Total and methyl-mercury in hair and milk of mothers living in the city of Porto Velho and in villages along the Rio Madeira, Amazon, Brazil

High fish consumption and extended breastfeeding are hallmarks of traditional lifestyle in Western Amazonia. We studied sources of mercury exposure, fish-methylmercury (meHg) and dental-amalgam filling, in 75 urban and 82 rural lactating mothers. Total mercury was determined in all samples while meHg concentrations were determined in subsamples of milk (45) and hair (27) of urban mothers living in Porto Velho (PV) and in hair (46) and milk (37) of mothers living in traditional communities (TC) of the Rio Madeira. The TC mothers showed significantly higher median hair-Hg concentrations (8.2 μg g−1) than PV mothers (1.3  μg g−1). Median total Hg in milk of PV mothers (0.36 ng g−1) was significantly lower (p = 0.0000) than that found in milk of TC mothers (2.30 ng g−1). The median meHg concentrations in milk of TC mothers were also significantly higher (1.0 ng g−1) than in milk of PV mothers (0.07 ng g−1). For urban mothers with low fish consumption rates (and relatively higher dental amalgam fillings) the proportion of inorganic Hg in milk was higher (85%) than in TC (62%). In TC mothers 51% of breast milk Hg concentrations were above 2 ng g−1 (world median concentrations), contrasting with 8% in PV mothers. Despite this, there was no significant correlation between total Hg concentrations in milk and either amalgam filling or daily fish consumption. Socioeconomic changes occurring in Western Amazonia are causing changes in fish-eating habits of urban mothers. However, traditional lifestyle and attendant high fish consumption in riverine populations can still impact total Hg and methylmercury concentrations in mothers’ milk and hair.