Scientists study the effects of air pollution on the respiratory system.
I have not seen anyone studying the effects of air pollution on the digestive tract. Why is it important? About half of the mucus we produce in our respiratory system, some of which traps air pollutants, ends up in our stomachs. This is a potent mechanism for the introduction of air pollutants into our digestive tracts.
There has been about a 400% increase in major bowel disease in the US in just the last 50 years or so. This cannot be due to genetics. It is due to lifestyle (a mega-variable that includes diet and stress management). But could air pollution also be a contributor, a hidden variable? Was bowel disease once also really bad when the industrial revolution took hold? Did rates subside, as industry became more environmentally conscious, only to increase again, thanks to the ever increasing population of drivers driving automobiles producing soot from small particles? I clean our cars every week and am amazed at the level of soot trapped in microfiber cloths. We are breathing this stuff and we are eating this stuff. Yuck!