Which particulate matter poses the greatest health risk?
Researchers at the Paul Scherrer Institute PSI, together with colleagues from several European institutions, have investigated whether particulate matter from certain sources can be particularly harmful to health. They found evidence that the amount of particulate matter alone is not the greatest health risk. Rather, it may be the so-called oxidative potential that makes particulate matter so harmful.
Particulate matter is one of the greatest health risks posed by air pollution and, according to estimates from several studies, is responsible for several million deaths every year. This makes poor air quality and particulate matter one of the five most important health risk factors alongside high blood pressure, smoking, diabetes and obesity. However, it is not yet known exactly what makes particulate matter so dangerous. Researchers at the Paul Scherrer Institute PSI have now discovered, as part of an international team, that the amount of particulate matter is not the only decisive factor when it comes to health risks.
Oxidative potential of particulate matter as a health risk
"We were particularly interested in two aspects of the study," says Kaspar Dällenbach from the Gas Phase and Aerosol Chemistry research group at PSI. "Firstly, which sources in Europe are responsible for the so-called oxidative potential of particulate matter, and secondly, whether the health risk of particulate matter is caused by its oxidative potential."
The oxidative potential of particulate matter is defined as its ability to break down antioxidants, which can lead to damage to body cells and tissue. In a first step, the researchers exposed cells from the human airways, known as bronchial epithelial cells, to particulate matter samples and examined their biological reaction. When the cells are under stress, they release a signaling substance for the immune system, which triggers inflammatory reactions in the body. The researchers were able to show that particulate matter with increased oxidative potential intensifies the inflammatory reaction of the cells. This suggests that the oxidative potential determines how harmful the particulate matter is. According to Dällenbach, the causal link between increased oxidative potential and a health risk has still not been clearly established. "However, the study is a further clear indication that this link does indeed exist."
A partner study led by the University of Bern showed that cells from patients suffering from a specific pre-existing disease, known as cystic fibrosis, have a weakened defense against particulate pollution. While an antioxidant defense mechanism was able to stop the progression of inflammatory reactions in healthy cells, the defense capacity in diseased cells was not sufficient. This led to increased cell mortality.
Where does particulate matter and its oxidative potential come from?
The researchers also collected particulate matter samples at various locations in Switzerland. They analyzed the composition of the particulate matter using a mass spectrometry technique developed at PSI. The resulting chemical profile of each particulate matter sample allows conclusions to be drawn about the source from which it originated. In addition, colleagues in Grenoble used the same samples to determine their oxidative potential in order to obtain an indication of their danger to health. Using detailed analyses and statistical methods, the researchers then determined the oxidative potential for all relevant emission sources. Based on this experimental data, they used a computer model to calculate the locations in Europe with the highest oxidative potential from particulate matter over the course of a year and identified conurbations such as the French capital Paris or the Po Valley in northern Italy as critical regions.
"Our results show that the oxidative potential of particulate matter and the amount of particulate matter are not determined by the same sources," summarizes Dällenbach. The majority of particulate matter consists of mineral dust and so-called secondary inorganic aerosols, such as ammonium nitrate and sulphate. The oxidative potential of particulate matter, on the other hand, is mainly determined by so-called anthropogenic secondary organic aerosols, which mainly originate from wood combustion, and metal emissions from brake and tire abrasion from road traffic. In addition, the researchers found that the population in urban areas is not only exposed to a higher amount of particulate matter, but that the particulate matter in these regions has a higher oxidative potential and is therefore more harmful to health than particulate matter in rural areas. "Our results show that regulating the amount of particulate matter alone may not be effective," says Dällenbach. The study by the University of Bern also suggests that population groups with pre-existing conditions could particularly benefit from appropriate measures to reduce particulate matter pollution.
