Trend analyses of persistent organic pollutants in human milk from first-time mothers in Norway between 2002 and 2021.

Introduction: Persistent organic pollutants (POPs) are stable compounds characterized by their resistance to degradation. From the 1960-70's organochlorine pesticides (OCPs), such as DDTs and polychlorinated biphenyls (PCBs) raised concerns regarding health and environmental impacts. This has led to the banning of POPs in the USA and Europe including Norway in 1980 and worldwide under the 2004 Stockholm Convention. The exposure of nursing infants to POPs has been a significant focus, prompting extensive research into the presence of these substances in human breast milk. In this study, we explored the temporal trends of POPs concentrations in breast milk sampled between 2002 and 2021 by comparing the concentration across the mother's year of birth.

Method: Two Norwegian cohorts of lactating women were utilized (the HUMIS study and the "Iodine in Early Life"-Study). Concentrations of 15 different POPs, including PCBs, OCPs, and brominated diphenyl ethers (BDEs) were measured in 513 breast milk samples that had been collected over two decades in a subset of first-time mothers.

Results: Time trend analysis indicated a steady decrease in concentration levels when adjusted for maternal age. The largest reduction was observed in β-HCH, age-adjusted (-17.1%, 95% CI -18.7, -15.4), followed by ∑BDE (-9.1%, 95% CI -10.5, -7.7), ∑PCBs (-7.1%, 95% CI -7.7, -6.5), and ∑DDTs (-7.0%, 95% CI -8.0, -6.0). In contrast, an increasing trend was noted in the median concentrations of β-HCH, ∑DDTs, and ∑BDE in the mothers born in 1990-1994 to 1995-2002.

Conclusion: Our study demonstrates a decline of most POPs in breast milk, likely attributed to international regulatory efforts like the Stockholm Convention. Notably, an increase in the 95th percentile concentrations of β-HCH, ∑DDTs, and ∑BDEs was noted in mothers born in 1990-1994 compared to those born in 1995-2002 suggests demographic shifts that may influence exposure levels. Further research is needed to explore and understand the underlying factors for the rise in median concentrations of ∑BDEs.