New research carried out in the UK suggests that both organic and inorganic fertiliser may contribute to concentrations of microplastics in agricultural soils.
The research paper, published in the scientific journal Nature, was authored by researchers from Lancaster University and Rothamsted Research, an agriculture and environment research institute based in Hertfordshire in England.
The researchers said that their study demonstrated that microplastic concentrations increased at higher rates in soils that are “amended” with either organic (farmyard manure) or inorganic fertiliser between 1966 and 2022.
The results were determined using soil samples collected by Rothamsted Research at 18 separate time points over the course of some 180 years.
A significant increase in microplastic concentrations was observed between 1966 and 2022 across the three soil treatment types that were examined, namely farmyard manure, inorganic fertiliser, and ‘nil treatment’ (no treatment with fertiliser).
In the samples taken up to the year 1914, no microplastics were detected, consistent with the creation of ‘modern plastics’ some 100 years ago.
In the samples taken between 1914 and 1966, the microplastics detected were likely not from agricultural sources but instead reflected increased plastic use in wider society, especially in infrastructure, fashion, and domestic use, the research paper said.
However, the research indicated that, in the samples taken between 1966 and 2022, microplastic amounts in soil treated with farmyard manure and inorganic soil were significantly different than amounts in untreated soil, but not significantly different from each other.
The researchers said that these findings indicate that the application of organic and inorganic fertiliser “is directly contributing” to the microplastic load in the soil beyond baseline concentrations.
“We demonstrate that microplastic concentrations in agricultural soils increase over time and that the application of organic and inorganic fertilisers are significant contributors of microplastics to soil beyond baseline concentrations,” the researchers said.
They added: “The impacts of microplastic pollution on agricultural activity are largely unquantified and unreliable, due to the lack of longer-term field trials and the use of unrepresentative concentrations in many studies.
“Given that microplastic concentrations will likely continue to accumulate in agricultural soils from agricultural and non-agricultural sources, the effects of microplastics in agricultural systems must be better understood.
“With no immediate solution to remediate microplastic pollution on the horizon, it is critical to reassess our relationship with plastic use in agriculture and beyond,” the researchers added.
