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Dong Wang - One of the best experts on this subject based on the ideXlab platform.
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concentrations in soil and efficacy of drip applied 1 3 d chloropicrin and metam sodium in plastic mulched sandy soil beds
Crop Protection, 2007Co-Authors: B L Candole, A S Csinos, Dong WangAbstract:Abstract Concentrations in soil and efficacy of 1,3-dichloropropene (1,3-D)+chloropicrin and Methyl Isothiocyanate (MITC) against the survival of Phytophthora capcisi , Rhizoctonia solani and yellow nutsedge ( Cyperus esculentus L.) were studied in plastic-mulched Southern Georgia sandy soil beds. Beds were treated with InLine (60.8% 1,3-D+33.3% chloropicrin) at 93.5, 187, and 280.5 l ha −1 and Vapam (42% metam sodium) 233.8, 467.5 and 701.3 l ha −1 . 1,3-D+chloropicrin and MITC concentrations in soil were monitored after drip application for 7 d and 240 h, respectively, from pre-selected sites in beds. 1,3-D+chloropicrin and MITC concentrations decreased with time and distance from the emitter. Survival of P. capsici , R. solani and yellow nutsedge in treated beds was higher with distance from the emitter. These Methyl bromide alternatives did not diffuse laterally at effective concentrations beyond the point of application. Improved application techniques are required to improve the lateral distribution of these alternatives.
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effects of soil fumigants on methanotrophic activity
Atmospheric Environment, 2007Co-Authors: Kurt A Spokas, Dong Wang, Jennifer Y King, Sharon K. PapiernikAbstract:Negative impacts on methane (CH4) oxidation capacity have already been observed for a variety of agronomic practices, but the effect of soil fumigation on CH4 oxidation has not been investigated. Fumigation is a common practice in agricultural crop and nursery seedling protection. Soils from various agricultural experiment stations, forest nurseries, and a landfill were evaluated for effects of 1,3-dichloropropene (1,3-D), Methyl Isothiocyanate (MITC), and chloropicrin (CP) on CH4 oxidation capacities. All three fumigants significantly reduced CH4 oxidation rates in historically non-fumigated soils (>50%). 1,3-D enhanced CH4 oxidation in 3 out of 5 previously fumigated soils and MITC increased CH4 oxidation rates in all historically MITC-fumigated soils compared to controls. CP universally decreased oxidation capacity regardless of fumigation history. These results support the conclusion that CH4 oxidation effects are fumigant specific and that prior fumigation history plays a vital role in determining the impact on CH4 oxidizer community functionality, which may have implications on the global CH4 cycle.
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emission distribution and leaching of Methyl Isothiocyanate and chloropicrin under different surface containments
Chemosphere, 2007Co-Authors: Y Zhang, Dong WangAbstract:Abstract The environmental fate of fumigants Methyl Isothiocyanate (MITC) and chloropicrin (CP) is of great concern for potential air and groundwater contamination while retaining sufficient concentrations for pest control efficacy. The emission, gas phase distribution, leaching, and persistence of MITC and CP were examined in repacked columns filled with sandy soils under three surface conditions: tarp without irrigation, tarp with limited irrigation, and 5-d irrigation without tarp cover. For MITC, cumulative emission constituted 62%, 36%, and 0.3% of the amount applied under tarp without irrigation, tarp with limited irrigation, and 5-d irrigation without tarp surface conditions, respectively. The corresponding cumulative emission losses were 45%, 30%, and 5.4% for CP. During the first 24 h after injection, soil air concentrations of the two fumigants were much higher in the 15–25 cm depth range than other depths in the soil profile. Small amounts of leaching occurred for both fumigants, indicating potential for groundwater contamination should heavy rain fall or irrigation occurs immediately after soil fumigation. Very small amounts of residual MITC and CP (
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distribution and efficacy of drip applied metam sodium against the survival of rhizoctonia solani and yellow nutsedge in plastic mulched sandy soil beds
