Pathways of LRTAP-derived human exposure

For decades, many countries and intergovernmental organizations have taken measures to prevent the formation and release of PCDD/PCDFs, and have also banned or severely restricted the production, use, handling, transport and disposal of PCBs. As a consequence, release of these substances into the environment has decreased in many developed countries. Nevertheless, analysis of food and breast-milk show that they are still present, although in levels lower than those measured in the 1960s and 1970s. At present, the major source of PCB exposure in the general environment appears to be the redistribution of previously introduced PCBs. 

PCDD/PCDFs are today found in almost all compartments of the global ecosystem in at least trace amounts. They are ubiquitous in soil, sediments and air. Excluding occupational or accidental exposures, most human background exposure to dioxins and PCBs occurs through the diet, with food of animal origin being the major source, as they are persistent in the environment and accumulate in animal fat. 

Importantly, past and present human exposure to PCDD/PCDFs and PCBs results primarily from their transfer along the pathway atmospheric emissions air deposition - terrestrial/aquatic food chains - human diet. Information from food surveys in industrialized countries indicates a daily intake of PCDD/PCDFs on the order of 50-200 pg I-TEQ/person per day for a 60 kg adult, or 1-3 pg I-TEQ/kg bw per day. If dioxin-like PCBs are also included, the daily total TEQ intake can be higher by a factor of 2-3. Recent studies from countries that started to implement measures to reduce dioxin emissions in the late 1980s clearly show decreasing PCDD/PCDF and PCB levels in food and, consequently, a lower dietary intake of these compounds by almost a factor of 2 within the past 7 years. 

PCDD/PCDFs accumulate in human adipose tissue, and the level reflects the history of intake by the individual. Several factors have been shown to affect adipose tissue concentrations/body burdens, notably age, the number of children and period of breastfeeding, and dietary habits. Breast-milk represents the most useful matrix for evaluating time trends of dioxins and many other POPs. Several factors affect the PCDD/PCDFs content of human breast-milk, most notably the mothers age, the duration of breast-feeding and the fat content of the milk. Studies should therefore ideally 

The general population is mainly exposed to PCBs through common food items. Fatty food of animal origin, such as meat, certain fish and diary products are the major sources of human exposure. Owing to considerable differences in the kinetic behaviour of individual PCB congeners, human exposure to PCB from food items differs markedly in composition compared to the composition of commercial PCB mixtures. 

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