Potentially Toxic Metal Levels in Breast Milk and Their Determinants Among Lactating Mothers of the DSAN-12 M Birth Cohort in the Reconcavo Baiano, Brazil

Potentially toxic metals (PTMs) can be transferred from mothers to infants through breast milk (BM), representing an important route of early-life exposure. Although PTM concentrations in breast milk have been extensively investigated, relatively few studies have evaluated the environmental determinants associated with these concentrations, particularly in prospective birth cohorts from socially vulnerable populations. This study aimed to determine PTM concentrations in BM and identify environmental, sociodemographic, and dietary determinants associated with these concentrations among lactating women from the prospective Socioenvironmental Determinants of Child Neurodevelopment at 12 Months (DSAN-12 M) birth cohort in northeastern Brazil. BM samples were collected from 48 exclusively breastfeeding women and analyzed for arsenic (As), cadmium (Cd), mercury (Hg), manganese (Mn), and lead (Pb) using inductively coupled plasma tandem mass spectrometry (ICP-MS/MS). Independent determinants of BM metal concentrations were investigated using multivariable linear regression models. Median concentrations (µg/L) were 1.22 for As, 0.42 for Cd, 3.58 for Hg, 5.56 for Mn, and 14.34 for Pb. Over 65% exceeded internationally proposed reference values for As, Hg, Mn, and Pb, whereas 25% exceeded the reference value for Cd. Household water supply was independently associated with Pb and Mn concentrations, household waste burning with Mn concentrations, and municipality of residence with Hg concentrations after multivariable adjustment. These findings indicate widespread co-exposure to multiple PTMs among lactating women in this socially vulnerable population and suggest that structural environmental conditions are important determinants of maternal exposure. Strengthening environmental infrastructure, human biomonitoring, and environmental health policies may reduce maternal and infant exposure to PTMs.