UNEP calls for ‘targeted solutions’ to reducing microplastics in soils

Yesterday (1 August), the United Nations Environment Programme (UNEP) released its Foresight Brief detailing the increasing problem of plastics in agriculture practices.

green shoots in soil

Plastics in agriculture – an environmental challenge is designed to introduce specific issues concerning climate change to a general public audience. The document explores the ongoing problem of soil pollution – caused by plastics use agricultural practices – and the impact this has on the environment and food security.

According to the body, such contamination seriously impacts the health and productivity of soil, thus impacting the quality and quantity of food grown. Research is referred to demonstrating the impact on soil health, biodiversity, and productivity a presence of plastics in soil has.

Plastics entering agricultural fields often end up entering nearby ecosystems, UNEP notes. Caused by surface run-off, erosion, or by natural vegetation moving plastics further into the soil through tunnels created by earthworms, these plastics begin to contaminate areas external soil sites and waterways, threatening the environment overall.

Contributors of plastic pollution in soil

Despite limited research on the impact of plastics on soil, the report highlights, it is apparent how microplastics can change soil properties. In particular, microbial communities, soil invertebrates, and soil physio-chemical properties are at risk from microplastics in soil. Microplastics can also decrease the number, diversity, movement, and rate of reproduction of biota; decrease biomass of soil fauna; increase the biomass of microbes; and increase microbial activity, according to research from the Bulletin of Environmental Contamination and Toxicology.

Nevertheless, wider research suggests that as the colour, texture, chemical composition, surface characteristics and sorption capacities of microplastics change over time, they may become more efficient in absorbing other soil contaminants such as heavy metals and organic pollutants, exposing less contaminants to soil biota and plants.

The report further underscores the use of biosolids, derived from sewage sludge from wastewater treatment plants (WWTPs), as a big contributor of microplastics into soil. With high usage in Australia, North America, the EU, and the UK – each using 40-75 per cent of biosolids as fertiliser – it is estimated that the annual input of microplastics to agricultural land in Europe and North America could exceed the amount of microplastics estimated to be in surface waters in the global ocean.

Looking at other causes of soil pollution, the report shifts focus to biodegradable plastics. Despite their ability to decompose in the environment, the UNEP says, they often are not able to in soil because the lack of required conditions, including light, oxygen, moisture, and microorganisms, are not present in the soil.

Beyond this, the report adds that biodegradable surface plastics like mulch films are frequently swept off of soil by wind or surface run-off to more atmospheric or aquatic landscapes where they do not have the conditions to decompose, becoming as polluting as non-biodegradable plastics.

Recommendations moving forward

Reflecting on its findings, UNEP details forward solutions to reducing the amount of plastic entering the environment through these practices. First, while highlighting difficulties caused by the variety of composition and size of polluting plastics, it points to efforts to reduce plastic content in sewage sludge coming from WWTPs. For example, the introduction of filters into washing machines to prevent the leakage of microplastics from textiles entering municipal water streams.

However, this is not a standard yet adopted by washing machine manufacturers, and there is little targeted research investigating the removal of microplastics from sewage sludge. Despite this, new research into ultrasound in moving microplastics from sludge before it is used in agriculture gives more promise, resulting in a removal of nearly 40 per cent of polyethylene microspheres

Second, the report divulges into the work being done to improve the biodegradability of polymers used in agricultural products. An example of this research is a sprayable biodegradable polymer membrane to be used as mulch film, formulated from seaweed, sugar cane, or leather.

The report also considers the use of waste products from timber and agricultural industries to produce bio-based polymers for seed coatings. This would reduce the amount of food resources, such as corn or sugar cane, used to create more expensive biodegradable alternatives. Controlled release fertilisers (CRFs), formed from polylactic acid (PLA), okara (soy pulp), linseed, polyurea and corn starch hydrogel, is another alternative for plastic seed coatings.

Third, the brief explores nature-positive approaches, like natural mulch cover crops, to reduce plastic contamination in soils. Looking at this solution, it is emphasised that specific information and training would be needed for a widespread introduction of this. This option could also lead to a reduction in yields and increased cost for the producer.

Overall, alternative solutions to the use of plastics in food production is a hard sell, due to the cost effectiveness and ease-of-use plastics provide. UNEP suggests government incentives and levies on un-sustainable practices as two optional ways interdisciplinary organisations can create positive change in agriculture practices.

Specifically, the body recommends introducing standards for the use of sewage sludge-derived biosolids, manufacturing changes to reduce the use of plastic in agricultural products, and the education of consumers on textile choices to prevent plastic leakage from municipal water.

The foresight brief echoes a report previously shared by the UN Food and Agriculture Organisation (FAO), published in December 2021, detailing the implication of agricultural plastics on food security, human health, and the environment.

Sharing concerns explored in the brief, the FAO report exposes many problems linked to the presence of plastics in agriculture, causing reduced yields, harming wildlife through indigestion, and the dispersal of pathogens and toxic chemicals in oceans.

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