Photo credit: Canva
There is an increasing body of evidence demonstrating that plastics are now ubiquitous across the biosphere, with micro-plastics now detectable in even the remotest of environments. Micro-plastics are present in deep oceans, polar ice-caps, and agricultural soils across the world, whilst nano-plastics have even been found in the tissues and fruits of food-crops. Micro-plastics (plastic pieces under 5 millimetres (mm) in size), and nano-plastics (plastic particles under 1 micrometre (μm)) are pervasive globally. These micro- and nano-plastics are the result of the breakdown and shedding of plastic objects including machinery, vehicles and synthetic fabrics, or intentionally created and added to products such as paints, cosmetics and toothpastes.
Microplastics are inside us.
Research has found that micro-plastics, including nano-plastics, are routinely inhaled in dust in homes, workplaces and the wider environment, and ingested in our food and drink. Plastics have been found in shellfish, crop plant and animal tissues, and are known to migrate up the food chain. Micro-plastics have now been found in the urine, blood, placentas, and deep in the lung tissue of living people. Studies in mice have demonstrated that exposure to micro-plastics can cause them to accumulate in living tissues.
These new and potentially alarming findings lead to urgent questions around what, if any, the impacts on human health might be.
Photo credit: Canva
Our UK team has recently finished sampling agricultural fields for plastics large and small as part of the MINAGRIS project. During this time, it has become increasingly clear that we have a compost problem.
Municipal compost is made with our kitchen countertop and garden green waste collections. When it first arrived at scale as an option for farmers to apply this valuable source of organic matter to their fields and boost their soil carbon, it seemed like a win-win. It had the potential to bring otherwise wasted nutrients back into the food system, saving them from stinking out our bins before ending up in landfill or an incinerator. This was a bold shift towards a more circular economy, which had the potential to be great for soils and farm profitability.
The problem is the high plastic content. Farmers and growers initially eager to make use of this black gold to improve their soil health quickly realised that the plastic content of municipal compost was so high that they were no longer happy putting it on their land. This came up repeatedly in our farmer interviews and whilst we were sampling. Our initial enquiries indicate that this seems to be a widespread understanding within the farming and market gardening communities, not just in the UK but Europe-wide.
Read more: Farmers give up using municipal compost due to high plastic content.
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.
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| 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).
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| 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).
This video, filmed by Marina Pintar whilst on holiday in Croatia, shows an ant colony carrying plastic debris across an agricultural field. MINAGRIS will strive to assess the environmental implications of having these plastics present in soils across Europe. Watch this video to find out.
