SEVESO, Italy -- The Seveso dioxin leak on July 10, 1976 was one of the worst industrial/ecological accidents of the modern age even though its historical impact has been diluted since by worse incidents such as the leak at Bhopal, India and the nuclear disaster at Chernobyl, Ukraine in 1986.

On July 10, 1976 at the Icmesa factory -- a plant that produced a chemical for use in the pharmaceutical and cosmetic industries -- overheating caused a safety valve to break.

There was a 20-minute leak of substances including dioxin (full name 2,3,7,8 tetrachlorodibenzo-para-dioxin).

The leak contaminated four communes north of Milan -- Seveso, Meda, Desio and Cesena Maderno -- with Seveso and Meda the worst affected.

Fortunately the unusually high wind speed of 5m/sec may have avoided a worse disaster. The contamination may have been spread over a larger area but it was less concentrated.

It was not until July 12 that the Icmesa building was closed and the day after animals started to die.

On July 14 the first human casualties came to light. Many were children and suffered from burns. Months later chloroacne, a fierce skin rash on the face, developed. Some have carried scars into adulthood.

In all 736 people were evacuated and 193 people -- many children -- needed medical treatment. Many animals died and many more were slaughtered.

The Roche Group that owned the Icmesa site paid $240 million to those affected.

Studies have already showed a higher than normal incidence of tumors, diabetes and most strikingly a very low ratio of baby boys born to affected parents (a rate of 60 boys to every 100 girls).

The original factory site has been converted into leisure facilities while the most contaminated area has been transformed into a parkland with a wide diversity of wildlife.

In 1982 the European Union adopted the Seveso Directive, setting down new procedures and safety standards for industry.