DEFINITIONS

Dissolved Metals: "The concentration of elements determined in a sample after the sample is filtered through a 0.45 micron filter". The determination of dissolved metals is directed at only those particles, molecules, and elementary forms of the metal that are able to pass through a 0.45 micron filter. The sample must be filtered at the time of collection, but before the addition of any acid preservation.

Total Metals: "The concentration of elements extracted from an aqueous or solid sample following a reflux period with dilute mineral acids". The determination of total metals is directed at all forms of a metal in the sample, including dissolved metals and the metals in all particulates. The sample undergoes a volume reduction step, then repeated refluxing (with the continued addition of acid) until the reaction is complete. The sample is then brought up to volume with reagent water and filtered. Note: The sample should NOT be filtered at the time of collection.

Total Recoverable Metals: "The concentration of elements in either a solid sample or in an unfiltered aqueous sample following treatment with hot, dilute mineral acid". The determination of total recoverable metals is directed at metals weakly bound to particle surfaces plus dissolved metals. The sample undergoes a volume reduction step, then refluxed in hot, dilute mineral acid(s) for 30 minutes. The sample is then brought up to volume with reagent water and filtered. Note: Unfiltered samples with turbidity < 1 NTU (nephelometric turbidity unit) do not require digestion. Results for these samples are reported as "total recoverable" metals.

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