Emory Report | September 21, 1998 |
Volume 51, No. 5 |
First Person: Minerals are links between Earth and human health Even as we become increasingly aware of our power to change the earth's environment, we can say that, geologically, the earth is in great shape. Humankind, however, may not be doing as well. The earth is our primary life-support system, supplying our basic needs for minerals, water and air. Our increased interest in how the earth works is due, in part, to the connection between geology and health. First a question: What chemicals do you associate with the following conditions: osteoporosis, anemia, dizziness, and heat stress? Most people would probably answer calcium, iron, sodium and water, because we relate a deficiency in them with the corresponding condition. What is surprising is that, when asked where these chemicals come from, many people answer that our body "makes them." Sound incredulous? Well, consider the next question: When cell division takes place in the human body, where do the chemical elements come from that make up the new cells? Again, many people say that the body makes these chemicals. A more accurate answer is that these chemicals come from the cycling of air, water and minerals between the earth and the human body. In fact, the earth's crust contains most of the mineral nutrients our body needs, and the chemical composition of a rock, such as granite, is strikingly similar to the composition of the human body. However, the minerals in granite usually are not in a form easily assimilated and dissolved in the body. So, if you grind up a chunk of granite in hopes of getting your daily mineral supplement, you would probably end up either clogging your intestine or ripping the lining of your digestive tract. So instead of eating chunks of granite for our mineral nutrients, we rely on geologic processes such as weathering to chemically break down rocks into other natural materials, such as soil, that contain minerals more easily dissolved by the acid around roots of plants. The dissolved mineral elements are then incorporated into the plant and stored for our consumption or by some other animal that we later eat (top carnivores have choices!). What are these common chemical elements found in rocks and our body? We are mostly water, about 62 percent by weight, and we must replenish our water budget daily or our body functions will be affected. Our planet is called the "Blue" or "Water Planet" because about 75 percent of the surface of the earth is covered by water. The earth's crust contains most of the 100 or so chemical elements discovered thus far. Only eight of them make up more than 98 percent of the crust. These are, in order of abundance, oxygen, silicon, aluminum, iron, calcium, magnesium, sodium and potassium. In addition to water, we are composed of about 6 percent minerals: calcium, phosphorous, potassium, sulfur, sodium, chlorine, magnesium and iron. Do you see the similarity? Our body contains many additional chemical elements, like iodine and fluorine, in very small but functionally significant amounts. Some of them are easy to identify; teeth and bones are composed of calcium phosphate. Iron is a very common element in rocks and critical to our good health. When we inhale, the oxygen in the air is bonded to the iron contained in hemoglobin. In this way oxygen is transferred from our lungs to the bloodstream. We need to recycle iron on a daily basis because we lose some of it in our urine, feces and menstrual blood. Luckily our body has a nice storehouse for iron, the liver, that helps prevent short-term iron anemia. It is a hard enough job keeping up with our daily needs for the right balance of air, water and mineral nutrients to maintain good health. Now think about what happens when the air we breathe is fouled, the water we drink is polluted and the food we eat is tainted with contaminants. The maintenance of a good internal environment (homeostasis) is increasingly strained by the degradation of the earth's external environment. Try to picture yourself hooked up to the earth's life support with contaminated delivery systems. Our body has a defense mechanism working to destroy or neutralize this unwanted pollution, as well as viruses, bacteria and cancer cells. Our immune system is on surveillance duty all the time looking for these invaders. However, there is a limit to how effectively your immune system can work. For example, during a volcanic eruption, people living nearby may inhale volcanic ash. In children and the elderly, who have smaller lung capacities, this can lead to inflammation and chronic airway resistance or emphysema. Similarly, drinking water contaminated with sewage or animal waste runoff may spread cholera. The resulting diarrhea may result in severe loss of water and electrolytes, which can be fatal to those who already have an impaired immune system. And other contaminants, such as lead in drinking water and mercury in fish, are even more difficult to neutralize. These neurotoxins can accumulate in the body over a life span, causing various losses in our sensory systems. Certainly children, the elderly and people with impaired immune functions are the early targets for these contaminants, hence the relationship of high ozone levels and smog alerts with the number of emergency breathing disorders. But what about people who have strong immune systems and well-developed respiratory, digestive and circulatory systems? What happens to them when they inhale sulfur and sulfuric acid coming from coal-burning power plants? Or when they eat food containing trace amounts of arsenic, nickel or petrochemicals? The effect on them is probably more morbidity than mortality. They just do not feel well, are lethargic or have a certain malaise that does not go away. The good news in all of this is that the more we know and understand about chemical cycling and interactions between the earth and human body, the better position we will be in to make informed decisions about the environmental quality of where we choose to live and work, the food they choose to eat, the water we drink and the air we breathe. Some people have more opportunity to make changes and choices in these things, but everyone benefits from knowing more about how we and the earth work. Bill Size is associate professor and director of the Geosciences Program, interim director of the Human and Natural Ecology Program, and chairman of the Senate committee on the environment.