A new study has found that the global average of microplastic ingestion could be as high as five grams a week per person, which is the equivalent of eating a teaspoon of plastic - or a credit card - every week.
The study was commissioned by the World Wide Fund for Nature (WWF) and carried out by the microplastics research team at Australia's University of Newcastle.
It collated the findings of 50 international research papers in an attempt to provide an accurate calculation of ingestion rates.
It found that based on "conservative assumptions" people are consuming about 2000 tiny pieces of plastic each week.
The study focused on microplastic less than 1mm in size, which are the most commonly ingested contaminants.
Water is the main source
University of Newcastle researcher Thava Palanisami said water, both bottled and tap, was the largest single source of plastic ingestion.
"In water it's mostly fibres which could come from industrial activities," he said.
"It's released with other gases and chemicals and this can then ultimately sink into the freshwater bodies and that gets into the drinking water.
"And there are no filtration systems for bottled water that could filter out those sub-micron phase particles."
One study confirmed that bottled water from groundwater sources was mostly free of plastics, Dr Palanisami said.
Of the consumables studied, those with the highest recorded plastic levels included shellfish, beer and salt.
Dr Palanisami said microplastics were an emerging contaminant and there was little specific data for Australia, but he would expect ingestion rates to be lower there due to lower seafood consumption rates and a cleaner environment.
He said the next phase of their research will be to better understand the human health impact of ingesting plastics.
"What is the real impact? This needs to be explored," Dr Palanisami said. "What will happen if you ingest 5g of plastic a week? Is it toxic or an inert material?"
The report titled No Plastic in Nature: Assessing Plastic Ingestion from Nature to People has been under consideration for academic publication, but was released early to coincide with WWF's campaign for action on plastic pollution.
A similar study by the University of Victoria in Canada was published in the Journal of Environmental Science and Technology last week. It analysed 26 research papers and found that people are consuming at least 50,000 pieces of microplastic a year.
Urgent global action needed
WWF said the leakage of plastic into the environment and food chain has been met with an inadequate global response from governments.
"These findings must serve as a wake-up call to governments," said Marco Lambertini, WWF international director-general.
"Not only are plastics polluting our oceans and waterways and killing marine life - it's in all of us and we can't escape consuming plastics.
"We need urgent action at government, business and consumer levels, and a global treaty with global targets to address plastic pollution."
A WWF petition calling for a legally binding treaty on marine plastics pollution has so far gathering more than half a million signatures.
The group said that since 2000 the world has produced as much plastic as all the preceding years combined, a third of which is leaked into nature.
It said 104 million metric tons of plastic could be released into the environment by 2030 unless drastic action is taken.
This week Canada announced it would move to ban single-use plastic items by as early as 2021.
It followed the European Union's decision in March to ban plastic items such as plastic cutlery, cotton buds, straws and stirrers by 2021.