Assessing zinc from a nail clipping using mono-energetic portable X-ray fluorescence

Assessment of X-ray fluorescence capabilities for nail and hair matrices through zinc measurement in keratin reference materials

BACKGROUND

Novel and emerging biomarkers of zinc status are being developed to help study and address zinc deficiency around the world. Two potential biomarkers, nail and hair, involve the measurement of zinc from easily accessible keratin-based components of the body. Portable X-ray fluorescence (XRF) is a relatively new approach to the assessment of zinc in nail or hair, and has a number of compelling advantages compared with other techniques. The aim of the current study was to test the ability of XRF to measure zinc in keratinized reference materials (RMs) designed to simulate nail and hair.

METHODS

Four Keratin Matrix RMs were prepared and characterized for numerous trace elements by the New York State Department of Health's Wadsworth Center. The Keratin Matrix RMs consisted of powdered samples of caprine (goat) horns pooled from several animals. Concentrations of zinc, as assessed by inductively coupled plasma mass spectrometry (ICP-MS), were similar to what would be expected from human nail or hair tissues. Repeat measurements of the RMs were made using a portable XRF system. The XRF zinc results were compared with the ICP-MS zinc concentrations. Three different approaches to quantifying the zinc content by XRF were performed: (1) zinc signal to total signal ratio, (2) zinc signal to sulfur signal ratio, and (3) system output zinc concentration.

RESULTS

The portable XRF results from a given RM were found to be consistent across repeat trials under all three approaches to XRF quantitation. Precision, calculated as the relative standard deviation of repeat measurements ranged from an average result of 0.8 % (using the system output zinc concentration method) to 6.1 % (using the zinc signal to sulfur signal ratio method). Measurement of the RMs provided XRF zinc results which scaled well with ICP-MS zinc concentration, particularly when using the XRF zinc to total and system zinc concentration methods. A Bland-Altman plot showed that the XRF system zinc concentration output exceeded the ICP-MS zinc concentration by, on average, 10.2 % ± 1.2 %.

CONCLUSION

Overall, both accuracy and precision of measurement were found to be promising for portable XRF, provided appropriate conversions to concentration are introduced. The results of this study indicate that portable XRF is an effective and dependable method of assessing zinc concentration in keratinized tissue RMs. This will have implications for the future use of portable XRF to monitor zinc status in humans through measurements of nail and hair.

Estimating the potential of spices for mineral provision in a refugee context in East Africa

Micronutrient deficiency remains an enormous problem in refugee settings. Transforming refugees’ food systems through the scaling up of kitchen gardening and fortifying relief food crops with minor food components including nutrient-dense spices can help improve the quality of staple foods. Globally, spices are indispensable in the daily diet and play an important role in the socio-cultural setting of different communities. Forty turmeric and curry powder samples were collected from different market establishments and geographic locations in East Africa. The samples were analyzed for selected elements using Portable X-Ray Fluorescence (PXRF). The contents of potassium (K), calcium (Ca), zinc (Zn) and strontium (Sr) in turmeric powder were statistically different among geographic origins (Ethiopia, Kenya and Uganda). We also aimed to determine if a small portion of spices (turmeric (5 g) and curry (4 g)) would contribute to an adequate intake (AI) or recommended dietary allowance (RDA) for selected minerals, for refugee men and women aged between 19 and 50 years as defined by the Food and Nutrition Board of the Institute of Medicine (IOM). For the reference groups, the contributions of turmeric and curry powder to AI/RDA for K, Ca and Zn varied between 0.48 to 4.13%. On the other hand, turmeric was identified to contribute > 20% AI/RDA for refugee men and women aged between 19 and 50 years for two micro minerals: manganese (Mn) and iron (Fe). Considering turmeric and curry powder of East African origins are good sources of minerals and present acceptable toxic metal(loid)s loads coupled with low cost, these spices particularly turmeric should be more widely popularized and recommended for food-to-spice fortification among the refugee population located in East Africa.

Okra (Abelmoschus esculentus) in a refugee context in East Africa: Kitchen gardening helps with mineral provision

Kitchen gardening is considered a way to reconnect with agriculture and complement the cereal-based relief food offered to refugees in East Africa. This work aimed at profiling mineral content of okra in four refugee camps and settlements located in Ethiopia and Uganda and its contribution to adequate intake (AIs) or recommended dietary allowances (RDAs) for young children and pregnant and lactating women (PLW). The study also evaluated the applicability of portable X-ray fluorescence (PXRF) as compared with inductively coupled plasma mass spectrometry (ICP-MS) for mineral profiling of okra powder samples. The contents of minerals (mg kg-1) from the ICP-MS readings were in the following ranges: K (14,385-33,294), Ca (2610-14,090), P (3178-13,248), Mg (3896-7986), Cu (3.81-19.3), Fe (75.7-1243), Zn (33-141) and Mn (23.1-261). Regardless of geographic origin, at low-end consumption probability (17 g day-1 for young children and 68 g day-1 for PLW), okra could contribute ˂ 15% (2.7-12.9%) AI for macro-minerals (K and Ca). In addition, the contributions to RDA values for Fe and Zn, elements of known public health interest, ranged from 4.5 to 34.7% for young children. Interestingly, regression lines revealed strong agreement between ICP-MS and PXRF readings for Mn and Zn, with R2 values > 0.91. This information is useful in support of nutrition-sensitive kitchen gardening programs through scaling culturally important crops in refugee settings.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s42452-021-04898-6.

