Environmental Fate and Transport of Pesticides - Pesticides: Evaluation of Environmental Pollution - page 30

and aquifers in the United States and around the world have resulted in considerable research
efforts dedicated to investigating their environmental fate and transport. This information is
essential for understanding and assessing the potential exposure and risks of the pesticides
to the environment and ecosystem, providing proper guidelines for pesticide registration and
management practices, and developing effective remediation strategies. This chapter mainly
focuses on current knowledge of the fate and transport of pesticides in the environment.
2.2 Source
A report of Environmental Protection Agency (EPA) estimates that in 2001, more than
5 billion pounds of pesticides were used worldwide, with the United States using over
1.2 billion pounds, which was more than 20% of the total global use (Kiely et al. 2004). In
the United States, approximately 888 million pounds of active ingredients were used in the
pesticides, and the agricultural sector was the largest user (76% of total active ingredients
used), followed by industry/commercial/government sector (12.5%) and home and garden
sector (11.5%). Another 2.6 billion pounds of chlorine/hypochlorite-containing pesticides
were used as disinfectants.
In addition to the deliberate sources, pesticides can also be present in remote areas by
long-distance transport from their origins. This happens for many volatile or semivolatile
pesticides that undergo evaporation at higher temperatures and condensation at lower
temperatures (Bloomfield et al. 2006). This condensation effect has caused, for example,
high levels of persistent bioaccumulative toxicants (i.e., PBTs; many currently used pes-
ticides are considered PBTs) in remote areas far from the source of pollution (Blais et al.
2006). Once having entered the hydrological paths, pesticides can also be transported by
flows or via the vehicle of mobile particles (e.g., colloids and nanoparticles) or migratory
animals (Blais et al. 2006).
2.3 Fate and Transport
Pesticides undergo many different pathways once they enter the environment ( Figure 2.1 ),
including transformation/degradation, sorption-desorption, volatilization, uptake by
plants, runoff to surface waters, and transport to groundwater. Among them, transfor-
mation/degradation is the most important pathway that eliminates pesticides from the
environment, whereas many other pathways merely lead to the migration of pesticides.
The following sections provide detailed descriptions of these pathways in different envi-
ronmental compartments.
2.3.1 Transformation and Degradation
Transformation or degradation is one of the key processes that governs the environmental
fate and transport of a pesticide, which also comprises different processes including abiotic
degradation (e.g., oxidation, hydrolysis, and photolysis) and biodegradation. During this pro-
cess, a pesticide is transformed to a degradation product or completely mineralized to carbon
dioxide. The faster the degradation takes place, the less time a pesticide stays in the applied