17 June 2022

Tracking microplastics with spiderwebs

Researchers at the University of Oldenburg, Germany, are investigating if they can track plastic particles in urban air by examining cobwebs.

© George Rosema

On inner-city streets with varying levels of traffic, they have found mainly the plastic PET, they believe from textiles, as well as particles from the abrasion of car tyres and polyvinyl chloride (PVC). The amounts of plastic particles found depend on the location.

Spider webs, the team concludes, are a simple and inexpensive means of monitoring air pollution by microplastics in the city and identifying particularly polluted areas. 

'Their sticky webs are an ideal trap for anything that floats through the air,' explains Dr Barbara Scholz-Böttcher. Previous studies have shown that pollutants such as heavy metals or magnetic particles get stuck in the webs, she adds. 'however, no one has yet examined spider webs for microplastics'.

To find out whether microplastics can be detected in spider webs and whether there are certain distribution patterns, Rebecca Süßmuth, Student of Environmental Sciences, has collected spider webs from the upper area of semi-covered bus stops at different times for her thesis.

The bus stops are located along roads with different levels of traffic in the city of Oldenburg in north-western Germany. The samples have been prepared in the laboratory and the particles adhering to the webs are concentrated on filters.

The team has examined the filters microscopically and found, for example, fibres presumably stemming from textiles, as well as soot particles. They have then heated the samples at very high temperatures in the absence of oxygen (pyrolysis) and separated the resulting plastic fragments using a gas chromatograph. A downstream mass spectrometer makes it possible to assign and determine the different types of plastic.

'All the spider webs were contaminated with microplastics,' reports Isabel Goßmann, who was involved in the study as part of her PhD-thesis. In some cases, the plastic content accounts for a tenth of the total weight of a web. Almost 90 per cent of the plastic consisted of PET (polyethylene terephthalate), PVC and material from car tyres. The proportion of tyre debris varies greatly – depending on the traffic on the adjacent road.

'Our results also indicate that the abrasion of road markings is another important source contributing to the microplastic load along roads,' adds Scholz-Böttcher. 

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