Elemental speciation, reactivity and environmental processes
From an environmental and biological perspective, of critical importance is not the total amount of a metal in solution but its component species or fractions. Our research has focused on the speciation and fractionation of trace metals in natural fresh and estuarine waters using both analytical techniques and fractionation methods coupled with speciation modelling. We have studied metals directly in natural and engineered waters (e.g. sewage and landfill effluents) and in model solutions as surrogates for natural waters.
Electrochemical measurements coupled with speciation modelling
Measurements of dissolved nickel in rivers and estuaries have indicated that Ni is strongly complexed by a single or number of unidentified ligand(s). Data derived from electrochemical measurements can be coupled with thermodynamic calculations, using software such as WHAM v6, to model the speciation of Ni in the water column. This information is used to predict the reactivity, availability, transport and fate of Ni in the estuarine environment.
Above: Calculated speciation of dissolved Ni in the Tweed estuary. NiL denotes strong conmplexation by undefined ligands
Octanol-water partitioning studies
The partitioning of a chemical between the amphiphilic, lipid-like solvent, 1-octanol and water affords a measure of its hydrophobicity, hence its propensity to undergo hydrophobic interactions in aquatic environments. This approach is normally reserved for the study of distinct organic contaminants. However, we have applied a similar protocol to study the partitioning of trace metals in natural waters, and in particular those metals that form complexes with organic matter. Determining partition constants as a function of pH and coupling measurements with speciation measurements afford valuable information on the nature of the hydrophobic complexes. Models have also been developed that relate the overall octanol-water partitioning of a metal and the partitioning of its component species.
Above: Percentage of lead soluble in octanol in different contaminated fresh waters as a function of pH. Also shown is the percentage of organically complexed lead computed for 1 mM of organic ligands as humic and fulvic substances
Publications
Achterberg, E.P., Herzl, V.M.C., Braungardt C.B. and Millward, G.E. (2003). Metal behaviour in an estuary polluted by acid mine drainage: The role of particulate matter. Environmental Pollution 121, 283-292.
Cobelo-Garcia, A., Millward, G.E., Prego, R. and Lukashin, V. (2006). Metal concentrations in Kandalaksha Bay, White Sea (Russia) following the spring snowmelt. Environmental Pollution 143, 89-99.
Dale, A.W., Prego, R., Millward, G.E. and Gomez-Gesteira, M. (2004). Transient oceanic and tidal contributions to water exchange and residence times in a coastal upwelling system in the NE Atlantic: the Pontevedra Ria. Marine Pollution Bulletin 49, 235-248.
Doucet, F.J., Lead, J.R. Maguire, L., Achterberg, E.P. and Millward, G.E. (2005). Visualisation of natural aquatic colloids and particles-a comparison of conventional high vacuum and environmental scanning electron microscopy. Journal of Environmental Monitoring 7, 115-121.
Fitzsimons, M.F., Millward, G.E., Revitt, D.M. and Dawit, M.D. (2006). Desorption kinetics of ammonium and methylamines from estuarine sediments: Consequences for the cycling of nitrogen. Marine Chemistry 101, 12-26.
Martino, M., Turner, A. and Millward, G.E. (2003). Influence of organic complexation on the adsorption kinetics of nickel in river waters. Environmental Science and Technology 37, 2383-2388.
Martino, M., Turner, A., Nimmo, M. and Millward, G.E. (2002). Resuspension, reactivity and recycling of trace metals in the Mersey Estuary, UK. Marine Chemistry 77, 171-186.
Millward, G.E. and Liu, Y-P. (2003). Modelling metal desorption kinetics in estuaries. The Science of the Total Environment 314/316, 613-623.
Millward, G.E., Sands, T.K. Nimmo, M., Turner, A. and Tappin, A.D. (2002). Nickel in the Humber plume: Influences of particle dynamics and reactivity. Estuarine, Coastal and Shelf Science 54, 821-832.
Monterroso, P., Pato, P., Pereira, M.E., Millward, G.E., Vale, C. and Duarte, A.C. (2007). Metal-contaminated sediments in a semi-enclosed basin: Implications for recovery. Estuarine, Coastal and Shelf Science 71, 148-158.
Neal, C., Leeks, G.J.L., Millward, G.E., Harris, J.R.W., Huthnance, J.M. and Rees, J.G. (2003). Land-ocean interactions: functioning and environmental management from a UK perspective. The Science of the Total Environment 314/316, 3-11.
Prego, R., Cobelo-Garcia, A., Lukashin, V., Goordeev, V. and Millward, G.E. (2003). Particulate nickel distribution and fluxes in the sediments and suspended particulate matter of Kandalaksha Bay (White Sea, Russia). Oceanology 43, S173-S178.
Punt, A.G., Millward, G.E. and Harris, J.R.W. (2003). Modelling solute and suspended sediment transport in the Tweed Estuary, UK. The Science of the Total Environment 314/316, 715-725.
Tappin, A., Millward, G.E. and Fitzsimons, M/F. (2007). Distribution, cycling and recovery of amino acids in estuarine waters and sediments. Environmental Chemistry Letters 5, 161-167.
Turner, A. (2007). A binary aqueous compoent model for the sediment-water partitioning of trace metals in natural waters. Environmental Science and Technology 41, 3977-3983.
Turner, A. (2007). A binary aqueous component model for the sediment-water partitioning of trace metals in natural waters. Environmental Science and Technology 41, 3977-3983.
Turner, A. and Martino, M. (2006). Modelling the equilibrium speciation of nickel in the Tweed estuary, UK: Voltammetric determinations and simulations using WHAM. Marine Chemistry 102, 198-207.
Turner, A. and Millward, G.E. (2002). Suspended particles: their role in estuarine biogeochemical cycles. Estuarine, Coastal and Shelf Science 55, 857-883.
Turner, A. and Williamson, I. (2005). Octanol-water partitioning of chemical constituents in river water and treated sewage effluent. Water Research 39, 4325-4334.
Turner, A. and Williamson, I. (2005). On the relationship between Dow and Kow in natural waters. Environmental Science and Technology 39, 8719-8727.
Turner, A., Fitzer, S. and Glegg, G.A. (2008). Impacts of boat paint chips on the distribution and availability of copper in an English ria. Environmental Pollution 151, 176-181.
Turner, A., Le Roux, S.M. and Millward, G.E. (2004). Speciation and partitioning of cadmium and zinc in two contrasting estuaries: The role of hydrophobic organic matter. Limnology and Oceanography 49, 11-19.
Turner, A., Le Roux, S.M. and Millward, G.E. (2008). Adsorption of Cd to Fe and Mn oxides along a salinity gradient. Marine Chemistry 108, 77-84.
Turner, A., Millward, G.E. and Le Roux, S.M. (2001). Sediment-water partitioning of inorganic mercury in estuaries. Environmental Science and Technology 35, 4648-4654.
Turner, A., Millward, G.E. and Le Roux, S.M. (2004). Significance of oxides and particulate organic matter in controlling trace metal partitioning in a contaminated estuary. Marine Chemistry 88, 179-192.