Menachot 25: The Power of the Tzitz, Frontplatm

A new Mishna shares what should be done when the kometz, the handful of meal-offering taken by a priest, becomes tamei, ritually impure.  The Mishna teaches that the offering is valid even if it is sacrificed in a state of ritual impurity.  This is because the tzitz, the frontplate worn by the high priest, provides atonement for ritual defilement in the Temple. If, however, the meal-offering was removed from the Temple grounds and thus became tamei, the tzitz will not atone for the ritual impurity.

The rabbis discuss the Mishna's prevention of its suggestion in the past tense: a ritually impure kometz "that was sacrificed".  This might suggest that the the sacrifice should not be brought at all.  It would only be accepted as valid after-the-fact.  We are told that Rashi (Masechet Gittin 54) says that sacrificial blood that had become tamei could be sprinkled and the kometz could be sacrificed according to Torah law.  Rabbinic law is more stringent.  Later in Masechet Pesachim (34) Rashi comments that the tzitz only atones for ritual impurity in the Temple after-the-fact, but it cannot permit sacrifices brought in the best possible way.

The rabbis disagree about how and in which circumstances the tzitz will atone for tumah.  We learn that the Tosefta report Rabbi Akiva's ruling: the tzitz even has the power to atone for offerings that were taken out of the the Temple grounds.