140
Pesticides, Organic Contaminants, and Pathogens in Air
Since MITC is a natural product, released at ppm levels from broccoli and
other cole crops, organic farmers make use of it by fnely chopping waste
broccoli and then adding it to soil or water to achieve some nematode and
pathogen control effects from liberated MITC. Species of mustard have been
selected for cultivation for use as a nematocidal powder, earning the title
of “biofumigant” from Marrone BioInnovations. MITC use in California,
primarily as MITC or its precursor salt metam sodium or potassium, has
decreased from 8.2 million pounds in 2009 to 3.1 million pounds 2016
(Table 8.1). It is used primarily for treating strawberries, hops, and a number
of other fruits and vegetables.
There have been sporadic reports of excessive exposure to people living
around felds treated with MITC or a precursor. In one situation, a number of
people near Bakersfeld were exposed to higher-than-normal levels of MITC,
apparently caused by a change in weather after application. Everyone recovered, but fnes were levied for not adhering to weather restrictions while
using MITC. As with all pesticides and all fumigants, the CDPR provides
oversight in case of spills or exposures to people from use of pesticides in
California.
The application technique can help minimize the risk of exposure.
Woodrow and Seiber reported on MITC levels in air above fallow strawberry
felds treated via direct fumigation in Orange County, California (Woodrow
et al., 2008). Air levels were measured for several days after treatment. Levels
were higher when the MITC was applied via shank injection vs when it was
added to driplines.
Vince Hebert, at Washington State University, compared the use of shank
injection of MITC with surface chemigation, a common practice among potato
growers in Washington (Littke et al., 2013). The result was that shank injection led to lower emissions of the fumigant to air. It was recommended that
potato growers use shank injection in addition to buffer zones. Emissions
were even lower when only the beds were treated instead of the entire feld.
The highest concentrations observed were well below threshold limit values recommended by Cal EPA and Cal Occupational Safety and Health
Administration (OSHA). Minimal noticeable levels of MITC were observed
in air.
Unfortunately, the risks associated with MITC do not stop there. MITC is
converted by oxidation to methyl isocyanate (MIC) in the air during and after
release (Lu et al., 2014) (Figure 8.11). This is an issue for concern since MIC is
more toxic than MITC. Its persistence is measured in half-lives calculated for
MITC and MIC (Table 8.7).
MIC was the toxicant released during an industrial accident in Bhopal,
India, in 1984, resulting in death or extreme illness to thousands of villagers
in the downwind direction of the chemical plant where the accident occurred
(Varma and Varma, 2005). Although this was not related to agricultural applications of MITC or precursor metam salts, the event reinforced the need for
rigorous safety standards to protect agricultural workers and rural residents
Pesticides, Organic Contaminants, and Pathogens in Air
Since MITC is a natural product, released at ppm levels from broccoli and
other cole crops, organic farmers make use of it by fnely chopping waste
broccoli and then adding it to soil or water to achieve some nematode and
pathogen control effects from liberated MITC. Species of mustard have been
selected for cultivation for use as a nematocidal powder, earning the title
of “biofumigant” from Marrone BioInnovations. MITC use in California,
primarily as MITC or its precursor salt metam sodium or potassium, has
decreased from 8.2 million pounds in 2009 to 3.1 million pounds 2016
(Table 8.1). It is used primarily for treating strawberries, hops, and a number
of other fruits and vegetables.
There have been sporadic reports of excessive exposure to people living
around felds treated with MITC or a precursor. In one situation, a number of
people near Bakersfeld were exposed to higher-than-normal levels of MITC,
apparently caused by a change in weather after application. Everyone recovered, but fnes were levied for not adhering to weather restrictions while
using MITC. As with all pesticides and all fumigants, the CDPR provides
oversight in case of spills or exposures to people from use of pesticides in
California.
The application technique can help minimize the risk of exposure.
Woodrow and Seiber reported on MITC levels in air above fallow strawberry
felds treated via direct fumigation in Orange County, California (Woodrow
et al., 2008). Air levels were measured for several days after treatment. Levels
were higher when the MITC was applied via shank injection vs when it was
added to driplines.
Vince Hebert, at Washington State University, compared the use of shank
injection of MITC with surface chemigation, a common practice among potato
growers in Washington (Littke et al., 2013). The result was that shank injection led to lower emissions of the fumigant to air. It was recommended that
potato growers use shank injection in addition to buffer zones. Emissions
were even lower when only the beds were treated instead of the entire feld.
The highest concentrations observed were well below threshold limit values recommended by Cal EPA and Cal Occupational Safety and Health
Administration (OSHA). Minimal noticeable levels of MITC were observed
in air.
Unfortunately, the risks associated with MITC do not stop there. MITC is
converted by oxidation to methyl isocyanate (MIC) in the air during and after
release (Lu et al., 2014) (Figure 8.11). This is an issue for concern since MIC is
more toxic than MITC. Its persistence is measured in half-lives calculated for
MITC and MIC (Table 8.7).
MIC was the toxicant released during an industrial accident in Bhopal,
India, in 1984, resulting in death or extreme illness to thousands of villagers
in the downwind direction of the chemical plant where the accident occurred
(Varma and Varma, 2005). Although this was not related to agricultural applications of MITC or precursor metam salts, the event reinforced the need for
rigorous safety standards to protect agricultural workers and rural residents