I live in an Easter European major city and when traveling to a civilized country (yes fellow eastern europeans, hate me for saying this) I'm always take aback by the quality of the air. I've recently visited Stockholm and the amount and variety of mushrooms growing in small urban parks surprised me -- I'm sure there's many orders of magnitude less pollution there than where I live.
(my father tells a story of how in the 50s he only had one work shirt and 10 removable collars - he'd wear the same shirt for 2 weeks just changing the collar daily)
I refer you to London's "Great Stink" of 1858 during which the smell was so bad that Parliament seriously considered moving to a different city: https://en.m.wikipedia.org/wiki/Great_Stink
Bollocks man!
In early Victorian London, like most cites of the time, ones shit was directed into a cesspool. These were regularly emptied by 'nightsoil' men who took the waste away as fertiliser. (The drains in the streets were only for rainwater).
What caused the Great Stink was, paradoxically, the invention of the water closet (the flushing bog to you and me) which massively increased the volume of liquid waste, which was then discharged into the Thames and caused the famous Great Stink.
I can assure you, our Victorian ancestors were not animals that regularly shat in the streets.
One would have been grateful to be on The New River company's list of clients.
There's an excellent book also called "The Great Stink" on the problem and on Bazalgette's solution of them.