Courtney Carignan from Harvard sends a link to an update on the research.
… a new study published online in the journal Environment International, co-authored by School of Public Health researchers, reports that popular gymnastics training equipment contains mixtures of flame-retardant chemicals that have been linked to increased risks of ADHD, cancer, and brain development delays.
The study found higher levels of those chemicals in gymnasts’ urine, indicating that gymnastics-training—specifically, pit cubes found in foam pits—are a source of exposure to toxic flame retardants. …
While prior studies have found high levels of such retardants in the air and dust of gyms, the new study, which analyzed foam pits in 11 US gyms, found that 89 percent of pit cubes sampled contained flame-retardants. …
Managers of the gyms reported that they had been required by local fire marshals to purchase equipment containing flame retardants. …
In the short term, one way that gymnasts can reduce their exposure is by washing their hands with soap and water after practice, rather than just with hand-sanitizer, Carignan said. …
For more information gymnastcollaborative.org
Gymnastics Coaching.com 
Good article,but again the study focuses on competitive gymnasts. A competitive level gymnasts knows pit is just a training tool, thus they spend less time in it.
Preschool and rec gymnasts would spend the whole class in there is we let them, thus there exposure is more. There should be a study with them.
Simple solution is too cover the cubes.
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