"We should not be in the business of trading a neurotoxin."

Trading emission allowances makes sense for carbon dioxide, which affects the entire planet. Trading allowances for heavy metals such as mercury does not.
The News Journal reports that DNREC understands the distinction and has decided to push ahead with a new program to reduce the most dangerous emissions from power plants:

"It's been our position since day one that we should not be in the business of trading a neurotoxin," said Ali Mirzakhalili, DNREC air-quality program manager.