Food standards in Whole Foods are closer to UK norms than other American supermarkets. US food safety rules allow a host of things that are banned by the EU (chemically washed meat, pesticides with carcinogenic properties, growth hormones in beef and pork farming, etc.), and regular US supermarkets are full of such foods.
If you are concerned about food standards, Whole Foods are like an extra picky version of Waitrose. Very expensive by US standards, though.