Greenpeace's Arctic Sunrise blocked the Probo Koala for three days. ©Christian Aslund/Greenpeace

"It is shocking that toxic waste from Europe reached the Ivory Coast causing so much human suffering and damage to the environment," Dimas said.

The cases is a "clear violation of European and international law with deadly results," Dimas said, who urged EU member states to ensure "that criminal cases like this will not go unnoticed and will not be repeated in the future."

Estonian officials detained the ship on Wednesday and launched a criminal investigation based on suspicions the crew of the Panamanian-registered ship tried to dump waste into the port of Paldiski without permission.

Test results from the ship showed traces of "environmentally dangerous, poisonous chemicals," according to a statement by Estonia's state prosecutor's office.

The ship, called the Probo Koala, will remain at the Paldiski port "as long as the proceedings require," the statement said.

The impoundment of the ship was requested by a judge heading the Ivorian government's investigation into the toxic waste scandal and by Greenpeace, which used one of its own ships to block the Probo Koala on Tuesday.

Estonian officials said their inquiry was not related to the Ivorian investigation. Dutch authorities are also investigating an alleged attempt by the ship to unload the waste in Amsterdam in July.

The toxic waste scandal that first came to light in early September, nearly two weeks after the tanker delivered 400 metric tons of petrochemical waste to the Ivorian port city of Abidjan.

The waste, which contained a mixture of gasoline, water and caustic washings, was unloaded in Abidjan on August 19 and then dumped in open air sites throughout the densely populated city. Fumes from the waste have killed eight people, including four children, and forced more than 75,000 individuals to seek medical treatment for intestinal and respiratory ailments, including vomiting, nausea and nose bleeds.

Although Trafigura contends the waste consisted largely of gasoline residue and caustic washings, tests have shown it contains hydrogen sulfide, a poisonous gas that smells like rotten eggs.

Two Trafigura executives have been arrested by Ivorian authorities in connection with the tragedy. The company has denied any wrongdoing and contends it informed port authorities of the shipment and had a legitimate contract with an Ivorian company to legally dispose of the waste. Two owners of the Ivorian company have also been arrested along with six officials who oversee customs and operations.

The toxic waste crisis prompted the Ivory Coast's prime minister to dissolve his 32-member cabinet and the city has been rocked by protests over the government's handling of the tragedy. Angry residents set fire to the home of the Abidjan port director and attacked the country's transport minister.

A French firm began clean up of the waste more some 10 days ago and has said the waste will be shipped to France for disposal next month.

At the request of the Ivory Coast, the United Nations Environmental Program is also investigating reports that the toxic waste may have been illegally exported.

Under the terms of the 1989 international hazardous waste treaty, known as the Basel Convention, any nation exporting hazardous waste must obtain prior written permission from the importing country, as well as a permit detailing the contents and destination of the waste.

If the waste has been transferred illegally, the exporter is obliged to take back the waste and pay the costs of any damages and clean-up process.

But the accord does not prohibit waste exports to any location except Antarctica and several parties to the convention were quickly convinced it did not go far enough. In 1995, an amendment to the treaty was established to prohibit waste exports from developed nations to the rest of the world - this ban applies export of hazardous waste, even recycling.

The amendment has been implemented in the European Union, but has not entered into force globally. A long list of countries has failed to ratify the treaty, including wealthy nations who oppose the ban, such as the United States, Canada and Australia. Developing countries, including India, Pakistan, Bangladesh, Philippines, and the Ivory Coast have also not approved the amendment.

Environmentalists say the events Abidjan are a sad reminder that the Basel Convention has failed to stem the dumping of waste in the 3rd world.

"Its time the Basel Convention Parties once and for all agree to an interpretation that puts this much needed ban into the force of international law," said Jim Puckett, a hazardous waste trade expert with the Basel Action Network (BAN). "There can be no excuse not to accomplish this at the first opportunity and how fitting it will be to do so in the first ever Basel meeting to take place in Africa this November."

BAN also called for the Dutch government to accept responsibility for the tragedy. The toxic waste watchdog said Dutch officials mistakenly allowed Trafigura to pump the suspect waste back on board the Probo Koala and then let it sail onward to other destinations and final export in Abidjan.

"It is sad but true that the tragedy that transpired in Africa could have been avoided had the Dutch done their job and stopped the criminal intentions of Trafigura early in the game," said Puckett. "Thankfully Trafigura is a Dutch company and the Dutch government can hopefully, while admitting the part they played in the scandal, seek justice from Trafigura through unyielding diligent prosecution."