contaminated, macrotidal estuary (Mersey, UK). Dissolved Ni concentrations were determined by adsorptive cathodic stripping voltammetry, and labile and non-labile forms were discriminated by ligand exchange with dimethyl-glyoxime. Particle–water interactions were examined by monitoring the uptake and release of the beta-emitting nuclide, 63Ni, by suspended estuarine particles. Concentrations of total dissolved Ni measured during four seasonal transects of the estuary ranged from about 10 nM in seawater to about 230 nM in mid-estuary during summer. Seasonal and axial variations in concentration appeared to be controlled by the dilution of natural and anthropogenic sources of Ni in the catchment (i.e., variations in river flow), and the magnitude of a persistent, but seasonally variable source of Ni to mid-estuary. The ratio of labile to non-labile Ni was reasonably uniform throughout the salinity gradient during each survey, but the magnitude of this ratio exhibited seasonal differences. Results of complexing capacity titrations indicated that Ni forms complexes with a class of strong ligands (stability constants ∼ 1018) and that these ligands are saturated by ambient Ni concentrations. Speciation calculations predict that about 70% of dissolved Ni is complexed by these ligands throughout the estuary. The equilibrium sediment–water distribution coefficient for 63Ni ranged from about 200 ml g−1 in the upper estuary, to about 1200 ml g−1 in the marine end-member, and 63Ni added to riverine sediment exhibited little tendency to desorb when resuspended in saline water. The relatively low particle-reactivity displayed by Ni (compared with many other transition metals in estuaries) appears to be the result of the competing effects of dissolved complexing ligands and particle sorption sites for aqueous Ni, while the increase in particle-reactivity with increasing salinity is interpreted and modelled in terms of the salting out of Ni-organic complexes. Mass balance calculations indicate that mid-estuarine peaks of dissolved Ni are likely the result of desorption of labile and non-labile Ni from highly contaminated particles that are tidally resuspended into the local water column. A general implication of this study is that the geochemical behaviour of Ni in contaminated environments is determined, to a significant extent, by the abundance or availability of complexing ligands, and the interactions of the resulting complexes with suspended particles and dissolved salts.

Nickel speciation and complexation kinetics in freshwater by ligand exchange and DPCSV.

A technique of ligand exchange with DMG (dimethylglyoxime) and DPCSV was applied to determine Ni speciation in lake, river, and groundwater samples. The working conditions related to ligand-exchange equilibrium were optimized, and the ligand-exchange kinetics were examined. The observed pseudo-first-order rate, kobsd, was about 3 x 10(-5) (s-1) for Ni(DMG)2 complex formation with an excess of DMG (microM) over Ni (nM) at pH 7.1-7.7. The second-order exchange kinetic constants, kexch, were between 1.2 x 10(2) and 5.7 x 10(3) s-1 M-1 for ligand exchange of NiEDTA with DMG and between 5 x 10(2) and 7 x 10(3) s-1 M-1 for exchange of natural ligands with DMG in the freshwater samples under similar conditions. Ni ligand exchange between natural ligands and DMG occurred over days with half-lifes of 5-95 h. Total dissolved Ni concentrations in samples from various freshwater systems in Switzerland ranged from 4 nM in an oligotrophic lake to 30 nM in a small river affected by inputs from sewage effluents and agriculture. Free ionic Ni2+ concentrations were determined in the range of 10(-13)-10(-15) M (pNi = 12.2-14.7), indicating that more than 99.9% of dissolved Ni was bound by organic ligands with strong affinity (log K 12.1-14.9) and low concentrations (13-100 nM) at pH 7.2-8.2. Because of slow ligand-exchange kinetics, Ni speciation in natural waters may in many cases not reach equilibrium.

Dissolution of nickel and tissue response observed by X-ray scanning analytical microscopy

The recently developed X-ray scanning analytical microscope (XSAM) was applied for the analysis of the soft tissue of rat in which Ni was implanted and serious inflammation occurred. Our aim is to investigate the relationship between tissue response and elemental distributions. The XSAM observation was conducted in air without pretreatment and staining of samples. Mapping images of P, S, Ca, Fe and Ni, which were the elements with low concentration in soft tissue, were obtained from the soft tissue blocks of rat where Ni was implanted. S mapping image showed the localization of S in muscle and in hairs. Ca mapping image showed the localization of Ca in muscle and hair roots. Fe distribution was also observed and the localized area was consistent with the hemorrhagic area. The Ni dissolution area was clearly detected around the Ni implant. Comparison with the histological observation showed that the Ni dispersed area was consistent with the inflammatory area and the degree of tissue damage was closely related to the dissolved Ni concentration.

