Determining factors affecting the accuracy of SEM-EDX data-based quantitative chemical analysis for identifying naturally occurring individual carcinogenic erionite fibers.

Erionite is a fibrous zeolite classified as a Group 1 carcinogen and may pose a significant public health hazard when aerosolized into individual respirable-sized fibers. SEM-EDXA has been widely used to identify individual erionite fibers in environmental samples as it combines morphological imaging with elemental analysis. However, the reliability of SEM-EDXA data when applied to the quantitative chemical analysis of individual erionite fibers rather than bulk samples remains uncertain. This study analyzed 325 individual erionite fibers (obtained from a bulk sample with high-purity) across a range of fiber widths and four commonly used sample preparation methods, using two different SEM-EDS systems. SEM-EDXA results were compared with previously acquired EPMA reference data from the bulk sample to assess analytical accuracy. Systematic overestimations of Si and Mg and underestimations of Al, K, and Ca were observed. Framework elements (Si and Al) exhibited relatively stable detection in fibers > 0.5 μm. However, preparation methods-deionized water dispersion and hydrogen peroxide digestion-introduced greater variability, likely due to ion exchange and cation mobilization. Despite the purity of the erionite bulk sample, none of the analyzed individual fibers fully met the established quantitative chemical criteria for erionite identification. These results highlight the need for pre-calibration with erionite standards and the application of correction index to improve SEM-EDX accuracy, and subsequent confirmation of mineralogy using TEM-SAED, when determining whether individual fibers found in airborne samples are erionite.