Colloidal Metals in the Tamar Estuary and their Influence on Metal Fractionation by Membrane Filtration

Kate A. Howell; Eric P. Achterberg; Alan D. Tappin; Paul J. Worsfold

doi:10.1071/EN06004

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Colloidal Metals in the Tamar Estuary and their Influence on Metal Fractionation by Membrane Filtration

Kate A. Howell ^A ^B , Eric P. Achterberg ^A ^C , Alan D. Tappin ^A ^D and Paul J. Worsfold ^A

+ Author Affiliations

- Author Affiliations

^A School of Earth, Ocean and Environmental Sciences, University of Plymouth, Plymouth, PL4 8AA, UK.

^B Present address: College of Oceanic and Atmospheric Sciences, Oregon State University, Hatfield Marine Science Center, Newport, OR 97365, USA.

^C Present address: National Oceanography Centre Southampton, University of Southampton, Southampton, SO14 3ZH, UK.

^D Corresponding author. Email: atappin@plymouth.ac.uk

Environmental Chemistry 3(3) 199-207 https://doi.org/10.1071/EN06004
Submitted: 11 January 2006 Accepted: 27 April 2006 Published: 10 July 2006

Environmental Context. Trace metals play an essential role in the growth and function of aquatic organisms; however, enhanced metal concentrations can have detrimental effects on ecosystems. The distribution of metals between filterable and filter-retained phases is key to their bioavailability and biogeochemical cycling. Studies on rivers have shown that separating dissolved metals from particle-associated metals may introduce significant artefacts in the resulting filtrate concentrations. Comparable studies on turbid estuarine waters are necessary to improve the design of water sampling programmes.

Abstract. Total filterable and colloidal metals were measured in the Tamar Estuary. The colloidal fraction (M_c) was highly variable for each metal, both spatially and temporally. In April 2001, Al_c and Co_c were higher in the river than the estuary, Cd_c, Cr_c and Pb_c were lower, and Mn_c and U_c were similar. In September 2001, Cd_c was higher in the river than the estuary. Colloidal Al and Mn were positively correlated with concentrations of suspended particles, whereas the colloid contents of the other metals were primarily determined by additional factors. The effect of the colloidal metal content on resultant metal filtrate concentrations, as a function of sample volume filtered, was examined. The amount of Al, Cd, Cu, Pb, and U in the filtrate decreased significantly in at least one case, whereas Mn initially increased in some cases. There was no change for Co, Cr, and Zn. The implications of these results for the study of trace metals in moderately turbid estuaries are discussed.

Keywords. : colloids—estuary—filtration—speciation—trace elements

Acknowledgements

We thank Drs Veronique Herzl and Andy Fisher (University of Plymouth) for their practical help. KAH was supported by NERC studentship GT 4/98/MS/234.

References

Colloidal Metals in the Tamar Estuary and their Influence on Metal Fractionation by Membrane Filtration

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