As we have learned before, teruma are given to kohanim as kodashim. As such, it can only be eaten if it is tahor and must be treated with care so that it should not become defiled or destroyed. If it becomes tameh, everyone agrees that it still belongs to the kohen, and he is entitled to benefit from it, for example, by using it for fuel or feeding it to his animals.
If, however, the teruma is in a situation of safek (doubt), i.e. it may or may not have become tameh, we find a difference of opinion as to whether the kohen still needs to be careful with it.
Our Gemara quotes a Mishna which brings two opinions about a barrel of teruma that is safek tameh, that is, we are not sure whether or not it is tameh.
In the case of a barrel of teruma produce with regard to which uncertainty developed with regard to its impurity, and which therefore may not be eaten, Rabbi Eliezer says that one must nevertheless safeguard the teruma from ritual impurity. Therefore, he maintains: If the barrel was resting in a vulnerable place, where it may come into contact with impurity, one should place it in a concealed place, and if it was exposed, he should cover it.
Rabbi Yehoshua says: That is not necessary. Rather, even if it was placed in a concealed place, he may place it in a vulnerable place if he chooses. And if it was covered, he may expose it, as he need no longer safeguard this teruma from impurity.
According to some commentaries, even Rabbi Yehoshua does not mean that one is obligated to put such teruma in a place where it will more likely become tameh; rather he is allowed to do so if he wants to. Rabbenu Hananel suggests that we recommend that the teruma be put in a place where it will likely become tameh in order to solve a problem. Ritually pure teruma must be eaten. Ritually defiled teruma cannot be eaten, but it can be used in other ways that benefit the kohen. When we are in a situation of safek – of uncertainty – the kohen cannot eat the teruma, but he cannot do anything to destroy it. Therefore, in its present state, we will be best off if the teruma develops a definite status, so the recommendation is to leave it in a place where it will become tameh.