More than 90 percent of table salts sold and consumed around the world may contain microplastics, according to a study published in Environmental Science and Technology. That means the average adult may consume an estimated 2,000 microplastics each year from salt alone.

These plastic pieces measure less than 5 millimeters long (or about the size of a sesame seed) and are made when larger pieces of plastic degrade, says the National Ocean Service. They are also found as microbeads in health and beauty products, cleaners, and toothpaste. When flushed or drained, these plastics are small enough to pass through water filtration systems and make their way to water systems globally – and, ultimately, onto your plate.

To understand how pervasive microplastics are in salt sold for human consumption, researchers in South Korea teamed up with Greenpeace East Asia to compare the geographic spread of microplastics in salt with plastic pollution found in the environment.

Of 39 brands of sea salt sourced from 21 countries in Europe, Africa, Asia, and North and South America, all but three were found to contain microplastics, including the US and Canada. The amount of microplastics varies between different brands. While the researchers did not publish brand names in their study, they note microplastic levels were especially high for salts consumed in Asia, one of the world’s most polluted regions, particularly Indonesia. Additionally, the salt derived from seawater contained the highest levels of the contaminant. Sea salt is produced by evaporating ocean water and, since it involves very little processing, often leaves behind trace minerals and elements (including plastics). Lake salt and rock salt mined from underground deposits also contained high levels of microplastics.

Only three brands of salt produced in Taiwan (refined sea salt), China (mainland rock salt), and France (unrefined sea salt produced by solar evaporation) were not found to contain microplastic particles.

“The findings suggest that human ingestion of microplastics via marine products is strongly related to plastic emissions in a given region,” said Professor Seung-Kyu Kim, corresponding author of the study, in a statement. “In order to limit our exposure to microplastics, preventative measures are required, such as controlling the environmental discharge of mismanaged plastics and more importantly, reducing plastic waste.”

The health impacts of consuming microplastics are not yet known because it’s a relatively new field of study. According to the United Nations Environmental Program, plastic microbeads first started showing up in products around 50 years ago and have steadily replaced natural ingredients ever since.

A growing body of work illustrates how microplastics are now found in nearly every pocket of the world, including in Arctic ice. A study earlier this year suggests people could be eating more than 100 microplastic pieces in every meal from household dust.