Megan Gibson, Time

CHINA -This just might be the saddest news you will hear today—a giant panda, living in China’s Jinan Zoo, died after accidently being gassed with carbon monoxide and chlorine.

An autopsy released on Tuesday revealed that the 21-year-old panda, Quan Quan, inhaled the gases that were being used to disinfect a nearby former air raid shelter. The toxic gases caused her lungs to collapse and despite attempts to save her, Quan Quan died in the hospital.

(See TIME’s photo essay on panda Tai Shan’s journey to China)

Zoo officials say that the gases had come through ventilation pipes that the zoo shared with the raid shelter. Activists are already pointing to Quan Quan’s death as another indication of how zoos should improve their treatment of animals in captivity.

(See the viral sneezing panda clip in TIME’s 50 best YouTube videos)

“These pandas are being bred for a life in captivity,” said Kati Loeffler, a veterinary advisor for the International Fund for Animal Welfare. “Why are they being bred? Just so they can circulate through zoos and live next to old air raid shelters?”

As pandas are on the endangered species list, Quan Quan was reportedly considered a “heroic mother” in China, because she has given birth to seven cubs.