But a new animal study led by researchers at Southeast University in China challenges that assumption. The study provides the first long-term investigation into how starch-based microplastics (SMPs)—which result from the degradation of these bioplastics—impact mammalian biology. The results suggest that chronic exposure to SMPs, even at levels comparable to real-world environmental exposure, may trigger serious metabolic and endocrine disruptions.
SMPs are microscopic fragments formed when starch-based plastics degrade over time. Though these bioplastics are marketed as biodegradable, they can still break down into persistent microparticles that linger in the environment and enter the human body through food, water, and even the air.
In the study, SMPs were characterized using electron microscopy and size-distribution analysis to ensure they mirrored the shape and size of particles found in actual environments. These invisible particles are small enough to pass through the intestinal lining and infiltrate organs.
Over 90 days, female mice were exposed to 14–81 SMP particles daily—a level that researchers noted is consistent with what might be encountered through daily environmental intake.
To put that in perspective:
This comparison suggests humans may already be exposed to biologically significant levels of microplastics, including those from bioplastic sources.
After three months of exposure, the mice showed significant biological changes, including:
Collectively, these outcomes indicate that SMPs may act as endocrine disruptors, interfering with natural hormone function and metabolic processes.
These findings suggest that starch-based bioplastics are not inherently safe, particularly when used in food contact materials, where they are most likely to degrade and be ingested. The presence of SMPs in internal organs, combined with molecular evidence of metabolic dysfunction, raises concerns about their long-term safety in consumer applications.
As bioplastics become more embedded in sustainable packaging strategies, regulators and industry leaders may need to revisit risk assessments and material certifications. While these materials may break down faster than petroleum-based plastics in landfills, their biological impacts remain largely unstudied.
This study underscores the importance of applying a full life-cycle and toxicological lens when evaluating alternatives to conventional plastics. Sustainable solutions must not only reduce environmental footprints—they must also demonstrate biological safety across real-world exposure scenarios.
Until more human-centered data are available, the assumption that "bio" equals "benign" should be reconsidered.
