Heat and humidity. Humidity more than the heat in my experience. Spools of pla get brittle if left in a humid environment.

This is not true. To elaborate on what the other person who replied said… there is no safe level of lead in consumer products because lead accumulates in the body. Also, lots of consumer products still contain lead because there are loopholes. And the regulations any way aren’t that stringent.

Bambu labs all the way. Unless you want your hobby to become printer maintenance.