The seminar seemed straightforward enough. Four experts planned to talk about whether artificial grass, which is used on playgrounds and sports fields nationwide, has health risks for children.

But January’s seminar never happened, after the four speakers were sued for defamation by Polyloom, an artificial-turf maker, based on promotional material for the seminar.

“This was before we even said a word,” said Kyla Bennett, an ecologist formerly with the Environmental Protection Agency who is one of the four defendants.

Polyloom and the artificial-turf industry is responding to a growing body of scientific research showing the presence of harmful chemicals in synthetic turf, and potential environmental and health implications. All this is happening as demand for artificial turf, which is made from plastic and mimics the look and feel of natural grass, is booming globally.

Once mainly used in places like professional football or baseball stadiums, today, artificial grass is common in city parks, community playgrounds and fields for high-school football and soccer. It’s even in some suburban backyards where homeowners want to avoid the need to water or mow the lawn.

Between 1,200 and 1,500 large artificial turf fields were installed in 2023, bringing the total in the United States to around 19,000 fields, according to the latest figures from AMI Plastics, an industry data organization.