Plastics in agricultural soils

The negative impact of plastic in aquatic ecosystems has been observed by science and the public for some time. From images of plastic whirlpools in the ocean to findings of microplastics in marine life. The discussion regarding the impact on plants, animals and humans is omnipresent.

But plastic can now also be found in our agricultural soils. NABU estimates that total plastic emissions to agricultural soils amount to min 19,055 tonnes per year, of which about 19 % are attributable to the agricultural sector itself. The majority of this, just under 70 %, is introduced into the soil through components in fertilisers. The rest is generated by soil improvement, plant protection products and seeds, as well as plastics in fodder production, plant aids and containers and irrigation systems.

The remaining 81 % of total emissions are not attributed to agriculture, although just over half of them are caused by the application of sewage sludge, a practice for which agriculture is responsible. A further 38 % are attributable to littering. The remaining 8 % are caused by misthrow in composts.

While the impacts of plastics in oceans and rivers are being intensively researched, there are still gaps in the assessment of terrestrial ecosystems. However, according to current knowledge, the impact of plastics can already be roughly estimated.

Plastics in soil can change the physical properties such as storage density, pore volume and water content of soil and thus have an influence on its ecosystem function. The influence essentially depends on the size of the plastic particles. For example, small particles can result in better soil aeration and larger plastic fibres can lead to channel formation, i.e. to increased water transport and thus to soil drying. Studies also show an influence on the pH value and changes in chemical soil properties due to the leaching of additives and plastics. As already observed in water bodies, microplastics accumulate pollutants on the surface and could thus also lead to increased pollutant transport in soil and groundwater. More detailed research in this regard is still pending.

In addition to this indirect toxicity through pollutants, direct toxicity can also be assumed. The particles can cause damage to tissue and membranes of organisms. Nanoparticles, which can pass through cell walls and be taken up by plant roots due to their small size of 50-100 nm, pose a particular risk. The respective effect depends on the type of plastic.

Larger soil organisms such as earthworms and other animals in the soil also take up microplastics directly or through the food chain. There are indications of impairment of vitality, enzyme activity and the growth and immune system of the organisms. An influence on humans through consumption of polluted plants or animal products polluted by animal feed is conceivable and requires further research.

To reduce plastic emissions, educational initiatives are needed in agriculture to increase recycling rates or to replace conventional plastics with more degradable materials. There is also a need to develop suitable measurement methods to check the respective soil contamination. Also on the part of the law, there can be further specifications and tightening of the limits for plastics as foreign components, as well as a limitation of the degradation time for plastic applications in the environment. NABU also calls for a limit on the application of sewage sludge.

Further information can be found in the report by the Fraunhofer Institute for Environmental, Safety and Energy Technology UMSICHT and Ökopol on behalf of the German Nature and Biodiversity Conservation Union NABU.

In any case, plastics in soils are a burden on our ecosystem that has received too little attention so far. The MuP Group will therefore focus more on this area in future in order to make a further contribution to a healthy environment. Engineering for a better tomorrow.

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