Pest Management Science, 2007Co-Authors: B L Candole, A S Csinos, Dong WangAbstract:The effects of metam-sodium application rate on soil residence time, spatial and temporal distributions of Methyl Isothiocyanate and pest control efficacy were studied in a Georgia sandy soil. Metam-sodium 420 g L−1 SL was drip applied at rates of 147 and 295 L ha−1 in plastic-mulched raised beds. Methyl Isothiocyanate concentrations in soil air space were monitored from four preselected sites: 10 and 20 cm below the emitter, and 20 and 30 cm laterally away from the emitter at 3, 12, 24, 48, 72, 120 and 240 h after chemigation. A higher rate of metam-sodium application resulted in higher Methyl Isothiocyanate concentrations in the soil. Highest Methyl Isothiocyanate concentrations were found at 20 cm below the emitter, and lowest at 30 cm laterally away from the emitter. Methyl Isothiocyanate concentrations decreased with time and distance from the emitter. Lower Methyl Isothiocyanate concentration × time product values at 20 and 30 cm away from the emitter resulted in lower mortalities of Rhizoctonia solani Kuhn and yellow nutsedge (Cyperus esculentus L.). The results demonstrated that Methyl Isothiocyanate can be delivered at lethal doses with drip-applied water downward within the beds. Lateral diffusion of Methyl Isothiocyanate from the point of application did not reach biologically active concentrations to affect the survival of R. solani or yellow nutsedge. Further studies on the lateral distribution of Methyl Isothiocyanate in sandy soils are needed to circumvent this limitation. Copyright © 2007 Society of Chemical Industry
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greenhouse gas production and emission from a forest nursery soil following fumigation with chloropicrin and Methyl Isothiocyanate
Soil Biology & Biochemistry, 2005Co-Authors: Kurt A Spokas, Dong Wang, Rodney T VentereaAbstract:Soil fumigation is commonly used to control soil-borne pathogens and weeds. Our aim was to examine the effects of soil fumigation with chloropicrin (CP) and Methyl Isothiocyanate (MITC) on CH4 ,N 2O and CO2 production and emission. These effects on a SE USA forest nursery soil were examined in field and laboratory experiments. Following field fumigation, CH4 surface emissions and concentrations in the soil atmosphere were unaffected. Both fumigants increased N2O emissions rates significantly compared to nonfumigated controls, and the effects were still evident after 48 d. These findings are in contrast to fertilizer-induced N2O emissions, which generally return to background within 2 wk after application. Depths of N2O production were different for the two fumigants as determined by soil gas sampling, suggesting fumigant-specific stimulation mechanisms. CO2 emissions (0‐15 d) were not altered significantly, although sub-surface CO2 concentrations did increase following fumigation with CP or MITC and remained elevated for CP treatment on d 48. CP-induced N2O production was also stimulated in aerobic laboratory incubation studies, with surface soils exhibiting 10 to 100-fold greater production rates. MITC and a combination of CP/MITC also stimulated N2O production, but the effect was significantly less than for CP alone. MITC suppressed and CP did not effect CO2 production in the laboratory incubation. By comparing sterilized to non-sterile soils, O95% of these effects appear to be of biotic origin. q 2004 Elsevier Ltd. All rights reserved.
Husein A Ajwa - One of the best experts on this subject based on the ideXlab platform.
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reduction of Methyl Isothiocyanate atmospheric emissions after application of metam sodium by shank injection
Journal of Environmental Quality, 2013Co-Authors: Husein A Ajwa, M T Holdsworth, Ryan D Sullivan, David A. Sullivan, Shad D NelsonAbstract:Abstract Regulatory initiatives in the United States have created the impetus to reassess application methods for metam sodium (sodium -Methyldithiocarbamate), a Methyl Isothiocyanate (MITC) generator, to reduce flux to the atmosphere. This paper compares flux rates in the years 1990 through 2002 with flux rates based on four studies conducted during the period 2008 through 2010 in California, Michigan, Wisconsin, and Washington using current shank-injection/compaction methods. Up to a 100-fold reduction in peak flux rates and total loss of MITC have been observed. A combination of the following factors led to these reductions in flux: soil moisture goals set at 70% of the field water holding capacity; improved design of shank-injection systems to break up the voids after injection; effective shank compaction to further reduce volatilization; and the use of water sealing, where applicable. These refinements in the application methods for metam sodium provide a means to merge environmental and agricultural goals in the United States and in other countries that use metam sodium. This paper documents the reduced atmospheric emissions of MITC under commercial production conditions when applied using good agricultural practices. This research also shows that MITC flux can be effectively managed without the use of high barrier tarp material.
