how much sodium in 1 tablespoon of baking soda

Sodium in 1 Tbsp Baking Soda: 3,780 mg (Bagel Bath Math)

One level tablespoon of baking soda holds about 3,780 mg of sodium. Here is that against the 2,300 mg limit, why a tablespoon is not a dose, and a bagel recipe with a 1 tbsp boil bath.