The Materials Safety Data Sheet for arsenic trioxide classifies it as a confirmed carcinogen that may cause damage to blood, kidneys, liver, the cardiovascular system and the central nervous system, and cautions, “Keep locked up. Do not ingest. Do not breathe dust. Wear suitable protective clothing. If ingested, seek medical advice immediately.” Until 1958, Giant Mine was pumping as much as 7,400 kg of arsenic trioxide dust into the air every day, and as the mine produced more and more gold, the byproduct floated through the sky and precipitated onto the earth, coating the landscape and poisoning the water.
https://thenarwhal.ca/canadas-northern-zombie-mines-lingering-multi-billion-dollar-problem/