If those particles are smaller than 5 microns this is not an issue - we have a boatload of "metal particles" in us all the time - called IRON.
What is the relevance of your message here?
No one doubts that scientists can detect whether a few particles are magnetic or not.
I also don’t understand why you mentioned that there is iron in the blood, which is common knowledge.
Iron in your blood is not magnetic. If it was, everyone getting an MRI would die.