Mercury in breast milk from women in the Federal District, Brazil and dietary risk assessment for breastfed infants

Mercury is a toxic metal, ubiquitous in nature; it is excreted in breast milk from exposed mothers and may affect infant neuro-development. In this study, 224 breast milk samples provided by eight human milk banks in the Federal District of Brazil were analyzed for total mercury (THg), of which 183 were also analyzed for methyl mercury (MeHg), the most relevant form of this metal for the breastfed infants. Samples were acid digested in a microwave oven and THg determined by atomic fluorescence spectrometry (LOQ of 0.76 μg/L). Samples were lyophilized, ethylated and MeHg determined in a MERX automated system (LOQ of 0.10 μg/L). Inorganic mercury (IHg) levels were estimated from the THg and MeHg determined in the samples. Most of the samples were collected 1-2 months postpartum, with 38% during the first month. Over 80% of the samples had THg values above the LOQ, reaching a maximum of 8.40 μg/L, with a mean of 2.56 μg/L. On average, MeHg accounted for 11.8% of THg, with a maximum of 97.4%. Weekly intakes were estimated individually, considering the baby's age and body weight at the time of milk collection. Mean weekly intake for MeHg was 0.16 ± 0.22 μg/kg bw, which represented 10% of the PTWI; in only one case, the intake exceeded 100% of the PTWI (1.90 μg/kg bw, 119% of PTWI). Mean intake for IHg was 2.1 ± 1.5 μg/kg bw, corresponding to 53% PTWI. These results indicate no health concern for the breastfed babies, a conclusion that can be extended to the consumers of breast milk donated to the milk banks, primarily immature and low weight babies.