Standing on the Upper East Side with opponents of the plan to build a waste transfer on East 91st Street, Thompson, the only black candidate in the race, said, “To utter that, and direct it at a black person, at a black man in New York City … those words hurt. Those words are damaging.”

He said he was “stunned and shocked.”

Asked whether he thought the episode reflected on Quinn’s temperament, an issue his supporters have drawn attention to in the past, Thompson said, “You have to ask yourself why would someone utter the phrase environmental racism. Is it anger? What prompted that?”

He also said, “I don’t know why someone would be that reckless with their comments.”

Quinn’s campaign denied Thompson’s characterization of her remarks.

“Let’s be clear, Chris Quinn never called anyone an environmental racist and any suggestion otherwise is simply not true,” Quinn’s campaign spokesman Michael Morey said in a statement today.

He reiterated Quinn’s support for the controversial plan, but rephrased her characterization of the critics.

“You’re either for reducing asthma rates in low-income communities, getting trucks off the road, or you’re not,” Morey said. “This is a matter of environmental justice.”

The facility is slated to open on East 91st Street and York Avenue, across the street from two public housing projects.

The project is opposed by Democratic mayoral candidates Anthony Weiner and Sal Albanese, City Councilman Robert Jackson (who, like Thompson, is black) and a number of city and state legislators based on the Upper East Side.

Other mayoral candidates, including Bill de Blasio and John Liu, have expressed reservations about the site but have not categorically opposed it.

UPDATE: In a statement, de Blasio said, “I believe residents have valid concerns that must be addressed in the implementation process, but I continue to support the five-borough plan and the construction of the East 91st Street facility.”