Greenpeace has called for a new clean-up plan at a site for toxic waste used mostly by Switzerland's chemical industry.
The environmental group warned on Thursday that dioxin deposited at the site could pose a health risk for planned clean-up operations.
Greenpeace said Basel-based chemical companies had dumped a considerable amount of dioxin at the Bonfol site near the French border between 1961 and 1975.
The organisation is now calling for a review of the clean-up project - presented by the chemical industry in 2003 - for the 114,00 metric tons of solvents, pesticides and pollutants.
It said pockets with a high concentration of dioxin at the site were a serious health hazard for workers.
Greenpeace also accused the Basel chemical industry of downplaying the amount of dioxin dumped at the site in northwestern Switzerland, but gave no details.
The chemical industry said the Greenpeace study contained no new information. The company in charge of carrying out the clean-up operation said special safety measures had been planned.
According to a company spokesman, the quantity of dioxin deposited at the site is minor compared with the total amount of contaminated waste at Bonfol in canton Jura.
He added that he hoped the chemical industry and the cantonal authorities would soon agree on funding for the clean-up operation at what is one of Switzerland's largest waste dumps.
The Jura cantonal government said it welcomed the Greenpeace report, which gave more details than the chemical industry had provided.
In 2000 the authorities demanded that the chemical waste site be cleaned up. A project was presented three years later by the chemical industry, but it has since stalled.
The industry refuses to pay all the costs of the operation, while the Jura government wants financial guarantees before it gives the green light for the project.
The plan is to remove all the chemical waste, plus another 36,000 tons of contaminated soil.
The waste would be treated and then incinerated, mainly in Germany. The operation is expected to cost SFr280 million ($216 million).
Environmental groups have criticised the chemical industry for not taking the project seriously enough.
swissinfo with agencies
The Bonfol site was used from 1961 to 1975 by the Basel chemical industry, which dumped 114,000 metric tons of toxic waste there.
In 2000 the Jura cantonal authority called for the clean-up of the site.
The operation is expected to cost SFr280 million ($216 million).