The effect of long-time X-ray irradiation on Cr and Hg in a polypropylene disk certified reference material (PP disk CRM, NMIJ CRM 8136-a) during measurements by X-ray fluorescence (XRF) spectrometry was examined in the present study. The XRF intensities of Cr (K_α), Hg (L_α) and Pb (L_α), obtained by an energy-dispersive (ED)-XRF spectrometer, showed the different intensity trends and the obtained XRF intensity ratios of Cr/Pb and Hg/Pb revealed decreasing and constant ratios, respectively, for long-time X-ray irradiation of up to 430 h. A similar decreasing trend of the Cr/Pb intensity ratio was also observed by wavelength-dispersive (WD)-XRF measurements for 120 h. Moreover, Cr, Hg and Pb in the PP disks obtained after long-time measurements by the WD-XRF spectrometer were measured by an ED-XRF spectrometer, and the loss of Cr was confirmed. From these results, Cr in the PP disk CRM, whose chemical form was an organometallic compound, was considered to be possibly lost during the XRF analysis for long-time or frequent measurements.