COLLOIDAL ALUMINUM AND IRON IN SEAWATER - AN INTERCOMPARISON BETWEEN VARIOUS CROSS-FLOW ULTRAFILTRATION SYSTEMS

Aluminum (Al) and iron (Fe) were measured on samples from 13 different cross-flow ultrafiltration (CFF) systems representing five manufactur ers at both Colloid Intercomparison experiments conducted in August 19 94, at Woods Hole Oceanographic Institute (WHOI), Massachusetts, and J anuary 1995 in Kona, Hawaii. Most systems displayed characteristics of contamination for Al and scavenging of Fe. No correlation was found b etween these artifacts and filter type. The percent of the colloidal f raction associated with Al and Fe was calculated, but showed that, for Al, Amicons tended to retain more of this fraction than did the Filtr ons, Osmonics or Membrex systems tested. The percentage of colloidal A l identified in the Pacific ocean sample ranged from < 1% to similar t o 11%. There was also substantial variability between the colloidal fr actions retained by individual filter types of the same manufacturer; this apparent inconsistency between the same type of filter and manufa cturer is attributed to differences in system composition and system c lean-up. Conclusions are made based on the need for future work concer ning the monitoring of mass balances in all fractions during an ultraf iltration run, and the understanding and reduction of trace-metal sour ces or sinks in these systems.