Photo of an iron oxide sphere taken with the electron microscope. Image: Rachel Housen, Whatcom Middle School / Bellingham High School.
How high the pollutant load of the air is, can be determined by a magnetic examination of the leaves of road trees. To this conclusion, American researchers have come. They compared leaf samples from trees along busy roads with those of quieter back roads and those collected in more rural areas. The inner-city leaves proved to be up to ten times more magnetic than the land-based counterparts. High levels of pollutants in the air are literally reflected on the leaves of the trees. Especially when braking, the abrasion causes, among other things, the release of the finest metal particles, which are deposited on the leaves of road trees or even penetrate them. Buses are among the main causes. The researchers' theory: The more traffic there is, the greater the air pollution and the more magnetic the blades would have to be.

To test this theory, they collected leaf samples from the trees of the broadleaf maple tree (Acer macrophyllum) once in July, once in August and once in September. They also compared roads with different levels of traffic: an arterial road, a quieter parallel street where no buses drove, and a rural road.

The leaves of major roads were up to eight times more magnetic than those of the quieter back roads and even up to ten times more magnetic than the leaves of the land. Leaf samples as bioindicators therefore provide simple and quick information about the tendency of pollutants to be polluted on roads. This could, for example, be helpful in the planning and coordination of bike paths and bus routes: since people also inhale the particles, whereby they reach the lungs, it makes sense to guide cycle paths through streets with the least possible load.

Bernie Housen and Luigi Jovane: Lecture at the Annual Meeting of the American Geological Society (GSA) in Portland. ddp / science.de - Mascha Schacht advertisement

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