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