Page 392 - Environment: The Science Behind the Stories

Industry and manufacturing

Consumer products Workplace products Medicines and materials Pesticides and fertilizers Waste Waste Waste

Medical facilities Agriculture: crops, Water: surface
Home Work and public spaces rangeland, feedlots Soil and groundwater Air

Food Plant growth
Workplace exposure
Drinking water Non-target effects Drinking water Air for breathing
Consumer products
Medicines and materials
Air for breathing

Humans Hunting and harvesting
Genes, womb,
breast milk

Nonhuman biota
Human fetuses and babies
Figure 14.12 Synthetic chemicals take many routes in traveling through the environment. People take
in only a tiny proportion of these compounds, and many compounds are harmless. However, people receive
small amounts of toxicants from many sources, and developing fetuses and babies are particularly sensitive.

chemicals such as DDT and PCBs persist for decades. Atra- Toxicants may accumulate and move CHAPTER 14 • Envi R onm E n TA l H EA lTH A nd T o xi C ology
zine, our most widely used herbicide, is highly variable in its up the food chain
persistence, depending on environmental conditions.
Persistent synthetic chemicals exist in our environment Of the toxic substances that organisms absorb, breathe, or
today because we have designed them to persist. The synthetic consume, some are quickly excreted, and some are degraded
chemicals used in plastics, for instance, are used precisely into harmless breakdown products. Others persist intact in the
because they resist breakdown. Sooner or later, however, most body. Substances that are fat-soluble or oil-soluble (including
toxicants degrade into simpler compounds called breakdown organic compounds such as DDT and DDE) are absorbed and
products. Often these are less harmful than the original sub- stored in fatty tissues. Substances such as methylmercury
stance, but sometimes they are just as toxic as the original (CH Hg ) may be stored in muscle tissue. Such persistent
+
3
chemical, or more so. For instance, DDT breaks down into toxicants accumulate in an animal’s body in a process termed
DDE, a highly persistent and toxic compound in its own right. bioaccumulation, such that the animal’s tissues have a greater
Atrazine produces a large number of breakdown products concentration of the substance than exists in the surrounding
whose effects have not been fully studied. environment. 391

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