Bolt head corrosion in soup. Toxic? Zinc? Cadmium? This may not be quite the right forum for this question, but please help me if you can.

I recently repaired the lid of my grandma's crockpot using a bolt I found in a miscellaneous fastener box in the garage. I've been using the crockpot quite a lot since then, and I just noticed that the bolt head is corroding with white gunk. I also noticed a white film floating on the middle of the soup I left cooking all night, obviously from some of the corrosion dripping onto the soup. My grandma and I had both tasted the soup before I noticed the corrosion and film. I've been doing a little research to try and identify the bolt's coating by its appearance, and I am concerned that it might be zinc or cadmium, which are apparently highly toxic. [EDIT: apparently zinc is not highly toxic, so I guess my main concern is: is this cadmium? Also, the bolt may well be over 50 years old, as it's from my grandparents' garage]

I'm hoping someone here who's more familiar with these materials can tell me:


What metal this corrosion looks like
Whether I should be concerned about toxicity considering the quantities present




I'm including a picture of another bolt that matches the one in question, with yellow zinc plated wood screws and some U.S. currency for visual reference.


I will of course be replacing the bolt with something explicitly food-safe, but having already consumed some of the soup, I want to know if we should be high-tailing it to the emergency room, or if in fact it's safe to finish the soup (it's good soup!).
You can test for cadmium at home, but the ~US$30 price for the test kit (with 1,5-diphenylcarbazone) is probably more than the soup is worth, and the test might not be sensitive enough to detect sub-acute toxic amounts of Cd.

Considering the highly toxic nature of the metal, you might check with your family physician if you and anyone else sampling the soup should have a blood or urine test.

As has been mentioned, the small amount of zinc that might have been absorbed had the bolt been galvanized (unlikely, anyway) is not significant. The US NIH recommends ~10 mg of Zn in the diet per day as a nutrient.