The small, spongy black beads used as fill material in most artificial turf fields are called crumb rubber, which has long been touted as a major win for recycling. However, conflicting studies have alternately identified crumb rubber as either safe for people to play atop or dangerous to human health.
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In a nearby elementary school, they first took out the grass field (too expensive to maintain), then covered it with asphalt, then carved out a play structure area and covered it with this rubberized stuff.
Won’t be surprised if twenty years from now, it turns out this was the ‘lead paint’ of our time.