Environmental Engineering Reference
In-Depth Information
ten-year period. More than 400 scientists analyzed 11 million samples
for more than 600 chemicals. They detected pesticides in 94 percent of
all water samples (and in 90 percent of fi sh samples).
39
Many of the
pesticides have not been used for decades, but they continue to persist
in the environment. Persistent toxins do not break down and go away;
they keep polluting the water they are in. Clearly, ending the application
of chemical pollutants into the environment does not immediately end
their presence in our water.
In a study published in November 2009, the EPA reported that
mercury, a pollutant released primarily from coal-fi red power plants, was
present in all fi sh samples it collected from 500 lakes and reservoirs. At
half the lakes and reservoirs, mercury concentrations exceeded levels the
EPA deems safe for people eating average amounts of fi sh (fi gure 1.7).
And a person does not need to eat much fi sh for a seafood meal to raise
mercury levels. In an experiment in 2006, David Duncan of National
Geographic ate some halibut and swordfi sh in San Francisco and the
next day had his blood drawn and tested for mercury content. The level
of mercury had more than doubled from an earlier blood test—from 5
micrograms per liter of blood to 12 micrograms. There is no way to
Figure 1.7
Wet deposition of mercury from the atmosphere, 2006. (Environmental Protection Agency)
