Microplastics are a growing concern in soil, but it’s still unclear how much is actually there—partly because different studies use different methods to measure them. This meta-analysis looked at data from 89 studies across 553 locations to compare microplastic levels in various land-use systems.
The average concentration found was about 2,900 microplastic particles per kilogram of soil, though this varied widely. The highest levels were found in soils with plastic mulch and greenhouse use, followed by farms using sewage sludge as fertilizer. Surprisingly, rural areas often had more microplastics than cities.
However, the biggest takeaway is that how researchers analyze the samples—such as the particle size they look for, how deep they sample, and how they separate microplastics from the soil—has a major effect on the results. For example, using denser liquids to separate plastics or removing organic matter after separation led to higher microplastic counts.
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