Soil nutrients taken up by plants are conveyed to animals and humans in food; thus soil chemistry has significant effects on the quality of life. At times, levels of mineral nutrients or soil conditions (such as pH, which affects removal of the nutrients from the soil) are not optimal, and difficulties ensue. Thus, there may be deficiency disorders at one end of the supply spectrum or toxicities at the other. The soil relationships of the micronutrient element selenium are a case in point. Selenium is recognized, at levels of less than 1 part per million (ppm) in the diet, to be an essential nutrient, yet in excess quantities a potent poison.