When ethanol prices at the pump rise, it becomes economically advantageous for drivers of dual-fuel vehicles to fill up with gasoline. But research indicates it’s a shift that is not good for the community’s health.

A study in Sao Paulo, Brazil, finds the substitution of gasoline for ethanol leads to a 30% increase in the atmospheric concentration of ultrafine particulate matter – particles with a diameter of less than 50 nanometers.

Paulo Artaxo of the University of Sao Paulo’s Physics Institute, co-author of the study published in the journal Nature Communications, says the polluting nanoparticles are so tiny they behave like gas molecules.

“When inhaled, they can penetrate the respiratory system’s defensive barriers and reach the pulmonary alveoli, so that potentially toxic substances enter the bloodstream and may increase the incidence of respiratory and cardiovascular problems,” he says in a statement.

Artaxo says between 75% and 80% of the mass of nanoparticles measured in the study corresponds to organic compounds – carbon in different forms – emitted by motor vehicles.

Levels of ultrafine particulate matter in the atmosphere are neither monitored nor regulated by environmental agencies, not only in Brazil but practically anywhere in the world, he says.

“What these compounds are exactly and how they affect health are questions that require further research.”

Artaxo says a consensus is forming in the U.S. and Europe based on recent research indicating these emissions are a potential health hazard and should be regulated.

Several U.S. states, including California, have laws requiring a 20%-30% ethanol blend in gasoline, which helps reduce emissions of ultrafine particulate matter.

Artaxo says data collection for his research was gathered from January to May 2011, and the analyses were conducted before, during and after a sharp fluctuation in ethanol prices – caused by factors such as the international price of sugar – leading consumers to switch motor fuels in Sao Paulo.

“These results reinforce the need for public policies to encourage the use of biofuels, as they clearly show that the public loses in health what they save at the pump when opting for gasoline,” he says.

In Sao Paulo, a city with 7 million motor vehicles and the largest urban fleet of flexible-fuel cars, Artaxo says incentives for electric, hybrid or biofuel vehicles are vital to reducing greenhouse-gas emissions.

“By incentivizing biofuels, we could solve several problems at once,” he says. “We could combat climate change, reduce harm to health and foster advances in automotive technology by offering a stimulus for automakers to develop more economical and efficient cars fueled by ethanol.”