Feasibility of using a novel optically filtered monochromatic portable X-ray fluorescence (MXRF) to quantify lead in wild bird bones.

Lead (Pb) threatens wildlife and humans through neurological, cardiovascular, and renal damage. Conventional tissue Pb assessment relies on costly wet-lab methods such as inductively coupled plasma mass spectrometry (ICP-MS). Monochromatic X-ray fluorescence (MXRF) enables rapid, non-destructive, field-deployable Pb detection with lower detection limits than prior portable XRF systems. We evaluated the feasibility, calibration, attenuation correction, and ICP-MS agreement of a doubly curved crystal (DCC)-enhanced MXRF (X-ray Optical Systems, East Greenbush, NY) for bone Pb quantification in American black vultures (Coragyps atratus). Thirty-eight bird bones were analyzed ex vivo (n = 19 femurs; n = 19 tarsometatarsi[TMT]) using an HD Mobile XRF (1-mm spot; Mo anode; silicon drift detector; 200s). Calibration used Pb-doped plaster phantoms (0-100 ppm) with polymethyl methacrylate soft-tissue equivalents (0-5 mm). Spectra (10.0-13.6 keV) were fit with a Gaussian Pb-peak on a smooth background and Compton sideband normalization. Matched samples were quantified by ICP-MS. Agreement was assessed by ordinary least squares (OLS) regression, Pearson r, Passing-Bablok, intraclass correlation coefficient (ICC; two-way, absolute), reduced major axis (RMA) regression, and Bland-Altman analysis. Detection limits were obtained using blank-and-slope calibration and 30 repeated measurements on two bones. Signal attenuated exponentially, limiting reliable quantification beyond ∼3 mm soft tissue. Calibration was linear (counts vs. ppm: R2 = 0.996; phantom nominal vs. MXRF: R2 = 0.994). MXRF agreed closely with ICP-MS (femur r = 0.959, ICC = 0.933; TMT r = 0.962, ICC = 0.953). Bland-Altman mean biases were small (femur: -1.73 μg/g; TMT: -0.42 μg/g) without proportional bias. Passing-Bablok slopes approached unity (≈0.86-0.96) with small intercepts. Practical DLs were 1.79 μg/g(femur) and 0.80 μg/g(TMT) and are the relevant benchmarks for biological measurement; the calibration-derived instrumental DL of 0.03 μg/g at 200 s is an idealized zero-matrix value. This DCC-based MXRF delivered rapid, non-destructive bone Pb estimates concordant with ICP-MS and low DLs. Attenuation correction and fixed geometry support ex vivo Pb surveillance, carcass triage, and program evaluation in birds, with extension to other species, including humans.