More than 4,000 tonnes of waste and top soil left on Friday to travel back to Taiwan.

The BBC's Caroline Gluck: "There is immense relief that the waste has left the country"

The waste, which contains high levels of mercury, was illegally dumped near the popular coastal resort of Sihanoukville in December by Taiwanese petrochemical giant Formosa Plastics.

Its discovery and the subsequent death of a dock worker who handled it sparked hysteria and rioting.

Four people were killed in traffic accidents as thousands of residents fled the province.

A container of waste is loaded for shipment

A sixth death - of a man who rummaged through the waste - has also been linked to the dumping, but environmental officials seeking compensation from Formosa say they have no evidence connecting any deaths directly to the waste.

The waste, which weighs nearly 3,000 tonnes without the topsoil, had been due to be moved from Cambodia to be disposed of in Westmoreland, California, in the US.

But the US Environmental Protection Agency (EPA) rescinded approval of its import after learning that its toxicity may exceed US safety standards.

The California-based disposal company Safety-Kleen Corp. had told the EPA that the mercury content of the waste was below the safety standards.

But in a statement it said that the waste was "more complex than initially believed".

Question remains

"Formosa Plastics Corporation has made the decision to move the material back to Taiwan where it can be segregated and thoroughly analysed", the statement said.

Although the waste has now left Cambodia, the question of how it was allowed into the country in the first place remains unresolved.

Cambodians are relieved the waste has gone

There is growing frustration at the government's apparent reluctance now to pursue legal action against Formosa Plastics for compensation.

Senior government officials have alleged that up to three million dollars in bribes may have been paid to corrupt officials to allow the waste into Cambodia.

More than 100 government officials were suspended from their posts following the incident, but only three have been charged with endangering human life, property and the environment.

The head of a Cambodian import company, two Taiwanese men and their interpreter, have also been charged.

Formosa Plastics has apologised to Cambodia, but has refused to accept responsibility or pay compensation.

Environmental 'victory'

It continues to maintain that the waste posed no threat to human health.

Environmental activists in California have welcomed the EPA's decision not to allow the waste to be imported.

Bradley Angel of environmental organisation Greenaction said: "This is an enormous victory for health and environmental justice, and a big defeat for Safety-Kleen and Formosa Plastics who had hoped to turn tiny Westmoreland into an international toxic dump."