Dioxins and dioxin-like compounds
They are mostly by-products of burning or various industrial processes or, in the case of dioxin-like PCBs and PBBs, unwanted minor components of intentionally produced mixtures.
Mice lacking the AH receptor (knockouts) are sick with cardiac hypertrophy, liver fibrosis, reproductive problems, and impaired immunology.
The results have been comparable to TEQ levels measured by much more expensive gas chromatography-high resolution mass spectrometry in environmental samples.
The symptoms reported to be associated with dioxin toxicity in animal studies are incredibly wide-ranging, both in the scope of the biological systems affected and in the range of dosage needed to bring these about.
[4][1][3] Acute effects of single high dose dioxin exposure include reduced feed intake and wasting syndrome, and typically a delayed death of the animal in 1 to 6 weeks.
[24] Surprisingly, enzyme induction, several developmental effects and aversion to novel foods occur at similar dose levels in animals that respond differently to acute high-dose toxicity.
Babies born to Yusho and Yu-cheng mothers were smaller than normal, they had dark pigmentation and sometimes teeth at birth and tooth deformities.
[1] The contamination panel of the European Food Safety Agency (EFSA) recommended decreasing tolerable weekly intake (TWI) levels based on the Russian children study.
[20] This recommendation can be challenged, because it does not properly consider competing risks following from lost benefits of important and healthy food items such as certain fish.
The main problem is that similar associations can be found with many quite different POPs, which have only long half-lives and tendency to accumulate in lipids in common.
[29] E.g. absorption from bleached tampons claimed to be associated with endometriosis[39] is insignificant compared with daily dioxin intake from food.
[47] All this means that in case of important beneficial food items and breast feeding a thorough benefit/risk analysis is needed before setting limits, in order to avoid increased other risks or lost benefits.
[1] Because dioxins are eliminated very slowly, the body burden accumulated during the whole lifetime is high compared with daily doses, and occasional modest exceedances of limit values do not change it much.
[1] Specifically, the TDI has been assessed to guarantee the safety of children born to mothers exposed to such a daily intake of dioxins all their lifetime prior to pregnancy.
[57] Most intake of dioxin-like chemicals is from food of animal origin: meat, dairy products, or fish predominate, depending on the country.
[1][59][60] For the same reason, short term higher intake such as after food contamination incidents, is not crucial unless it is extremely high or lasts for several months or years.
The defoliant Agent Orange contained trace amounts of dioxin impurities and caused severe health issues as a result.
As a result of these concerns, incineration processes have been improved with increased combustion temperatures (over 1,000 °C (1,830 °F)), better furnace control, and sufficient residence time allotted to ensure complete oxidation of organic compounds.
[72] Ideally, an incineration process oxidizes all carbon to CO2 and converts all chlorine to HCl or inorganic chlorides prior to the gases passing through the temperature window of 400-700 °C where PCDD/F formation is possible.
In addition to dioxins, other harmful products of incomplete combustion - such as carbon monoxide - are also released when biomass is burned in low oxygen conditions.
The WHO panel re-evaluating the TEF values in 2005 expressed their concern that emissions should not be uncritically measured as TEQs, because all congeners are not equally important.
In a NIOSH study in the U.S., the average concentration of TCDD in exposed persons was 233 ng/kg (in serum lipid) while it was 7 ng/kg in unexposed workers, even though the exposure had been 15–37 years earlier.
[99] Handling and spraying of chlorophenoxy acid herbicides may also cause quite high exposures, as clearly demonstrated by the users of Agent Orange in the Malayan Emergency and in the Vietnam War.
[100] Dioxins are neither volatile nor water-soluble, and therefore exposure of human beings depends on direct eating of soil or production of dust which carries the chemical.
In 2011 in South Carolina, SCDHEC enacted emergency sludge regulations after PCBs were found to have been discharged to a waste treatment plant.
[101] PCBs are also known to flush from industry and land (aka sludge fields) to contaminate fish,[102] as they have up and down the Catawba River in North and South Carolina.
[1] A tank of recycled fats collected for animal feed production was contaminated by PCB oil containing about 1 g of dioxins and 2 g of DL-PCBs.
This caused a major alarm in the European Union, but due to relatively fast response and slow accumulation of dioxins in humans there were no health impacts.
The contamination was found to be due to zinc oxide used in pork feed, and caused reputational and financial losses for the country, as well as leading to the introduction of new food safety regulations.
[104] These episodes emphasize the importance of food control, and early detection guarantees that very slowly accumulating dioxins do not increase in humans to levels causing toxic effects.
