Whats the fire retardant that planes drop on wildfires? is it harmful to us or animals, if underneath it or if downstream from the drop? is is considered a toxic or cancer-causing liquid?

Benign: The forestry service uses mixtures of water and Ammonium phosphate along with a benign thickening agent and a coloring agent. The ammonium phosphate salt can have ecological impact especially in waterways, but is not toxic or cancer-causing for living animals. More info at https://www.fs.fed.us/rm/fire/wfcs/products/index.htm and https://www.fs.fed.us/rm/fire/wfcs/index.htm