Pesticide Residues in the Atmosphere - Pesticides: Evaluation of Environmental Pollution - page 224

In the future, this lack of experimental studies on the atmospheric degradation of
pesticides and their degradation products can be partially remedied by the use of large
chambers, such as the EUPHORE (EUropean PHOtoREactor) facility (Vera et al. 2007).
One advantage of large simulation chambers, such as those at EUPHORE with a vol-
ume of 200 m 3 , is that compounds with low vapor pressures can be introduced into the
chamber in the gas phase. Furthermore, as these chambers use real sunlight to produce
the reactions, it is possible to simulate almost real conditions without the meteorologi-
cal influences of the real environment (Vera et al. 2010; Muñoz et al. 2011; Feigenbrugel
et al. 2006).
7.5.2 Dry and Wet Deposition
Wet deposition is the uptaking of the pesticide at the Earth's surface by precipitation,
mainly in rainwater, but also in fog and snow. Wet deposition is determined by the precipi-
tation rate, the cloud and rain drop distribution, the Henry's law constant, the air-water
partition coefficient, and the washout ratio for particles (Van Pul et al. 1999; FOCUS 2008
and references therein). Several studies have been published on the detection of pesticides
in rainwater, as shown in the section Pesticides in Rainwater.
Dry deposition is the uptaking of the pesticide at the Earth's surface by water, soil,
and vegetation. This means that dry deposition is affected by the nature of the receiving
body. There are several studies on the dry deposition of selected pesticides, especially in
relation to the terrestrial environment, that is, bentazon, dichlorprop-p, chlorothalonil,
fenpropimorph, parathion-ethyl, and chlorothalonil in barley fields (Klöpel and Kördel
1997); chlorpyrifos in pine needles (Aston and Seiber 1997); and lindane, parathion,
and pirimicarb in cereals and also in water (Siebers et al. 2003). Duyzer and Van Oss
(1997) studied the uptake of a number of pesticides by water, soil, and vegetation. They
found that the most important parameters for describing dry deposition and further
re-emission are the Henry's law constant, the partitioning coefficients of the pesticide in
octanol-water (K ow ), soil organic carbon-water (K oc ), and octanol-air (K oa ), the leaf area
index (LAI), and the organic carbon content of the soil.
Pesticides adsorbed to aerosols are found mainly in wet deposition (Unsworth et al.
1999), while pesticides in the vapor phase are probably more evenly divided between wet
and dry depositions.
Deposition is not always the last step in the elimination of persistent pesticides from
the atmosphere, because under certain conditions they could be re-emitted into the atmo-
sphere (Bidleman 1999).
7.5.3 Transport
Once in the atmosphere, the pesticide is dispersed and transported like any other air pol-
lutant, for example, ozone or SO 2 (Van Pul et al. 1999). The actual distance traveled by an
air pollutant strongly depends on the amount of time it resides in the atmosphere. There
are several models used worldwide for describing the transport and deposition of pesti-
cides through the air (FOCUS 2008 and references there in). According to the FOCUS air
group, the EVA model is one of the most appropriate for estimating transport and deposi-
tion at short-range distances, whereas the CalTox, CEMC Level III, Chemrange, ELPOS,
and Simple Box are the best models for medium and long ranges. Nevertheless, other mod-
els are also valid.