Is it ok to put sea shells into a goldfish bowl?

Firstly, hopefully you do not have goldfish in the 'goldfish bowl' as they need at least 20 gallons for one goldfish.

That being said, you can add sea shells to a tank provided that you have washed the shells clean with one part bleach to 19 parts water (1 cup of bleach to 19 cups of water), rinsed the shells very well in water, then soaked it in treated water (water that you have added Prime or Amquel to for example) before adding them to your tank.