Microplastics are found in the soil of farms used to grow crops, reducing its quality, according to an analysis of six strawberry farms in California.
Plastics are used regularly in industrial agriculture, such as in irrigation pipes or the sheets that cover crops. Many studies have shown that small fragments of plastic, known as microplastics, are widespread in the environment, including on farms, but the effect this might have on soil isn’t well understood.
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Microplastic fibres affect plants by impacting soil as much as drought
“Microplastics might impair the soil’s properties, they might disintegrate and further leach into the groundwater system, and they can also interact with other existing co-contaminants in the environment, but we really don’t have much data about these things yet,” Ekta Tiwari at the California Polytechnic State University told the Goldschmidt geochemistry conference in Lyon, France, on 10 July.
To learn more, Tiwari and her colleagues took soil samples from 20 strawberry fields across six Californian farms and examined each for microplastics, which measure between 1 and 5 millimetres across. They then compared this to health indicators for the soil, such as its moisture content, its level of nutrients like nitrogen and its respiration rate, a measure of how much carbon dioxide microbes give off as they turn oxygen into energy, a proxy for soil microbial activity.
The team found that higher microplastic levels are closely linked with lower levels of soil moisture, nutrients and respiration. Each of these could lead to a reduced growth rate for plants and smaller fruit when they come to be harvested.
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In another part of the experiment, the researchers looked for larger pieces of plastic debris – macroplastics, measuring more than 5 millimetres across – across the fields, which they analysed to determine where the microplastics were coming from. The macroplastics that are most commonly used in farming – polyethylene, polypropylene and PVC – were also the main microplastics. “We found a huge number of plastic particles, which exceeded more than 200,000 macroplastic particles per hectare,” said Tiwari.
While previous studies have looked at microplastics in soil, the scale of this work was much larger, says Kip Solomon at the University of Utah. “It’s something we’ve been wondering about for quite some time.”
