The PCBs weren't found in all brands. Google it and you can find a link of the brands tested. GP was not tested so I don't know about it. Nordic Naturals and Carlsons tested PCB free but many other brands had it...Scary.
given cod liver oil has pcbs (as all northern atlantic cod do except for a few very small populations- i'll have to find the article).
how much is it processed to remove these?
how much does the processing change or damage the oils?
it wasn't just which brands process their oils enough to remove it.