SOURCES OF TRACE-METAL CONTAMINATION ARTIFACTS DURING COLLECTION, HANDLING, AND ANALYSIS OF FRESH-WATERS

Clean techniques are necessary for reliable measurement of trace metal s in freshwaters at ambient, though not necessarily regulatory concent rations. Conventional sample handling methods were compared to clean t echniques for 35 individual steps used in protocols for analysis of fi ltrate and filter-retained forms of Ag, Cd, Cu, and Pb, Approximately two-thirds of all steps contributed statistically significant amounts of contamination in the measurement of dissolved and particulate Cd, C u, and Pb, Average contamination for a single contributing step was 30 0%, 141%, and 200% for the three metals, respectively (where 100% repr esents no added contamination). Relative Cu contamination tended to be lower, partly because real levels in water are higher for this metal, Contamination generally was not a problem for Ag, when it was present in water at higher than background levels, With that exception, it do es not seem possible to abridge clean technique protocols, even when m easuring trace metals in polluted freshwaters where levels are moderat ely high, Our expectation is that most other metals (e.g., Zn, Cr, or Ni) will have contamination behavior that is similar to common Cd, Cu, and Pb, rather than the rare metal Ag.