It’s really hard to study because population is so diffuse and sometimes don’t align with geography.

My mom used to work in public health research, and one example that was hard to quantify was suspected cancer clusters around roads that were oiled gravel, where the oil was contaminated with industrial waste products. Basically, people who were outside in the summer near a road seemed to get lung cancer at higher rates due to road dust.

Issue was there just weren’t enough people or documentation of the supply chain to really prove it. They were able to stop the process of “donating” waste products to the highway departments.

In an urban environment, it’s easy. There are probably 500,000 people living along busy commercial corridors in NYC where you can reliably measure stuff like exposure to diesel particles or whatever.