During my workout the other day at McCarren Park, I saw a crew (two people) repairing the synthetic field at McCarren Park so I took the opportunity to ask them about the reported danger of the rubber infill. They said the danger was overblown and that one would need to physically EAT 21 cubic feet of the stuff to attain a measurable lead level. This sort of jibes with our thought that one should always be at least somewhat wary of what's underfoot in the City.
Still, I'm willing to run barefoot on the synthetic (carefully washing feet in shower afterward). This situation could not be more different from the dirt and gravel field that proceeded it, which even included screws, nails, and pieces of metal plate. A single person running across the field caused a major dust storm and during windy days, downwind soccer teams could not see the far goal.
Given the neighborhood's industrial past and high volume of trucks, I'm pretty sure that dust (which became airborn at the least wisp of breeze) delivered more lead on one afternoon than a lifetime on the artificial turf would do.
It's possible that the stuff is not as safe as it should be but I for one am grateful that it's there.
By the way, the repair team was not wearing dust masks or respirators. They had on rubber gloves but that's because they were using some nasty looking glue to hold the turf down.