Seveso Dioxin Spill – Italy – July 10, 1976

Due to faulty understanding of the chemical processes involved, workers allowed substantial quantities of dioxin to escape into the community of Seveso. This accidental release of dioxin had a revolutionary and costly series of consequences for the people of Seveso.

One of the most serious problems facing chemical factories is change from an original design. The reason for a change may be entirely justified but unless the implications are fully understood and the personnel involved informed of the change the result can be catastrophic. The explosion at Oppau in 1921 would never have happened if workers at the plant had been informed of the character of the new compound that had been introduced.

The explosion at Icmesa’s chemical plant in Seveso on July 10, 1976, was another example of a change in the mode of production, one that led to terrible consequences. It was not a dramatic event when it happened, but its effects were devastating. Observers said that a white cloud shot up from the factory and very soon thereafter they could smell an unpleasant odor. The odor belonged to a highly toxic organic compound known as dioxin that had escaped from the Seveso factory.

The managers of the Icmesa chemical plant at Seveso, near Milan in northern Italy, made a change in the production process after several years of production with the original design. The workers of the factory were very familiar with the original process and some of them had difficulty understanding some key parts of the new process. In particular, they failed to note that temperature control at all stages was absolutely essential. The original plan for the factory was to produce TCP for herbicides and medicines at low temperatures. The chemical process by which the TCP was manufactured created quite a lot of heat and this heat had to be dissipated as quickly as possible as part of the chemical cycle.

The method used to accomplish this involved evaporating another chemical, one that was able to cool the immediate environment. In order to lower the temperature even further, as soon as a batch of TCP was completed all parts of the chemical processes involved in production were immersed in a cold-water tank. The whole manufacturing sequence was thus maintained at a very low temperature, a vital consideration because of the dangerous byproducts that might appear under a high temperature regime.

If the temperature of the manufacturing cycle were to rise very high, a whole new product, dioxin, a highly toxic organic compound, would be created in place of the TCP. In addition to cancer, exposure to dioxin can cause severe reproductive and developmental problems. It can also damage the immune system and interfere with hormonal systems. Dioxin was the carcinogenic chemical that caused many tragic outcomes at Love Canal, New York. The great danger of allowing high temperatures to develop was somehow overlooked when a manager at the factory decided to change the original design. The alternative he chose was to use only water at all stages rather than the chemical that was selected for temperature control. Perhaps this was a lower cost approach. Whatever the reason for the change, it required more time and substantial quantities of water to keep temperatures as low as they had been maintained by the former method.

The accident that led to the formation and then the release of dioxin happened on a Saturday morning when workers went off shift, oblivious to the fact that the hot chemicals needed sufficient water to lower the temperature. The newer method of water control was a slow process and these workers did not want to take the time needed. Furthermore, they were unaware of the terrible consequences of overheating. There was one other unfortunate circumstance. On the vents above the reactor where the two chemicals were mixed there were rupture-discs that would open under pressure and remain open.

Had these rupture-discs been of the spring-loaded kind they would have snapped back once the pressure dropped. Thus less gas would have escaped. As it was, heat and pressure built up steadily in the absence of a water shield and dioxin formed. As the rupture-discs opened, a cloud of gas which carried more than two pounds of the lethal dioxin spread out into the surrounding area. It was not accompanied by the kind of noise that would have alerted people to its presence. All that was visible was a small cloud rising above the factory.

A breeze blew the gas southward over Seveso and several communities bordering Milan. The first people to observe the gas plume from the factory and detect a very unpleasant odor rushed home and shut their doors. They found that the smoke and smell were already in the house when they arrived. Through the night they suffered headaches and nausea. Next morning the children had swollen eyes and skin blisters but doctors were unable to say what the problem was. For more than a week, none of the residents of the affected area knew the cause of the discomforts they were experiencing. Their knowledge of the effects of dioxin was quite limited.

People did quickly note that animals were dying by the thousands and leaves on trees were withering. Doctors and hospitals were swamped with patients who had skin problems. People were being evacuated from the most contaminated area and consumption of all local produce was banned. About one week after the explosion Icmesa’s officials urged a mass evacuation from the whole contaminated area. The reality had become clear— there had been a medical catastrophe and the effects were likely to last a long time. One regional health officer declared that Seveso had experienced its own Hiroshima.

