Plastic is hardly a source of nutrition for us, yet every week each one of us ingests a plastic credit card’s worth of polymer particles, which is to say 5 grams of microplastics, according to the World Wide Fund for Nature.

That finding comes from a study conducted last year for the environmentalist group by researchers at the University of Newcastle in Australia, who discovered that we each consume some 2,000 tiny pieces of plastic every week, or  21 grams a month and 250 grams a year.

Microplastic pollution, most of which is invisible to the naked human eye, has reached endemic proportions and tiny polymer particles from plastic waste have permeated the food chain in the planet’s oceans. According to a new study, for which scientists examined five popular types of seafood (oysters, prawns, squid, crabs and sardines) they had bought at food markets in Australia, every single item contained microplastic particles to varying degrees.

Specifically, researchers at the University of Exeter in the United Kingdom and the University of Queensland in Australia analyzed raw seafoods (five wild blue crabs, 10 farmed tiger prawns, 10 farmed oysters, 10 wild squid, and 10 wild sardines) with a newly developed method that helped them identify and measure five different plastic types at the same time.

They found plastic levels of 0.04 milligrams per gram of tissue in squid, 0.07mg in prawns, 0.1mg in oysters, 0.3mg in crabs and 2.9mg in sardines.

“Considering an average serving, a seafood eater could be exposed to approximately 0.7 milligrams of plastic when ingesting an average serving of oysters or squid, and up to 30 mg of plastic when eating sardines, respectively,” observes Francisca Ribeiro, a lead author of the study who researchers dietary exposure to plastics at the University of Queensland.

“For comparison, 30mg is the average weight of a grain of rice,” she explains. “Our findings show that the amount of plastics present varies greatly among species, and differs between individuals of the same species. From the seafood species tested, sardines had the highest plastic content, which was a surprising result.”

The plastic particles that end up in the tissue of marine creatures we consume largely come from plastic packaging and synthetic textiles: polystyrene, polyethylene, polyvinyl chloride, polypropylene and polymethyl methacrylate. In other words, as plastic waste disintegrates in the oceans, it carries on polluting by entering marine organisms and lodging into their tissues.

That happens because a myriad of creatures large and small from planktons to whales unwittingly ingest microplastics with potentially dire consequences for their own and their ecosystem’s health.

Nor is it only seafood that poses threats to us. Earlier studies have found that microplastics have contaminated even bottled water and table salt. A group of scientists who did tests on 17 types of commercially available salt from eight countries, for instance, found extensive plastic contamination in salts people use in their kitchens.

“Out of the 72 extracted particles, 41.6% were plastic polymers, 23.6% were pigments, 5.50% were amorphous carbon, and 29.1% remained unidentified,” they write in a study. “The particle size (mean ± SD) was 515 ± 171 μm. The most common plastic polymers were polypropylene (40.0%) and polyethylene (33.3%). Fragments were the primary form of MPs (63.8%) followed by filaments (25.6%) and films (10.6%).”

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