Toxic chemical dioxin

Hormone response elements (for steroids, T3, retinoic acid, peptides, etc) act as—or in conjunction with— enhancers or silencers (Chapter 43). Other processes that enhance or silence gene expression—such as the response to heat shock, heavy metals (Cd and Zn +), and some toxic chemicals (eg, dioxin)—are mediated through specific regulatory elements. Tissue-specific expression of genes (eg, the albumin gene in liver, the hemoglobin gene in reticulocytes) is also mediated by specific DNA sequences. 

The famous herbicide agent orange contained as an additive 2,3,7,8-tetrachlordibenzo-p-dioxin (2,3,7,8-TCDD), the most toxic chemical substance created by mankind. Dioxin makes up about 150-160 kg. in 24,000 tons of herbicide 2,4,5-T. This additive is enough to allow us to continue to discuss the consequences to humans and the environment in Vietnam from not one, but two wars the herbicide and the dioxin [65]. 

In addition, the concern about e-waste not only focuses on its vast quantity generated daily, but also more on the need to handle the toxic chemicals embedded in it. It is well known that e-waste contains lead, beryllium, mercury, cadmium (Cd), and brominated flame retardants (BFRs) among other chemical materials [3]. Furthermore, highly toxic chemicals such as polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and polybrominated dibenzo-p-dioxins and dibenzo-furans (PBDD/Fs) can be formed during the recycling process [4]. 

Walker, M.K. and R.E. Peterson. 1994. Aquatic toxicity of dioxins and related chemicals. Pages 347-387 in A. Schecter (ed.). Dioxins and Health. Plenum Press, New York. 

The chlorinated chemicals assessed do not have the same risk profile. For the more volatile chemicals the safety margins between the actual exposure and the level at which no effect on the environment would be expected is quite high. For more persistent chemicals there is a need to look to the environmental compartment where they can be accumulated (mainly in sediments and biota). For some of these chemicals the safety margin is quite low and in worst-case situations serious effects may occur. For the very persistent, bioaccumulative and toxic chemicals (like dioxins, PCBs and DDT), acceptable environmental concentrations are so low and difficult to control that the industry is committed to reducing as far as possible releases to the environment through application of Best Available Techniques (BAT), mainly with respect to dioxins. For other chemicals (PCBs, DDT), production has already been halted for some years. 

On July 9, 1976, in Meda, Italy, near Seveso, a chemical reactor incident caused a release of dioxin (TCDD), which is a highly toxic chemical. The regulatory requirements developed as a result of this incident are referred to as the Seveso Directive. 

The manufacture and disposal of PVC creates another serious problem. Dioxin, shown in Figure 2.14, is a highly toxic chemical. It is produced during the manufacture and burning of PVC plastics. 

TCDD (dioxin), long considered as a very toxic chemical, was reclassified as a known human carcinogen (see also 1971). 

Although this public health statement will focus on CDDs, it is important to note that CDDs are found in the environment together with other structurally related chlorinated chemicals, such as chlorinated dibenzofurans (CDFs) and polychlorinated biphenyls (PCBs). Therefore, people are generally exposed to mixtures of CDDs and other classes of toxicologically and structurally similar compounds. 2,3,7,8-TCDD is one of the most toxic and extensively studied of the CDDs and serves as a prototype for the toxicologically relevant or dioxin-like CDDs. Based on results from animal studies, scientists have learned that they can express the toxicity of dioxin-like CDDs as a fraction of the toxicity attributed to 2,3,7,8-TCDD. For example, the toxicity of dioxin-like CDDs can be half or one tenth or any fraction of that of 2,3,7,8-TCDD. Scientists call that fraction a Toxic Equivalent Factor (TEF). More information on TEFs can be found in Section 2.5. 

Addition of Dioxin and Dioxin-like Compounds Toxic Chemical Release Reporting Community Right-to-Know—Proposed rule Yes 62 FR 24887 EPA 1997c... 

EPA. 1997c. Addition of dioxin and dioxin-like compounds modification of polychlorinated biphenyls (PCBs) listing toxic chemical release reporting community right-to-know. U. S. Environmental Protection Agency. Federal Register. 62 FR 24887. 

The toxicity equivalent (TEQ) of TCDD is calculated by multiplying the exposure level of a particular dioxin-like compound by its toxicity equivalency factor(TEF). TEFs are based on congener-specific data and the assumption that Ah receptor-mediated toxicity of dioxin-like chemicals is additive. The TEF scheme compares the relative toxicity of individual dioxin-like compounds to that of TCDD. 

According to the Bay Area Air Quality Management District in San Francisco, more than 5.5 million pounds of toxic chlorinated substances are released in the area annually. This includes approximately 13,000 pounds of chloroform, 1.4 million pounds of freon, 2 million pounds of perchloromethylene, and trace amounts of dioxin. (Dioxin is one of the most toxic chemicals known.) A report released in September 1994 by the U.S. Environmental Protection Agency (EPA) clearly describes dioxin as a serious public health threat. The public health impact of dioxin may rival the impact that DDT had on public health in the 1960s. According to the EPA report, not only does there appear to be no safe level of exposure to dioxin, but levels of dioxin and similar chemicals have been found in the U.S. population that are at or near levels associated with adverse health effects. The EPA report also confirmed that dioxin is a cancer hazard, exposure... 

Dioxins are some of the most toxic chemicals known to science. Dioxins are unwanted by products of a wide range of manufacturing processes including smelting, chlorine bleaching of paper pulp, and the manufacturing of some herbicides and pesticides. In terms of dioxin release into the environment, waste incinerators (solid waste and hospital waste) are often the worst culprits, due to incomplete burning [115]. One of the most toxic chemical in the class is 2,3,7,8-tetrachlorodibenzo-/ /Y/-dioxin (TCDD) and probably the most toxic compound ever synthesized by man. 

The Stockholm Convention (UNEP 2009a) entered into force in 2004, restricting 12 persistent and bio-accumulating toxic chemicals. An additional 9 substances were included in 2009. In coming decades, the major issue under the convention will be the reduction of emissions of dioxins and furans from combustion. 

---