The average person eats and breathes in up to 120,000 particles of microplastics each year, a study has found.

The health effects of ingesting these particles are still unknown but some pieces are small enough to enter human tissues where they could potentially trigger immune reactions or release toxic substances.

Researchers estimated that the average person consumes between 74,000 to 121,000 microplastic particles every year depending on age and sex. People who drink only bottled water could consume an additional 90,000 microplastics annually.

This is probably a conservative estimation, according to the paper published in the journal Environmental Science & Technology.

The research, led by Dr Kieran Cox from the University of Victoria is the first study to estimate human ingestion of plastic.

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Since the mass production of plastics started in the 1940s, these versatile polymers have spread all over the world and disposing of them has become a growing problem. Microplastics are caused when large plastic products degrade in the environment or flake off during packaging.

Researchers reviewed 26 previous studies that looked at the amounts of microplastic particles in fish, shellfish, added sugars, salts, alcohol, tap or bottled water and air.

They then analysed how much of these foods people eat by looking at the recommended dietary intakes of the 2015 to 2020 Dietary Guidelines for Americans. Many food and drink types were not tested and the study only looked at 15 per cent of total calorie intake.

“These estimates are subject to large amounts of variation; however, given methodological and data limitations, these values are likely underestimates,” researchers wrote in the paper.

“These data suggest that microplastics will continue to be found in the majority, if not all, items intended for human consumption.”

Professor Richard Lampitt, leader of the Microplastic Research Team at the National Oceanography Centre, who was not involved in the research, said; “I think the paper is a careful assessment of the data which has to date been published and that the conclusions are sound.”

However, other researchers have criticised the findings.

Professor Alastair Grant, professor of ecology at the University of East Anglia, said: “The authors calculate consumption of microplastics from measured concentrations in food and air.

“They calculate that an adult male consumes 142 plastic particles per day by mouth and inhales another 170. The rather large numbers that are given most prominence are annual estimates. No evidence is presented that these rates of consumption are a significant danger to human health.”

Dr Stephanie Wright, a research associate at King’s College London, said some of the included studies should be interpreted with caution.