Biomedical Engineering Reference
In-Depth Information
values represent generic order-of-magnitude half-lives and should be
used with caution for any site-specific assessment of the fate and
transport of methanol. In Section 2.3, these rates are further evaluated
as a function of specific hydrogeologic (subsurface) and limnologic
(lake) conditions.
2.2 PARTITIONING OF METHANOL IN THE
ENVIRONMENT
2.2.1 Methanol Partitioning Among Environmental Media
The purpose of this section is to describe the equilibrium partitioning of
methanol released to the environment among air, water, and soil phases.
Partitioning is directly related to the physiochemical properties of
methanol, including solubility, vapor pressure, and adsorptivity, and
the physical and chemical characteristics of the environmental medium.
When any chemical is released into an environment consisting of more
than one medium (e.g., air and water), the chemical tends to distribute
itself between these two phases, a process that has been well described by
the science of chemical thermodynamics (e.g., Thibodeaux, 1996;
Schwarzenbach et al., 1993). In an enclosed system, the concentrations
of the chemical in each phase can be predicted assuming that an
equilibrium is achieved. In an open system, however, which is undergoing
dynamic changes, continual transfer between phases will occur. The rate
of these changes is important for predicting the fate and transport of the
chemical of interest in bothmedia. For purposes of this analysis, however,
the simple equilibrium model provides a basis for assessing the relative
distribution of a compound such as methanol between two or more
environmental media.
2.2.2 Air/Water Partitioning
The air/water equilibrium partitioning behavior of methanol can be
predicted using Henry's Law when methanol concentrations are
<
100,000 parts per million (ppm) (i.e.,
<
10% by weight). At higher
concentrations, nonideal fluid characteristics must be accounted for.
