A UN report on the incident, released on Wednesday, showed at least 15 people died and thousands were sickened from the waste.
"We still don't know, and we may never know, the full effect of the dumping," said Okechukwu Ibeanu, an independent human rights expert for the UN.
"But there seems to be strong prima facie evidence that the reported deaths and adverse health consequences are related to the dumping of the waste," Probo Koala, he added.
Trafigura, the world's third-largest independent oil trader, said it has "always maintained that the Probo Koala's slops could not possibly have caused deaths and serious or long-term injuries".
It also denied any liability for "events that occured in the Ivory Coast".
The National Federation of Victims of Toxic Waste, an Ivorian group, has said the offer of compensation offer did not go far enough.
Denis Titira Yao, president of the group, said: "They are talking about over 30,000 victims, but for us there are more than that.
"We also need a long-term resolution because there is still waste in Abidjan that has not been removed and there are zones that still need cleaning up."
Trafigura, a Dutch based company, agreed to an $198m out-of-court settlement
with the Ivory Coast government in 2007, which exempts it from legal proceedings in the West African country.