AN ULTRACLEAN CROSS-FLOW ULTRAFILTRATION TECHNIQUE FOR THE STUDY OF TRACE-METAL PHASE SPECIATION IN SEAWATER

A series of laboratory and field studies were conducted to test suitab ility and optimal sampling conditions of an Amicon ultrafiltration sys tem for the collection of colloidal material for trace metal phase spe ciation studies in marine environments. A cleaning procedure is requir ed between each sample processed to eliminate carry-over artifacts and achieve a low system blank. Mass-balance recovery of 88-109% was achi eved for ultrafiltration of trace metals (e.g., Cd, Cu, Ni, Pb, Mn, Fe , Zn, HE) from estuarine samples. Results of sample storage experiment s indicate that ultrafiltration should ideally be performed within 4 h of sample collection to prevent phase speciation shifts. The concentr ation of a number of trace metals in the permeate fraction, when plott ed as a function of concentration factor, was found to fit the steady- state macromolecular permeation model of Kilduff and Weber (1992). A r etentate concentration factor between 5 and 10 was optimal for most me tals based on modeling the permeate metal concentration. For Galveston Bay, the colloidal fraction (1 kDa-0.45 mu m) accounted for 65-85% of the Cu, 35-40% of the Ni, and 30-95% of the Pb in the filtered (< 0.4 5 mu m) fraction. Colloidal Cu, Cu-c (1 kDa-0.2 mu m) was 64%, Ni, was 6%, Pb-c was 9% of the filtered (< 0.2 mu m) fraction in deep Pacific water samples from the colloid intercomparison exercise.