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water and Methyl Isothiocyanate distribution in soil after drip fumigation
Journal of Environmental Quality, 2013Co-Authors: Shad D Nelson, Scott R Yates, Husein A Ajwa, Thomas J Trout, Mary E Stromberger, Shankar SharmaAbstract:Methyl Isothiocyanate (MITC) generators, such as metam sodium (Met-Na), are used for soil fumigation of agricultural land. The ban on the fumigant Methyl bromide has resulted in greater use of MITC generators. To understand the efficacy of MITC, it is necessary to assess its generation and disappearance kinetics when Met-Na is applied to soil. This study evaluated the movement of water and distribution and dissipation of MITC in soil after application of Met-Na through surface drip irrigation systems. The effects of varying water application volume (25, 50, and 75 mm) and rate (1.9, 5.0, and 7.5 L h m) were evaluated in a sandy loam soil. Good fumigant distribution within the sandy loam soil was observed under medium water application amount (50 mm) with slow to intermediate drip application rates (1.9-5.0 L h m). Low water application amount (25 mm) or high application rate (7.5 L h m) did not provide adequate MITC distribution throughout the soil bed width and rooting depth. Dissipation patterns of MITC in soil in all water application amounts and rates followed first-order kinetics, with a rate constant of 0.025 ± 0.004 h and a half-life of 27 ± 3 h. Simulated water distribution through the soil profile using HYDRUS 2D/3D fitted measured field data well, and the model accurately simulated MITC fumigant distribution in the soil.
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evaluating surface seals in soil columns to mitigate Methyl Isothiocyanate volatilization
2012Co-Authors: S D Nelson, Husein A Ajwa, Catherine R Simpson, Clinton F WilliamsAbstract:The banning of Methyl bromide (MeBr) as a pre-plant soil fumigant due to its implication as an ozone depleting substance, has led to increased interest in finding alternative soil fumigants to replace MeBr (United States Environmental Protection Agency [USEPA], 2009). One of the promising alternatives for certain crops is Methyl Isothiocyanate (MITC). Several MITC generating compounds, such as metam sodium®, metam potassium®, and dazomet® are being used to control a wide variety of fungal pathogens, weeds, and nematodes in soils. The physiochemical characteristics of MITC are significantly different than that of MeBr, such as that its effectiveness in regards to dissipation and movement in the soil is altered by multiple factors, such as soil type, texture, and soil moisture content. The largest challenge to soil fumigation is the prevention of fumigant loss to the atmosphere and especially to the nearby communities and homes adjacent to farm land. Rapid off-gassing or non-target release of the fumigant to the atmosphere can lead to poor pesticide performance and ineffective pest control. To combat this problem that is common to all soil fumigants currently on the market, various methods have been employed to reduce chemical offgassing. A few of these methods are tarping the soil surface immediately following chemical application with high density polyethylene plastic, incorporation of organic matter to the soil surface to absorb the fumigant, or altering chemical formulations. Another method of reducing fumigant loss can be applying a surface water application as a means of sealing the soil surface to prevent chemical volatilization. On-farm field scale studies have been performed to evaluate all of these methods to better evaluate the potential for reducing fumigant loss to the atmosphere. However, field-scale studies are expensive to perform, and experimental error is challenging to control and replicate due to diurnal temperature fluctuations, varying soil physical properties, and air current differences. Thus, the volatilization loss in one study will not represent the typical fumigant loss from site to site. A more controlled laboratory environment is needed to more adequately predict fumigant loss under specific conditions. Laboratory-scale columns can be used to study soil fumigant release from soils under a wide array of conditions and under controlled
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atmospheric flux of agricultural fumigants from raised bed plastic mulch crop production systems
Atmospheric Environment, 2010Co-Authors: Dan O. Chellemi, Husein A Ajwa, David A. SullivanAbstract:Abstract Atmospheric emission of Methyl Isothiocyanate (MITC), chloropicrin (CP), 1,3-dichloropropene (1,3-D), and diMethyl disulfide (DMDS) were measured in the field under fumigant application scenarios representative of raised bed–plastic-mulched crop production systems. For three fumigation sites located in Florida, cumulative emissions of 1,3-D, MITC and CP were less than 11%, 6% and 2%, respectively. For three fumigation sites in located in Georgia, cumulative emissions of MITC and CP were
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surface water seal application to minimize volatilization loss of Methyl Isothiocyanate from soil columns
Pest Management Science, 2010Co-Authors: Catherine R Simpson, S D Nelson, Jerry E Stratmann, Husein A AjwaAbstract:BACKGROUND: Metam-sodium (MS, sodium Methyldithiocarbamate) has been identified as a promising alternative chemical to replace Methyl bromide (MeBr) in soil preplant fumigation. One degradation product of MS in soil is the volatile gas Methyl Isothiocyanate (MITC) which controls soilborne pests. Inconsistent results associated with MS usage indicate that there is a need to determine cultural practices that increase pest control efficacy. Sealing the soil surface with water after MS application may be a sound method to reduce volatilization loss of MITC from soils and increase the contact time necessary for MITC to control pests. The objective of this research was to develop a preliminary soil surface water application amount that would potentially inhibit the off-gassing rate of MITC. RESULTS: Off-gassing rate was consistently reduced with increasing water seal application. The application of a 2.5–3.8 cm water seal provided significantly lower (71–74% reduction in MITC volatilization) total fumigant loss compared with no water seal. The most favorable reduction in MITC off-gassing was observed in the 2.5 cm water seal. CONCLUSION: This suggests that volatilization of MITC-generating compounds can be highly suppressed using adequate surface irrigation following chemical application in this soil type (sandy clay loam), based on preliminary bench-scale soil column studies. Copyright © 2010 Society of Chemical Industry
David A. Sullivan - One of the best experts on this subject based on the ideXlab platform.
