Microplastics in the food chain: A silent threat to public health

Plastic has transformed modern life, but its residues are transforming our health. From bottled water to seafood and even table salt, microplastics have infiltrated the global food chain. It is estimated that humans could ingest between 11,000 and 193,000 particles annually through beverages, with bottled water consumption being a risk factor that considerably increases exposure.

These tiny particles—less than 5 mm in size—result from the degradation of plastic through physical, chemical, and biological processes. Today, microplastics are not just an environmental concern: they represent an emerging public health challenge that requires urgent action and coordinated global policies.

Contaminants in food: Infiltration into the trophic chain

Various international studies have confirmed the presence of microplastics in virtually all analyzed water and food sources:

• Marine Food Chains: Microplastics primarily affect filter feeders and small fish, which are then ingested by larger predators. This accumulation allows microplastics to transfer along the trophic chain and ultimately reach humans.
• Direct Consumption Risk: The most robust evidence comes from the marine environment: multiple studies have revealed the presence of the endocrine disruptor bisphenol A (BPA) and the plasticizer DEHP (a phthalate) in a high percentage of seafood samples, with variations depending on the species and region. These findings imply a direct and relevant exposure for the consumer.
• Other Food Sources: In addition to seafood, microplastics have been detected in table salt, honey, and beer, confirming the omnipresence of these particles in the everyday diet.

Although water is a primary route of exposure, especially bottled water (which can contain from less than one particle up to more than 6,000 per liter), other foods contribute significantly to the total ingestion. Ingestion is the predominant route of exposure, followed by inhalation and, to a lesser extent, dermal contact.

Vectors of toxicity and mechanisms of cellular damage

Microplastics represent a dual risk: physical and chemical.

1. Physical Damage and Cellular Stress (Direct Risk): Due to their size and shape, they can interact directly with cells and tissues, causing oxidative stress, inflammation, and cellular damage. The evidence is especially solid for nanoplastics, which have been shown to cross biological barriers. For larger microplastics, the evidence is emerging but still limited.
   • Oxidative Stress and Inflammation: Exposure to microplastics, including nanoparticles, induces oxidative stress and chronic inflammatory processes, which are associated with neurological disorders, cardiovascular diseases, and certain types of cancer.
   • Cellular and Mitochondrial Damage: In vitro experiments with intestinal cell lines (Caco-2) and dermal cell lines (HaCaT) have shown reduced cell viability, mitochondrial damage, and increased pro-inflammatory cytokines. Mitochondrial damage is particularly critical, given the essential role of mitochondria in cellular energy generation.
   • Barrier Disruption and Translocation: Nanoplastics ($<1 \mu m$) can cross biological barriers, reaching the liver, kidneys, and lymphatic system, leading to hepatotoxic and systemic effects. These findings underscore the importance of differentially evaluating micro- and nanoplastics.

2. Vector Effect (Chemichal risk): Microplastics also act as vectors for toxic additives, such as BPA, phthalates, and other components, transferring persistent, bioaccumulative, and toxic substances to the food web.
   • Endocrine Disruption: BPA, phthalates, and other components can mimic or block natural hormones, affecting the cardiovascular, renal, gastrointestinal, neurological, and reproductive systems.
   • Carcinogenicity Risks: Some plastic compounds—such as styrene and certain phthalates—are classified as probable carcinogens or are linked to genotoxicity after prolonged exposure.

These discoveries suggest the imperative need to apply the precautionary principle: it is crucial to reduce exposure to microplastics and their additives immediately, without needing to wait for conclusive epidemiological evidence.

The water paradox and methodological challenges

Paradoxically, the infrastructure designed to protect us, such as wastewater treatment plants, can become microplastic redistribution points. Although they capture some of the particles, they discharge significant quantities into rivers and coasts, while residual sludge—used as fertilizer—reintroduces microplastics into the agricultural environment.

The metropolitan area of Monterrey, Mexico, exemplifies this paradox: a high dependence on bottled water, water scarcity, and increasing accumulation of plastic waste elevate the risk of exposure.

To face this global challenge, the scientific community and health authorities must close three critical gaps:

1. Standardize methods for sampling, treatment, capture, and identification using methods such as FT-IR or Raman, in addition to AI-assisted analysis.
2. Strengthen health surveillance, integrating exposure data in water and food, with attention to vulnerable populations.
3. Implement preventive policies, reducing single-use plastics, improving filtration in treatment plants, and reinforcing extended producer responsibility.

The future of public health depends on how quickly we act with the evidence already available. The cost of inaction is not theoretical: it accumulates, particle by particle.

Key figures on the microplastics issue:

• < 5 mm: Definition of microplastics; nanoparticles (< 1 µm) represent an emerging risk.
   
• 6,000+ particles/L: Maximum levels detected in bottled water worldwide.
   
• 42 particles/L: Average found in tap water and dispensers in Mexico City.
   
• 193,000 particles/year: Estimated maximum ingestion by an adult through water consumption.
   
• 70–80%: Proportion of seafood samples containing BPA and phthalates.
   
• 50x: Some studies report that bottled water can contain up to 50 times more microplastics than tap water.
   
• 100–300 particles/kg: Average levels found in commercial table salt.
   
• 2,400–9,400 particles/kg: Abundance reported in certain edible seaweeds.

(Figures can vary widely depending on analytical methods and minimum detectable sizes.)