48
Pesticides, Organic Contaminants, and Pathogens in Air
of how fog can accumulate and transport chemicals was in a recent study that
showed the occurrence of mono-methyl mercury cation in marine fog along
the California coast. It originated from dimethyl mercury that was formed in
the marine environment (see Chapter 7). In another earlier study of pesticide
distribution between vapor and fogwater, it was found that enrichment of some
chemicals in the water phase occurred over what would be expected from just
a simple water–air distribution (i.e., K aw ) (Glotfelty et al., 1987) (see Chapter 7). It
turned out that a signifcant particulate fraction in the water operated as a third
phase, which affected the denominator in the equation
K = C /C
(3.33)
aw
a
w
The third phase due to water-borne particulates may be signifcant in the
calculations of air–water distributions.
Fogs that occur in agricultural areas will absorb volatilized pesticides and
transport them from their intended targets. Heavy tule fogs are a common
occurrence in the heavily agricultural Central Valley of California during the
winter months. Before people realized that fog could be a transport medium
for chemicals, some farmers were fned by the state for misusing pesticides. It
turned out that the pesticide residues found on crops for which the chemical
was not registered were deposited by condensing fog from nearby felds that
had been legally treated.
Rainwater is another aqueous medium that can scrub/wash the air of particulates and chemicals during a rainfall. An example is a study that showed
the occurrence of water-soluble trifuoroacetic acid (TFA) in vernal pools
formed by rain events downwind of urban environments (see Chapter 9).
TFA is a conversion product of the replacements for chlorofuorocarbons
(CFCs), and an industrial solvent for Tefon ™ . An interesting aspect of rain is
that raindrops will often carry an electric charge (i.e., a mix of positively and
negatively charged raindrops (Gunn and Devin, 1953)). The electric charge
may infuence the nature of the absorption process.
3.4.2 Biota
When biota (e.g., fsh, plants, and humans) are exposed to a chemical contaminant in water or air, the contaminant is taken up at a certain rate and
eliminated at a certain rate. The bioconcentration index (BCI), defned as follows, can describe this process:
BCI= intake/
k 1
k 2 output
(3.34)
This allows the prediction of the BCF
BCF= C o /C w , a
(3.35)
Pesticides, Organic Contaminants, and Pathogens in Air
of how fog can accumulate and transport chemicals was in a recent study that
showed the occurrence of mono-methyl mercury cation in marine fog along
the California coast. It originated from dimethyl mercury that was formed in
the marine environment (see Chapter 7). In another earlier study of pesticide
distribution between vapor and fogwater, it was found that enrichment of some
chemicals in the water phase occurred over what would be expected from just
a simple water–air distribution (i.e., K aw ) (Glotfelty et al., 1987) (see Chapter 7). It
turned out that a signifcant particulate fraction in the water operated as a third
phase, which affected the denominator in the equation
K = C /C
(3.33)
aw
a
w
The third phase due to water-borne particulates may be signifcant in the
calculations of air–water distributions.
Fogs that occur in agricultural areas will absorb volatilized pesticides and
transport them from their intended targets. Heavy tule fogs are a common
occurrence in the heavily agricultural Central Valley of California during the
winter months. Before people realized that fog could be a transport medium
for chemicals, some farmers were fned by the state for misusing pesticides. It
turned out that the pesticide residues found on crops for which the chemical
was not registered were deposited by condensing fog from nearby felds that
had been legally treated.
Rainwater is another aqueous medium that can scrub/wash the air of particulates and chemicals during a rainfall. An example is a study that showed
the occurrence of water-soluble trifuoroacetic acid (TFA) in vernal pools
formed by rain events downwind of urban environments (see Chapter 9).
TFA is a conversion product of the replacements for chlorofuorocarbons
(CFCs), and an industrial solvent for Tefon ™ . An interesting aspect of rain is
that raindrops will often carry an electric charge (i.e., a mix of positively and
negatively charged raindrops (Gunn and Devin, 1953)). The electric charge
may infuence the nature of the absorption process.
3.4.2 Biota
When biota (e.g., fsh, plants, and humans) are exposed to a chemical contaminant in water or air, the contaminant is taken up at a certain rate and
eliminated at a certain rate. The bioconcentration index (BCI), defned as follows, can describe this process:
BCI= intake/
k 1
k 2 output
(3.34)
This allows the prediction of the BCF
BCF= C o /C w , a
(3.35)