A microscopic war is raging in your milk, and the plastic is winning.
Imagine pouring a cold glass of milk or enjoying a slice of cheese. Beyond the essential nutrients, you might also be consuming an invisible ingredient: microplastics. These tiny plastic particles, smaller than a grain of sand, have infiltrated our food chain, and dairy products are no exception.
Microplastics range from 1 micrometer to 5 millimeters in size
Found in milk, cheese, yogurt and other dairy products
Altering the delicate balance of milk's microbiome
Microplastics (MPs) are defined as plastic fragments ranging in size from 1 micrometer to 5 millimeters. They are classified as either primary (intentionally manufactured small particles) or secondary (resulting from the breakdown of larger plastic items like packaging) 5 .
Recent research has confirmed their widespread presence in our dairy products. A 2025 study published in npj Science of Food qualitatively and quantitatively analyzed microplastics in 28 dairy samples 1 .
Highest concentration
Significant levels
Lower but still concerning
| Polymer Type | Common Sources | Prevalence in Dairy |
|---|---|---|
| Polyethylene (PE) | Plastic bottles, bags, food wraps | High 1 5 |
| Polypropylene (PP) | Yogurt containers, bottle caps | High 1 5 |
| Polyethylene Terephthalate (PET) | Beverage bottles, food packaging | Most frequently identified 1 |
| Polystyrene (PS) | Disposable cutlery, takeaway containers | Detected 4 5 |
| Polyvinyl Chloride (PVC) | Pipings, cling films | Detected; toxicological concern 4 5 |
The most common shapes found were irregular fragments (77.4%), suggesting contamination from mechanical degradation of plastic equipment during processing, followed by fibers (22.2%), which likely come from synthetic textiles like protective clothing 1 . The majority of these particles are dangerously small, with the most common size range being 51–100 micrometers, particles small enough to potentially penetrate tissues 1 5 .
The presence of microplastics in dairy products is concerning enough, but their impact on microorganisms introduces a second layer of complexity. Microbes and microplastics interact in two primary ways: the plastic can alter microbial ecosystems, and certain microbes can, in turn, interact with the plastic itself.
A 2024 study on Airag, a traditional fermented mare's milk, compared traditional cow skin containers (khokhuur) with modern plastic containers. The findings were clear: the plastic containers sustained a less diverse microbial community 2 .
The plastic containers' high heat retention created a different environment, boosting lactate production and sustaining a lower pH. This environment favored Lactobacillus helveticus as the overwhelmingly dominant species (over 90%), while other lactic acid bacteria and environmental bacteria thrived better in the traditional khokhuurs 2 .
Key Finding: Plastic surfaces can act as a selective filter, narrowing the microbial biodiversity that is often desirable in fermented foods.
Perhaps more alarming is the role of plastics as a carrier for harmful bacteria. In aquatic environments, plastic debris acts as a resilient substrate for biofilm formation, a potential hotspot for pathogen colonization 7 .
A 2024 study submerged common plastic polymers in a lake and found that materials like polystyrene (PS) and styrene acrylonitrile resin (SAN) harbored a broader spectrum of bacteria compared to others 7 . These included potential human pathogens such as Klebsiella pneumoniae and Klebsiella oxytoca 7 .
Antibiotic Resistance Risk: All isolated bacteria from the plastic substrates displayed a high prevalence of antibiotic resistance, highlighting an emerging risk where plastic waste could facilitate the spread of multidrug-resistant bacteria into our ecosystems and potentially, our food chain 7 .
| Bacterial Species | Potential Pathogenicity | Primary Plastic Polymer Colonized |
|---|---|---|
| Klebsiella pneumoniae | Opportunistic pathogen | Polystyrene, Styrene Acrylonitrile Resin 7 |
| Klebsiella oxytoca | Opportunistic pathogen | Polystyrene, Styrene Acrylonitrile Resin 7 |
| Lysinibacillus fusiformis | Generally environmental | Polystyrene, Styrene Acrylonitrile Resin 7 |
| Exiguobacterium acetylicum | Generally environmental | Polystyrene, Styrene Acrylonitrile Resin 7 |
To understand how the scientific community uncovers these connections, let's examine the Airag fermentation study more closely. This research provides a elegant model for isolating the effect of container material on a milk-based microbiome.
