From Rabbi Sternbuch’s English Parsha sheet on Parshas Vayeishev:
“And they lifted their eyes and saw, and behold, a caravan of Yishmoelites was coming from Gilad, and their camels were carrying spices, balm, and lotus, going to take it down to Egypt” (37:25). Rashi: Why did the possuk publicize their burden? To let you know the reward of the righteous, for it is customary for Arabs to carry only paraffin and tar, whose odor is unpleasant, but for Yoseph spices were arranged, so that he should not be harmed by an unpleasant odor…
[Rabbi Sternbuch quotes the Brisker interpretation:]
Yosef did not divert his mind from Torah even for a moment, and if the Yishmoelites would have carried paraffin and tar, whose odor is very unpleasant, he would have been forbidden from thinking divrei Torah. Therefore Hashem orchestrated events such that Yosef would be able to continue delving in Torah also during his trip to Egypt.
I don’t know who the “Briskers” are in this case, but this doesn’t make sense to me.
If all naturally malodorous substances, including even paraffin and tar, are equivalent to tzo’ah, the Gemara should have mentioned the greater chiddush! How can a shochet recite בא”י אמ”ה אשר קדשנו במצותיו וצונו על השחיטה\על כיסוי הדם while surrounded by his labors? How can an unwashed mourner (or during Bein Hametzarim) or those next to him say berachos?! And so on.