下面的对文后有2项测试任务：(1)第23～26题要求从所给的6个选项中为第1～4段每段选择1个最佳标题；(2)第27～30题要求从所给的6个选项中为每个句子确定1个最佳选项。 Geology (地质) and Health 1. 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 iodine(碘), zinc(锌)and selenium(硒).
For example, soils with low iodine contents produce crops, and animals deficient
in iodine. A lack of iodine in the human diet leads to some serious
diseases. 2. The ultimate source of metals within the human body
is rocks, which weather into soil, gaining or losing some of their chemical
constituents. The crops we eat selectively remove from the soil the elements
that they require for growth. The water we drink contains trace elements leached
(过滤出) from rock and soil. Thus the geology and geochemistry of the environment
have effects on the chemistry and health of plants, animals and
people. 3. 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 inhaled.
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. 4. Heavy metals are persistent: they
do not break down to other chemicals in the environment. Industrially polluted
sites usually undergo intensive clean-up and rehabilitation because heavy metals
are a health concern once they enter the food chain. Some trace metals are
alleged to cause cancer and are also known to cause poisoning.
5. In contrast, naturally contaminated soils have not been subject to risk
assessment 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 criteria. 6. There is a
vital need to understand the potential risks and long-term health effects of
living on naturally contaminated soils. Future environmental investigations of
naturally polluted soils should concentrate on the potential pathways of metals
into the food chain and human body. Geologists 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 Health Effects on Children Paragraph 3______