Dioxins/furans and PCBs in Canadian human milk: 2008-2011

Human milk was collected between 2008 and 2011 as part of the Maternal - Infant Research on Environmental Chemicals (MIREC) study that was initiated to establish Canadian national estimates of maternal and infant exposure to a broad suite of environmental contaminants (e.g., persistent organic pollutants [POPs], trace elements, phthalates, etc.). Among the 1017 human milk samples collected, 298 were analysed for polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs). World Health Organization (WHO) toxic equivalency concentrations (WHO TEQ₂₀₀₅) for PCDD/F+dioxin-like (DL) PCB ranged from 2.2pg TEQ₂₀₀₅ g^-1 lipid to 27pg TEQ₂₀₀₅ g^-1 lipid. The relative contribution of PCDDs to the overall WHO TEQ₂₀₀₅ (PCDD/F+DL PCB) has decreased from earlier investigations into POP levels in Canadian human milk. Significantly higher PCB concentrations were observed in milk from women born in Europe relative to those born in Canada (p<0.001), in contrast to results for the PCDD/Fs (p=0.496). Age was found to significantly impact milk ∑PCB concentrations (p=0.018), with elevated concentrations observed in milk from women >30years relative to those <30years of age. While this trend was also observed for the PCDD/Fs, this relationship was impacted by parity. WHO TEQ₂₀₀₅ concentrations were significantly higher in milk from primiparous women (p=0.019) and those >30years relative to those <30years of age (p<0.001). No significant differences were associated with education level or pre-pregnancy body mass index. PCB and PCDD/F concentrations have continued to decline in Canadian human milk since the last sampling of human milk was performed.