PASSAGE 19
Geology and Health
The importance of particular metals in the human diet has been realized within the past few decades， and the idea that geology might be related to health has been recognized for a number of elements such as iodine1， zinc2 and selenium. For example， soils with low iodine contents produce crops， and animals deficient3 in iodine. A lack of iodine in the human diet leads to some serious diseases.
The ultimate source of metals within the human body is rocks， which weather into soil， gaining or losing some of their chemical constituents4. The crops we eat selectively rem
ove from the soil the elements that they require for growth. The water we drink contains trace elements leached5 from rock and soil. Thus the geology and geochemistry of the environments have effects on the chemistry and health of plants， animals and people.
So far there is no data to suggest that people living on metal-rich soils experience a potential health hazard. The levels of metals within naturally contaminated soils are generally not high enough to cause serious health problems. Living on metal-rich soils does not represent a health risk unless large quantities of soil are digested or metal-rich dust is inhaled6. However， small children are particularly exposed to metal-rich TOPsoil in playgrounds and gardens. They are also the most likely ones to eat potentially dangerous metal-rich soil.
Heavy metals are persistent7； they do not break down to other chemicals in the environment. Industrially polluted sites usually undergo intensive clean-up and rehabilitation8 because heavy metals are a health concern once they enter the food chain. Some trace metals are alleged9 to cause cancer and are also known to cause poisoning.
In contrast， naturally contaminated soils have not been subject to risk assessment10 studies and rehabilitation measures， despite the fact that they frequently possess metal concentrations well above those of such polluted by humans and above environmental quality criteria11.
There is a vital need to understand the potential risks and long-term health effects of living on naturally contaminated soils. Future environmental investigations12 of naturally polluted soils should concentrate on the potential pathways of metals into the food chain and human body. Geologists13 should be part of such studies as they can provide the essential background information on rock and soil chemistry as well as the chemical forms of heavy metal pollution.
A. No evidence to indicate bad effects of naturally contaminated soil
B. Potential hazards of human contaminated soils
C. Research on channels of heavy metals getting into human food chain
D. Geology and health problems
E. Rocks-the ultimate source of soil pollution
F. Long- term helth effects on children
1. Paragraph 1
2. Paragraph 3
3. Paragraph 4
4. Paragraph 6
A. industrially polluted soils
B. rock and soil chemistry
C. naturally polluted soils
D. the pathways of metals into the food chain
E. the element of iodine
F. the persistence14 of heavy metals
5. Some serious diseases is connected with deficiency of
6. It is extremely necessary to study the long-term effects caused by living on
7. Geologists are indispensable in the research project on geology and health due to their knowledge on
8. Industrially contaminated sites usually require a thorough clean-up due to
Key： DABCECBF
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