When plastic is released in the environment and exposed to the elements, it breaks into tiny pieces called microplastics. These bits of plastic can be found everywhere from arctic snow, to the sea floor, and even in human feces. With that in mind, it probably won’t come as a shock that microplastics are also prevalent in the soils that grow our food.
There’s much to learn about what happens to microplastics in the soil. Where do they go? How do they react to other things in the soil? Do pesticides in the soil stick to the microplastics? Will this expose plants to more or less of the pesticides? To explore this bounty of unknowns, Western Washington University undergraduate Emma Nordlund and Assistant Professor of Environmental Science Manuel Montaño spent the summer conducting an experiment examining microplastic impacts on corn.
“With a lot of these new and emerging chemicals, we tend to kind of treat their behavior like an individual monolith. We only look at pesticides on their own. We only look at microplastic effects on their own. So few studies are actually looking at the intersection on how these various contaminants interact with each other,” said Montaño.
The pair used a copper-based pesticide which is used to treat fungal infections like canker and blight in agriculture throughout the US. It utilizes copper-based nanoparticles, which are teeny tiny bits of copper -- much smaller than the eye can see, even smaller than your average microscope can see.
Copper has antimicrobial properties, and because of this, humans have been using copper to protect their crops from fungus and other pests since the 1700s. But copper pesticides that use nanoparticles are relatively new to the scene, and there’s still a lot we don’t know about them.
Nanoparticles are a unique size and shape. They have very high surface area to volume ratio and because of this, their behavior in the environment is unlike other substances. The hope is that this can increase the pesticide’s success, but it also makes it difficult to predict the environmental effects and potential toxicity.
Nordlund said she was interested in the project because she worries about the lack of testing done on pesticides like this.
“I think we're doing a lot of things without thinking them through. We're like ‘Cool! We have nanoparticles! Let's make them into pesticides and put them on plants!’” said Nordlund, but she warns that there’s more to investigate before putting these products to use.
This summer, Nordlund and Montaño utilized the biology greenhouse on Western’s campus and grew 36 corn plants (see Nordlund tending her corn plants in the image above). One third of the plants were grown with copper pesticides and microplastics in their soil, one third with just the copper pesticide, and one third as a control.
The goal was to observe the way the pesticide interacted with microplastics in the soil, if this changed the way the chemicals could be taken up by the plants, and how it all affected plant growth. In addition to this greenhouse experiment, they conducted a variety of benchtop experiments to quantify the bioavailability of the copper pesticide in a soil environment containing variables such as microplastic addition and the presence of synthetic root exudate, which is the liquid that plants secrete from their roots, to mimic the complexity of the soil environment.
Currently the team is working on data analysis for the project; for more information, contact Manuel Montaño at firstname.lastname@example.org.