Researchers collected Airag samples from three households in Mongolia that used both plastic containers and traditional khokhuurs over five to six days. Samples were taken at multiple time points in the daily production cycle 2 .
Temperature sensors were placed in both container types to log thermal fluctuations over the sampling period 2 .
The pH, lactate, ethanol, and lactose levels of each sample were quantified using tools like pH meters and High-Performance Liquid Chromatography (HPLC) 2 .
Bacterial genomic DNA was extracted from all samples. The V3-V4 region of the 16S rRNA gene was amplified and sequenced using Illumina technology to identify the precise bacterial composition in each sample 2 .
The results confirmed that the physical container dictates the microbial environment. The khokhuur, with its wider temperature fluctuations, supported a significantly higher diversity of lactic acid bacteria and environmental bacteria. In contrast, the stable, warm environment of the plastic container led to a microbiome dominated by a single species 2 .
This experiment is crucial because it moves beyond simply detecting plastic and demonstrates how plastic can fundamentally alter the biological processes in fermented foods, potentially affecting their flavor, nutritional value, and safety.
| Reagent / Material | Function in Research |
|---|---|
| Fourier-Transformed Infrared Micro-Spectroscopy (FT-IR) | Identifies polymer types of microplastics by measuring how they absorb infrared light, creating a chemical "fingerprint" 1 3 . |
| Raman Micro-Spectroscopy | Similar to FT-IR, it identifies polymer composition and is particularly useful for analyzing small particles down to 1 micrometer 4 . |
| 10% Potassium Hydroxide (KOH) | Used to digest organic material in food samples (like milk), leaving behind plastic particles for analysis 4 . |
| API Test Kits (e.g., API-Staph, API-20E) | Standardized biochemical kits for the preliminary identification of bacterial species based on metabolic properties 7 . |
| 16S rDNA Sequencing | A molecular technique considered the gold standard for accurate bacterial identification, based on sequencing a conserved region of the bacterial genome 2 7 . |
| Man Rogosa Sharp (MRS) Medium | A specialized nutrient broth used for the cultivation and enrichment of lactic acid bacteria 9 . |
In the face of this plastic predicament, could part of the solution lie within the microbes themselves? Emerging research suggests that probiotics—the beneficial bacteria found in fermented foods like yogurt—may help negate some of the toxic effects of plastics in our digestive systems 6 .
Microplastics and plastic additives enter the digestive system through contaminated dairy products.
Lactic acid bacteria strains bind to and neutralize harmful plastic additives like Bisphenol A (BPA).
Probiotics ameliorate inflammation and toxicity that microplastics promote in the gastrointestinal system.
Lactic acid bacteria strains, including Lactobacillus plantarum and Lactobacillus acidophilus, have demonstrated the ability to bind to and neutralize harmful plastic additives like Bisphenol A (BPA) 6 .
A 2017 study specifically tested dairy strains of lactic acid bacteria and found that some could remove over 50% of BPA from a solution, with heat-killed cells sometimes showing even higher efficiency 9 .
While probiotics are not a silver bullet and cannot remove plastic particles themselves, they may act as a defensive shield, ameliorating the inflammation and toxicity that microplastics promote in our gastrointestinal systems 6 . This promising area of research highlights the potential of harnessing beneficial microbes to combat the consequences of plastic pollution.
The evidence is clear: our dairy products, a staple of nutrition for millions, have become an unexpected frontier in the global plastic pollution crisis.
From the degradation of packaging and processing equipment to the alteration of microbial ecosystems and the potential introduction of harmful bacteria, the journey of plastic from the environment to our gut is both complex and deeply concerning.
While science explores innovative damage control, such as using probiotic bacteria, the ultimate solution lies in addressing the problem at its source. Reducing our reliance on single-use plastics, improving waste management, and developing safer, more sustainable materials for food packaging and processing are critical steps.
As consumers, staying informed and making conscious choices can drive industry change. The unseen battle in our milk is a reflection of a larger environmental challenge, one that we must collectively work to resolve for the health of our planet and ourselves.