Contents of Metal(loid)s in a Traditional Ethiopian Flat Bread (Injera), Dietary Intake, and Health Risk Assessment in Addis Ababa, Ethiopia

The traditional Ethiopian flat bread, injera, is a regular component of daily diets in Ethiopia and Eritrea. This bread is also popular among urban refugees particularly Eritreans in Addis Ababa. The levels of metal(loid)s in 40 composite (120 sub-samples) injera samples, representing 4 types of market establishments in Addis Ababa, were determined using inductively coupled plasma-mass spectrometry (ICP-MS) and portable X-ray fluorescence (PXRF). For ICP-MS analysis, the accuracy of the method was evaluated by the analysis of a certified reference material and recovery experiments. It was found that the correlations between the mean levels of Al and Fe and between Al and Mn in injera were highly significant (p < 0.001). It was also found that 1.5 fresh injeras would cover 48-75% of recommended dietary allowance (RDA) for Mg, 17-21% of RDA for K, 19-23% of RDA for Ca, and 60-72% of RDA for P for an adult group aged between 19 and 50. Daily intakes of Al, Fe, and Mn were found to be above the provisional tolerable daily intake (PTDI)/maximum tolerable daily intake (MTDI) values. The mean target hazard quotient (THQ) values for Fe and Mn were greater than 1. The total THQ values varied from 6.52 to 8.53 among market establishments. Estimating carcinogenic risk due to exposure to As, Cr, and Pb indicated that perennial injera consumers might remain at cancer risk. This would further escalate if other staple food items and spices are considered. Hence, there is a need for home-based strategies to reduce extrinsic soil-Al-Fe-Mn in injera/tef batter.

Portable X-ray fluorescence of zinc applied to human toenail clippings

Zinc is an essential trace element in humans. Zinc deficiency can result in a range of serious medical conditions which include effects on growth and development, the immune system, the central nervous system, and the gastrointestinal system. Diagnosis of zinc deficiency is often precluded by the lack of a noninvasive and reliable biomarker. Zinc concentration in nail is considered an emerging biomarker of zinc status in humans. Whether zinc in nail accurately reflects zinc status is beyond the scope of the current study, but is an important research question. The development of a portable method to quickly assess zinc concentration from a single nail clipping could be a useful advance. In this study, single toenail clippings from 60 individuals living in Atlantic Canada were measured for zinc using a portable X-ray fluorescence (XRF) technique. These samples were obtained from the Atlantic PATH cohort, part of the largest chronic disease study ever performed in Canada. Each toenail clipping was measured using three 300 s trials with a mono-energetic portable XRF system. Results were then assessed using two different approaches to the XRF analysis: (1) factory-calibrated zinc concentrations were output from each trial, and (2) energy spectra were analyzed for the characteristic X-rays resulting from zinc. Following the measurement of zinc using the non-destructive portable XRF method, the same clippings were measured for zinc concentration using the "gold standard" technique of inductively coupled plasma-mass spectrometry (ICP-MS). A linear equation of best fit was determined for the relationship between average XRF output zinc concentration and ICP-MS zinc concentration, with a correlation coefficient r = 0.60. Similarly, a linear equation of best fit was found for the relationship between a normalized XRF energy spectrum zinc signal and ICP-MS zinc concentration, with a correlation coefficient r = 0.68. Individual ICP-MS zinc concentrations ranged from 32 μg/g to 140 μg/g, with a population average of 85 μg/g. The results of this study indicate that portable XRF is a sensitive method for the measurement of zinc in a single nail clipping, and provides a reasonable estimation of zinc concentration. Further method development is required before portable XRF be considered a routine alternative to ICP-MS for the assessment of zinc in nail clippings.

Assessing arsenic in human toenail clippings using portable X-ray fluorescence

Arsenic is a toxic metalloid which has been associated with a wide range of health effects in humans including skin abnormalities and an elevated risk of skin, bladder, kidney, and lung cancer, diabetes, and cardiovascular disease. The measurement of arsenic concentration in nail clippings is often used in population studies as an indicator of arsenic exposure. Portable X-ray fluorescence (XRF) is an emerging technique for measuring arsenic in nail clippings. In the current study, single toenail clippings from 60 Atlantic Canadian participants were assessed for arsenic using a new portable XRF approach. A mono-energetic portable XRF system using doubly curved crystal optics was used to measure each clipping for a total of 900 s. Energy spectra from each clipping were analyzed for arsenic characteristic X-rays to provide a normalized arsenic signal. The same clippings were then analyzed for arsenic concentration using a "gold standard" method of inductively coupled plasma mass spectrometry (ICP-MS). Nail clipping arsenic concentrations measured by ICP-MS ranged from 0.030 μg/g to 2.57 μg/g, with a median result of 0.14 μg/g. Portable XRF results for arsenic were compared against ICP-MS arsenic concentrations, with a linear equation of best fit determined between the two variables. A correlation coefficient of r = 0.77 was found from the 59 nail clippings returning an ICP-MS arsenic concentration above the limit of quantitation. When the comparison was limited to the 20 clippings having an XRF normalized signal at least twice as large as the associated uncertainty of measurement, the correlation coefficient was r = 0.89. With the selection of an arsenic concentration of 0.1 μg/g as a cut-off value between "exposed" and "non-exposed" individuals, the XRF method provided a test sensitivity of 76% and a specificity of 81%. The corresponding positive predictive value was 88% and the negative predictive value was 65%. The portable XRF technique used in this study shows promise as a means of assessing arsenic concentration in toenail clippings.