Highways increase cancer risk in children

Greater risk of leukemia due to traffic emissions in residential areas next to roads with heavy traffic

At places of residence directly next to a motorway, pollution levels are much higher - and for children, the leukemia risk also increases significantly. © thinkstock / zhudifeng
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Sick with exhaust fumes: Children living near motorways or major roads are up to twice as likely to develop leukemia. Cause are probably carcinogenic substances in the traffic exhausts, my doctors from Switzerland. The youngest among the children are particularly vulnerable, the researchers warn, and just a few hundred meters distance to the road can be decisive.

Children are relatively less likely to develop cancer than adults. Nevertheless, there are more than 1, 500 cases of cancer among children under the age of 15 every year in Germany. The most common type of cancer that occurs in children is leukemia. The causes at this young age are largely unknown: unlike adults, long-term risk factors such as smoking do not yet have an effect. In addition to a certain genetic predisposition, the young cancer patients in particular suspect various environmental factors as triggers.

Leukemia due to exhaust gases depending on place of residence

One of these possible factors is air pollution from car exhaust gases: they contain benzene and other substances known to cause cancer. Physicians led by Ben Spycher of the University of Bern wanted to check whether traffic exhaust gases increase the leukemia risk in children. For this purpose, the scientists compared the data of over two million children from the Swiss census of 1990 and 2000 with figures from the Swiss Childhood Cancer Registry from 1985 to 2008. This register covers all cases of cancer in children under the age of 16.

The homes of the children were known in almost all cases, so that the researchers could also include the proximity to busy roads. They divided the places of residence into different distance groups: less than 100 meters, 100 to 250 meters, 250 to 500 meters and over 500 meters from the nearest motorway or major road. Then the researchers compared the leukemia frequency in the various distance categories.

Much higher risk in less than 100 meters to the street

The figures showed a significantly higher risk of leukemia in children living less than 100 meters from the nearest street: Compared with children living more than half a kilometer from the nearest highway, the risk increased by 47 percent. During the observation period, "only" 30 children actually had leukemia, says study leader Claudia Kuehni from the Swiss Childhood Cancer Registry. However, the differences are statistically significant despite the small number of cases. display

This was verified by the researchers based on the two years covered by the census and extrapolated for the entire period covered by the Childhood Cancer Registry: they estimated how many "person-years" All children living in Switzerland lived through the different distance groups between 1985 and 2008. For each lived calendar year, a child contributes a person-year.

Special danger for toddlers

After this estimate, there was even a 57% higher risk of leukemia in children living close to a busy street. This second method is less precise due to the lack of data before and after the census, but more than twice as many cases of cancer.

According to the data, the youngest children are particularly hard hit: Breakdown by age group showed the highest risk of cancer in newborns and children under the age of four. "In this age group, the leukemia risk at a place of residence within 100 meters of a highway was about twice as high as a distance of the apartment of 500 meters or more, " says first author Spycher.

Leukemia trigger benzene

For the other distance categories as well as for other cancers, such as brain tumors and lymphomas, the researchers found no clear evidence of an increased risk. The fact that only the risk of leucosis increases could, according to the authors, point to benzene as a possible cause. It is already known that high levels of benzene in the workplace can trigger leukemia in adults.

Although traffic pollution levels have declined significantly in recent years due to stricter regulations, the authors say. However, in the immediate vicinity of busy roads such as highways, the pollutant concentrations in the air are still greatly increased, but they drop rapidly within a few hundred meters.

Radiation and high voltage lines are eliminated

However, these few hundred meters make a decisive difference to cancer risk. "Several studies from other countries also found evidence of increased leukemia risk in children growing up near busy roads, " adds Kuehni.

The doctors also examined whether their results could possibly be explained by other factors. Therefore, they examined socio-economic differences, ionizing background radiation or the distance to power lines as possible causes.

However, these factors did not influence the results, Kuehni summarizes: "Overall, the results do suggest that air pollution from traffic may increase the risk of childhood leukemia, especially in infancy." (European Journal of Epidemiology, 2015; doi: 10.1007 / s10654-015-0091-9)

(University of Bern, 04.11.2015 - AKR)