X-ray fluorescence of selenium and zinc applied to toenail clippings from breastfeeding women of New Zealand and their infants

Abstract

Zinc and selenium are essential micronutrients that play essential roles in structures of zinc finger proteins and selenoprotiens, both of which have vital roles in complicated biological processes of human body. Micronutrient status is especially vital in postpartum women as their requirements significantly increase during breastfeeding, escalating the risk of deficiency. Moreover, in New Zealand, selenium content of most of the arable land is low and selenium deficiencies have been a major concern since first observed as white muscle disease in livestock in the 1980s. Toenail trace element concentrations have been shown to be reflective of their long-term status in several studies. The current study employs portable X-ray fluorescence (XRF) spectrometry as a means of investigating zinc and selenium levels in toenails of mothers and their infants from New Zealand. 240 XRF measurements were carried out using 20 matched-sets of toenail clippings of mothers and newborns participating in the MINI study. Strong linear relationships were found in the case of both elements with a “gold standard” technique, inductively coupled mass spectrometry (ICP-MS), that were all highly significant. These correlation coefficients were highest for zinc using the XRF system’s automated output (r = 0.82), and for selenium using normalized selenium signals from every spectral analysis (r = 0.73). Thickness contributions to XRF concentrations were found to be minor and ICP-MS concentrations showed similar trends against thickness as with the XRF techniques. Low selenium status was suspected in 3 mother-infant pairs whereas zinc levels were in the normal range. The results of this study indicate that portable XRF provides reasonable estimates of zinc and selenium concentrations. However, further method development is required before it can be considered as interchangeable with the ICP-MS method.