The U.S. Consumer Product Safety Commission (CPSC) is looking into the possible health risks related to lead found in artificial turf currently installed in schools, parks, and stadiums in the United States. The artificial-turf industry denied its products are dangerous.

Health officials have already closed down two fields in New Jersey after detecting what they found to be unexpectedly high levels of lead in the synthetic turf. This raised concerns that athletes could swallow or inhale fibers or dust from the playing surface.

According to the Synthetic Turf Council, there are approximately 3,500 synthetic playing fields made of various materials—including nylon and polyethylene—nationwide; about 800 are installed annually at schools, colleges, parks, and stadiums.

Use of artificial turf has grown exponentially in recent years and is seen as a way to cut costs and water use. However, pigment containing lead chromate is used in some surfaces to make the grass green, and to enable the turf to maintain its color under the fading effects of sunlight. It remains unclear how widely the compound is used.

The New Jersey Health Department found lead in both of the nylon fields it tested which were Astro Turf brand surfaces.