MINAGRIS, over the next 5 years, will explore the impacts of plastic debris on agricultural soil health. This blog explains what plastics are, the extent to which they are used in agriculture across Europe, and the potential environmental health threats posed by plastic debris in soil.

Photo credits: Plastics Europe, Wageningen Food & Biobased research, Tuinadvies, Kalliergeia, Future Farming, Teal Agrotechnologies

What are plastics?

Plastics consist of one or more polymer types. Polymers are chains of molecules, usually containing carbon. These polymers can be fossil-based or biobased. Fossil-based plastics are typically made from petroleum, whilst biobased plastics are made entirely, or partially, from renewable plant-based products including vegetable oils, corn starch, and even sawdust. You can learn more about biobased plastics via the European bioplastics website and this booklet.

Picture source: European bioplastics		Plastic mulches are used to control weeds, for temperature control, and to prevent moisture loss (picture credit: MINAGRIS project)

What are ‘biodegradable’ plastics?

Since the increase in public awareness surrounding the pollution caused by plastics, there has been a rise in the use of ‘biodegradable’ and ‘biobased’ plastics. These terms are often used interchangeably but mean different things. Biodegradable plastics are those which naturally break down due to microorganism (bacteria or fungi) activity over time, creating water and naturally occurring gases like carbon dioxide (CO₂), methane (CH₄), and biomass (e.g., due to microorganism population growth).

Not all biodegradable plastics are biobased, as some fossil-based polymers can also be biodegradable. Biodegradability is determined by the chemistry of the polymer, but also depends on environmental conditions: temperature, presence of microorganisms, presence of oxygen and water. The biodegradability and the degradation rate of a biodegradable plastic may, therefore, be different within and on soil, in humid or dry climates, surface waters, marine waters, or in human made systems like home composting, industrial composting or anaerobic digestion. Certification schemes are used to verify whether a plastics’ biodegradability is sufficient for claiming a particular end-of-life duration.

Plastic use in agriculture

A wide range of products which contain plastics are used in farming. These include greenhouses and their components, polytunnels, mulches used for pest control, plastic reservoirs, irrigation systems, materials for transporting produce (e.g., boxes), various nets (e.g., anti-bird), packaging (e.g., agrochemical cans), and nursery pots. Wear and tear of these products can be a source of plastic debris in soil. There are also unintentional sources of plastic debris in agriculture, including feed silage, compost and manure fertilisers, litter, and irrigation water, all of which may contain microplastics.

Demand for plastic-based products in agriculture is high.  A recent report by EIP-AGRI estimated that around 708,000 tonnes of plastics were used in EU agriculture in 2019 alone (see infographics below).

Source: EIP-Agri (2021)		Source: Plastics, the facts (2020) Plastics Europe

 Why are microplastics in agricultural soil concerning?

The environmental health implications of plastic debris in agricultural soils are largely unknown but there have been some studies which have already found that they may be profound.

Microplastic contamination of soils is increasingly being documented, with researchers finding that various types of plastic debris affect several aspects of soil health (see figure below).

Picture credit: Machado et al (2018)

A recent study found that microplastics originating from the soil, water or air are often detected in honeybees and stated that further research is needed to understand whether this presence can be considered a threat to bee health and survival. One aspect of the MINAGRIS project will be to determine whether micro- and nano-plastics accumulate in the gut of bees or whether they are excreted; if they accumulate, this may be having a profound impact on bee health.

Another study found that exposure to microplastics affects the gut microbiota of springtails (Collembola). As these species are at the bottom of the food web, this may have negative effects on other species higher up the food chain, particularly as these species have mutually beneficial (or symbiotic) relationships with other species.

Introducing MINAGRIS

MINAGRIS, over the next 5 years, is going to assess the impact of plastic debris in agricultural soils on biodiversity, plant productivity and ecosystem services and their transport and degradation in the environment. We will provide tools and recommendations for sustainable use of plastic in agriculture at the farm and field levels for ensuring safe and economically viable food systems in Europe.

This blog was written by Dr Charlotte Chivers (CCRI) and Maarten van der Zee (WUR).