Plastic pollution is turning up everywhere -- including the most remote parks in America -- and the source is surprising.
Tiny bits of microplastics from fragmented plastic bottles and frayed microfabrics from synthetic garments are falling out of the sky with the rain.
The pollution was found in the western United States at cherished national parks such as Joshua Tree, Grand Canyon and Bryce Canyon.
Researchers calculated 1,000 metric tons of tiny microplastic particles fall out of the sky each year in findings published in the journal Science.
The trash particles are tiny, under 5 millimeters, but it adds up to the equivalent of 120 million plastic water bottles.
How do pollutants wind up in the wilderness?
Washing machines flush man-made fibers into water treatment facilities where they pass through untreated and into oceans via wastewater.
Plastic litter breaks down in the ocean and on land but never goes away.
Weather systems blow the particles all over the world. Winds whip fragments into the air and rain scrubs the sky, washing the particles to the ground.
Scientists collected both a bucket of rainwater and a dry air sample. The researchers also modeled where each particular rainstorm had originated to get a sense of how far plastics travel.
They discovered 98% of samples collected over a year contained microplastic particles.
On average, 4% were actually synthetic polymers. The particles that fell in rain were larger than those deposited by wind -- lighter particles are more easily caught up in air currents.
Unlike acid rain, which has been reduced by power plant scrubbers and catalytic converters on cars, plastic waste is expected to increase by 200 million tons over the next 10 years.
Recycling can offset plastic waste
Plastic bottle material is recyclable and so is the cap. Even with two different types of plastics, both can be recycled with the cap attached.
The plastics recycling industry in the past was not able to effectively recycle bottle caps with older methods.