Clean techniques are necessary for reliable measurement of trace metals in freshwaters at ambient, though not necessarily regulatory concentrations. Conventional sample handling methods were compared to clean techniques for 35 individual steps used in protocols for analysis of filtrate 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, Cu, and Pb. Average contamination for a single contributing step was 300%, 141%, and 200% for the three metals, respectively (where 100% represents 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 does not seem possible to abridge clean technique protocols, even when measuring trace metals in polluted freshwaters where levels are moderately 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.
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