Okay, this is way outside my area of expertise, but I thought this was really interesting. It seems that some organisms can adapt to what would normally be lethal levels of chemical pollutants. A paper published in Science reports that genetic adaptions in the Atlantic killifish (Fundulus heteroclitus) allow it to survive what, in unpolluted environments, would be lethal levels of bioaccumulative dioxin-like contaminants. The authors suggest that the killifish is able to adapt rapidly due to its large population sizes and high levels of genetic diversity.

Reid et al., Science 354 (6317): 1305-1308.