ASTA Statement: Potential XRF Elemental Interference in Spices May Produce Erroneous Heavy Metal Readings

The following statement is attributable to the American Spice Trade Association.

It has come to the attention of the American Spice Trade Association that the use of X-ray Fluorescence (XRF) may result in erroneous detections of mercury and other elements in spices, depending on the specific equipment and calibration. In collaboration with the North Carolina Mecklenburg County Public Health Department and Eurofins, ASTA supported an investigation of high readings of mercury in a number of spice samples using XRF. Upon laboratory confirmation with Inductively coupled plasma mass spectrometry (ICP-MS), it was found that the initial detections were not confirmed. ASTA worked with SciAps, Inc. the manufacturer of the XRF equipment used in the initial screenings to investigate the discrepancy, which were determined to be false positives for mercury due to elemental interference with bromine.

According to a representative of SciAps,Inc:

Our X550 soil calibration is fine-tuned for elements within a soil matrix; using this calibration on soil-adjacent matrices (for instance, spices) can provide very accurate results, but it should be noted that subtle differences in the matrix composition can account for some variance. Furthermore, the soil calibration is made for a specific subset of elements-- certain elements are not calculated in this calibration, meaning that the presence of these elements in a sample can throw off readings of neighboring elements. In particular, bromine is not included in the soil calibration. Bromine also generates peaks in the XRF spectra close to some of mercury's peaks-- therefore, if bromine is sufficiently present in the sample, the XRF will determine this is due to the presence of mercury. This elemental interference between bromine and mercury can cause for some alarming false positives of mercury, but examination of the spectra in full will determine whether or not mercury is truly present.

ASTA recommends that any heavy metal findings in spices using XRF be confirmed using laboratory analysis with ICP-MS and that investigators consult with XRF equipment manufacturers to explore potential elemental interference with heavy metals to avoid the potential of false positive findings of mercury and/or other elements.