Trace metal composition of colloidal organic material in marine environments

Marine colloidal material (1 kDa-0.2 mu m) was isolated by cross-flow ultra filtration followed by diafiltration and freeze-drying from surface waters of the Gulf of Mexico and the Middle Atlantic Eight (MAB), as well as from estuarine waters of Galveston Bay. Elemental characterization of isolated c olloidal material included organic carbon (OC) and selected trace metal (Cu , Pb, Zn, Cd, Co, Ni, Cr, Be, Fe, Al, Mn, V, Ba, and Ti) determinations. It was found that levels of these metals in marine colloids ranged from < 0.1 to similar to 50 mu g/g colloidal matter, except for Fe which generally ha d a concentration > 120 mu g/g. Most metals (Cu, Pb, Zn, Ni, Al, Mn, V, and Ti) had an average concentration > 1 mu g/g while concentrations of Cd, Co and Be were usually < 1 mu g/g. Metal concentrations (mu g/g) in isolated colloids were, in general, higher in Galveston Bay than in the Gulf of Mexi co, suggesting either high abundance of trace metals in estuarine waters or differences in organic matter composition. Higher colloidal metal concentr ations in the MAB than in the Gulf of Mexico might be due to higher terrest rial inputs in the MAB. Colloidal metal concentrations (mu g/g) were genera lly lower than those in average soils, continental crust and suspended part icles. However, metal/aluminum ratios (Me/Al) in isolated marine colloids w ere significantly higher than those for average soils and continental crust . Most importantly, colloids had a metal composition and metal/CC ratio (Me /C) similar to humic substances and marine plankton, suggesting that marine colloids largely originate from planktonic sources and are composed of pre dominately organic components. The Me/C ratios of Galveston Bay colloids fo llowed the sequence of Cu > Ni, Clr, Zn > Mn > Co > Pb, Cd, which is simila r to the Irving-Williams order except for Mn, suggesting that the interacti on of metals with marine colloids is determined by the affinity of metals f or specific organic ligands. (C) 2000 Elsevier Science B.V. All rights rese rved.