(CNN) -- Every day we are ingesting tiny, often microscopic pieces of plastic -- "microplastics" -- with our food, beverages and with the very air we breathe.
Americans eat, drink and breathe between 74,000 and 121,000 microplastic particles each year depending on their age and sex, new research suggests.
Those who exclusively drink bottled water rather than tap water can add up to 90,000 plastic particles to their estimated annual total, according to the study published Wednesday in the journal Environmental Science & Technology.
The full impact on our health isn't known. Research shows some particles are small enough to enter our tissues, where they can trigger an immune reaction, or release toxic substances and pollutants absorbed from the environment, including heavy metals.
Where microplastics come from
How do microplastics get into our food and beverages?
To gain a handle on individual ingestion levels, the researchers reviewed 26 previous studies that analyzed microplastic particle consumption in eight categories: air, alcohol, bottled water, honey, seafood, salt, sugar and tap water. Other foods, including meats and vegetables, were not included in their analysis owing to insufficient data.
Next, the researchers estimated average consumption in these eight categories based, in part, on United States Department of Agriculture reports and the 2015-2020 Dietary Guidelines for Americans. Inhalation rates of tiny plastic particles were estimated using data from the US Environmental Protection Agency.
Total annual ingestion and inhalation of microplastics amounted to approximately 81,000 particles for boys, 121,000 for men, 74,000 for girls and 98,000 for women, according to the study.
Whether you drink tap or bottled water is key to annual ingestion of micro-plastics: The researchers estimated annual particle intake via drinking water to be approximately 75,000 for boys, 127,000 for men, 64,000 for girls and 93,000 for women if bottled water is the only source.
For those who consume only tap water, additional microplastic intake for boys is 3,000 particles, 6,000 for men, 3,000 for girls and 4,000 for women.
"Our estimates of American consumption of microplastics are likely drastic underestimates overall," the study authors concluded.
More research of 'nanoplastics' needed
Other scientists take issue with some of the study's findings.
Professor Richard Lampitt, leader of the microplastic research team at the National Oceanography Centre in the United Kingdom, told Science Media Centre that "the paper is a careful assessment of the data which has to date been published" and "the conclusions are sound." Still, Lampitt, who was not involved in the research, criticized the study's lack of a definition of "microplastics."
"Particle size is only mentioned in passing ... and yet this has a massive effect on the data presented and the conclusions reached," he said: Many of the studies on which the study's database is built will have failed to detect very small particles that some consider to be "nanoplastics and outside of this present study."
Alastair Grant, professor of ecology at University of East Anglia in the UK, also criticized the study's scope. Grant, who was not involved in the research, told Science Media Centre: "No evidence is presented that these rates of consumption are a significant danger to human health."
He also said that "the figure for inhalation... does not take into account the systems that our bodies have to remove particles from the air that we breathe."
Stephanie Wright, research associate at King's College London's analytical and environmental sciences department, told Science Media Centre that the researchers have synthesized information from existing studies of plastic particle consumption and simply "reiterate" what is already known.
"Some of the included studies should be interpreted with caution, especially those which only rely on visual means to identify microplastics," said Wright, who was not involved in the research. "These current estimates suggest microplastic exposure is relatively low" and more research is needed to quantify individual exposures to "smaller microplastics, for example in air."
Ultimately, the impact on our health remains "unknown," she added. "It is difficult to interpret the current findings beyond the fact that we consume microplastics."
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