Are microplastics killing us? | Weekly newspaper of the islands

By Russell Barsh, Director of KWIAHT.

Over the last decade, San Juan County officials and environmentalists have shifted public attention from reducing our use of biocides (pesticides, herbicides) to reducing our use of plastics, starting with single-use items such as straws, cups and bags.

This shift in focus is part of a broader national trend that is benefiting biocide manufacturers like Dow and Bayer. We continue to spray toxic chemical compounds on our lawns, gardens, home foundations and ponds; And while most of these toxic products are sold in single-use plastic containers, we behave as if the environment is more threatened by empty bottles than by the poisons many of them once contained.

Meanwhile, images of rafts of floating plastic bottles have recently been replaced by revelations about the ubiquity of “microplastics” and reports that they have been found in breast milk, blood and human brains. How worried should we be?

First of all, the most widely used plastics such as polyethylene (PE), polypropylene (PP) and polyester (PET) are neither toxic nor “poisonous” as such. Most of them eventually break down in the environment into carbon dioxide and water. Health problems associated with plastics are either mechanical in nature (e.g. gastrointestinal constipation in animals that selectively eat plastic waste) or are related to toxic compounds added to plastic products to make them more attractive (plasticizers, dyes, fragrances ) sold or stored in plastic containers. or adsorbed on plastic waste from the environment.

The National Oceanic and Atmospheric Administration defines “microplastics” as particles ranging in size from 5 millimeters (about a quarter of an inch) to a nanometer, which is smaller than a single protein molecule in a living cell. Most microplastics are only visible through a microscope and are created by abrasion and decay of larger plastic objects. The largest source of microplastics in our oceans appears to be the washing, fraying and disposal of plastic clothing (nylon, polyester) rather than plastic bags, bottles or straws.

How do microplastics get into the chest or brain? They must be small enough to fit between cells in the walls of blood vessels: less than a thousandth of a millimeter (a micrometer), or one-sixth the size of a human red blood cell. Smaller particles can squeeze between the phospholipid molecules that make up the cell walls. Microplastics in this size range are often referred to as “nanoplasts”.

Nanoplastics are not the only extremely small particles that our stomachs and lungs are regularly exposed to. “Particles” are particles of matter in the micrometer range. Many particles are of natural origin, such as mineral dust from sand and soil, water droplets and tiny parts of decaying animals and plants. Soot from burning fossil fuels, dust from manufacturing, and, yes, fragments of decomposing plastic products are also part of the particulate matter pollution in the air we breathe and the water we drink. Reducing particulate matter in air and drinking water has been the responsibility of the Environmental Protection Agency since its creation by Congress in 1972.

Do plastic particles pose a greater threat to human and animal health than non-plastic particles? The science on this question is complicated and much remains uncertain. Natural and artificial particles that are smaller than cells have been linked to reduced heart and lung function. In addition, particles attract and adsorb oily chemical compounds from the environment. This can include biocides as well as industrial waste, pharmaceuticals and cleaning products. Therefore, particles can cause physical damage to organs and cells, as well as accumulating and carrying chemical pollution, causing toxic compounds to enter the stomach, lungs and bloodstream of wildlife and humans.

Particles made from quartz sand, glass, metal, rubber and plastic differ in which compounds they adsorb best. Oily PCBs absorb strongly into plastics, as do many currently widely used pesticides. Man-made rubber (think car tire dust) is also highly absorbent of oily contaminants, which is one of the reasons road runoff can be so harmful to lakes and wetlands: It is rich in rubber particles coated with oils and toxins from burned engine fuel, such as PAHs .

And this is where the microplastic story takes a particularly surprising turn. There is an entire industry that produces customized particles, many of them plastic, for use in consumer products.

These so-called “microparticles” are manufactured to facilitate the spraying, distribution and delivery of compounds that are not soluble in water. Microparticles are coated or filled with the active ingredients in products as diverse as cosmetics, processed foods and pharmaceuticals, as well as pesticides and herbicides. Surfactants are routinely added to keep the microparticles suspended and uniformly mixed in the liquid or other matrix in which the active ingredients are delivered. Microparticles and surfactants are classified as “inactive” ingredients in the US (but not Europe) and therefore do not need to be disclosed on product labeling.

Microparticles used in industry and medicine vary in composition, but many are made of plastics such as polystyrene. Microplastic particles in personal care, household and garden products can enter the air and water. The widespread use of microparticles in products such as cosmetics and “medicines” also explains why plastics are found in human blood and organs. Reports of microplastics in the human body do not always distinguish between post-consumer waste such as microfibers from synthetic fabrics and the microparticles used in products that we intentionally ingest or smear on our bodies.

We should pay more attention to the fate of microparticles in our bodies and the environment. But let’s not forget that the potential health effects of microplastics, including microparticles, are mainly due to the biocides we continue to use in our homes, gardens and backyards. Reducing the outdoor use of biocides and their “collateral damage” to non-target organisms should be our priority.