The teen researcher studying microplastics on the farm
David Liu is a rising senior at Phillips Exeter Academy in Exeter, NH, and he’s on a mission to share knowledge about the risks and threats of microplastics in agriculture. He shared his research during a recent presentation for NOFA/Mass.
The EPA defines microplastics as plastic particles ranging in size from 5 mm (about the size of a pencil eraser) to 1 nanometer. For comparison, a strand of human hair is about 80,000 nanometers wide. Microplastics come from the degradation of plastic waste through a variety of processes including mechanical stress, UV exposure and weathering.
Liu said, “It’s really hard to deal with them … they’re really small and they’re also hard to degrade and they stay in the environment for a long time.”
According to Liu, empirical evidence about the impacts of microplastics in the environment and on human health is limited. What researchers do know is primarily based on ocean and marine systems. There are very few long-term studies or field-related studies about microplastics within agricultural and food systems.
With interests in environmental science, economics and biology, Liu hopes to change that. He said, “The two main questions that I wanted to look into was first, what are microplastics doing to farms? What are they doing to agriculture? And also, what does that mean on an economic scale?”
One common way microplastics enter a farm system is from plastic mulch films which degrade over time through UV radiation and mechanical stress. As these films break down, microplastics are released into the soil and surrounding plants. Organic fertilizers such as manure, compost and biosolids can introduce microplastics into soils.
For example, Liu explained, microplastics can accumulate in manure from animals that had microplastics in their digestive systems, and the particles remain in the manure when it’s applied to plants. Additionally, irrigation water has been frequently found to be contaminated with microplastics.
There is evidence that microplastics can impact biological activity of soil. They alter soil microbial communities, shifting them toward microbes that are tolerant of or able to feed on microplastics instead of beneficial microbes. They also have been found to decrease soil enzyme activity involved in nitrogen and phosphorus cycling – critical nutrient cycles for plant health. Soil fauna populations like earthworms and nematodes decline when they ingest microplastics. Together, these impacts reduce biological activity and weaken soil resilience.
Microplastics also affect soil structure. They disrupt soil aggregation – how soil clumps together. Their presence as foreign particles makes it harder for soil to bind normally. Liu said, “When the soil is clumping together weirdly and when there’s microplastics clogging up the pores, then oxygen, water, all these other essential nutrients that filter and cycle through the soil, it’s now harder for them and it’s less connective.”
Microplastics that accumulate in farm soils can enter plants through the roots. They can also be taken up by a plant’s leaves. New evidence shows plant leaves absorb airborne microplastics. Once on the plant surface, they can move inward and have been found to penetrate all three main tissue layers, meaning they can reach deep internal tissues.
Inside the plant, microplastics can accumulate in vascular tissues, the plant’s transport system for water and nutrients, where they can cause blockages and reduce circulation and flow throughout the plant. Their presence also triggers internal stress responses. Cells exposed to accumulated microplastics show a shift from normal to oxidative stress which damages cellular components and contributes to declines in plant health. Microplastics can also reduce the efficiency of photosynthesis.
While more is being learned about the impacts of microplastics on soil and plant health, less is known about yield and economic impacts. Liu cited studies on staple crops such as corn, rice and wheat that have found that yield losses connected to microplastic contaminations range from approximately 4% to potentially over 14%.
Liu noted that it’s difficult for models and studies to accurately gauge how much microplastics are actually affecting yield. Even when studies do measure yield impacts, it’s difficult to establish a direct correlation between the amount of microplastics in soil or plants and the specific amount of yield being lost.
Removing microplastics from the soil is virtually impossible. Physical removal methods, such as separating based on density, are not practical at scale. Biological removal using microplastic‑degrading microbes and fungi is too slow and inefficient for the current level of contamination. Liu does see some promise in using biochar to reduce microplastic contamination.
Additional research is needed to better understand how microplastics are impacting farming systems. Liu thinks multi-year, field-scale studies that mirror real-world farming conditions should be a top priority. Another research priority is understanding how various soils and crops respond to microplastic contamination.
Additionally, there is no standardized way to measure microplastics in soil or plants, making it difficult to compare studies across regions or time periods. Liu also identified the impacts of microplastics on human health as another important research priority.
Looking ahead to college and a potential career, Liu is interested in studying the economic impacts of microplastics and how to make sustainable alternatives more cost-effective, since, he said, economic incentives drive policy and adoption.
Liu is optimistic that as more attention is brought to this issue, solutions will evolve. “It is really, really hard to combat this issue of microplastics. But I think we’ve proven as a human race and humanity time and time again that whenever there are problems we do figure out a way to solve them,” he said.
by Sonja Heyck-Merlin
