STOCKHOLM, Jan 16 (Reuters) - Rapeseed oil used as a green alternative to conventional vehicle fuels can produce 10 times more cancer-causing emissions and pollutants than diesel, a Swedish research report showed on Tuesday.

Rapeseed oil or rapeseed methyl ester (RME) had been considered one of the best alternatives among bio-diesels.

Its use as a green alternative was rising in Europe, especially in Germany, associate professor Jim Olsson at the Department of Physical Chemistry at Chalmers University of Technology in the southwestern city of Gothenburg told Reuters.

In the study, scientists burned rapeseed oil at temperatures equivalent to those in a combustion engine and compared the emissions with those formed when burning a superior grade of diesel oil, SEC1.

"Rapeseed oil and RME produced factor 10 more 1-alkenes, dienes and benzene in comparison with diesel SCE1,'' the report said.

"The reactive intermediate organic compounds produced during oxidation of rapeseed oil and RME have strong ozone-forming potentials. Subsequently they can promote formation of organic smog,'' it said.

Some of the rapeseed products such as alkene, 1.3 butadiene and benzene are also considered to be carcinogenic, it added.

"When it comes to alternative fuels people often advocate the advantages and overlook the disadvantages. I think this is a disadvantage which has been overlooked,'' Olsson said.

Somewhat lower and less dangerous emissions could be achieved if engines were optimised for rapeseed oil but this would only reduce, not eliminate, the disavantage compared with diesel, he said, adding: "People tend to use them (rapeseed oils) in ordinary diesel engines, and that is a problem.''