Table 5 Characteristics of relevant biomarkers used in children

Hair

Reflects the exposure during the 2–4 months before sampling [81]

Easy to collect, store and manipulate, non-invasive, most consistent and valid biomarker in pediatric epidemiology [85]

Pigmentation and potential external contamination [86]

Blood

With a half-life of 4 or 39 days due to different elimination pathways [79]

Obtained easily and less influence of external contamination [87]

Correlated poorly with exposure [88]

Teeth

Reflects the exposure from 13 to 16 weeks after gestation to approximately one year of age [83]

Non-invasive, provides precise exposure information, distinguishes the prenatal and postnatal exposure [82]

Caries and teeth with attrition contained less metal [89], relatively difficult to obtain and measure

Saliva and urine

secretes 0.8 to 1.5 L of saliva each day, only a small fraction of Mn eliminates in urine [90]

Non-invasive and easy to collect [90]

Correlated poorly with exposure [88, 91, 92], fairly large variation [93]

Toe nail

Reflects an exposure of 7–12 months before sampling [94, 95]

Easy collection, storage and transport [96], correlated with exposure [91]

Difficult to collect sufficient toenail from infants and potential external contamination [97]

Cord blood

Reflects an exposure of the last trimester [97]

Correlated with manganese in dentin [98]

Not feasible to obtain at different stages of pregnancy [98]

Maternal blood

Mn enters the fetus via an active transport mechanism [99]

Readily sampled [98]

Maternal Mn biomarkers may not accurately reflect Mn levels in fetal tissues [98]