Validation and in situ application of an automated dissolved nickel monitor for estuarine studies

The validation of a fully automated dissolved Ni monitor for in situ estuarine studies is presented, based on adsorptive cathodic stripping voltammetry (AdCSV). Dissolved Ni concentrations were determined following on-line filtration and UV digestion, and addition of an AdCSV ligand (dimethyl glyoxime) and pH buffer ( N-2-hydroxyethylpiperazine- N′-2-ethanesulphonic acid). The technique is capable of up to six fully quantified Ni measurements per hour. The automated in situ methodology was applied successfully during two surveys on the Tamar estuary (south west Britain). The strongly varying sample matrix encountered in the estuarine system did not present analytical interferences, and each sample was quantified using internal standard additions. Up to 37 Ni measurements were performed during each survey, which involved 13 h of continuous sampling and analysis. The high resolution data from the winter and summer tidal cycle studies allowed a thorough interpretation of the biogeochemical processes in the studied estuarine system.

Validation and in situ application of an automated dissolved nickel monitor for estuarine studies

The validation of a fully automated dissolved Ni monitor for in situ estuarine studies is presented, based on adsorptive cathodic stripping voltammetry (AdCSV). Dissolved Ni concentrations were determined following on-line filtration and UV digestion, and addition of an AdCSV ligand (dimethyl glyoxime) and pH buffer ( N-2-hydroxyethylpiperazine- N′-2-ethanesulphonic acid). The technique is capable of up to six fully quantified Ni measurements per hour. The automated in situ methodology was applied successfully during two surveys on the Tamar estuary (south west Britain). The strongly varying sample matrix encountered in the estuarine system did not present analytical interferences, and each sample was quantified using internal standard additions. Up to 37 Ni measurements were performed during each survey, which involved 13 h of continuous sampling and analysis. The high resolution data from the winter and summer tidal cycle studies allowed a thorough interpretation of the biogeochemical processes in the studied estuarine system.

Chemical speciation of chromium and nickel in the western Mediterranean

The chemical speciation of dissolved Cr and Ni was measured onboard ship in the western Mediterranean Sea using cathodic stripping voltammetry (CSV) during the winter of 1992 and summer of 1993. Vertical profiles for dissolved Cr(III) in the water column showed concentrations between 0 and 1·4 nM, with highest concentrations in the surface layer, possibly caused by photochemical conversion of Cr(VI) to Cr(III) during summer periods and by atmospheric inputs during winter periods. Enhanced Cr(III) levels also were encountered in the deeper Mediterranean waters and were attributed to mineralisation of sinking biological material and diffusion from sediments. Dissolved Cr(VI) concentrations ranged between 2 and 3 nM, and total dissolved Cr concentrations between 2 and 3·5 nM. Lowest concentrations of total Cr and Cr(VI) occurred in the surface Atlantic waters and highest levels in the deeper Mediterranean waters.Total dissolved Ni concentrations ranged between 1·5 and 5 nM. Between 10 and 20% of the total dissolved Ni in the western Mediterranean appeared to be strongly organically complexed. Both labile and total dissolved Ni concentrations were lower in the surface Atlantic waters than in the Mediterranean deeper waters. Little difference was observed between the data sets for winter and summer, indicating that the influence of seasonal changes on the speciation of Ni was small. A clear nutrient-like behaviour was not apparent for Ni and Cr, and their vertical and horizontal distributions were mainly determined by physical processes.Dissolved budget results for Cr and Ni for the Valdivia and Discovery (data in parentheses) cruises of -572 (55) and -439 (369) t yr−1 were calculated, indicating that the dissolved budgets for these elements were well balanced. The budget deficits and surpluses for dissolved Cr and Ni were small compared to the mass fluxes involved in the calculation of the mass balances.