74
Pesticides, Organic Contaminants, and Pathogens in Air
allows one to evaluate multiple sources of exposure and multiple chemicals simultaneously for risk assessment and risk management. Modeling is
important for assessing environments with changing geographies, meteorology, and use (e.g., schools, hospitals, playgrounds), and wherever sensitive
subpopulation exposures might occur. However, it is important to remember: “A model is an imitation of reality, which stresses those aspects that are
assumed to be important, and omits all properties considered to be nonessential” (Schwarzenbach et al., 2002).
5.2 Empirical vs Computational Models
Empirical laboratory/feld models can be divided into microcosms and
mesocosms. A microcosm is typically enclosed in a laboratory chamber
system (glass, Tefon®) that is constructed to simulate natural systems on
a reduced scale, for measuring responses to varying conditions (e.g., moisture, nutrients, sunlight, and temperature) over time. When a chemical, or
a mixture, is placed in the chamber, one can measure the water, air, plant,
and animal concentrations of radio labelled precursors under different sets
of conditions to obtain approximations of how the chemical might behave in
the outdoor environment. A mesocosm is any outdoor experimental system
that examines the natural environment under controlled conditions. Possible
scenarios could include dosing experiments to evaluate the impact of chemical exposures (e.g., pesticides and solvents) on organisms or communities in
their natural habitats. Mesocosm studies may be conducted in an enclosure
or partial enclosure that is small enough so that key variables can be brought
under control.
Numeric computer-based methods are attractive alternatives or ancillaries,
ideally suited to the needs of the desk-bound scientist or regulator who does
not have ready access to lab or feld facilities. Numbers or data that represent environmental compartment variables (e.g., wind speed, temperature,
sunlight intensity, and chemical properties) can be used as input to calculate
the effect on the output. That is, it is possible to get immediate information
on the effect of each variable. Volatilization, dispersal, and downwind transport models are useful in predicting exposure to downwind residents and
workers, and the time needed for chemicals to be reduced in concentration
to safe levels by ventilation or breakdown to hopefully by-products that are
less toxic. Soil and water models are useful for predicting, for example, the
movement of toxic chemicals into the groundwater or in runoff water. The
processes are complex but can be described and predicted by modeling tools
that have been relatively recently developed. Chemicals that are stable in the
air can undergo long-range transport, a characteristic that can be quantifed
and used to encourage replacement or even banning of some chemicals.
Pesticides, Organic Contaminants, and Pathogens in Air
allows one to evaluate multiple sources of exposure and multiple chemicals simultaneously for risk assessment and risk management. Modeling is
important for assessing environments with changing geographies, meteorology, and use (e.g., schools, hospitals, playgrounds), and wherever sensitive
subpopulation exposures might occur. However, it is important to remember: “A model is an imitation of reality, which stresses those aspects that are
assumed to be important, and omits all properties considered to be nonessential” (Schwarzenbach et al., 2002).
5.2 Empirical vs Computational Models
Empirical laboratory/feld models can be divided into microcosms and
mesocosms. A microcosm is typically enclosed in a laboratory chamber
system (glass, Tefon®) that is constructed to simulate natural systems on
a reduced scale, for measuring responses to varying conditions (e.g., moisture, nutrients, sunlight, and temperature) over time. When a chemical, or
a mixture, is placed in the chamber, one can measure the water, air, plant,
and animal concentrations of radio labelled precursors under different sets
of conditions to obtain approximations of how the chemical might behave in
the outdoor environment. A mesocosm is any outdoor experimental system
that examines the natural environment under controlled conditions. Possible
scenarios could include dosing experiments to evaluate the impact of chemical exposures (e.g., pesticides and solvents) on organisms or communities in
their natural habitats. Mesocosm studies may be conducted in an enclosure
or partial enclosure that is small enough so that key variables can be brought
under control.
Numeric computer-based methods are attractive alternatives or ancillaries,
ideally suited to the needs of the desk-bound scientist or regulator who does
not have ready access to lab or feld facilities. Numbers or data that represent environmental compartment variables (e.g., wind speed, temperature,
sunlight intensity, and chemical properties) can be used as input to calculate
the effect on the output. That is, it is possible to get immediate information
on the effect of each variable. Volatilization, dispersal, and downwind transport models are useful in predicting exposure to downwind residents and
workers, and the time needed for chemicals to be reduced in concentration
to safe levels by ventilation or breakdown to hopefully by-products that are
less toxic. Soil and water models are useful for predicting, for example, the
movement of toxic chemicals into the groundwater or in runoff water. The
processes are complex but can be described and predicted by modeling tools
that have been relatively recently developed. Chemicals that are stable in the
air can undergo long-range transport, a characteristic that can be quantifed
and used to encourage replacement or even banning of some chemicals.