[RubberFrog]

The "balls" in the thermometer are mercury....

This is simply not true. Most thermometers do not use mercury. Either way, the mercury would be in the fluid, not the ballast. As such, all of the advice that followed it is incorrect as well.

The "balls" are simply ballast used to keep the thermometer righted. Typically they are made of lead or steel.

Unless you have a thermometer pilfered from a research lab, I doubt you need worry about mercury.

Clean out the balls just to be safe, and do a good water change to remove any possible alcohol that may have gotten in the water.

 

[RubberFrog]

Radlations. Your questions have already been answered.

You've been told what the liquid is and what the "balls" are.

There is no law mandating what the ballast be made of. However, they are usually steel or lead.