Environmental Engineering Reference
In-Depth Information
chemicals ranging from pesticides and solvents to gasoline hydrocar-
bons, manufacturing additives, disinfection by-products, and more.
Low concentrations of 130 of those chemicals were found in streams
and rivers before they entered public drinking water treatment
plants. Almost two-thirds of the chemicals also were in the water
after
treatment. The water treatment technology and processes did
not remove the contaminants. The greater the proportion of agri-
cultural and urban land in a watershed area, the greater the number
of chemicals and the higher their concentration. More chemicals
at higher concentrations also turned up when wastewater was dis-
charged upstream from a community water treatment plant, accord-
ing to the report. “Most of the chemicals were at levels equivalent to
one thimble of water in an Olympic-sized pool,” USGS offi cials said
in releasing the report.
5
“Low-level detection does not necessarily indicate a concern
to human health, but rather indicates what types of chemicals we
can expect to fi nd in different areas of the country,” adds the USGS
report's lead scientist, Gregory Delzer, national coordinator of
source water-quality assessments, USGS. “What was surprising was
that conventional water treatment
did
in fact remove a number of
these compounds. Another surprising fi nding was that because con-
ventional water treatment was not specifi cally designed to remove
those contaminants, mixtures became pretty evident—75 percent
of all our samples had at least fi ve of the compounds present and
50 percent of the compounds had about fourteen of these
compounds present in every sample,” said Delzer.
Scientists don't know the actual effects of the chemicals in
low concentrations on humans. However, the study points out
that “the common occurrence of chemical mixtures means that
the total combined toxicity may be greater than that of any single
contaminant present.”
Among the rivers tested for chemicals were:
White River (Indiana)
Elm Fork Trinity River (Texas)
Potomac River (Maryland)
Neuse River (North Carolina)
Chattahoochee River (Georgia)