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reduction of Methyl Isothiocyanate atmospheric emissions after application of metam sodium by shank injection
Journal of Environmental Quality, 2013Co-Authors: Husein A Ajwa, M T Holdsworth, Ryan D Sullivan, David A. Sullivan, Shad D NelsonAbstract:Abstract Regulatory initiatives in the United States have created the impetus to reassess application methods for metam sodium (sodium -Methyldithiocarbamate), a Methyl Isothiocyanate (MITC) generator, to reduce flux to the atmosphere. This paper compares flux rates in the years 1990 through 2002 with flux rates based on four studies conducted during the period 2008 through 2010 in California, Michigan, Wisconsin, and Washington using current shank-injection/compaction methods. Up to a 100-fold reduction in peak flux rates and total loss of MITC have been observed. A combination of the following factors led to these reductions in flux: soil moisture goals set at 70% of the field water holding capacity; improved design of shank-injection systems to break up the voids after injection; effective shank compaction to further reduce volatilization; and the use of water sealing, where applicable. These refinements in the application methods for metam sodium provide a means to merge environmental and agricultural goals in the United States and in other countries that use metam sodium. This paper documents the reduced atmospheric emissions of MITC under commercial production conditions when applied using good agricultural practices. This research also shows that MITC flux can be effectively managed without the use of high barrier tarp material.
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Comparison of field Methyl Isothiocyanate flux following Pacific Northwest surface-applied and ground-incorporated fumigation practices.
Pest Management Science, 2012Co-Authors: Matt H Littke, Jane T. Lepage, David A. Sullivan, Vincent R. HebertAbstract:Background A fumigant volatilization emission was conducted in Washington State in the fall of 2008 to estimate flux following applications of metam sodium by modified low-boom-height (LBH) center-pivot chemigation and soil-incorporated shank injection. This study was performed in a commercial potato field circle to assess emission rates and total cumulative field loss of Methyl Isothiocyanate (MITC) (the biologically active conversion product of metam sodium) under conditions typical for fall Pacific Northwest potato preplant fumigation. This assessment provides regionally specific MITC emission rate information for modeling appropriate field-edge set-back buffer distances for bystander protection. Results Soil-incorporated shank injection appreciably reduced MITC emissions, with lower periodic flux compared with low-drift surface-applied LBH chemigation during treatment applications and over the 4 day post-fumigation experimental timeframe. The estimated total cumulative fumigant loss was 13% by shank injection compared with 47% by LBH chemigation over the application/post-application monitoring period. Conclusion The greater adoption of shank-injection fumigation will immediately aid in reducing bystander inhalation exposure to MITC, especially in high-soil-fumigation regions existing at the rural–urban interface.© 2012 Society of Chemical Industry
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atmospheric flux of agricultural fumigants from raised bed plastic mulch crop production systems
Atmospheric Environment, 2010Co-Authors: Dan O. Chellemi, Husein A Ajwa, David A. SullivanAbstract:Abstract Atmospheric emission of Methyl Isothiocyanate (MITC), chloropicrin (CP), 1,3-dichloropropene (1,3-D), and diMethyl disulfide (DMDS) were measured in the field under fumigant application scenarios representative of raised bed–plastic-mulched crop production systems. For three fumigation sites located in Florida, cumulative emissions of 1,3-D, MITC and CP were less than 11%, 6% and 2%, respectively. For three fumigation sites in located in Georgia, cumulative emissions of MITC and CP were
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control of off gassing rates of Methyl Isothiocyanate from the application of metam sodium by chemigation and shank injection
