There are 3 ways to make lye, NaOH, with a Chloralkali
process.
Coca-Cola owns 9 currently operating plants in the USA
that use the Mercury Cell Chloralkali method.
Here is an excerpt from a Mother Jones article dating
back to 2004.
Here is a more
scientific post in regards to the missing mercury.
Here is what the FDA had to say when fronted with the
loss of mercury into the food supply and the runoff into local water supplies.
The EPA declared that "the fate of all the mercury
consumed at mercury-cell chlor-alkali plants remains somewhat of an
enigma."