Toenail manganese as a potential biomarker for in utero and early childhood exposure studies

Michael Georgieff,Irina Stepanov,Raghavendra Rao,Shannon S. Cigan,Kriti Choudhary,Patricia M. McGovern,Neely C. Miller

doi:10.1038/s41598-018-35112-0

Michael Georgieff, Irina Stepanov + Show 5 more

Open Access

https://doi.org/10.1038/s41598-018-35112-0

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Abstract

Elevated in utero and early childhood exposure to manganese may have adverse effects on neurodevelopment. We conducted preliminary analyses to evaluate toenails as a matrix for investigating manganese exposure in infants. Infant and maternal toenail and hair samples were collected from 25 infants (7 months old) and their mothers. A subset of mothers was recruited in the third trimester of pregnancy and some also provided pre-natal toenail, hair, and blood samples, cord blood, and additional post-natal samples. Collected samples were analyzed by inductively coupled plasma mass-spectrometry. Toenail manganese levels in infants ranged from below the limit of detection (LOD) to 2.80 µg/g. Only 1 toenail sample and 4 hair samples contained levels of manganese below LOD. Associations between infant and maternal biomarkers were not statistically significant. Analysis of multiple post-natal toenail samples from a single infant-mother pair showed an increase in the infant’s toenail manganese and a decrease in maternal toenail manganese over the first year of the infant’s life. Overall, our findings suggest that toenails may serve as a valuable biological matrix for measuring manganese exposure in newborns and infants; however, additional studies are needed to determine the impact of the timing of toenail sample collection on its utility in assessing early life exposure and health outcomes.

Highlights

Manganese (Mn) is an essential nutrient that plays an important role in normal growth and development, including a variety of physiological processes[1,2,3,4]; emerging literature suggests that childhood exposure to even low levels of environmental Mn may have adverse neurodevelopment effects and could be a contributor to the rise in neurobehavioral disorders[5,6,7,8,9,10]
Most of the studies investigating Mn exposure have analyzed its effects in school-aged children; in utero and early childhood exposures are of particular concern because this is a critical time in brain development
Toenail and hair samples collected from infants showed substantial variation in Mn concentrations, ranging from below the limit of detection (LOD) to 4.59 μg/g and from below LOD to 6.08 μg/g, respectively

Summary

Introduction

Manganese (Mn) is an essential nutrient that plays an important role in normal growth and development, including a variety of physiological processes[1,2,3,4]; emerging literature suggests that childhood exposure to even low levels of environmental Mn may have adverse neurodevelopment effects and could be a contributor to the rise in neurobehavioral disorders[5,6,7,8,9,10]. Other studies employed a biomarker-based approach and reported that high Mn levels in children’s blood and hair are associated with poor memory[13,14,15], low cognitive scores[16,17], and impaired motor function[15]. Despite this growing evidence, U.S.-based studies of Mn exposure and neurobehavioral outcomes in children are scarce: one exploratory study demonstrated an association between Mn levels in tooth enamel and behavioral disinhibition in children[18], and another recent study found an association between high levels of Mn in blood and hair with lower IQ scores in children living near a ferromanganese refinery in Ohio[19]. A single recent study, conducted in Bangladesh, used toenails to investigate prenatal exposure to Mn from drinking water in mother-infant pairs; the findings of the correlation between maternal and infant toenail Mn levels were inconsistent across the two regions included in the study[30]

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