Not all 'toxic' wildlife is our fault. Mercury content of fish can be naturally occuring.

Generally top food chain critters end up collecting the toxins that are in all the stuff they eat which is why shark fin soup has so much mercury in it and polar bears are considered so toxic.

A note on that though 'toxic' doesn't always mean 'poison'. One of the most toxic things to eat in a polar bear is it's liver. Most automatically assume that it's because that's where all the blood toxins are collected from the toxic critters it's been eating...but that's not the case. A polar bears liver will kill you because it has more Vitamin A than your body can handle due to it's diet of seals and such which also have a very high Vitamin A content (eating Seal liver is also not recommended from what I know).

Can we blame humanity on that? Some will try but I think we need to be a little smarter before we start pointing fingers.