Thank you for your comment. I think Ryan Gilley provides a good answer (thank you, Ryan, for replying).

In terms of our bodies' failure to deal with Covid-19, I think pre-existing medical conditions and old age, both of which impairs the immune system to some degree, are more substantial risk factors for severe Covid-19 than chemicals and nanoparticles lingering in our environment.

But it's also true that health effects of such environmental pollutants are difficult to study in humans, so we are not quite sure of what health impacts they have. Another way to look at it from an environmental stressor perspective is the role of chronic mental stress (from work or relationships), which is capable of weakening the immune system in humans.