In July 1976, a runaway reaction occurred in the trichlorophenol synthesis vessel of a chemical plant near Seveso, Italy. An uncontrollable surge in temperature and pressure caused the rupture of a safety valve, resulting in release into the air of a fluid mixture of chemicals. This toxic cloud containing TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin), then widely believed to be one of the most toxic man-made chemicals, contaminated a densely populated area about six kilometres long and one kilometre wide, lying downwind from the site. This event became internationally known as the Seveso disaster, after the name of a neighboring municipality that was most severely affected. More than 700 people were evacuated, and restrictions were applied to another 30,000.

The Impact

Although no immediate fatalities were reported, the full horror of the incident slowly emerged over the following days, months and years. More than 200 people have been treated for dioxin poisoning and countless thousands of animals died, or killed to prevent further impact along the food chain. More than five square miles of land and vegetation were contaminated. A monitoring program was initiated for environmental systems and media to determine the level of exposure, the extent of contamination, and the behavior and fate of TCDD released into the environment. Information about exposures was also obtained from signs/symptoms. Blood samples were collected and analyzed for TCDD and blood chemistry. The early screening of thousands of children revealed chloracne as the main health effect.

Long-term effects studies of mortality and cancer incidence were designed using the populations from four contaminated and seven uncontaminated towns, who were resident at the time of the incident and for the following eight years. The ten-year mortality study revealed an increased occurrence of cardiovascular diseases that might have been related to stressors caused by the disaster. Results from the cancer incidence study showed an increased risk of hepatobiliary cancer in some subjects, particularly those residing for more than five years. Some men had an increased risk of leukemia, and women exhibited an increase in multiple myeloma and myeloid leukemia. In another zone, subjects experienced an elevated incidence of soft-tissue sarcomas. The researchers claimed that these findings were consistent with previous knowledge of TCDD’s effects on animals and humans. The mortality and cancer incidence investigations were planned to continue for at least 20 years after the release. Case–control studies have been initiated to investigate the possible role for markers of susceptibility to TCDD.

Cancer incidence in Seveso

Cancer incidence at Seveso, ten years after the accident: Average dioxin found in ground expressed in microgram I-TEQ per square meter. Average dioxin found in blood expressed in parts per trillion (ppt).

Recently, the WHO has declared the Seveso type dioxin (2,3,7,8 TCDD) as a human carcinogen, based on the consequences of severe accidents in several chemical works, where workers received extreme high levels of this dioxin type (tenthousends of times higher than background!). The rise of cancer incidences in a life time was app. 40% for the highest exposed people. That has to be compared with a 20 times (or 2,000%) rise in cancer incidence for smokers...

The other 209 types of chlorinated dioxins and furans are not classified until now, because of lack of reliable data.

The Seveso Directive

Nations downstream from other nations will always be threatened by environmental spills and accidents caused by upstream nations. Hungary, with 95 percent of its surface waters originating abroad, is particularly vulnerable.

For this reason, international treaties and laws governing transboundary pollution are crucial for preventing disasters. They are needed to resolve issues related to liability and compensation. They are also needed to protect countries from domestic disasters caused by the carelessness or exploitative activities of foreign companies.

Numerous treaties and laws do now exist. Some include Hungary and Romania as "contracting parties"
Legislation aimed at the prevention and control of accidents involving dangerous substances in the EU was significantly prompted by one particular disaster from the past. The disaster at Seveso, Italy resulted in releasing large amounts of poisonous dioxins into the air, contaminating ten square miles of land and vegetation. Over 600 people were evacuated with as many as 2,000 treated for dioxin poisoning.

As a result, in 1982, the Seveso Directive (Council Directive 82/501/EEC) on the major accident hazards of certain industrial activities was adopted, later amended in light of two other major accidents. The first was the 1984 chemical disaster at the Union Carbide factory in Bhopal, India, where over 2,500 people died. The second was the 1986 catastrophe at the Sandoz warehouse in Basel, Switzerland, where a major chemical leak laden with mercury led to the massive pollution of the Rhine River and the death of half a million fish.

In 1996, the Seveso Directive II (Council Directive 96/82/EC) replaced its predecessor. Still in effect, it aims to prevent major accidents involving dangerous substances and to limit their consequences for humans and the environment. It covers industrial activities and the storage of dangerous chemicals, expands the public's right to access information and requires governmental authorities to carry out regular inspections.

Seveso Directive- as fallout to the disaster

There was no professional engineer in the plant at the time of the accident. The temporary modification was constructed by people who did not know to design large pipes equipped with bellows. The Flixborough plant contained approx. 400 MT of inventory of which 40 or 50MT escaped. The inventory was large because the conversion was low and most of the material had to be recovered and recycled. The most important lesson that Flixborough taught is the need to minimize inventories of hazardous materials.

The disaster led to a widespread public outcry over industrial plant safety, and significant tightening of the UK government's regulations covering hazardous industrial processes. All refineries and related petrochemical industries were shocked from the accident, although they were aware of the risk of plant modifications and immediately improved their procedures and checklists in order to approve plant modifications. Temporary modifications were even excluded in some cases or approved after thorough examination. Although many modification accidents occurred, Flixborough is still the stock example, the most disastrous of them all.

The Lessons Learnt from the Disaster

At the time of the Seveso disaster, the complexity of communication problems under conditions of severe uncertainty was recognized, if not fully managed. Before the gas release, no one outside the plant neither residents nor political or health authorities - had any idea that there was a hazard of such magnitude. The explosion and release were greeted by incredulity, followed by alarm and dismay. The firm's initial behavior led to subsequent suspicion about their motives; various instructions for precautionary measures were issued almost immediately, but the firm denied knowledge of the toxic substances involved. Ten days passed before the firm confirmed that dioxin had been released. Only then did the governmental authorities and the public learn that there was a grave risk. Even so, it was impossible to assess the danger with any precision. There was an onset of genuine dread, about illness in general and about malformed babies in particular. The widespread illness and deaths of animals of many species was an ominous sign. The authorities had their own severe problems of decision-making under uncertainty, including the definition of different polluted zones, programmes of evacuation of endangered residents, and disposal of contaminated material.

From the very beginning of the disaster, situational uncertainty was salient; decisions had to be taken, sometimes under conditions of great urgency' in the nearly complete absence of information that might guide actions. Scientific uncertainty was salient local investigating magistrates closed off the site within eight days of the accident. Societal uncertainty was severe because there had been no previous institutional preparation or consultation for the accident. Legal/moral uncertainty was also severe One of the few relatively straightforward aspects of the accident was the low level of proprietary.