Humans are ingesting, inhaling and being injected with microplastics at every stage of life, from the womb through to the hospital ward. A scoping review of roughly 350 peer-reviewed studies has identified around 60 different polymer types being released from plastic products during routine use, with microplastic shedding built into every plastic product's lifecycle.

The review, Exploring Everyday Microplastic Exposures, was compiled by Dr Heather Leslie, the environmental chemist whose 2022 research in Environment International was the first to confirm microplastics in human blood. Commissioned by the Plastic Soup Foundation, a Netherlands-based environmental organisation, and the Flotilla Foundation, it maps the points at which products shed particles across five categories: food and food preparation, indoor environments, outdoor sources, children's products, and personal care and healthcare.

"This is not just about waste or environmental pollution, it is about the materials that manufacturers have built into our world, and the particles they continuously release into the spaces we live in," said Leslie.

Much of the data concerns the kitchen. A Canadian study found that a single synthetic tea bag brewed for five minutes released approximately 2.3 million microplastics and 14.7 billion nanoplastics into a single cup. That number is worth sitting with. New plastic kettles shed between five and 35 million particles per litre in their early weeks of use, though this appeared to tail off over time. And microwaving takeaway food in plastic containers daily could mean swallowing 150 million particles a year, according to one estimate.

But ingestion is only part of the picture. Humans inhale six litres of air per minute, and much of what is in that air comes from the products around us. A single coat of paint across 100 square metres contains an estimated 17-68 quadrillion polymeric particles, which begin releasing as the paint weathers and chips. In the Netherlands, professional and domestic painting together account for roughly 490 tonnes of microplastics emissions annually. Tumble drying a polyester blanket for 20 minutes released between 1.6 and 1.8 million particles per cubic metre of indoor air.

The youngest and most vulnerable

The review's most uncomfortable reading concerns babies and children. Microplastics have been detected in amniotic fluid, placentas and umbilical cord blood, meaning exposure begins before birth. Baby bottles released up to 16.2 million microplastics per litre of formula, rising further when sterilised with hot water. Once mobile, young children ingest more settled dust than adults through floor play and breathe more air per kilogram of bodyweight.

For premature babies in neonatal units, exposure can be even more direct. A study of parenteral nutrition circuits found PET and polyethylene in the solutions being fed intravenously, and estimated that a one-kilogram neonate could receive between one and 115 microplastic particles over 72 hours depending on the solutions used. In operating rooms nearby, airborne microplastic deposition onto surfaces reached up to 9,258 particles per square metre during 12-hour sampling periods. Syringes, infusion sets and IV fluids all tested positive.

Outdoors, the largest source by volume is tyre wear, with a global estimate of nearly six million tonnes of tyre particle emissions per year. Electric vehicles, being heavier, produce 24 per cent more than conventional cars. Perhaps the review's most unexpected finding concerns solar geoengineering. Multiple patents exist for injecting polymeric microparticles into the stratosphere at altitudes of 10-20 kilometres, and SAI programmes measure their output in "teragrams per year" - one teragram being one billion kilograms. Leslie describes this as "a yet unquantified but potentially tera-scale source of intentionally added airborne microplastics."

What the report is and is not

Leslie is open about the report's advocacy purpose, writing in the epilogue that it presents "data with a cause, because knowledge is needed to act both individually and collectively." It was commissioned by a campaigning organisation and its conclusions invoke the precautionary principle.

The underlying evidence has limitations. Many studies reviewed used small sample sizes. Quality control in microplastics analysis is still maturing, methodologies are not harmonised across laboratories, and particle counting and mass concentration methods sit awkwardly alongside each other. The report does not attempt to calculate total exposure.

But Leslie argues these caveats do not undermine the central finding. Improvements in analytical quality control, she writes, "will not fundamentally change the conclusion that our plastic products are shedding significant quantities of microplastics and creating significant sum exposure scenarios for humans." Her practical recommendation is material substitution where possible - swapping a plastic chopping board for a wooden one, or using a tea infuser with loose leaves instead of a synthetic tea bag.