Heptachloronorbornene
From Coastal Wiki
Heptachloronorbornene is a very hydrophobic chemical intermediates
Heptachloronorbornene can be converted to hexachloronor-bornadiene which is an intermediate in the syntheses of the stable chlorinated cyclodiene insecticides such as aldrin and isodrin.
It has a very high tendency to bioaccumulate.
Therefore, it is not surprising that these compounds were identified as contaminants in edible fish from rivers in the USA.