3
Physical and Chemical Properties of
Pesticides and Other Contaminants:
Volatilization, Adsorption, Environmental
Distribution, and Reactivity
3.1 Introduction
When a chemical is released into the environment, it can contact and reside
in one or more phases—air, water, soil, and biota. Chemicals can then be
distributed in varying ratios into different compartments such as the atmosphere, hydrosphere, lithosphere, and biosphere (Figure 3.1).
Because many chemicals are released directly to the air frst—by spraying,
as with fumigants, or in combustion effuent—the air phase has been the
focal point of much research over the years. The primary processes affecting
distribution of these chemicals in the environment—volatilization, adsorption, and reactivity (stability)—are extensively discussed in this chapter. As
we learn more, the details of chemical behavior in the environment emerge
so that we can predict likely behavior and effects of contaminants before the
release occurs.
3.2 Volatilization
Volatilization is a generalized process that is applied to both liquids and solids to describe the transition from the condensed phase to vapor. In closed
containers, a substance will volatilize until equilibrium is reached. If the
substance is exposed to the open atmosphere, however, equilibrium will
not be achieved, since the open atmosphere acts as a transport medium and
as an “infnite” reservoir for volatile chemicals. For liquids, volatilization is
called evaporation; for solids, it is called sublimation. Common examples
of volatile liquids include water and organic solvents. Depending on vapor
DOI: 10.1201/9781003217602-3
25
Physical and Chemical Properties of
Pesticides and Other Contaminants:
Volatilization, Adsorption, Environmental
Distribution, and Reactivity
3.1 Introduction
When a chemical is released into the environment, it can contact and reside
in one or more phases—air, water, soil, and biota. Chemicals can then be
distributed in varying ratios into different compartments such as the atmosphere, hydrosphere, lithosphere, and biosphere (Figure 3.1).
Because many chemicals are released directly to the air frst—by spraying,
as with fumigants, or in combustion effuent—the air phase has been the
focal point of much research over the years. The primary processes affecting
distribution of these chemicals in the environment—volatilization, adsorption, and reactivity (stability)—are extensively discussed in this chapter. As
we learn more, the details of chemical behavior in the environment emerge
so that we can predict likely behavior and effects of contaminants before the
release occurs.
3.2 Volatilization
Volatilization is a generalized process that is applied to both liquids and solids to describe the transition from the condensed phase to vapor. In closed
containers, a substance will volatilize until equilibrium is reached. If the
substance is exposed to the open atmosphere, however, equilibrium will
not be achieved, since the open atmosphere acts as a transport medium and
as an “infnite” reservoir for volatile chemicals. For liquids, volatilization is
called evaporation; for solids, it is called sublimation. Common examples
of volatile liquids include water and organic solvents. Depending on vapor
DOI: 10.1201/9781003217602-3
25