A new study has revealed a surprising source of microplastics that have been silently filling the oceans and spreading into sea life.

Of the seven trillion pieces of microplastics that end up in the San Francisco Bay every year, much of it can be traced back to car tires.

As people drive, tires shed microscopic plastic particles that collect on street surfaces and are then washed out into the bay by rain waters.

Scroll down for video

A new study found that car tires are the main source of the 7 trillion microplastic particles end up in the San Francisco Bay each year

The study, by the San Francisco Estuary Institute and The Aquatic Science Center, found that car tires produced 300 times more microplastics than those produced by washing polyester clothes or microbeads contained in beauty products.

Microplastics have also been found in rainwater and snow samples in the Rocky Mountains.

Earlier this year, microplastics were also found in the Arctic Circle, which scientists believe were transported their via win

Researchers believe that microplastic particles can travel hundreds, and potentially thousands, or miles through the air.

New research shows that cars produce three times the amount of microplastic particles as washing polyster clothing or runoff from soaps containing microbeads.

Humans ingest an estimated 73,000 bits of plastic a year, mainly through eating and drinking.

One study found that the average human consumes the equivalent of a credit card worth of plastic every week.

Plastics have had a significant impact on animal life both in the sea and on dry land.

Researchers found that plastic particles in the ground was stunting the growth of earthworms.

Microplastics enter the waterways through a variety of means and finish suspended in the liquid. They can be transported long distances both in water and via the air, taking them to the furthest corners of the world

WHAT ARE MICROPLASTICS AND HOW DO THEY GET INTO OUR WATERWAYS? Microplastics are plastic particles measuring less than five millimetres (0.2 inches). They have hit the headlines over recent years, as improper disposal has resulted in tonnes of waste making its way into the ocean. Each year, tonnes of plastic waste fails to get recycled and dealt with correctly, which can mean they end up in marine ecosystems. Although it's unclear exactly how they end up in the water, microplastics may enter through simple everyday wear and tear of clothing and carpets. Tumble dryers may also be a source, particularly if they have a vent to the open air. Plastics don't break down for thousands of years and it is estimated that there are already millions of items of plastic waste in the oceans. This number is expected to rise. Studies have also revealed 700,000 plastic fibres could be released into the atmosphere with every washing machine cycle. Current water systems are unable to effectively filter out all microplastic contamination, due to the varying size of particles. The amount of plastic rubbish in the world's oceans will outweigh fish by 2050 unless the world takes drastic action to further recycle, a report released in 2016 revealed. More than 80 per cent of the world's tap water is contaminated with plastic, research published in September 2017 revealed. The US has the highest contamination rate at 93 per cent, followed by Lebanon and India, experts from the University of Minnesota found. France, Germany and the UK have the lowest levels, however, they still come in at 72 per cent. Overall, 83 per cent of water samples from dozens of nations around the world contain microplastics. Scientists warn microplastics are so small they could penetrate organs. Bottled water may not be a safer alternative, as scientists have found contaminated samples. Creatures of all shapes and sizes have been found to have consumed the plastics, whether directly or indirectly. Previous research has also revealed microplastics absorb toxic chemicals, which are then released in the gut of animals. Advertisement

Microplastics in the ocean have doubled in volume every year since 1940 according to Jennifer Brandon, a biologist specializing in microplastics at UC San Diego.

'We're using more and more plastic and it's showing up as a footprint on the seafloor,' Brandon told the LA Times.

A UN study published in August found microplastics were present in bottled water.

'Based on the limited information we have, microplastics in drinking water don't appear to pose a health risk at current levels,' the World Health Organization's Dr. Maria Neira said.

'But we need to find out more. We also need to stop the rise in plastic pollution worldwide.'