Toxic release Seveso, Italy

Most, if not all, occupational illnesses associated with 2,4,5-T (such as chloracne) have been found to be the result of product contamination with TCDD. TCDD is extremely toxic to animals, and exposure has also been associated with liver function impairment, peripheral neuropathy, personality changes, porphyria cutanea, hypertrichosis, and hyperpigmentation in humans. TCDD is a chlorinated dioxin, one of a large number of related compounds referred to as dioxins it has no functional use and is not intentionally produced. It has been identified as the responsible toxic agent in several industrial disasters, such as accidental releases at Nitro, WV in 1949, and at Seveso, Italy in 1976. " The role of dioxin contaminants must also be considered in the discussion of 2,4,5-T toxicology. 

In Seveso, Italy, an explosion occurred during the production of 2,4,5-T and a cloud of toxic material including 2,3,7,8-TCDD was released (Cerlisi et al. 1989 MMWR 1988 Mocarelli et al. 1991). Debris from the cloud covered an area of approximately 700 acres (2.8 km2). The total amount of 2,3,7,8-TCDD released during the accident was estimated to be 1.3 kg. Soil samples from this industrial accident were measured in three areas Zone A, the most contaminated zone where residents were evacuated Zone B, the moderately contaminated area where residents were advised not to eat locally raised produce and Zone R, where 2,3,7,8-TCDD contamination in soil was lowest of the three areas. Mean soil concentrations in these 3 areas were 230 g/m2 (maximum 5,477 g/m2) in Zone A, 3 g/m2 (maximum 43.9 g/m2) in Zone B, and 0.9 g/m2 (maximum 9.7 g/m2) in Zone R (MMWR 1988). 

There are two main accidents connected with the release of toxic chemicals. In July 1976, in Seveso, Italy, more than... 

Runaway reactions were an underlying cause of other industrial accidents such as that which occurred in Seveso, Italy in 1976. The nearby chemical plant was producing 2,4,5-trichlorophenol, an intermediate for manufacturing of a medical disinfectant hexachlorophene. The runaway reaction of 1,2,4,5-tetrachlorobenzene with sodium hydroxide went out of control and resulted by an explosion and release into atmosphere of an unintended byproduct of this reaction, highly toxic 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The nearby communities were thus exposed to TCDD. This accident triggered industrial environmental safety regulations passed by the European Community in 1982 and termed Seveso Directive. 

More typically, chemical releases have an impact over a long period of time. An example is the release of dioxins into the air and soil at Seveso, Italy, in July 1976. The release was related to the production of trichlorophenol at a plant about twenty miles north of Milan. No explosion occurred. Instead, the release occurred more than six hours after a chemical reaction within a chemical reactor at the plant had been completed. The chemical reaction produced heat, which raised the temperature of the contents of the reactor. This rise in temperature led to additional, spontaneous chemical reactions that increased pressure within the reactor. The increased pressure ruptured a seal, which led to release of the reactor contents into the atmosphere. The resulting toxic cloud of vapors released from the plant contaminated several thousemd acres of a densely populated cu ea of Seveso. Vegetation, birds, and animals near the plant were affected within days of the release. Many herbivorous animals (e.g., rabbits, sheep) died from eating contaminated plants. Nine days cifter the release, dioxins were found to be present in the plants, cmimals, and soils of the ctfea. Skin lesions were reported by residents, especially in children who had more direct contact with the contaminated soils than adults. Two... 

The use of an unnecessarily hot utility or heating medium should be avoided. This may have been a major factor that led to the runaway reaction at Seveso in Italy in 1976, which released toxic material over a wide area. The reactor was liquid phase and operated in a stirred tank (Fig. 9.3). It was left containing an uncompleted batch at around 160 C, well below the temperature at which a runaway reaction could start. The temperature required for a runaway reaction was around 230 C. ... 

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 Seveso disaster began on July 10, 1976 at the Industrie Chimiche Meda Societa Azionaria (ICMESA) chemical plant in Meda, Italy. This event became internationally known as the Seveso disaster, after the name of the most severely affected community. An increase in pressure due to an exothermic reaction in a 2,4,5-trichlorophenol-production reactor caused the rupture disk of the safety valve to burst. About 3000 kg of chemicals were released into the air. The release included 2,4,5-trichlorophenol, used in the manufacture of herbicides, and possibly up to 30 kg of the dioxin TCDD (2,3,7,8-tetrachloro-dibenzo-p-dioxin). Dioxin first came to widespread public notice during the Vietnam War, when it was identified as a component of the defoliant Agent Orange. Dioxin has also been considered to be the most toxic human-made substance. 

The Flixborough nylon plant accident in the UK (1974) was caused by an open-air explosion of a flammable gas released into the air. It killed the 28 plant employees present and caused extensive property damage in the surrounding area. The failure to perform a full technical assessment of a modification was given as the main cause of the event. The Seveso pesticide plant accident in Italy (1976) is well known for the dangerous release of dioxin due to poor plant safety features and to the underestimation of the possibility of a runaway reaction. The Bhopal incident in India (1984), at another pesticide plant, killed an estimated 4000 (although the total number is still unknown). This disaster was attributed to too large an inventory of toxic substances and to very poor staff attention to the operability of safety features. 

The Seveso disaster took place on July 10,1976, when a toxic cloud escaped from the ICMESA chemical plant located in the community of Mead in Lombardy (Italy). The accident was caused by reactor overheating which served to produce 2,4,5-trichlorophenol. At the beginning, a certain vagueness was involved about the released product. There was some thought about 1,2,4,5-tetrachlorobenzene and of polyethylene, but the development of chloracne allowed identification of 2,3,7,8-TCDD, called the Seveso dioxin. 

---