Arsenic, cadmium, lead, mercury, and PFAS exposure during pregnancy or lactation and respective concentrations in human milk: Systematic review.

Contaminant exposure during pregnancy or lactation may result in contaminant transfer into human milk (HM). This systematic review (PROSPERO# CRD42024530326) assessed relationships between arsenic, cadmium, lead, mercury, and per- and polyfluoroalkyl substances (PFAS) exposure measured by various biospecimen concentrations collected during pregnancy or lactation and respective concentrations in HM using studies conducted in countries rated 'high' or 'very high' on the Human Development Index. CAB Abstracts, CENTRAL, CINAHL, Embase, and MEDLINE, were searched for peer-reviewed English language articles through April 2, 2025. Direction, magnitude, and statistical significance of reported correlations (r, ρ, β, or unspecified) were synthesized narratively. Risk of bias (ROB) was assessed using ROBINS-E. Certainty of evidence was assessed using GRADE. From 3836 records identified, 48 articles from 46 studies (16 prospective cohorts, 30 cross-sectional) conducted in 25 countries were included (arsenic n = 4 articles, cadmium n = 5, lead n = 18, mercury n = 15, PFAS n = 10). Higher exposure to lead, mercury, PFOA, and PFOS during pregnancy or lactation correlated with higher concentrations of these contaminants in HM, respectively (correlation = 0.05-0.88 for lead, 0.0265-0.66 for mercury, 0.353-0.97 for PFOA, and 0.32-0.97 for PFOS). Certainty of evidence was moderate for lead, PFOA, and PFOS, and low for mercury. The evidence for arsenic and cadmium was limited and inconclusive, as well as evidence about these contaminants specifically from foods. In conclusion, higher exposure to lead, mercury, PFOA, and PFOS during pregnancy or lactation correlated with concentrations of these contaminants in HM. Reducing contaminant exposure during pregnancy or lactation could potentially reduce concentrations in HM.