New York Times: What may be the nation`s largest spill of coal ash lay thick and largely untouched over hundreds of acres of land and waterways Wednesday after a dam broke this week, as officials and environmentalists argued over its potential toxicity. Federal studies have long shown coal ash to contain significant quantities of heavy metals like arsenic, lead and selenium, which can cause cancer and neurological problems. But with no official word on the dangers of the sludge in Tennessee, …