According to an article at Front Page Magazine, celery produces carcinogens when it comes under attacks from insects. It's a defense mechanism. (So, people, please stop calling celery a "defenseless vegetable".)
So, now you get to choose between chemically-coated celery or carcinogenic celery. Tough choice.
A better choice is just avoid it all. Do the right thing, buy carrots or maybe a nice parsnip or okra. Just say NO to celery.