If you go to the New Millennium Concepts Site (the makers of Big Berkey filters) you'll find in the FAQ why they don't give micron ratings.

Essentially they say that there are two different rating systems; International (absolute) and U.S.(Nominal); and it has led to confusion in the past. You can decide for yourself whether it sounds legit or not. If it's such a big deal I'd include both, but instead New Millennium decide to provide neither. Also, due to "Proprietary This" and "Trade Secret That" type of language they don't say what materials the filters are made of or contain.

What Millennium Concepts will say is this: "the Black Berkey® elements remove greater than 99.9999999% of pathogenic bacteria such as E.coli. To our knowledge, no other personal filtration element can match that capability. In fact, the Black Berkey® elements are so powerful, they are unique in their ability to mechanically remove food coloring from water."

Also, while Millennium Concepts doesn't mention activated carbon and chemical filtration with the Black Berkey Filter Elements specifically, they list many VOCs (Volatile Organic Compounds) that are removed by their filters.

Since I wrote all that I figured I'd offer the standard disclaimer that I'm not affiliated with Millennium Concepts or Big Berkey in any way. I'm simply interested in the product and my interest in what the filters can do was piqued enough for me to track down the information.
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