Inflammation, cancers, pollution : le rôle des microplastiques - Dialogue avec Jean Demarquoy

In this discussion, Fabrice Vidal, a philosopher and host, sits down with Jean-François De Marcois, a Professor of Nutrition Physiology at the University of Burgundy. De Marcois, who also serves as a health security expert for French and European agencies, provides a comprehensive look at the pervasive and often invisible world of microplastics. The conversation aims to clarify what these particles are, the risks they pose to human health, and the practical steps individuals and society can take to mitigate their impact. **The Ubiquity and Scale of Plastic** The central premise of the discussion is that plastic is now everywhere: in the air we breathe, the water we drink, and even within our own bodies. De Marcois explains that while plastic as a material is relatively new—becoming widespread only in the 1950s—it does not truly disappear. Instead, it fragments. A plastic bag left outside will eventually "vanish" from sight, but it has simply broken down into millions of microscopic pieces. To illustrate the sheer scale of global plastic production, De Marcois offers a startling comparison. We produce approximately 460 million tons of plastic annually. Given that there are about 8 billion people on Earth with an average body weight of 60kg, the total mass of all humans is roughly 480 million tons. Essentially, humanity produces its own weight in plastic every single year. While only a small percentage (1% to 4%) ends up as microplastics, the cumulative total over decades of production amounts to tens of millions of tons of microscopic waste circulating in the environment. **Defining Microplastics and Nanoplastics** Microplastics are generally defined as particles smaller than a few millimeters. However, the conversation highlights the even more concerning category of nanoplastics. These are so small they are invisible to the naked eye; for context, a human hair is about 100 microns wide, whereas a nanoplastic particle is significantly smaller. This size difference is critical for health. While larger molecules struggle to enter the human body, smaller particles can easily bypass biological barriers. De Marcois notes that research into nanoplastics is particularly urgent because their minute size allows them to penetrate cell membranes in a less controlled manner than larger substances, potentially interfering with cellular functions directly. **Health Risks: The "Trojan Horse" Effect** When discussing health, De Marcois is careful to maintain a scientific and non-alarmist tone. There are no clinical studies where humans were intentionally fed plastic to observe the results. However, in vitro and animal models suggest two primary concerns: "low-grade inflammation" and oxidative stress. This "cellular malaise" occurs when the body’s immune system responds to the constant presence of foreign particles at a low but persistent level. Beyond the physical presence of the plastic itself, microplastics act as a "Trojan Horse" or "chemical sponge." Because of their chemical structure and high surface area, they attract and carry toxic substances. These include heavy metals, pesticides, and endocrine disruptors like Bisphenol A (BPA). BPA is often added to plastic to make it flexible, but it can be released when the plastic is chewed or heated. Endocrine disruptors are particularly insidious because they act at extremely low doses—doses that would normally be considered non-toxic for other chemicals. They interfere with the hormonal system, which regulates everything from metabolism to reproduction. De Marcois cites an example of sheep losing their ability to reproduce after eating clover containing natural estrogens to illustrate how even small hormonal disruptions can have massive biological consequences. **Sources of Exposure: From Laundry to Tires** One of the most surprising insights from the transcript is that exposure doesn't just come from obvious sources like plastic bottles. Textiles are a massive contributor; synthetic clothes release between 10,000 and 700,000 plastic fibers during a single wash cycle. These fibers eventually find their way into the oceans. Other major sources include tire abrasion—particles of plastic and rubber are shed every time a car drives or brakes—as well as paints, construction materials, and even tea bags. Some studies have shown that tea bags, which often use plastic fibers to maintain their shape in hot water, can release significant amounts of microplastics directly into the drink. Interestingly, De Marcois mentions a study suggesting that even glass bottles can contain microplastics, likely due to the industrial cleaning and capping processes. **Practical Solutions: Individual and Collective Action** The experts suggest several ways to reduce exposure and environmental impact. On an individual level, the most important rule is to avoid combining heat and plastic. One should never microwave food in plastic containers or with plastic film, and hot drinks should not be consumed from plastic cups. For the home, De Marcois recommends: 1. **Materials:** Returning to durable materials like glass, stainless steel, and wood. 2. **Laundry:** Washing synthetic clothes at lower temperatures, using shorter cycles, and ensuring the machine is full to reduce the friction that breaks off fibers. 3. **Air Quality:** Regularly airing out the home to prevent the accumulation of fibers shed by carpets, upholstery, and paints. 4. **Diet:** Choosing bulk goods (le vrac) and reading labels on cosmetics to avoid synthetic polymers used for texture. On a collective level, De Marcois argues that recycling is not a complete solution. The primary goal must be a global reduction in plastic production. He emphasizes that the countries contributing most to microplastic pollution are not necessarily the ones producing the most plastic, but those with the poorest waste management systems. Improving how we handle plastic waste—preventing it from entering the natural environment where it can fragment—is the most effective way to stem the tide of microplastics. While organizations trying to clean the "seventh continent" of plastic in the ocean are doing noble work, De Marcois suggests that prevention at the source is the only truly viable long-term strategy.