The food has lead or other contaminants in it.

i think (without proof / reference) that plant is harder to fool with. if the environment is not suitable (too much heavy metal, salty water, too acidic/basic) then the plant either die or grows very slowly and it's not pretty (colorful leaf due to excessive iron), basically you don't want to eat it just by looking at it

animals, on the other hand, are much easier to fool with. here, bad people 'rejuvenate' 3-days old meat by soaking it in formalin and fresh blood.

actually, i meant to say that animals are more hardy/sturdier than plants; thus, can sustain more abuse/pollutions

NB: there are hardy plants that absorb heavy metals (like water hyacinth) by simply growing too fast, they are employed by water treatment facilities ... but people don't normally eat those plants, maybe not edible

Various members of the mustard family are used for phytorememdiation. People eat many members of the mustard family.

You realize, right, that you are reasoning from a very shaky foundation and using that reasoning to make advice about health and safety. My advice: Don't do that any more.

"Various members of the mustard family are used for phytorememdiation. People eat many members of the mustard family."

it's akin to say "water is used to clean dirt. People drink water"

for every hypothesis, there will always be special case(s) to refute it.

thx for your concern, but really, i'm more interested in what you say about the topic: what should we eat? where can we get the polutant-free food?

And what is the effect on filtered water of water contaminated with various substances?

I'm not sure that's true. I've read that heavy metals in motor oil are not absorbed into plants growing in contaminated soil.

Can you show otherwise?