Are Biodegradable Microplastics Really Safer? A New Study Weighs the Risks

Redacción HC
21/03/2025

As the world races to replace petroleum-based plastics with eco-friendly alternatives, biodegradable microplastics like polyhydroxyalkanoates (PHA) have emerged as promising candidates. Marketed as less harmful to both the environment and human health, these materials are increasingly used in packaging, utensils, and medical applications. But are they truly safer?

A groundbreaking study published in Environment International (February 2025) puts this assumption to the test. Led by researchers from Zhejiang University and the University of Auckland, the study directly compares the health impacts of PHA microplastics versus polypropylene (PP) microplastics—a common non-biodegradable plastic—on mice exposed through inhalation and ingestion, the two most realistic exposure pathways for humans.

Plastic in the Air and Food: A Modern Health Concern

Microplastics have become an inescapable component of modern life, contaminating the air we breathe and the food we eat. Yet, while many studies have explored the environmental fate of plastics, few have examined comparative health effects of biodegradable vs. conventional plastics in living organisms.

This new study addresses a critical question:

Do biodegradable PHA microplastics cause less harm to lungs, liver, gut, and microbiomes than conventional PP microplastics when inhaled or ingested?

The answer could influence global regulatory decisions and reshape the plastics industry’s shift toward sustainable materials.

How the Study Was Designed: A Closer Look at Exposure and Analysis

Experimental Design in Animal Models

Mice were exposed to either PHA or PP microplastics through two routes:

• Inhalation, simulating airborne exposure (e.g., indoor dust, polluted air).
• Oral ingestion, simulating contaminated food or water intake.

Advanced “Multi-Omics” Approach

Researchers used high-resolution, multi-omic tools to evaluate the biological impact of both plastic types:

1. Microbiome sequencing (nasal, lung, and intestinal 16S rRNA) to track bacterial community shifts.
2. Metabolomics (lungs and blood serum) to profile metabolic disruptions.
3. Transcriptomics (liver) to detect gene expression changes.
4. Toxicological assessments using standard biomarkers for liver damage (AST, ALT) and histological examination of lung tissue.

Important Caveats

• Animal model (mice) may not fully replicate human biology.
• Exposure doses were relatively high and short-term.
• Chronic and low-level exposure remains untested.

Key Findings: PHA Plastics Show Lower Toxicity

1. Respiratory Toxicity and Microbiome Disruption

• PHA inhalation led to minor alterations in nasal and pulmonary microbiota and induced mild changes in pulmonary metabolism. Only mild lung toxicity was observed.
• In contrast, PP exposure caused severe lung and liver toxicity, with significant damage in tissue and metabolism.

2. Gastrointestinal and Hepatic Effects

Both PHA and PP disrupted the gut microbiome. However:

• PHA-exposed mice showed lower liver enzyme levels (AST, ALT)—indicating less hepatic stress.
• PP microplastics led to pronounced metabolic changes in the liver and systemic circulation.

3. Microbial Biomarkers as Early Warning Signals

The study identified specific microbial taxa associated with plastic type:

• PHA exposure increased Allobaculum (nasal) and Alloprevotella (lung).
• PP exposure raised levels of Lactobacillus and Acinetobacter—bacteria often linked to inflammatory responses.
• Ingestion of PHA boosted Faecalibacterium, a beneficial gut bacterium; PP, meanwhile, increased the presence of potentially harmful Erysipelatoclostridiaceae.

These distinct microbial shifts correlate with the varying toxicological outcomes of each plastic.

Implications for Health Policy and Plastic Substitution

Safer Substitutes, But Not Harmless

The study concludes that PHA microplastics are significantly less toxic than PP microplastics in both primary exposure routes. However, “less toxic” does not mean “non-toxic.” The observed mild biological responses to PHA still merit careful monitoring—especially as these materials become more widespread.

Informing Public Health and Regulation

1. Support for sustainable plastic alternatives: This evidence favors regulatory approval of biodegradable plastics like PHA in consumer products, especially food packaging and inhalable medical devices.
2. New role for microbial biomarkers: Specific changes in nasal, pulmonary, and gut microbiota may serve as early indicators of plastic toxicity in future regulatory screening.
3. Need for chronic exposure research: The authors urge long-term studies using lower, real-world doses and human-relevant models.

“Our findings suggest that PHA is a promising low-toxicity alternative to PP, but regulatory frameworks must still evaluate each material thoroughly,” the researchers noted.

Real-World Relevance: From Laboratory to Policy

For Industry and Consumers

• The food packaging industry, especially in regions heavily reliant on imports and plastics, could safely transition to PHA-based materials with fewer health risks.
• Consumers concerned about microplastic exposure in household air or diet can favor biodegradable-labeled products, though full risk elimination is not guaranteed.

For Regulators and Researchers

• Biodegradable does not mean inert. Regulatory agencies must establish toxicity benchmarks even for “green” materials.
• Monitoring microbiota in vulnerable populations (e.g., factory workers, children) could help detect harmful exposure early.

Conclusion: Not All Plastics Are Created Equal

This study delivers a rare comparative view of microplastic toxicity using real-world exposure routes. While both biodegradable and conventional microplastics disrupt biological systems, PHA appears to be a safer bet—posing fewer risks to respiratory, digestive, and liver health.

Still, the presence of any plastic particles in food or air raises broader questions about how societies manage materials that inevitably end up in human bodies.

“As we rethink our material future, safety should be as much a priority as sustainability,” concludes lead author Hua Zha.

Topics of interest

Health Pollution