Seveso poison

The lethal doses of the various very toxic compounds can vary over a wide range the LD50 value of the well-known Seveso poison 2,3,7,8-tetrachloro-di-benzo-dioxin (TCDD) indicates higher toxicity than potassium cyanide by a factor of 10 000, but it is less toxic than botulinus toxin by nearly the same factor. 

The toxicity of the isomers varies considerably among the different PCDD s and PCDFs. Only about 17 out of the 210 dioxin and fiiran congeners are toxic. The greatest toxicity possesses the 2,3,7,8-tetra-CDD (the so-called Seveso poison ), and the 2,3,7,8-tetra-CDF. By convention, the toxicity of a mixture of PCDD s and PCDF s is determined as Total Toxic Equivalent = TEQ by multiplying the concentration of the different congeners with a specific Toxic Equivalent Factor = TEF ... 

The necessary emergency measures to be taken following accidental spillage or poisoning have to be assessed, and national fire control legislation will also apply. Exceptional risks to the community surrounding a chemical plant may have to be evaluated under major accidents hazards legislation, such as the European Community (EC) Seveso Directive [4]. 

Small quantities of PCDDs are produced as by-products of the industrial manufacture of chlorinated phenolic chemicals and pesticides. They are especially hazardous environmental pollutants, since they have carcinogenic and teratogenic properties. Their release in 1976 in an industrial explosion at Seveso, Italy was implicated in the widespread poisoning of livestock and contamination of the local population. 

It is claimed that PVC, when burned, prodnces dioxins, which are known to be deadly poisons and powerful carcinogens [16]. In a recent accident in Seveso, Italy, when four villages were contaminated with dioxins, many people had to be evacuated and the area had to be decontaminated [17]. There is also an example of dioxins being found in cow s milk in the Lickebaert area, Netherlands, which was linked to the incineration of PVC waste in a nearby municipal waste incinerator [18]. 

In Europe, in the 1970s one major chemical accident in particular prompted the adaption of legislation aimed at the prevention and control of major accidents in the chemical process industry. The Seveso accident in northern Italy in 1976 occurred at a chemical plant manufacturing pesticides and herbicides. A dense vapor cloud containing dioxin was released due to an uncontrolled exothermic reaction. The poisonous and carcinogenic dioxin is lethal in microgram quantities and contaminated ten square miles, and more than 2,000 people were treated for exposure. Luckly, there were no immediate fatalities. 

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