These emanations are poisonous and can kill delicate plants if watered by a woman in her menses. Even foodstuff like pickles and wine get spoiled if handled by a woman in her menses. The very air around her gets polluted. Even her breath smells foul. Spiritual impurities are known as 'DRUJ' in Avesta.
Impure blood is a dead part of the human body and therefore it becomes druj.
It is said that the magnetic emanations from a menstruating woman can damage the aura of a saintly person upto a distance of around 10 feet. Such is the effect of menses, even though it may be a normal monthly affair for all women. Not only women, but even if a priest has a festering wound, or bleeding wound, he is not allowed to perform religious ceremonies. Sickness, disease, unnatural menses are NOT of Ahura Mazda. It is pertinent to understand that ahreman has vowed to destroy all God's good creations.