Tentative reference ranges for calcium and strontium in Spanish children’ scalp-hair.

Resumen

BACKGROUND AND AIM: To identify the burden of calcium (Ca) and strontium (Sr) in healthy children’s born and residing in Alcalá de Henares (Madrid Region, Spain) by monitoring scalp-hair. Tentative reference intervals are suggested. METHOD: : Scalp-hair was collected from 120 children (6 to 9-years-old; 70 girls). Both elements were monitored by ICP-MS after appropriate removal of exogenous contamination using Triton X-100/bath sonication. Reference ranges were calculated according to IUPAC, which recommends the non-parametric computation of a 0.95 coverage interval, with confidence intervals for the reference limits of 0.95. RESULTS: : Results were processed using the NADA package in R owing to the high levels of censored data identified (46.7% and 23.5%; LoDs=162.14, 0.19 in µg/g, for Ca and Sr, respectively). Levels were significantly higher in girls’ hair for both metals (p-value=4.9E-10, 1.18E-10), which are presented as median and percentiles for female participants [221.525 (163.988, 299.326) and 0.689 (0.359, 1.162)] and as P95 and ranges for male participants [252.692 (162.172-336.696) and 0.751 (0.191, 0.958)], for Ca and Sr, respectively. The levels of Sr were much lower to the concentration reported in hair from 6-10 years-old individuals living in Madrid city (0.411 vs. 1.70) although within the reference range proposed for these authors (0.20-6.73). Tentative reference ranges (provided as the CI95 lower/upper) for Ca (9.694-14.565) and Sr (0.360-0.758) for children living in Alcalá, resulted lower than those reported in children living in Elche (Spain; 35-1100, 0.3-13; aged 3-12). Moreover, they were lower than those proposed for Ca in Korean children (120-365; aged 3-6) and for Sr in Italian (0.31-3.65; aged 3-15). CONCLUSIONS: Our results would suggest that children living in Alcalá would have been less exposed to Ca and Sr from environmental/dietary sources. Owing to the lack of standardised methods to calculate reference ranges, our intervals should be only used with children living in the Madrid Region.