A slum is a residential area where dwellings are unfit for human habitation by reasons of dilapidation , overcrowding , faulty ventilation , light or sanitation facilities or any combination of these factors which are detrimental  to the safety and health.
Causes of pollution:-
Slums lack infrastructural facilities .Resources are not clean. The water that they use is not clean and purified. It is contaminated and attracts flies and mosquitoes This water is often stored which causes diseases like malaria.
Also no proper sanitation facilities are there and the lack of this causes diseases like diarrhea, jaundice , cholera, parasitic worms etc.
Thus a slum is an area which is not clean and it thus causes pollution in different ways which too become harmful for people living there.
This is all because they are not aware of the new or mordern techniques for reducing pollution. They live in overcrowded areas. They too dont have proper sanitation facilities which inturn cause air and land pollution. Secondly, they also dont have appropriate water resources. Hence they use nearby lake rivers and pond for household and commercial uses , polluting them.