ATHENS, GREECE - JUNE 26: Plastic cups used by tourists on the Aegean sea beach near Athens on June 26, 2018 , Greece . The Mediterranean is one of the seas with the highest levels of plastic pollution in the world .More than 200 million tourists visit the Mediterranean each year causing the 40% increase in marine litter during summer  using  single use plastics including straws and stirrers, plastic cups, water bottles , inflatable pool toys etc which   leads to the general pollution of water and beaches along Mediterranean. (Photo by Milos Bicanski/Getty Images)
Plastic pollution is killing these animals
01:22 - Source: CNN
CNN  — 

Cars may be doing more damage to our environment than we realized.

The harmful effects that fossil fuels have on our environment are well documented – a study from March found that global fossil-fuel emissions account for nearly 70% of climate cooling. But cars appear to be polluting in a way that hasn’t been deeply studied.

According to a study from the San Francisco Bay Microplastics Project, the biggest source of microplastic pollution in California’s coastal waters may come from car tires.

Microplastics are defined by the National Oceanic and Atmospheric Administration (NOAA) as fragments of plastic that are less than 5 mm in length (think the size of a sesame seed).

Microplastics have been found in the stomachs of a number of marine organisms, and chemical additives from microplastics can also bleed out into the ocean, according to the NOAA. It is also possible that contaminants from the water may adhere to microplastics.

The NOAA has not yet been determined if these contaminants transfer through the food chain.

The San Francisco Estuary Institute teamed up with the 5 Gyres Institute to complete a three-year study in what they claim is the first comprehensive regional study of microplastic pollution.

The study found that more than 7 trillion pieces of microplastics wash into the San Francisco Bay each year, with much of it coming from tire particles that were left behind on streets.

Those 7 trillion pieces of microplastics are 300 times greater than the discharge that comes from all wastewater treatments plants discharging into San Francisco Bay annually.

The study of microplastic pollution is a relatively new field, and microplastics are difficult to study because their size and seemingly endless sources. There is no accepted standard for sample collection, processing, analysis and reporting.

The San Francisco Bay Microplastics Project aims to contribute to the development of those standards, to discover a baseline for future monitoring and to ultimately facilitate policy options with recommendations on the reduction of microplastics.