58
Pesticides, Organic Contaminants, and Pathogens in Air
Exposure to paraquat could occur by inhalation of aerosolized spray during application (Woodrow et al., 1989). Anecdotal evidence has been offered
in support of this hypothesis—yet to be proven with controlled studies.
Paraquat was once widely used, in a joint effort by Mexico and the United
States in the 1990s, to destroy marijuana plants to reduce availability of
then illegal “weed” or “pot.” Yet another source of exposure was believed
to be from inhaling smoke from cannabis cigarettes, assuming that cannabis could retain paraquat in sprayed marijuana that did not succumb to the
spray. An agricultural link might have been exposure to spray by applicators of paraquat during its use, widespread in California and some southern
states and in Arizona, to defoliate cotton prior to harvest of cotton lint and for
weed control. Defoliation was used to reduce the load of cotton gin trash and
improve quality of the lint harvested during spindle picking of cotton lint.
4.2.2 Petroleum-Based Weed and Dormant Oil Pesticides
Petroleum oils are commonly used to control weeds using primarily diesel
and mineral oil fractions (see Table 2.2). This practice is now discouraged
because these petroleum fractions can lead to formation of photochemical
smog (San Joaquin Valley Air Pollution Control District, 2012). Oils are also
applied to new crops and as harvest aids (Woodrow et al., 1986). These oils
can volatilize with lower-molecular-weight fractions volatilizing frst giving
way to residue of heavier hydrocarbons which then dissipate by other means
(e.g., microbial metabolism).
Spills of crude oil occur during accidents, and the risks of spills increase
during hurricanes and other natural disasters. For example, the Deepwater
Horizon spill, caused by multiple failures while closing up the well, spilled
more than 700,000 tons to the Gulf of Mexico. Prior to that, 27,000–37,000 tons
of oil were released during hurricane Katrina from various sources in the
Louisiana parish that is heavily involved in the oil industry.
In both events, it is estimated that half of the spilled oil evaporated (a familiar thought about things disappearing in the vast air) (Farrington, 2013). In
these cases, oil was spilled in the relatively warm water in the Gulf of Mexico
(NCEI NOAA, 2018b; U.S. EPA, 2015a). The warm water (up to 32°C in summer
months) plus the windy conditions led to high evaporation rates. The 1989
Exxon Valdez oil spill occurred in Prince William Sound, Alaska, a region of
cooler water with an average high of 14°C in summer months (NCEI NOAA,
2018a). The spilled oil did not evaporate as much initially as the spills in the
warmer Gulf of Mexico, but overtime loss to the air by volatilization and
other dissipation mechanisms was signifcant. Also, the Deepwater Horizon
accident released a lighter volatile crude oil compared to the heavy crude
oil released in the Exxon Valdez incident in Alaska (Atlas and Hazen, 2011).
The lighter crudes are more volatile and more readily biodegradable. Plus, in
the Gulf of Mexico, microorganisms are adapted to degrading hydrocarbons
(Atlas and Hazen, 2011).
Pesticides, Organic Contaminants, and Pathogens in Air
Exposure to paraquat could occur by inhalation of aerosolized spray during application (Woodrow et al., 1989). Anecdotal evidence has been offered
in support of this hypothesis—yet to be proven with controlled studies.
Paraquat was once widely used, in a joint effort by Mexico and the United
States in the 1990s, to destroy marijuana plants to reduce availability of
then illegal “weed” or “pot.” Yet another source of exposure was believed
to be from inhaling smoke from cannabis cigarettes, assuming that cannabis could retain paraquat in sprayed marijuana that did not succumb to the
spray. An agricultural link might have been exposure to spray by applicators of paraquat during its use, widespread in California and some southern
states and in Arizona, to defoliate cotton prior to harvest of cotton lint and for
weed control. Defoliation was used to reduce the load of cotton gin trash and
improve quality of the lint harvested during spindle picking of cotton lint.
4.2.2 Petroleum-Based Weed and Dormant Oil Pesticides
Petroleum oils are commonly used to control weeds using primarily diesel
and mineral oil fractions (see Table 2.2). This practice is now discouraged
because these petroleum fractions can lead to formation of photochemical
smog (San Joaquin Valley Air Pollution Control District, 2012). Oils are also
applied to new crops and as harvest aids (Woodrow et al., 1986). These oils
can volatilize with lower-molecular-weight fractions volatilizing frst giving
way to residue of heavier hydrocarbons which then dissipate by other means
(e.g., microbial metabolism).
Spills of crude oil occur during accidents, and the risks of spills increase
during hurricanes and other natural disasters. For example, the Deepwater
Horizon spill, caused by multiple failures while closing up the well, spilled
more than 700,000 tons to the Gulf of Mexico. Prior to that, 27,000–37,000 tons
of oil were released during hurricane Katrina from various sources in the
Louisiana parish that is heavily involved in the oil industry.
In both events, it is estimated that half of the spilled oil evaporated (a familiar thought about things disappearing in the vast air) (Farrington, 2013). In
these cases, oil was spilled in the relatively warm water in the Gulf of Mexico
(NCEI NOAA, 2018b; U.S. EPA, 2015a). The warm water (up to 32°C in summer
months) plus the windy conditions led to high evaporation rates. The 1989
Exxon Valdez oil spill occurred in Prince William Sound, Alaska, a region of
cooler water with an average high of 14°C in summer months (NCEI NOAA,
2018a). The spilled oil did not evaporate as much initially as the spills in the
warmer Gulf of Mexico, but overtime loss to the air by volatilization and
other dissipation mechanisms was signifcant. Also, the Deepwater Horizon
accident released a lighter volatile crude oil compared to the heavy crude
oil released in the Exxon Valdez incident in Alaska (Atlas and Hazen, 2011).
The lighter crudes are more volatile and more readily biodegradable. Plus, in
the Gulf of Mexico, microorganisms are adapted to degrading hydrocarbons
(Atlas and Hazen, 2011).