Review: Microplastics might harm our soils, but how will soil organisms change their impact?

Maxwell S. Helmberger, Lisa K Tiemann and Matthew J.Grieshop,

Microplastics—tiny plastic beads, fragments, and fibers released from personal care products, plastic waste, and laundering of synthetic fabrics—have long been understood to contaminate the ocean. Only recently have scientists learned they’re also prevalent in the soils human society depends on. It’s important to understand the threat microplastics pose to soils so we can safeguard them for future generations. So far, most research has focused on how microplastics affect different soil organisms such as earthworms, woodlice, and microbes. Although it’s important to understand how microplastics might harm these organisms, if that’s all we know, we risk missing microplastics’ true dynamics in real-world soils, since soil organisms may also affect microplastics.

Plastics can already be “micro” when they reach a soil, carried by water, wind, or human inputs, or they can start “macro” and break down into smaller fragments. Plastic isn’t usually thought to biodegrade, but some soil microbes can break it down, using it as a carbon source just like a piece of natural detritus. This is slow, and some plastics are more biodegradable than others, but there’s still potential for microbes to physically break up larger pieces of plastic such as agricultural film and garbage into microplastics. Also, when microbes colonize plastics (large or small), that may make soil animals more likely to eat them, since when animals eat decaying plant matter or other natural detritus, they’re usually doing it to get at the microbes growing on it, like eating a cracker covered in peanut butter. Animals may also be able to create microplastics from larger debris, or change the size and shape of pre-existing microplastics that pass through their gut, which can change how other organisms interact with them. Finally, animals can disperse microplastics through the soil, and some, like earthworms, actually incorporate them into their burrows, with unknown implications for the unique microbial and animal communities inhabiting them. Future research will hopefully increase our understanding of how soil organisms themselves alter the effects microplastics have on their communities.

Read the paper in full here.

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