Just blocks from San Francisco’s southern border with San Mateo County, Crocker Amazon Playground’s natural grass fields in the early mornings look more like a wildlife refuge than an athletic complex. A great blue heron gobbles a gopher. A red-tailed hawk swirls among the cypress trees. 

But the surrounding chain-link fences are creaky, and the grass is lumpy and wet. Everyone agrees: It could use sprucing up.

That has led the San Francisco Giants and the city to propose splitting the cost of a $45 million renovation of the park. Jazzing up the place and replacing the natural grass with artificial turf fields, and installing lights, will allow more playing time, day and night, they say. 

But the plan has gotten swept up into rising public concern — or panic — over microplastics, a health threat that some are comparing to the environmental lead crisis that afflicted past generations. Like plastic water bottles and food packaging, artificial turf is a vehicle for tiny particles of plastic to enter our bodies and waterways, causing major health problems, critics contend. Though the science over microplastics remains unsettled, one Bay Area county this year came close to outlawing these types of fields on public land. 

Microplastic opponents liken it to other substances that have become heavily regulated. “It took a long time with lead and tobacco,” said Sophie Constantinou, who serves on the San Francisco Park, Recreation, Open Space Advisory Committee. “We should at least say we have learned from these mistakes.”

Totaling about 40 acres, the Crocker Amazon park has been a site for team sports for nearly a century. On its southeastern corner are five existing artificial-turf soccer pitches. There’s also a skate park, tennis courts, playgrounds, and a clubhouse. In the early morning, joggers cut through the park, while Asian seniors exercise in groups.

For about five years, the Giants’ philanthropic arm has eyed the area as an opportunity to bring more baseball and softball to the neighborhood, according to team executive Jack Bair. He said inclement weather causes the grass fields to be unplayable for long stretches of time. That wouldn’t be a concern with turf, which has the additional benefit of not needing watering or mowing.

“We’re trying to just expand the opportunity for people in San Francisco that a lot of people, frankly, in other parts of the Bay Area, already have: state-of-the-art facilities that have lights and that are available shortly after a rain,” Bair said.

The renovation would add five artificial turf fields, plus a natural grass one. Batting facilities, an expanded parking lot, and an area for food trucks are also part of the plans. 

“I couldn’t walk a foot without running or stepping into a gopher hole,” said Dan Mauer, who is leading the project for the Recreation and Parks Department. “I’m not throwing shade at our maintenance staff, but they should be doing other things than chasing gophers.”

However, the plans for more artificial turf have alarmed Bob Hall. The retiree has devoted his free time to raising concerns about the fields. He isn’t opposed to the improvement of the park, but would like the Giants and city to reconsider the use of artificial turf. 

Standing near soccer pitches at Ocean Beach, Hall pointed to the plastic green blades and rubber tire infill that have become loosened and blown about by the wind into nearby plants and storm drains. 

“It’s not like getting a plastic shunt in your heart or something where you have to have that plastic in order to live,” he said. “This is just something that we’ve decided to do out of convenience, which is a lot of our problems in society.”

The potential dangers from plastics have been studied for decades. But concerns over microplastics have heated up considerably in the last five years. 

In the case of turf fields, the main concern is the shedding of the plastic green blades that mimic grass. The material contains “forever chemicals” that some scientists say are linked to neurological, cardiovascular, and fertility issues. Known as PFAS, the chemicals are used to help with the extrusion of the plastic during the manufacturing process.

Susanne Brander, an ecotoxicologist at Oregon State University who has studied the effects of artificial turf, said her research is revealing “multi-generational” effects of plastic. “Particles are getting into muscle tissue in fish and interfering with function. And a lot of the things we’re seeing in fish, other labs are seeing in rodents.”

Beyond San Francisco, others are raising concerns about artificial turf. 

In Santa Clara County, a proposition to phase out artificial fields narrowly failed a January vote by the supervisors. A state bill in 2023 that sought to ban chemicals of concern in artificial turf was vetoed by Gov. Gavin Newsom. That same year, a Philidelphia Inquirer investigation suggested artificial turf may have been a contributing factor in the cancer deaths of six former professional baseball players from the Phillies. 

The San Francisco Recreation and Parks Department, which oversees 12 artificial turf sites, said it is doing all it can to mitigate concerns around the health and environmental impacts.

The department is phasing out rubber-crumb infill and plans to use cork or sand instead, though there’s debate over whether the existing material is unsafe. The department and Public Utilities Commission have tested water runoff from existing artificial turf and concluded it was not harmful. 

“It had no primary concern from their perspective; it was more of a public relations issue that they wanted to kind of curtail,” Mauer said of the testing. Nonetheless, he said, a system to capture and filter stormwater runoff will be part of the Crocker Amazon project. 

When asked if advocates’ calls for real grass may be met, Mauer said the artificial turf is “non-negotiable,” since anything else would defeat the purpose of expanding usership of the park.

Recreation and Parks, along with the Giants, held a community meeting on the issue in February and are working on another iteration of the plan. The hope is to start construction in 2027 or 2028. 

But opponents say the city needs to act fast — and make a decision about whether it’s real or fake grass coming to Crocker Amazon. 

Peering through her binoculars, Lydia Bruno, an avid bird-watcher, said artificial turf would irreparably change the green space.

“Even if you’re not a birder, you hear the birds,” she said. “You feel them. Silence would change how this whole place feels.”

Correction: A previous version of this story mischaracterized a January proposal in Santa Clara County to ban artificial turf fields.