Pesticide Residues in Surface Water and Groundwater - Pesticides: Evaluation of Environmental Pollution - page 262

in water can reach levels detrimental to plant and fish species in water. Numerous factors,
such as rainfall, watershed soil type, land use, landscape, slope, etc., affect runoff and, there-
fore, pesticide concentrations in surface water (Dabrowski et al. 2002; Leu et al. 2004b; Holvoet
et al. 2007). For instance, soils situated on steeper slopes are particularly susceptible to surface
runoff. However, these factors are regarded as a constant for a given watershed. The tempo-
ral and spatial changes of pesticide concentrations in surface water are primarily dependent
on precipitation and pesticide use as the two major environmental variables dictating the
dynamics of pesticide transport via runoff into surface water in a watershed (Müller et al.
2003; Guo et al. 2004). Precipitation, as the amount of daily rainfall, determines the total
amount of runoff water, and pesticide use, as daily amount of used pesticide, represents the
source of contamination. Concentrations of pesticides in environmental waters are the highest
in late spring and early summer, following the spring application, coinciding with the great-
est agricultural runoff from crop lands (Pereira and Hostettler 1993).
Another entry route of pesticides into water is through atmospheric long-range transport
from agricultural to urban areas (Foreman et al. 2000; Grynkiewicz et al. 2001; Blanchoud et al.
2002; De Rossi et al. 2003) or to remote mountain areas (Kirchner et al. 2009; Tremolada et al.
2009; Bradford et al. 2010). Pesticides can be transported in the gas phase by volatilization
from the crops on which they were applied, dissolved in water droplets by spray drift during
pesticide application by spraying and adsorbed on solid particles (as suspended particulate
matter) by wind erosion from the soil surface (Dörfler and Scheunert 1997; Bach et al. 2001;
Grynkiewicz et al. 2001). Once airborne, the scale of pesticide transport through the atmo-
sphere will depend on a variety of meteorological conditions as well as pesticide physicochem-
ical properties. From the atmosphere, pesticides can be removed by photochemically driven
reactions or physical depositional mechanisms, such as dry and wet deposition. Pesticides that
are susceptible to photochemical reactions are usually transported through short distances
from the source. Pesticides that are less susceptible to these chemical removal processes can
be transported through greater distances (Foreman et al. 2000). Pesticides in the gas phase are
usually removed by wet deposition and dissolution in rainfall. Particle-bound pesticides can
be washed out by precipitation (wet deposition) or removed by dry particle deposition (Sauret
et al. 2009; Foreman et al. 2000; Majewski et al. 2000). The concentration of pesticides in precipi-
tation samples revealed seasonal fluctuations, with higher concentrations observed during the
application period (Dörfler and Scheunert 1997; Grynkiewicz et al. 2001; De Rossi et al. 2003).
For volatile pesticides, losses after application due to volatilization can be as high as
90% (Carter 2000; Grynkiewicz et al. 2001; Bedos et al. 2002). This is especially important
for short-range transport from application areas (Siebers et al. 2003). However, the impact
of their later precipitation is negligible compared to that from their direct agricultural
application (Dörfler and Scheunert 1997; Carter 2000). The volatilization rate depends on
the vapor pressure of pesticide, weather conditions, humidity of the soil, type of the plant
surface, etc. (Reichman et al. 2000; Grynkiewicz et al. 2001).
When a pesticide is applied as a spray near a water body, a key route to surface water is
the spray drift. Drifting pesticide spray is a complex problem in which equipment design,
application parameters, spray physical properties and formulation, and meteorological con-
ditions interact and influence the pesticide loss (Gil and Sinfort 2005). The contribution of
pesticide spray drift to surface water pollution is thought to be rather small (Kreuger 1998;
Huber et al. 2000; Neumann et al. 2002; Röpke et al. 2004). The amount of pesticide that drifts
to water 1 m from its application to crops can be ranging from 0.3% to 3.5% (Carter 2000).
The total airborne spray drift is usually 0.8% of the applied dose (Wolters et al. 2008). In gen-
eral, the amount of spray drift entering the water body increases with decreasing distance
from the water body. Deposition is also influenced by landscape, as bankside vegetation and