They have tried to clean up The Hammer. Its not easy.
Past metallurgical coke production needed for primary steelmaking, which once happened here, had a pretty good side product, call coal tar.
Coal tar was sold to process into all sorts of clothing dyes, among other things, but it was rich in benzenes, which are none too healthy for you. A bunch of it would just spill our out when way hot and just soak into the ground.
Then about 40 years past a big plastics recycling facility that burned for days that had all sorts of nasties as a by product. Destroyed the finish on a bunch of the fire fighting vehicles, so imagine how nice were all the bits that settled on the ground, and washed into the storm water.
There is a pile of toxic crap known to exist in the harbor, called Randall Reef.
When they tried to clean that up everyone on the barge over it got short term fast sick.
So all that combined with the mess the are the varied SewerGates, and it isn't too pretty.
Yes the upthread study may be flawed, but there are factors not good for you from past industrial activity.
There may be a very good reason that North End and and Keith areas have a distinct lack of nice housing.
If you can afford to you want to live further away from brown field or worse sites .