A Field-based Evaluation of Portable XRF to Screen for Toxic Metals in Seafood Products

Portable X-Ray Fluorescence (XRF) has become increasingly popular where traditional laboratory methods are either impractical, time consuming and/or too costly. While the Limit of Detection (LOD) is generally poorer for XRF compared to laboratory-based methods, recent advances have improved XRF LODs and increased its potential for field-based studies. Portable XRF can be used to screen food products for toxic elements such as lead (Pb), cadmium (Cd), mercury (Hg), and arsenic (As), manganese, (Mn), zinc (Zn) and strontium (Sr). In this study, 23 seafood samples were analyzed using portable XRF in a home setting. After XRF measurements were completed in each home, the same samples were transferred to the laboratory for re-analysis using microwave-assisted digestion and Inductively Coupled Plasma Tandem Mass Spectrometry (ICP-MS/MS). Four elements (Mn, Sr, As and Zn) were quantifiable by XRF in most samples, and those results were compared to those obtained by ICP-MS/MS. Agreement was judged reasonable for Mn, Sr, and As, but not for Zn. Discrepancies could be due to 1) the limited time available to prepare field samples for XRF, 2) the heterogeneous nature of "real samples" analyzed by XRF, and 3) the small beam spot size (~1mm) of the XRF analyzer. Portable XRF is a cost-effective screening tool for public health investigations involving exposure to toxic metals. It is important for practitioners untrained in XRF spectrometry to (a) recognize the limitations of portable instrumentation, (b) include validation data for each specific analyte(s) measured, and (c) ensure personnel have some training in sample preparation techniques for field based XRF analyses.