It has long been known that in a certain region of the United States a goiter belt exists. The incidence of goiter formation correlates inversely as the concentration of iodine in the soil. In areas of high soil selenium content there are a large number of cases with gastric or intestinal dysfunction as well as hepatic dysfunction. Will epidemiological studies show higher gastric cancer in this region? Multiple sclerosis and other neurological diseases may be correlated with areas having greater amounts of lead in earth's crust than that considered "normal".

Again, one can not draw simple conclusions or simple correlations on soil deficiencies or excesses of certain elements. While a deficiency of copper in the soil may affect crops and stock, there is no indication of any areas where copper deficiency is found in man. However, man's food does not come solely from one geographic source.

Correlative studies are being made between the trace element content of the soil and the incidence and type of tumor of the human population of the region. In some parts of Europe a relationship was found between the number of inhabitants who developed stomach cancer and the distribution of minerals in the local soil. In some French areas a lack of magnesium oxide content seems to be reflected in a greater occurrence of cancer. Higher silicon dioxide content of the soil in some parts of the Netherlands regions seems also to be associated with greater number of cancer patients; the effects of the high silica concentration seem to be overcome by a high calcium oxide content. Results found may be related to the fact that tumors have a low calcium content, which may decrease the adhesiveness of these special cells and thus contribute to their increased invasiveness.

Similar studies undertaken in Great Britain on the relationship between cancer incidence and types and percentages of trace elements in the soil have shown that chalk and limestone areas have low cancer rates. Some correlations between high zinc and chromium content of the soil and stomach cancer appear to be positive. In North Montgomeryshire, the mortality rate for gastro intestinal cancer for the years 1946-1959 exceeded that of the rest of England and Wales. An inconclusive study was made to find some common denominator, like a carcinogen, or special radioactive drinking water, but no examination was made of the mineral content of the soil. The idea has been expressed that the most reliable data will be obtained from statistics on inhabitants who have resided in one region for forty years or longer. It seems indicated now that epidemiologic studies should be made of regions that have soils deficient in one or more trace elements, such as cobalt, or have a large excess of some element like selenium.

Besides plants as a source of trace or minor elements in nutrition, the human is constantly being exposed to abnormal amounts of these trace chemicals in processed foods. Equipment used may be subject to abrasion, and the container cans may have many impurities. As a result, arsenic, lead, copper, zinc, nickel, mercury, and antimony may be ingested in processed foods. A symposium held in Scotland by the Nutrition Society brought these facts to light. Cooking utensils and coatings of utensils may also be a source of metals. Nickel is used as a catalyst for the hydrogenation of oils to fats.

How many minerals do city dwellers inhale from automobile exhausts, or from smokes and smog, and how many carcinogenic hydrocarbons are contained in our polluted air?

Geological studies on the content of carcinogenic hydrocarbons should also be considered. Decaying plant life or microbial synthesis may give rise to these compounds in the soil, and, indeed, these carcinogenic agents have been found in rural areas away from automobile exhaust gases or industrial wastes. Are these hydrocarbons taken up by plants?