Seveso toxic release accidents

The risk of toxic release accidents into the atmosphere or watercourses is very real, and there have been many examples. Four very notable and well-known examples - Seveso, Bhopal, Mississauga and the Sandoz chemical spill into the Rhine - are briefly outlined below, together with a more detailed description of a less well-known incident. 

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. 

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. 

It is well known that during the process the highly toxic dioxin (TCDD) is produced, albeit in minute quantities, as long as the nominal range of the reaction parameters is maintained. A deviation of the reaction parameters was the cause of the Seveso accident (cf. [24]), in which an estimated quantity between 0.45 and 3 kg of TCDD was released into the environment. 

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. 

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