What is the impact of microplastics on human health?

Scientists have recognized plastic pollution as an environmental problem for a long time, but recently it has increased substantially and become more urgent to manage. Besides the visible plastic pollution, like bags and bottles, the focus also has come on the invisible form – the microplastic particles. The study of microplastic contamination of food products and its impact on human food safety is an emerging field.

Microplastics are tiny pieces of plastic material that vary greatly despite their similarity of being very small in size. The smallest parts are not visible to the naked eye. Their composition can be any kind of plastic material, such as polyethylene (PE), polybutylene succinate (PBS), or polyvinyl chloride (PVC). They can also have different shapes, colors, sizes, and densities.

The small pieces of plastic can be grouped into primary and secondary microplastics based on where they come from before they end up in nature. Primary microplastics are already tiny when disposed of, coming from cosmetic products and various industries. Secondary microplastics come from larger pieces of plastic such as bags, bottles, and fishing nets that are disposed of and are subjected to weathering and then fragment into micro and nano plastics. Secondary microplastics account for most of those found in the oceans, ingested by marine animals.

Microplastics can also carry chemicals
Microplastics may act as vehicles or carriers for environmental contaminants and other chemicals added during manufacturing. Chemicals such as styrene, toxic metals, phthalates, and bisphenol A, may be absorbed on the surface of microplastics and may act as "substrates." These pollutants and additives can be transferred from ingested microplastics to animal tissues and cause impairment of crucial body functions.

Food and beverage operators need robust and accurate characterization tools and methodologies to understand the scale of microplastic contamination and reduce consumer exposure. Taking a proactive stance on microplastics is also a positive step from a brand reputation perspective.

Industrial spiral freezers, for example, are based on plastic wear strips to achieve acceptable friction. When the belt moves alongside the drum on plastic-coated guides, the friction wears on the plastic and releases small microscopical parts. These wear strips has a typical acceptable wear of 1-2 mm over 20,000-30,000 hours of operation. A conventional 35 tier 700 mm wide belt spiral freezer has a total length of 1,250 m belt wear strips in tier carriers. The total area with 14 mm wear surface is 18 dm2. That gives a total volume of worn off plastic (1.5 mm wear) equivalent to 27 liters of microplastic, not counting wear strips in center drum.

Microplastics are in salt, beer, fresh fruit and vegetables, and drinking water. Airborne particles can circle the globe in a matter of days and fall from the sky like rain. Seagoing expeditions to count microplastics in the ocean produce incomprehensible numbers, which have multiplied over time as more tonnage of plastic waste enters the oceans every year and disintegrates.

Human tissues contamination
As microplastics began turning up in the guts of fish and shellfish, the concern was focused on the safety of seafood. Shellfish were a particular worry, because in their case, unlike fish, we eat the entire animal—stomach, microplastics and all. In 2017, Belgian scientists announced that seafood lovers could consume up to 11,000 plastic particles a year by eating mussels, a favorite dish in that country.

By then, however, scientists already understood that plastics continuously fragment in the environment, shredding over time into fibers even smaller than a strand of human hair —particles so small they easily become airborne. A team at the U.K.'s University of Plymouth decided to compare the threat from eating contaminated wild mussels in Scotland to that of breathing air in a typical home. Their conclusion: People will take in more plastic by inhaling or ingesting tiny, invisible plastic fibers floating in the air around them—fibers shed by their own clothes, carpets, and upholstery—than they will by eating the mussels.

So, it wasn't much of a surprise when, in 2022, scientists from the Netherlands and the U.K. announced they had found tiny plastic particles in living humans, in two places where they hadn't been seen before: deep inside the lungs of surgical patients, and in the blood of anonymous donors. Neither of the two studies answered the question of possible harm. But together they signaled a shift in the focus of concern about plastics toward the cloud of airborne dust particles we live in, some of them so small they can penetrate deep inside the body and even inside cells, in ways that larger microplastics can't.

US biochemist Janice Brahney, calculated that just in the western U.S., more than 1,000 metric tons of tiny particles are carried by the wind and fall out of the air every year.

Measuring possible adverse effects of plastics on humans is far more difficult than on animals—unlike quail and fish, human subjects can't intentionally be fed a diet of plastics.

A 2018 study by ecotoxicologist Dick Vethaak, found plastics in the blood of 17 of 22 healthy blood donors; the lung study found microplastics in 11 of 13 lung samples taken from 11 patients. Virtually nothing is known about either group that would help inform the level and length of exposure—two essential attributes to determine harm.

In both studies the plastic particles found were primarily nanoplastics, which are smaller than one micrometer. The ones found in the blood study were small enough to have been inhaled—though Vethaak says it's also possible they were ingested. Whether such particles can pass from the blood into other organs, especially into the brain, which is protected by a unique, dense network of cells that form a barrier, isn't clear.



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