Assessing impact of plastic use in agricultural soil
Research into the existence of microplastics in the soil is relatively new. While awareness of the issue is growing, our knowledge about the amount of plastic, where it is, and what it is doing to our environment and our health, is still limited. “One reason for this is the challenge of actually measuring microplastics in soil,” explains SOPLAS(opens in new window) project coordinator Peter Fiener from the University of Augsburg(opens in new window) in Germany. “If you want to examine microplastics in water, you might use a net dragged by boat to collect samples, or pump water over a filter. Collecting and analysing microplastics from a cubic metre of soil is much more difficult.”
Determining the plastic content of soil
The EU-funded SOPLAS project, supported by the Marie Skłodowska-Curie Actions(opens in new window) programme, sought to address this by training up 14 early-stage researchers (ESRs). One key area of research was to pioneer new methods for determining the plastic content of soil. “To measure microplastics, you need to get plastic particles out of the soil matrix,” says Fiener. “In 100 g of soil, there might be billions of particles, but only maybe 100 particles of microplastic.” Another issue is that microplastics in soil can be highly variable. To get an accurate picture of the microplastic soil contamination of an individual field requires a large number of sampling points. To address this, new and efficient methodologies were partly developed within several ESR projects. “This work is only just starting,” adds Fiener.
Biodegradable plastic impact on agricultural land
Groups of ESRs also looked at how plastic enters the soil, in part through running trials at commercial compost facilities. Biodegradable plastic was also tested to assess its biodegradability. “One thing we found was that biodegradable plastic does not always biodegrade within the compost facilities,” says Fiener. Researchers also tested biodegradable mulch films on fields, to see if they have an impact on water run-off and erosion. As expected, plastic that had not degraded had an adverse impact. Remote sensing and AI were also used to try to more accurately estimate the use and spatial distribution of plastic film on agricultural land in Germany. “We also looked into the ecotoxicology of different plastic types on animals such as earthworms,” notes Fiener. “This was a very tricky thing to do; on the one hand, you want to assess the impact of microplastics on animals, but you also don’t want to exaggerate natural conditions.”
Measuring health and ecological impacts
Fiener believes that important advances have been made in this emerging field of study, thanks in part to the multidisciplinary nature of the project. One ESR for example focused on the socio-economic elements of plastic use in agriculture. “We were able to measure some of the effects of microplastics in soil, and develop new techniques to do so,” he remarks. “The main success for me though has been the training up of 14 PhD students. Microplastic research in general is a complex area of work, and they were on a very steep learning curve.” A great deal is to be discovered in terms of health and ecological impacts. “We are still a long way from accurately knowing just how much microplastic is in our soil,” concludes Fiener.
