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Dutch Marine Police have carried out an inspection of ocean-going vessels at the port of Rotterdam in an attempt to clamp down on alleged illegal bunker fuel blending practices at the port.

"During three days, we checked whether 30 vessels had the correct documentation. In 12 cases, documents were forged, or the environmental law was violated," Hans Tuinder, head of the Criminal Investigation department for the Marine Police, told Xinhua.

The three-day inspection of ships follows a study conducted by independent research organisation CE Delft last year, which claimed that some ocean-going vessels has been bunkered with fuel oil contaminated with hazardous waste materials.

Fuel oil 'naturally' contains a variety of hazardous substances in high concentrations. These are substances present in the crude oil feedstock from which the fuel oil derives. They end up in a concentrated form in the residue during the refining process.

However, it is claimed that illegal practices are raising the level of hazardous substances in fuel oil. Instead of taking their waste material to a recognized waste processing company, some oil firms are said to have blended them into the fuel oil in order to substantially lower their costs.

"There is strong evidence that many [bunker] ships blend their waste material with heavy fuel oil. That is very lucrative for them because you not only don't need to pay for delivering your waste material, but also will even get paid for the blended oil," said Marine officer Tim Tichelaar.

The study showed that such practices not only cause serious damage to ship engines, but also pose health risks to staff members and residents in surrounding areas.

Speaking to Ximhua, Tichelaar said that due to the lack of relevant legislation it was extremely difficult to clamp down on these illegal activities.

"The law doesn't prescribe which waste materials are allowed in the fuel oil, so the only thing that is clearly prohibited is to blend the waste materials without the interference of an approved waste treatment plant," Tichelaar said.

Eelco Leemans, director of the North Sea Foundation, is said to have found it peculiar that the Dutch government does not organize a large-scale sample check to test the composition of the fuel.

"I think this is partly because the interests are too big. The authority of the port of Rotterdam is probably too scared that bunker vessels will turn to other harbors in Europe," he said.

Although some regulations do exist internationally, they are not satisfactory, said Leemans.

"The International Maritime Organization (IMO) has laid down standards for bunker fuel. But these standards only set maximum limits on fuel sulphur content, which is just a small part of the emitted particles of waste material," he added.

Currently, around 13 million tonnes of marine fuel are bunkered in Rottertdam on an annual basis with over 22,000 ships refuelling per annum. Rotterdam is the largest bunker port in Europe.