Personally, I mostly buy the 'loose' leafy greens but, even if they came in a package, I would still do the same thing: soak them in a bowl of cold water with a good splash of dishwasher liquid in it, leave there for 10 or 15 minutes, agitate, agitate, agitate and then rinse, rinse, rinse. And I do it with organic stuff, too because a friend of mine once lost all her budgies and half her tiels from an e-coli infection from organic kale.
https://www.msn.com/en-us/health/nutrit ... =chromentp