If you're an urban cyclist, a new study reveals a dangerous side effect of this green mode of transport: you may be inhaling high levels of black soot.

The new University of London study found that urbanites who cycled to work had 2.3 times more black carbon in their lungs than pedestrians.

Black carbon is present in car exhaust fumes and is created by the combustion of fossil fuels. "Pedestrians breathe in these miniscule particles of soot, but bikers inhale even more because they are closer to the fumes and take deeper breaths," reported health website MyHealthDailyNews on the study on September 27.

"This could be due to a number of factors, including the fact that cyclists breathe more deeply and at a quicker rate than pedestrians while in closer proximity to exhaust fumes, which could increase the number of airborne particles penetrating the lungs," said study researcher Chinedu Nwokoro in a statement released this week.

But rather than give up cycling forever, Nwokoro stated that cyclists should plan less-trafficked routes to minimize their exposure to exhaust fumes.

Previous research has shown that black carbon is linked to a wide range of serious health issues, including reduced lung function and a higher risk of respiratory diseases and heart attacks, noted MyHealthDailyNews.

The study was presented at the European Respiratory Society's Annual Congress in Amsterdam on September 23.