3,625. Bodily Tumah Outside of Israel

Hilchos Bikkurim 5:13

Those who have bodily forms of impurity may recite the bracha and separate challah outside of Israel. There’s no problem with such a person touching challah, only eating it. A kohein who is a minor, or an adult kohein who immersed in a mikvah, who is permitted to eat challah as was discussed in halachos 10-11, may eat it at the same table as a non-kohein. The is because it doesn’t combine to form a prohibited mixture, even if the mixture is 50% challah and 50% secular food. This challah may be given to an unlearned kohein because the one who separated it is ritually unclean from the air of other lands. The prohibition against a kohein soliciting priestly gifts doesn’t apply here. If a person outside of Israel wants to eat first and take challah later, it is permitted because the obligation is a Rabbinic enactment.

Hilchos Bikkurim 5:14

Challah is called terumah, so it may only be taken from dough in the same location, the same as is the case with terumah. Optimally, one should not take ritually clean dough as challah for unclean dough.