The heaviest blow of all came still later, after the gas cloud was gone. A report from the U.S. Food and Drug Administration made it clear that dioxin, even in very small doses, can damage kidneys, livers, and lungs. It is also extremely dangerous for fetuses, much worse than thalidomide, so the fear of having deformed children swept across Italy. Doctors in Seveso warned that if they found deformed fetuses in pregnant women they would recommend abortions. This caused heated debate everywhere because Italy is a Catholic country and the Roman Catholic Church opposes abortions.

To stop the spread of contamination, an army of veterinarians in protective suits destroyed all the surviving animals in the affected areas. This was followed by the destruction of cornfields and vegetable gardens, but no one knew how to ensure a complete cleanup. Reports from other countries were not encouraging. In Britain, eight years earlier, a dioxin spill occurred at a chemical factory. The only solution was to pull down the whole factory building and bury it deep in an abandoned mineshaft. Vietnamese experts who had to deal with the effects of defoliation from their recent war warned that it would be difficult to limit the contamination to the area around Seveso. One of the main components of the defoliation in that war was dioxin.

One valuable consequence of the Seveso disaster was the creation of the European Community’s (EC) Seveso Directive, a new system of industrial regulation. Within the EC, each country previously followed its own rules for managing industrial safety. Urgent discussions about a new ECwide regulatory framework for ensuring the safety of hazardous installations started after the explosion at Flixborough in 1974 and then Seveso. Neither the residents of Seveso nor the local and regional authorities suspected that the Icmesa plant was a source of risk. They did not even know much about the type of production processes and chemical substances that occurred there.

The factory had been in existence for thirty years and the only occasional complaints from nearby residents related to unpleasant smells. Of much greater significance were the changes that had been made at both Seveso and Flixborough. These were changes in plant or processes which compromised the safety of the facilities but were not communicated to the authorities responsible for public health and safety. In light of these disastrous accidents it was clear that new legislation was needed to improve the safety of industrial sites, to plan for off-site emergencies, and to cope with the broader regional aspects of industrial safety.

The Seveso Directive, adopted by the Council of Ministers of the European Communities in June 1982, is the result of those efforts. A central part of the Directive is a requirement for public information about major industrial hazards and appropriate safety measures in the event of an accident. It is based on the recognition that industrial workers and the general public need to know about hazards that threaten them and about safety procedures. This is the first time that the principle of “need to know” was enshrined in European Community legislation. The “need to know” principle is not as strong as the “right to know” principle that is widely applied in the United States.

Although the Seveso Directive grew out of deficiencies in the existing system of industrial regulation, it is not only intended to provide protection against hazards. It also serves to equalize the burden of regulation on industry. The creation of a single hazardous industry code ensures a “level playing field” for trade within the European Community by depriving unscrupulous industrial operators of competitive advantages they might gain by exploiting differences among individual countries. Adoption of the “need to know” principle increases the political equality of decision making and adds a valuable new tool to the regulatory process.

Twenty-five years after the events of 1976 there is a three-hundred-acre park, Seveso Oak Forest Park, where once stood the Icmesa Chemical Plant. It is a popular picnic site. Beneath it lie the poisonous remains of the dioxin spill stored in two enormous concrete tanks. They contain the top sixteen inches of soil from all contaminated areas, the bodies of animals that had to be slaughtered, and the factory that caused the tragedy. It was taken apart brick by brick by workers in protective suits and placed below ground in the concrete tanks. Water periodically seeps from the tanks into another container where any dioxin remnants are treated.

One extraordinary finding emerged in the years that followed the dioxin leak. Within the first seven years, those mothers who had experienced some contamination, but not sufficient to require an abortion, brought more female babies to birth than males. The proportions were quite exceptional, forty-six females to twenty-eight males among the whole population of births. This was the first discovery of a molecule that could change the sex ratio.

In 1976, Dr. Mocarelli was put in charge of a lab to test affected people. He decided to take a blood sample from each of the 30,000 most affected and keep these samples in refrigerated storage in the hope that one day a test would be developed to tell levels of dioxin from a person’s blood. That discovery was made eleven years later and so, as a result of Dr. Mocarelli’s foresight, Seveso is today a world capital of expertise for dioxin’s effects on humans. Twenty-five years of patients records coupled with original blood samples are available to researchers.