82. Temporal variation of total mercury levels in the hair of pregnant women from the Maternal-Infant Research on Environmental Chemicals (MIREC) study (lay summary)

Lukina AO, Fisher M, Khoury C, Than J, Guay M, Paradis JF, Arbuckle TE, Legrand M. Chemosphere 2020 Sep 24;264(Pt 1):128402. doi: 10.1016/j.chemosphere.2020.128402

Mercury is a naturally occurring metal in soil that accumulates in wildlife and some foods over long periods of time.  High mercury exposure is a concern to human health because a number of different body systems may be affected. Pregnant women and children are particularly susceptible to the toxic effects of mercury because mercury can cross the placental and the blood-brain barriers.  Consumption of fish, particularly large predatory fish such as fresh or frozen albacore/white tuna, is one of the most common sources of mercury.

Measuring concentrations of mercury in an individual’s blood and hair provides an estimate of total exposure levels.  Measurement in hair is advantageous because it is non-invasive and allows measurement of mercury concentrations over time.  Sections of hair closer to the scalp reflect recent exposure.  As hair grows about 1 cm per month, each 1 cm of hair strands represents exposure in the past few months.

The aim of this study was to measure mercury exposure in women from preconception through delivery and to compare hair mercury levels with levels in maternal and umbilical cord blood from the same stage of pregnancy and at delivery.

Hair samples of 328 MIREC women were cut into 1 cm segments and each segment analysed for mercury.  Mercury was also measured in 1st and 3rd trimester blood samples, as well as in umbilical cord blood.  Information on characteristics of participants and their fish consumption during pregnancy was collected by questionnaire.

The Health Canada researchers observed that hair and blood mercury concentrations decreased throughout pregnancy and that hair concentrations were higher than blood concentrations.  In addition, researchers observed that women who more frequently ate predatory fish tended to have higher hair and blood mercury concentrations.

Slightly higher mercury levels were found among mothers who were 35 years of age or older, foreign-born, with university degree and/or underweight-normal pre-pregnancy BMI.

The results provide some of the first data on hair mercury concentrations throughout pregnancy for Canadian women.  Researchers concluded that hair is a valuable biological sample for measuring mercury concentrations throughout pregnancy and during the critical windows of fetal development.  Future research can build upon these findings by examining associations between maternal hair mercury concentrations and child health.