Environmental Engineering Reference
In-Depth Information
Declining DDT concentrations in whole fish
4000
3500
3000
2500
90th percentile
2000
1500
1000
500
0
Median
1969
1974
1979
1984
1989
1994
1999
FIGURE 8.23
DDT concentrations in fish from 1969 to 1999. (From United States Geological Survey (USGS), Pesticides in
the nation's streams and groundwater, 1992-2001—A summary, USGS Fact Sheet 2006-3028, Washington, DC,
2006b.)
the United States remained constant during the 1980s and early 1990s, Figure 8.23 shows
that the concentration of the pesticide DDT has steadily declined in fish tissue during
this same period (USGS 2006b). Since DDT is bioaccumulative, this event marks some
progress.
Permethrin and toxaphene are two other widely used compounds in insecticides and
pesticides, respectively. The fate and transport concern with permethrin centers around
its use as an insect repellent, application to crops, and flea treatment for pets. All these
activities involve human exposure (ATSDR 2005c,d), and with a half-life of approximately
28 days, there is often adequate time for human contact.
The now-banned pesticide toxaphene strongly sorbs to soil particles (Figure 8.4) and is
not very soluble in water (SRC 2009). Common sinks of toxaphene include sediments and
soil, where it bioaccumulates in fish and mammals. Toxaphene is also in the atmosphere
since it evaporates when in a solid form or dissolved (ATSDR 1997b). It is estimated that the
half-life of toxaphene is more than 10 years in soil (SRC 2009), so there is a good chance it
is still present at appreciable concentrations in the environment.
8.4.6.2 Dioxins
Since one method of dioxin formation is through incineration and combustion, dioxin
compounds are present in the atmosphere and have been detected around the globe
(ATSDR 2006a). When dioxins are released at the surface, they sorb to soil particles and are
often detected in sediments in lakes, rivers, and streams acting as sinks (ATSDR 2006a).
Dioxin compounds are considered bioaccumulative contaminants (Section 8.3.4), with the
potential to build up in the food chain and yield detectable concentrations in the tissues
of many animals (ATSDR 2006a; USEPA 2009d). Due to the presence of chlorine in their
atomic structure, dioxins do not readily degrade once they are formed and released into
the environment (USEPA 2006).
8.4.6.3 Fertilizers
The most common fertilizers include nitrogen (N), phosphorus (P), and potassium (K).
A major sink for fertilizers is surface water because they are applied to the soil surface
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