I've just heard that old Celery is bad too, I don't remember why. By old they mean the Celery that is kind of flexible (celery gets bendy and noodle-like as it ages)

A white mold fungus is commonly found on celery. A mycotoxin. I grow celery.

My guess is the older the celery, the more wide spread the fungus.

Edit:I have also read where Dr. Andrew Weil said to be careful with Celery because of this mold, however, many fruits and vegetables are susceptible to fungus. Wash your produce and don't eat old fruits or vegetables.

I like Celery Juice. The best juice comes from the long, green ribs. It's much better than the yellowish Hearts. I've never had an experience with old celery. I guess anything can get toxic, if it's old enough......WY