While all the attention is focused on the impacts that microplastics are having in our oceans, researchers say that most microplastics are accumulating on land, including in agricultural areas. An estimate by Environmental Science & Technology suggests that each year 107,000 to 730,000 tons of microplastics may be ending up on farmland in the US and Europe, compared to 93,000 to 236,000 tons entering the oceans.

In recent years, environmental experts and stakeholders have paid much attention to microplastic pollution in soil. As a persistent pollutant, microplastics have a significant impact on soil ecology, agricultural production and the overall health of the ecological environment. Microplastics can influence the biophysical-chemical properties of the soil and the mobility of other pollutants in the soil, with potentially important implications in the functionality of its ecosystem. Thus, functions including litter decomposition, soil accumulation, or those related to nutrient cycling may be altered. Furthermore, microplastics can affect soil biota at different trophic levels and even threaten human health through food chains. Most of the talk about plastic pollution focuses only on marine ecosystems, but according to a UN study the spotlight as turned on the risks it possesses in soil pollution.

Researchers from Germany are warning that the impacts of microplastics in soil, sediment and drinking water can have a negative and long-term impact on these ecosystems. They say that terrestrial microplastic pollution is much higher than marine pollution, ranging from 4 to 23 times higher depending on the environment.

Although very little research has been done in this aspect, they concluded that the results they have obtained so far are disturbing. Plastic fragments are present practically all over the world and can cause side effects. The study shows that ⅓ of all plastic waste ends up in soil or drinking water. Most of this plastic breaks down into particles smaller than 5 mm which break down into nanoplastics which are less than 0.1 in diameter.

A research done by Mary Beth Kirkham

A plant physiologist and professor of agronomy at Kansas State University has done research on microplastic pollution in soil. Her expertise is based on the relationships between plants, water and the absorption of heavy metals. She has cultivated some wheat plants exposed to microplastics alone, some exposed to cadmium alone, and plants exposed to microplastics and cadmium together. She then compared these plants to those grown naturally without the additive. Cadmium was used in the experiment because it is poisonous, carcinogenic and ubiquitous in nature due to human activity. It breaks down from car tires or even batteries, and in its natural form, it's found in phosphate rocks that are used to make agricultural fertilizer. "I read in the literature that cadmium and other toxic elements multiply when these plastics are in the soil, which really worried me." says Kirkham.

At the end of the experiment she took the wheat plants for analysis and confirmed previous reports, the flowers grown with microplastics were contaminated with cadmium. "These plastics play the role of a vector for cadmium absorption," she says.

Sixteen days into the microplastics and cadmium experiment, the plastic-treated plants began to turn yellow and wilt. Water remained on the soil in the plastic-treated plants, but to keep the experiment consistent, she watered all the flowers with the same level of water. "Plastic particles began to clog soil pores, prevented soil aeration and caused plant roots to die." says Kirkham.

Whereas the plants without microplastics, even those contaminated only with cadmium (without plastic), were in a much more regular condition. She concluded that it was the plastics that controlled the growth more than the cadmium.

Microplastics also enter agricultural soil through the degradation of plastic materials used by farmers. Kirkham says that in the 1950s, plastic sheeting replaced glass in greenhouses. Plastic litter became popular and became a global necessity. This compost is split into sheets to suppress weeds, warm the soil and maintain moisture but is challenging to recycle and expensive to dispose of.

(source: EHN.org)