Huge gaps exist in scientific knowledge, but California is about to set the world’s first health guidelines for microplastics in drinking water. Yet no one agrees how to test water for the tiny bits of plastic, or how dangerous they are.

Lea este artículo en español.

California is poised to issue the world’s first guidelines for microplastics in drinking water despite no data on how plentiful they are in the state, no scientific agreement on how to test water for them and little research on their health risks.

The pieces of plastic — smaller than an ant, some so tiny they can be seen only with a microscope — have contaminated wildlife and human bodies through their food, air and water.

Under a 2018 state law, California must require four years of testing for microplastics in drinking water, and the state must consider guidelines to help water providers and consumers determine what levels may be safe to drink.

Now the state Water Resources Control Board is blazing a trail to issue a preliminary health-based threshold and testing methods by July 1.

The state’s aim is to take a precautionary approach, moving to tackle potential threats posed by microplastics.

“Is it too early to do something? No, it is actually a bit late.”


But there are big obstacles to such early action: Research into the consequences of ingesting tiny plastic fragments is still in its infancy. No one knows how widespread microplastics in California’s drinking water really are. There isn’t even a standardized method to test for them. And no one knows what dose may be “safe” to consume, since the human health effects are largely unknown.

California’s water regulators are pushing to close those gaps. “To be honest, if the legislature hadn’t given us such an aggressive deadline, with rather high goals, this might not happen this year,” said Scott Coffin, a research scientist with the State Water Resources Control Board. “It really is accelerating the field quite a bit.”

Theresa Slifko, chemistry unit manager at the Metropolitan Water District of Southern California, which provides imported water to 19 million Californians, warns that monitoring drinking water for microplastics is going to be “very complicated and time consuming, and that’s why it’s expensive.”

Developing a health guideline for microplastics is “a tough one,” said Razmik Manoukian, the Los Angeles Department of Water and Power’s director of water quality.“But there’s a lot of studies worldwide done on plastic exposures … so it could be they can come out with a preliminary number.”

Researchers applaud California’s efforts to move forward, even though they caution that drinking water is not thought to be the biggest source of microplastics people consume. People probably absorb more simply by breathing.

“We now know that we live in a soup of plastic that is getting ever denser. And we don’t seem to be changing our ways. And the contaminants, they live longer than we do, meaning that the soup will get thicker,” said Rolf Halden, director of the Biodesign Center for Environmental Health Engineering at Arizona State University.

“So is it too early to do something? No, it is actually a bit late.”

Awash in microplastics

Microplastics have contaminated the environment and the bodies of animals around the world: Ice cores in the Arctic, invertebrates in Antarctica, humpback whales in the North Seaseals and seabirds in the Southern Ocean, fish and shellfish on six continents and even human placentas. 

California banned microbeads in toiletries like facial scrubs and toothpaste five years ago. But sources of tiny plastic are still ubiquitous: Synthetic clothing sheds microplastics in wash cycles that discharge into sewers, fragments rub off car tires and ever-increasing plastic waste crumbles into tiny particles. All of these particles can wind up in waterways that provide drinking water, such as the massive, 444-mile long California Aqueduct.The California Aqueduct near Huron, CA in the San Joaquin Valley. Runoff carrying microplastics can pollute open channels like one which provides much of the imported water to the Metropolitan Water District. Photo by Michelle Sneed, US Geological Survey

Runoff carrying microplastics can pollute open channels such as the California Aqueduct, which provides much of the imported water to the Metropolitan Water District’s 19 million customers in Southern California. Photo by Michelle Sneed, US Geological Survey