ACCURACY AND PRECISION OF GEOCHEMICAL ANALYSES OF CONTAMINATED AND BACKGROUND SEDIMENTS USING A PORTABLE X-RAY FLUORESCENCE ANALYZER

Environmental assessments of historical mining and industrial sites often require fast and economical evaluations of potentially toxic metals in soils and sediments. However, limitations on the accuracy and precision of these analyses often raise questions for the use of screening-level data for more in-depth scientific analysis. This poster reports on a series of tests to compare metal analyses of river sediment samples using a portable x-ray fluorescence analyzer (XRF) to the results of traditional methods involving acid extractions and ICP-AES analysis. Stream sediment samples used in this study have been affected by undisturbed, urban/industrial, and mining inputs in Missouri, Wisconsin, and North Carolina. Calcium, copper, iron, lead, manganese, and zinc are targeted for analysis because they are typically used to indicate environmental toxicity and/or geochemical associations in sediments. Accuracy will be assessed by comparison with traditional methods and USGS geochemical standards. Precision will be determined by replicate testing and statistical evaluation of errors. Correlations between paired samples using the different methods will provide the basis for determining the effectiveness of portable XRF analysis for scientific studies. In addition, XRF results determined on intact soil cores in the field will be correlated with XRF results for the same sample analyzed in the laboratory under more controlled conditions. Preliminary results indicate that in most cases, there is a good correlation between Cu, Pb, and Zn concentrations determined by the two methods and the precision is adequate. However, the relatively high detection limits of the XRF make it difficult to discriminate among lower background levels of metals in some of the sediment samples evaluated.