Plastic Roots: How Microplastics Are Affecting Maize Physiology

Redacción HC
17/09/2023

When we think of plastic pollution, our minds usually drift to ocean debris, floating bottles, or marine wildlife entangled in nets. But a quieter—and potentially more insidious—form of pollution is taking root underground. New research reveals that microplastics can be absorbed by crop roots, altering vital physiological functions in plants like maize.

Published in Science of the Total Environment, the study conducted by researchers from Chile and Spain offers the first isotopic evidence that polyethylene microbeads adhere to maize roots in hydroponic systems, affecting water and nutrient uptake. These findings open a troubling new chapter in our understanding of how plastic pollution may be threatening food systems from the ground up.

From Oceans to Croplands: The Spread of Microplastics

While most attention has focused on marine ecosystems, the majority of plastic waste—an estimated 80-90%—accumulates in terrestrial environments, including agricultural soils. Microplastics, particularly those under 5 mm in size, are increasingly present in fertilizers, irrigation water, and plastic mulching films.

But how do these particles interact with plants? Can they be absorbed or retained by roots? More importantly, do they affect plant health and crop yield?

This study asked a focused question:

What happens when maize is exposed to polyethylene (PE) microbeads in a hydroponic system?

Testing Plastic Impact: Hydroponic Maize as a Model

To isolate the effects of microplastics, scientists grew maize (Zea mays) in a controlled hydroponic system. They introduced polyethylene microbeads (~50 μm) to the root zone and employed carbon isotope analysis (δ¹³C) to trace plastic-derived carbon within the plant.

This innovative isotopic method allowed researchers to distinguish fossil-based carbon from PE versus the plant's natural organic carbon, providing clear evidence of microplastic presence in the rhizosphere.

They then measured key physiological variables:

• Transpiration rate
• Nitrogen content
• Biomass accumulation
• Water and nutrient uptake efficiency

What the Data Revealed: Plastic Presence and Plant Stress

1. Plastic Adsorption Confirmed

The study found that approximately 30% of carbon in the maize root zone came from polyethylene, confirming that microplastics were adhering to the root surfaces. While they were not internalized by the plant or detected in leaves or stems during the short experimental window, their presence in the rhizosphere was unequivocal.

“Our results confirm significant adsorption of polyethylene on maize roots,” the authors report.

2. No Translocation to Aboveground Tissues

Contrary to some concerns, no microplastics were detected in the plant’s aerial parts. However, the authors caution that this does not rule out future translocation over longer growth periods or under different environmental conditions.

3. Physiological Impacts

Plants exposed to microplastics experienced notable physiological stress:

• Reduced transpiration rates, which may limit gas exchange and cooling
• Lower nitrogen content, essential for chlorophyll and protein synthesis
• Decreased biomass, suggesting impaired growth and productivity

These effects likely result from disrupted root function—perhaps due to blockage of root pores or interference with nutrient channels.

Why This Matters: Implications for Agriculture and Food Safety

Contaminated Roots, Compromised Food Systems

Though microplastics were not found in the edible parts of the maize, their accumulation in the roots poses a threat to plant health, especially in crops used for animal feed. This raises questions about indirect impacts on livestock and, ultimately, humans through the food chain.

Hydroponics Not Exempt from Pollution

Hydroponic systems are often viewed as clean, efficient alternatives to traditional farming. Yet this study shows that even controlled environments are vulnerable to plastic contamination, particularly if water sources or substrates are not rigorously filtered.

Policy and Practice Gaps

Current agricultural regulations often overlook microplastic pollution. This research supports the need for:

• Stricter controls on agricultural plastic use
• Biodegradable alternatives to synthetic materials
• Routine monitoring of plastic residues in soils and water

Looking Ahead: Research and Action Needed

Expand Beyond Hydroponics

The authors recommend follow-up studies in soil-based systems, across diverse plastic types and particle sizes, to better understand long-term effects and potential accumulation pathways.

Understand Long-Term Exposure

The lack of plastic in maize shoots may be time-dependent. Longer studies are needed to see if microplastics eventually translocate through the plant system, especially during fruiting stages.

Redesign Agricultural Inputs

This study adds urgency to calls for eco-safe agricultural inputs, from mulching films to drip irrigation tubing, which often degrade into microplastics.

Conclusion: A Silent Threat Beneath Our Feet

As the global food system strains under climate change and soil degradation, the emergence of microplastics as an agricultural pollutant cannot be ignored. This research offers compelling evidence that polyethylene microbeads, even when invisible to the eye, can impair plant health at the root level.

For farmers, consumers, and policymakers, the message is clear:

Plastic pollution doesn’t end at the shoreline—it’s taking root in our crops.

Topics of interest

Pollution Health