No abstract

Field and laboratory experiments indicate that a number of factors associated with filtration other than just pore size (e.g., diameter, manufacturer, volume of sample processed, amount of suspended sediment in the sample) can produce significant variations in the “dissolved” concentrations of such elements as Fe, Al, Cu, Zn, Pb, Co, and Ni. The bulk of these variations result from the inclusion/exclusion of colloidally associated trace elements in the filtrate, although dilution and sorption/desorption from filters also may be factors. Thus, dissolved trace element concentrations quantitated by analyzing filtrates generated by processing whole water through similar pore-sized filters may not be equal or comparable. As such, simple filtration of unspecified volumes of natural water through unspecified 0.45-μm membrane filters may no longer represent an acceptable operational definition for a number of dissolved chemical constituents.

No abstract

Since 1987, the U.S. Geological Survey has sponsored numerous studies to evaluate its programmatic sampling, processing, and analytical equipment and procedures used for determining trace-element concentrations in surface water. The major finding of these evaluations was that, in many cases, the sampling and processing procedures used have resulted in traceelement concentrations which, for a number of constituents, appear to be biased by systematic and (or) erratic contamination. A new set of guidelines and procedures was developed that would permit the production of contaminant-free (at specific reporting limits) trace-element data from filtered surface-water samples. These guidelines and procedures have been incorporated into a new trace-element protocol. Concurrently, these procedures also were evaluated for their utility in collecting and processing water samples for the subsequent determination of other inorganic constituents (for example, nutrients and major ions) to determine if a single method for all inorganic constituents could be developed. Such a protocol was developed and is presented in this report. The new protocol represents a significant change in U.S. Geological Survey guidelines for the collection and processing of water samples for subsequent chemical analysis. It is intended to lead to the production of filtered inorganic-constituent data that are both defensible and interpretable at the microgram-per-liter level. The protocol contains detailed minimum, as well as recommended, quality-control requirements.

No abstract