The poisoning part isn't a myth. Air quality monitoring shows it. Also shows that it's bad near freeways and high-traffic rail lines and airports. Things like that generally make living nearby unhealthy. They also tend to limit property values, which makes it possible for people with low incomes or who are considered "undesirable" in a racist society to live there, which then results in poor health and quality of life outcomes. Yes, racism is part of the overall picture. No, the big boats (and trains (and trucks)) are not deliberately doing it because they're operated or controlled by racist people (which some are, but that's beside the point), unless the facilities located there because the property was cheap because "people of color" lived there. Which in some cases did in fact happen (freeways were notorious for that in the 1940s-60s).

(Tempted to launch into some ad hominem, but will resist the temptation...)