Predictors of mercury (Hg) exposure in breast-fed infants

Abstract

This study was designed to investigate potential factors that might affect Hg exposure in mothers and their breast-fed infants. Total Hg was measured in the urine and breast milk of 155 mothers (18-42 yrs) and 102 infants (2.5-12.8 mon) living in Riyadh, the Capital of Saudi Arabia. The median (25th-75th) of Hg levels in mother’s urine, breast milk, and infant’s urine were respectively: 0.98 (0.6-1.68?g/g-Cr), 1.08 (0.77-1.40?g/L), and 5.27 (1.97-10.09?g/g-Cr). 48% of mothers and 89% of infants had urinary Hg>1µg/g-Cr (the GerES reference value for adults and children without amalgam fillings). Though Hg in the urine of mother and their infants were correlated (P=0), borderline significant relationship was found between Hg in mother’s urine and breast milk (P=0.077). Bivariate analysis revealed that the use of skin-lightening creams was significantly associated with Hg in mother’s urine (P=0.029) and breast milk (P=0.048). The location of current residence was related to Hg in infant’s urine (P=0.002) and mother’s milk (P=0). Only Hg in infant’s urine was associated with smoking status (P=0.025). Urinary Hg levels were significantly higher in infants who are taking milk formula (P=0.022). No association was seen between the use of dental amalgam fillings or fish consumption and the levels of Hg in the urine or breast milk. Among demographic and socioeconomic factors, only parity (P=0.01), and the number of breast-fed children (P=0.005) had a negative effect on Hg in breast milk. Likewise, there was negative association between infant’s age and their urinary Hg levels (P=0.046). The results of the present study confirm the transfer of Hg from the mother to infants through breast-feeding. Though there might be other sources of Hg exposure that need further investigation, our current findings corroborate our earlier observation linking elevated levels in Hg to the use of skin-lightening creams.