Behaviour of platinum group elements in aquatic systems
Largely because of their use in the catalytic converter of motor vehicles, environmental concentrations of Rh, Pd and Pt (or the platinum group elements; PGE) have increased dramatically over the past two decades. Through physical and chemical stress of the washcoat layer of the catalyst, PGE are emitted as particulate matter at rates of up to some mg per km per vehicle. PGE are subsequently dispersed by the atmosphere or subject to localised accumulation, in road dust and urban soil for example, but ultimately undergo some degree of remobilisation and enter the aquatic environment. Mobility is generally greatest under acidic conditions or in the presence of complexants, including natural organic matter, following chemical oxidation of the metallic forms. The potential implications for environmental impact and health of the variable speciation and reactivity of the PGEs is unknown which is the major driver for our research.
Mobilisation in surface waters implies that the transport and impacts of PGE in aquatic systems are strongly influenced by their interactions with natural inorganic and biogenic particulate matter. Information on the adsorptive and removal characteristics of PGE is, however, lacking, and largely restricted to studies defining the uptake of selected PGE by synthetic sorbents. To this end, one component of the SEA group led by Dr Andrew Turner and Prof. Geoff Millward is investigating the fractionation and particle-water interactions of PGE in freshwater, estuarine and marine environments.
Since PGE occur at very low concentrations in surface waters, we add elevated concentrations as tracers to sediment suspensions or plankton cultures to investigate their behaviour. Currently we have two post-doctoral fellows, funded by the EU and by the EPSRC, and a self-funded PhD student focusing on the following areas:
- The kinetics of PGE uptake by different preparations of river sediment and influence of various dissolved organic constituents on particle-water reactions
- The adsorption of PGE under simulated estuarine conditions.
- Estimating the aquatic speciation of PGE using equilibrium calculations
- The uptake of PGE by cultures of marine plankton and by macroalgae
- The use of PGE as tracers for monitoring the transport of sediment under estuarine conditions simulated in a flume tank.
Above: Uptake of platinum group elements by Chlorella stigmatophora
Above: Microscopic image of Chlorella
Publications
Cobelo-Garcia, A., Turner, A. and Millward, G.E. (2008). Fractionation and reactivity of platinum group elements on estuarine mixing. Environmental Science and Technology (in press).
Cobelo-Garcia, A., Turner, A., Millward, G.E. and Couceiro, F. (2007). Behaviour of palladium (II), platinum (IV), and rhodium (III) in artificial and natural waters: influence of reactor surface and geochemistry on metal recovery. Analytica Chimica Acta 585, 202-210.
Couceiro, F., Turner, A. and Millward, G.E. (2007). Adsorption and desorption kinetics of rhodium (III) and platinum (IV) in turbid suspensions: Potential tracers for sediment transport in estuarine flumes. Marine Chemistry 107, 308-318.
Odjegba, V.J., Brown, M.T. and Turner, A. (2007). Studies on the effects of platinum group elements on Lactuca sativa L. American Journal of Plant Physiology 2, 183-194.
Odjegba, V.J., Brown, M.T. and Turner, A. (2007). Studies on the effects of platinum group metals on Lactuca sativa L. Comparative Biochemistry and Physiology A - Molecular and Integrative Physiology 146, S261.
Turner, A. and Wu, K. (2007). Removal of platinum group elements in an estuarine turbidity maximum. Marine Chemistry 107, 295-307.
Turner, A., Crussell, M., Millward, G.E., Cobelo-Garcia, A. and Fisher, A.S. (2006). Adsorption kinetics of platinum group elements in river water. Environmental Science and Technology 40, 1524-1531.
Turner, A., Lewis, M., Shams, L. and Brown, M. (2007). Uptake of platinum group elements by the marine macroalga, Ulva lactuca. Marine Chemistry 105, 271-280.
Turner, A. and Wu, K. (2007). Removal of platinum group elements in an estuarine turbidity maximum. Marine Chemistry 105, 271-280.Turner, A. (2007). Particle-water interactions of platinum groups under estuarine mixing. Marine Chemistry 103, 103-111.