RL Fernadez writes in A SIMPLE MATTER OF SALT: AN ETHNOGRAPHY OF NUTRITIONAL DEFICIENCY IN SPAIN (1990) about "mineral goitrogens." Ground water passing over bedrock limestone can dissolve calcium and fluorine and ener the water supply. He holds these mineral goitrogens are characteristic of part of his native Spain as well as the goiter belt of the midwest.
Wombat introduced me to this author. I'm still rereading...