Insalubrious
Definition: not conducive to health
This is the opposite of “salubrious” which means “favorable to or promoting health or well-being,” but I doubt that gets used as often.
Why I Looked It Up
It was used in a documentary about World War 1, referring to the conditions in the trenches of Verdun. I think it was used by a physician in a letter home during the time period.
Postscript
Added on
The opposite was used in a speech by Abraham Lincoln:
We find ourselves in sole peaceful possession, of the fairest portion of the earth, as regards extent of territory, fertility of soil, and salubrity of climate.