PARIS - It is a new stain on the already tarnished reputation of biofuels. After being accused of aggravating food insecurity and driving up food prices, accelerating tropical deforestation and even increasing greenhouse gas emissions, crop-based biofuels are now being accused of worsening air pollution and creating health problems.

The European Union’s target of 10% renewable energy in the transport sector by 2020 in order to reduce the effects of climate change, could in fact be aggravating ozone pollution and causing nearly 1,400 premature deaths every year, according to a new study published in the journal Nature Climate Change.

Researchers from England’s Lancaster University studied the production of wood-based energy and biofuel that is supposed to limit the use of polluting oil and coal.

In their case study, enough land area in Europe to meet the EU’s 2020 objectives – around 72 million hectares – was converted into short rotation coppice biofuel crops such as willow, poplar or eucalyptus trees in order to produce high amounts of ethanol.

These crops are characterized by high tree density (1500 to 3000 trees per hectare), in rotations of five to ten years and have high yields. They also have the characteristic of emitting higher levels of the chemical isoprene as they grow, than do the traditional crops they are replacing.

Isoprene is reactive volatile organic compound – that when mixed with other air pollutants (such as nitrogen oxide) produces toxic ozone, one of the most dangerous air pollutants.

Lung problems and premature deaths

This pollution can cause lung problems and affect the brain, kidneys and eyes, and is blamed for the deaths of about 22,000 people a year in Europe. The increase in isoprene emissions created by these new crops will lead, according to the study, to an extra 1,365 premature deaths per year, costing society $7.1 billion.

Another consequence: crop yields would be affected, since ozone impairs crop growth by reducing their gas exchange and chlorophyll. The study estimates that the production of wheat and maize would be reduced by 7.1 million tons (3.5% of current wheat crops) and 800,000 tons (1% of maize crops) each year, a loss of $1.5 billion.

"Growing biofuels is thought to be a good thing because it reduces the amount of carbon dioxide in the atmosphere," explains Nick Hewitt, one of the authors of the study. “Large-scale production of biofuels in Europe would have small but significant effects on human mortality and crop yields.”

The researchers suggest planting biofuel crops far away from population centers or zones of intense agricultural production with the aim of limiting ozone formation. Genetic engineering could be used to reduce isoprene emissions.

However, the study from the University of Lancaster did not compare the potential damage caused by biofuels to the impact on human health from producing coal, oil or natural gas. “We are not in a position to make that comparison,” said Hewitt. According the European Environmental Agency, overall air pollution, mainly from fossil fuels, causes around 500,000 premature deaths in Europe every year.

“‘There are many different biofuel crops, cultivation methods, production and processing systems post-harvest, and different final biofuels. Each one has advantages and disadvantages, which must be compared to the advantages and disadvantages of alternative options,” explains Professor Ottoline Leyser, Director of the Sainsbury Laboratory of the University of Cambridge.

Dr Angela Karp, Scientific Director for the Rothamsted Research Center says that ““Land use calculations of impacts for willows and poplars need to consider that they are among many biofuels crops being grown (most of which are not trees but grasses) and take into consideration the large land areas already under forests. For all these reasons we do not see that the UK needs to reconsider its interest in biofuels.”