Pesticide Residues in the Atmosphere - Pesticides: Evaluation of Environmental Pollution - page 209

According to Van den Berg et al. (1999 and references therein), data from field measure-
ments indicate that losses or emissions during the application of pesticides can range from
a few percent to 30% or more than 50%.
For instance, malathion can be transported in air by drift from the application site to nontar-
get locations. The California Food and Agriculture Department (Segawa et al. 1991) monitored
malathion in 1990 and found concentrations from 1 μg/m 2 to 101 μg/m 2 on locations where
the aircrafts specifically avoided spraying. The study pointed out that 92% of the malathion
applied remained on the surface of the target areas, while 8% was either degraded before
arriving at the ground, volatilized before sample collection, or drifted outside the target area.
Another study (Sanders 1997; Bradley et al. 1997) related to malathion involved the collection
of outdoor air samples near the center of the spray area during the application of pesticides
on five sites for four consecutive periods (24 h immediately before the spraying, during the
spray application, and two consecutive 24 h periods after the application). The highest aver-
age malathion level, 0.067 μg/m 3 (5.0 ppt), was found during the spray application. During the
24 h following the application, the malathion level stayed high, as it also did in the last two
24 h periods after the application, registering 0.049 and 0.042 μg/m 3 , respectively.
The main factors that affect pesticide loss during application are the manner in which
the pesticide is applied, that is, the spray characteristics (size of nozzles, etc.) together with
the equipment used and the viscosity and volatility of the formulation used, the environ-
mental conditions (wind speed, temperature, and humidity), and, finally, the operators
skills. Thus, losses can be reduced by improving the operators' skills in using the best
application technique together with the best formulation for any given problem (Gil and
Sinfort 2005; Gil et al. 2007).
Generally, spray drift is understood as the fraction of pesticide losses, in the form of
droplets (they can be dry particles or vapors), which move off-target through the air.
In the 1990s, many studies assessing spray drift were performed, for example, in the
United States (Bird et al. 2002; Bradley et al. 1997) or in Germany (Van den Berg et al.
1999). In the last few decades, different kinds of models offer the possibility of estimating
losses during the application of a pesticide (Klein 1995; Jarvis 1994; Vanclooster et al. 2000).
Although the models can be very useful, their critical parameters must be kept in mind
if one is to obtain values close to real ones. In this sense, it is essential to have both good
meteorological data and a droplet distribution assessment (Gil et al. 2007). On the other
hand, models must be fed experimental data to check their predictability (Ferrari et al.
2003). And, at the same time, the development of new technical methodologies or equip-
ment may lead to reductions in spray drift losses.
7.3.2 Volatilization from Soils
Once the pesticide is applied on the target area or soil surface or injected into the soil, it
can volatilize. Depending on the climatic conditions and the compound used, the vola-
tilization can reach as high as 90% of the application dose. For example, for atrazine, the
cumulative losses after 24 h are around 2% of the application dose (Bedos et al. 2002). Other
pesticides, such as lindane (nowadays banned in most of Europe, the United States, and
Canada) and trifluralin, present higher volatilization losses, probably because of the dif-
ferences in their Henry's law constants (see Table 7.1 ).
In a study conducted in the Italian province of Bologna, under agricultural conditions,
the volatilization rates of procymidone, malathion, and ethoprophos were determined
after soil application (Ferrari et al. 2003). As the field experiments were carried out in
different seasons, the authors could confirm that temperature and soil moisture affected