1.3.7.8- Tetrachlorodibenzodioxin

Some hquid defoamers are preemulsified relatives of paste defoamers. In addition to the fatty components mentioned above, kerosene [8008-20-6] or an organic cosolvent such as 2-propanol have been used to enhance stabiUty of the oil—water emulsion and the solubiUty of the defoamer s active ingredients. These cosolvents are used less frequently as concerns increase about volatile organic emissions (VOCs) from the paper machine. Additionally, the use of ultrapure mineral oil in defoamers has become commonplace. Concern about the creation of 2,3,7,8-tetrachlorodibenzodioxin (TCDD) and 2,3,7,8-tetrachlorodibenzofuran (TCDF) in the pulping process has led to the discovery of unchlorinated precursor molecules, especially in recycled mineral oil and other organic cosolvents used in defoamer formulations (28). In 1995 the mineral oil that is used is essentially free of dibenzodioxin and dibenzofuran. In addition, owing to both the concern about these oils and the fluctuating cost of raw materials, the trend in paper machine defoamers is toward water-based defoamers (29). 

When pushed to the limit by overriding human health concerns, residue chemists have achieved detection limits of Ippt (Ingkg ) or even into the low ppqr (1 pg kg ) range. An example at the 1 ppt level is provided by methods for 2,3,7,8-tetrachlorodibenzodioxin (TCDD) in milk and TCDD in adipose tissue. Eor relatively clean matrices such as water and air, preconcentration on solid-phase adsorbents followed by GC or gas chromatography/mass spectrometry (GC/MS) can provide detection limits of 1 ng m and less for air (examples in Majewski and Capel ) and 1 ngL and less for water (examples in Larson et A summary of units of weight and concentration used to express residue data is given in Table 1. 

In the production of the herbicide 2,4,5-T (2,4,5 tetrachlorophenoxyacetic acid), a dioxin (2,3,7,8 tetrachlorodibenzodioxine) is often formed. Not only has it been called the second most lethal chemical ever discovered but it can also produce birth defects. During the early 1970s there were court battles over whether 2,4,5-T should be banned because of the possible presence of the dioxin. The Dow Chemical Company maintained that no detectable dioxin was produced in its process and that therefore its product was safe and should not be taken off the market. In this instance, the removal and hence concentration of the dioxin would pose problems of such a magnitude that the only feasible reaction conditions are the ones that produce no dioxin. 

Phenoxyacids (PA) have been widely used as herbicides in agriculture, forestry, and, to a lesser extent, garden activities. The principal products are represented by 2,4-D (2,4-dichlorophenoxyacetic acid) 2,4,5-T (2,4,5-trichlo-rophenoxyacetic acid) and MCPA (4-chloro, 2-methylphenoxyacetic acid) (Stevens and Sumner, 1991). 2,4,5-T has been banned in many countries for a long time because of contamination of the commercial formulations of 2,4,5-T by 2,3,7,8-tetrachlorodibenzodioxin. At present, dioxin contamination of these formulations has been reduced to very low concentrations. 

A publication summarises all the then available technical evidence related to the Seveso accident, and recommends operational criteria to ensure safety in commercial processes to produce trichlorophenol [4], All the plant scale incidents were characterised [ 1 ] by the subsequent occurrence of chloracne arising from the extremely toxic and dermatitic compound 2,3,7,8-tetrachlorodibenzodioxin (structure IX, p. S-3), formed dining the thermal runaway reaction and dispersed in the ensuing explosion. It is also extremely resistant to normal chemical decontamination procedures, and after the 1968 explosion, further cases occurred after transient contact with plant... 

When chlorinated phenols are heated for analytical purposes with calcium hydroxide-potassium nitrate mixtures, chlorinated benzodioxins analogous to the extremely toxic tetrachlorodibenzodioxin may be formed. 

There are 210 different isomeric possibilities, 75 of which are PCDDs and 135 are PCDFs. The toxicity of these isomers varies greatly, and only 15 exhibit extreme toxicity, the most toxic of which is 2,3,7,8-tetrachlorodibenzodioxin (2,3,7,8-TCDD). The toxicity of the other isomers is therefore expressed as a toxicity equivalent of 2,3,7,8-TCDD. The PCDDs and PCDFs are poorly water soluble but are fat soluble and are therefore able to accumulate in tissue fat, thus allowing them to bio-accumulate in living organisms. The origin of dioxins in the pulp and paper industry is not entirely clear. They may be produced from the chlorination of dibenzodioxin which may be present in recycled oils used to make defoamers, but they may also arise from wood chips which have been treated with polychlorophenol to prevent sap stain formation. It is also possible that they are derived from lignin by chlorination. Dioxins are also known to be formed naturally by combustion of material such as wood, and forest fires have been particularly identified as a likely major cause of dioxin emissions. 

Trichlorophenoxyacetic, 2,4,5 Acid Dioxin and Related Compounds Dioxin and Related Compounds HxCDF Hexachlorodibenzofurans TCDD Tetrachlorodibenzodioxins TCDF Tetrachlorodibenzofurans Disubstituted and Polysubstituted Benzene Hydrocarbons Diethyl Benzene... 

TCDD Tetrachlorodibenzodioxins under Dioxin and Related Compounds... 

Polychlorinated dibenzo-para-dioxins (other than 2,3,7,8-tetrachlorodibenzodioxin)... 

Alkanes can be simultaneously chlorinated and chlorosulfonated. This commercially useful reaction has been applied to polyethylene (201—203). Aromatics can be chlorinated on the ring, and in the presence of a free-radical initiator alkylaromatic compounds can be chlorinated selectively in the side chain Ring chlorination can be selective. A patent shows chlorination of 2,5-di- to 2,4,5-trichlorophenoxyacetic acid free of the toxic tetrachlorodibenzodioxins (204). With alkenes, depending on conditions, the chlorination can be additive or substitutive. The addition of sulfuryl chloride can occur to form a 2-chloroalkanesulfonyl chloride (205). 

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