Question

why there is a increase of concentration of toxic levels in each level

Answer 1

Their is a increses of concentration of toxic levels in each level of food chain because, what one eat (harmful toxic substances) can't be digested because of lack of enzymes. So, they remain inside our body and thus, when higher trophic level eats it, it get rendered to them also.

This is also known as $\textbf{Biological Magnification }$