<P> The highest body burdens were found in Western Europe in the 1970s and early 1980s, and the trends have been similar in the U.S. The most useful measure of time trends is concentration in breast milk measured over decades . In many countries the concentrations have decreased to about one tenth of those in the 1970s, and the total TEQ concentrations are now of the order of 10 - 30 pg / g fat (please note the units, pg / g is the same as ng / kg, or the non-standard expression ppt used sometimes in America). The decrease is due to strict emission controls and also to the control of concentrations in food . In the U.S. young adult female population (age group 20 - 39), the concentration was 9.7 pg / g lipid in 2001 - 2002 (geometric mean). </P> <P> Certain professions such as subsistence fishermen in some areas are exposed to exceptionally high amounts of dioxins and related substances . This along with high industrial exposures may be the most valuable source of information on the health risks of dioxins . </P> <P> Dioxins have no common uses . They are manufactured on a small scale for chemical and toxicological research, but mostly exist as by - products of industrial processes such as bleaching paper pulp, pesticide manufacture, and combustion processes such as waste incineration . The defoliant Agent Orange contained dioxins . The production and use of dioxins was banned by the Stockholm Convention in 2001 . </P> <P> PCB - compounds, always containing low concentrations of dioxin - like PCBs and PCDFs, were synthesized for various technical purposes (see Polychlorinated biphenyls). They have entered the environment through accidents such as fires or leaks from transformers or heat exchangers, or from PCB - containing products in landfills or during incineration . Because PCBs are somewhat volatile, they have also been transported long distances by air leading to global distribution including the Arctic . </P>

Who dioxins and their effects on human health