Theory:Torchwood television discontinuity and plot holes/Everything Changes


 * Jack pronounces estrogen at the very beginning of the episode as "ee-strogen". An American would pronounce it "eh-strogen".
 * Jack is from the Boeshane Peninsula; it could be a regional aspect to it, like ordinary accents. Flashbacks in "Adam" show a young Jack saying "Mum" instead of the more American "Mom." Alternatively, Jack may have been living in the UK long enough to have become used to pronouncing certain words in their British form. In THE STOLEN EARTH he says to Gwen and Ianto "Im sorry, we're dead" in a very english accent. Jack isn't American. He was only pretending to be American when he met the Doctor, and he kept the accent. Therefore he may say things differently.
 * Actually, that's Jack's real accent according to episodes such as Adam and Exit Wounds.
 * We don't know if the Boeshane Peninsula is even on Earth, let alone America. Over the years there in Cardiff I'd say likely he's found that he'll not be understood by his coworkers if he uses the American term rather than the British.