Environmental Engineering Reference
In-Depth Information
One relevant parameter linked to chemical properties is the Gustafson Ubiquity Score
(GUS) factor (Gustafson 1989), which makes a leaching classification, taking into account
soil mobility and soil persistence (Demoliner et al. 2010).
(
) ×
(
)
GUS
=
log
t
4
log
K
1 2
soil
oc
Molecules with a GUS above 2.8 are very likely to reach groundwater and those with a
GUS below 1.8 are considered nonleacher to groundwater. Molecules with a GUS higher
than 1.8 and lower than 2.8 are considered transition leachers.
Volatilization of pesticides and transformation products from soil surface and plant leaves
to the atmosphere and further deposition in aquatic environments represent another dif-
fuse source of entry of pesticide residues in surface waters. An increase in temperature
increases volatilization as the vapor pressure of most compounds increases with tempera-
ture. However, many of the pesticides currently in use have low vapor pressures, and
volatilization will not be a significant loss route. Those pesticides known as volatile com-
pounds have special usage instructions to minimize loss by this route, for example, soil
incorporation of trifluralin, chloropicrine, and 1,3-dichloropropene.
During the application of pesticides to the field crops, a part of the spray liquid may be
carried out of the treated area by wind and reach water bodies (Bach et al. 2001). The extent
of contamination of aquatic media is highly dependent on the method of application and
on factors such as wind direction and velocity (Gil and Sinfort 2005). Spray drift may be an
important means of organic compound losses in orchard regions or areas with a network
of ditches (Bach et al. 2001; Holvoet et al. 2007). A study revealed an offsite deposition of
aerially applied pesticide at 30, 60, and 120 m of 5%, 2%, and 0.8% of the material, respec-
tively (Bird 1995).
Likewise, entry of pesticides and/or transformation products into water bodies may
occur via accidental spills during filling of the sprayer, cleaning of the spraying equip-
ment, washing of the measuring utilities, leaks from the sprayer, or improper waste han-
dling and disposal.
Finally, nonagricultural use of pesticides may also represent a significant source of entry
of pesticide residues into the environment. In the United States, for example, it has been
estimated to account for approximately 25% of pesticide use by volume (Aspelin and Grube
1999). In the urban environment, significant pesticide uses include applications for orna-
mental pests and for control of aquatic weed management in recreational water, which
may involve direct application of herbicides to surface waters (Racke 2003).
4.2 Pesticide Degradation in the Water Compartment
When an active substance and/or its transformation products enter into the aquatic
compartment by the different processes detailed in the previous section, it is subject to
different physical, chemical, and biological processes. A combination of factors influ-
ences the transformation of xenobiotics over a time period of hours, days, or even years
and through different processes. Although some pesticides are biodegradable, by the
act of microorganisms ubiquitous in environmental waters, this is not the main route of
pesticide transformation in the aquatic environment (Boxall et al. 2004). Physical processes
in the water environment include dilution by the dispersion or diffusion of the pesticide
Search WWH ::




Custom Search