Animal dander would be the answer you're looking for.
Hope this helps :)
The odds are astronomical for a father with AB(IV) to have an O(I) child. The only possible way for this phenomenon to occur is if there was a nondisjunction in the ovogenesis for the 9th chromosome and the father also had a nondisjunction for the same chromosome(A sperm cell with no 9th chromosome fertilized an ovum with two 9 chromosomes).
A person with AB cannot donate to a person with O because the receiver has antibodies(alpha and beta) that bind to the antigens on the AB blood cells, causing death.
B water pollution is the answer
