???By Kevin Drum| Fri Dec. 23, 2011 1:21 PM ESTEarlier this morning I wrote that even with estimated benefits of $90 billion per year, the EPA may be selling short its new rules limiting emissions of mercury and other airborne toxins. (Most of that $90 billion estimate is due to reductions in particulate matter, not mercury.) After all, mercury is a dangerous neurotoxin, and the cost of cognitive