The soil is red from the rich iron deposits found in the Nambian deserts where the film was shot.
I only know this because where I am from in Oklahoma the soil is the same red color from the same kind of deposits the waters from millions of years ago deposited here as it did there before it receded.
But yes in the film the tumors were caused from sour soil, toxic air and ground water and everything else that came from that region where the war boys grew up.
I say this only from reading multiple articles and coming to the conclusion in my own words on how the apocalypse came about destroyed the earth & souring the soil and water leaving their bones irradiated and becoming half life.
I edited a comment above this explaining what was said during the scene where the "perfect baby" was taken In a make shift crude representation of a C-Section delivery.