Time Trends in Human Milk Derived from WHO- and UNEP-Coordinated Exposure Studies, Chapter 2: DDT, Beta-HCH and HCB

Abstract Temporal trends of DDT (“DDT complex” as sum of p,p′-DDT, o,p′-DDT, p,p′-DDD and p,p′-DDE), beta-hexachlorocyclohexane (beta-HCH) and hexachlorobenzene (HCB) were assessed using pooled human milk samples from 44 countries from all United Nations Regional Groups based on their repeated participation in WHO/UNEP-coordinated exposure studies performed between 2000 and 2019. In contrast to a general estimation of time trends based on results from all countries, this is a more precise approach, because levels among countries are often highly variable. The primary objective of these temporal studies is to provide monitoring data for the effectiveness evaluation of the Stockholm Convention on Persistent Organic Pollutants (POPs). For DDT, an overall decrease over 10 years between 50% and 80% was achieved in Africa, the Asia-Pacific region and in Latin America and the Caribbean region, and at a global level. Slightly lower decreases were observed in European countries because DDT was banned much earlier in these countries and only residual levels were depleting. Western European countries had the lowest median and the lowest maximum DDT concentrations. This is an indication that the decrease might be faster in regions with higher concentrations, compared to a slower decrease in less contaminated regions. The frequency distribution of the country-specific decrease ( decrease rate constants ) confirms these findings. For beta-HCH, an overall decrease over 10 years between 50% and 98% was achieved in all UN regions and at a global level. Country-specific decreases vary in the low background range (below 5 μg beta-HCH/kg lipid). Regarding HCB, all countries from Africa and many countries from the Pacific Islands and Latin America and the Caribbean were in the range of a low background contamination below 5 μg/kg lipid resulting in a wide range of reduction rates. In contrast, in countries with HCB concentrations above 30 μg/kg lipid in previous rounds, overall decreases over 10 years between 50% and 85% were observed. Therefore, the reduction rates should be seen also in context with the concentration range: A differentiation of levels above or in the range of the background contamination seems to be advised. If high levels are found, sources might be detected which could be eliminated. However, at low background levels, other factors, e.g. contamination of feed and food by air via long-range transport and subsequent bioaccumulation, cannot be influenced locally.