Early-life exposure to metals through breast milk and neonatal vulnerability in the Brazilian Amazon

Breast milk is the optimal source of nutrition during early life, but it can also act as a pathway of exposure to toxic and essential metals. Evidence from highly vulnerable and environmentally impacted regions, such as the Brazilian Amazon, remains scarce. This study aimed to quantify trace metal concentrations in breast milk from mothers living in urban and agricultural areas of the Brazilian Amazon and to evaluate associated health risks and perinatal outcomes. A cross-sectional study was conducted including 293 lactating women residing in the state of Rondônia, Brazil. Concentrations of Al, As, Ba, Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Sr, V, and Zn were determined in breast milk samples. Exposure was assessed using estimated daily intake (EDI), hazard quotients (HQ), and total hazard quotients (THQ). Associations with sociodemographic variables and perinatal outcomes were evaluated using multivariable regression models. Essential metals (Cu, Fe, Mg, Zn) were widely detected, while non-essential metals showed heterogeneous detection frequencies. Mothers living in agricultural areas exhibited higher concentrations of Al, Fe, Mn, and Ni. Metal concentrations varied across lactation stages, with decreasing trends for Zn and Cu and increasing trends for Fe and Mg. THQ values exceeded 1 in several exposure scenarios, particularly among preterm infants and during transition milk consumption; however, for essential elements such as Cu and Zn, these values should be interpreted with caution, as they may reflect intake approaching upper recommended levels rather than direct evidence of toxicity. Significant associations were observed between several breast milk metals and adverse perinatal outcomes, including birth weight and preterm birth, with effects differing by residential context. Breast milk in the Brazilian Amazon reflects complex environmental and nutritional exposure patterns. Although breastfeeding remains essential, the presence of mixed metal contaminants highlights the need for environmental monitoring and targeted public health strategies to reduce maternal and neonatal metal exposure in vulnerable Amazonian populations.