Atmospheric Environment, 2004Co-Authors: David A. Sullivan, M T Holdsworth, D J HlinkaAbstract:Abstract Fumigants are used to enhance the yield and quality of agricultural produce, which is critical to the maintenance of the production levels of carrots, potatoes, tomatoes, strawberries, melons, and many other crops grown in the US and throughout much of the world. With the worldwide phase-out of Methyl bromide in progress, the continued availability of the remaining alternatives, such as metam-sodium, 1,3-dichloropropene, and chloropicrin, is becoming increasingly important. Metam-sodium has been used for over 40 years and is the second most widely used fumigant in the United States. Reduction in off-gassing rates of fumigants can promote health and safety benefits and an increased dose in the treatment zone, thereby increasing the potential efficacy of these products. On this basis, there is a need to evaluate off-gassing rates as a function of application and sealing methods. This paper summarizes recent research into the volatilization of the principal transformation product of metam-sodium, i.e., Methyl Isothiocyanate (MITC), into the atmosphere as a function of application and sealing methods. Seven field studies were conducted from 1999–2001 to evaluate the off-gassing rates of MITC from applications of metam-sodium by shank injection and chemigation using two different water sealing methods, i.e., standard water sealing and intermittent water sealing. MITC is slightly soluble in water. Irrigation of a field following an application helps to retain the compound in the soil, minimizing off-gassing while increasing the dose to the target pests. Intermittent water sealing involves applying water on an intermittent basis to minimize off-gassing rates during nighttime periods when relatively poor atmospheric dispersion conditions often occur. Research conducted by the Metam-Sodium TASK Force indicates that intermittent water sealing significantly reduces off-gassing rates both for shank injection and chemigation applications when compared with standard water sealing practices.
Vincent R. Hebert - One of the best experts on this subject based on the ideXlab platform.
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laboratory measured emission losses of Methyl Isothiocyanate at pacific northwest soil surface fumigation temperatures
Bulletin of Environmental Contamination and Toxicology, 2017Co-Authors: Vincent R. Hebert, Glenn C. MillerAbstract:Temperature is a major environmental factor influencing land surface volatilization at the time of agricultural field fumigation. Cooler fumigation soil temperatures relevant to Pacific Northwest (PNW) application practices with metam sodium/potassium should result in appreciably reduced Methyl Isothiocyanate (MITC) emission rates, thus minimizing off target movement and bystander inhalation exposure. Herein, a series of laboratory controlled flow-through soil column assessments were performed evaluating MITC emissions over the range of cooler temperatures (2–13°C). Assessments were also conducted at the maximum allowed label application temperature of 32°C. All assessments were conducted at registration label-specified field moisture capacity, and no more than 50% cumulative MITC loss was observed over the 2-day post-fumigation timeframe. Three-fold reductions in MITC peak fluxes at cooler PNW application temperatures were observed compared to the label maximum temperature. This study supports current EPA metam sodium/potassium label language that indicates surface fumigations during warmer soil conditions should be discouraged.
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determination of Methyl isocyanate in outdoor residential air near metam sodium soil fumigations
Journal of Agricultural and Food Chemistry, 2014Co-Authors: James E Woodrow, Jane T. Lepage, Glenn C. Miller, Vincent R. HebertAbstract:The soil fumigant metam-sodium (CH3NHCS2Na) produces the bioactive respiratory irritant Methyl Isothiocyanate (MITC). Recent laboratory gas-phase oxidative studies indicate that MITC rapidly transforms to the more toxic Methyl isocyanate (MIC) in the lower atmosphere. Inhalation exposure risks from MITC plus MIC may therefore be an occupational worker and/or bystander health concern. To address this concern, MIC was monitored, along with MITC, in outdoor residential air in Washington state during the peak fall metam fumigation season. XAD-7 cartridges, coated with 1-(2-pyridyl)piperazine, were developed to retain MIC as its stable substituted urea derivative. Of the 68 residential air measurements of MIC, 15 (22%) were observed to be above the California Environmental Protection Agency’s chronic inhalation reference level of 1 μg/m3, with an observed maximum MIC air concentration of 4.4 μg/m3. This study indicates MIC air concentrations can be anticipated along with MITC in residential air where seasonal ...
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gas phase reaction of Methyl Isothiocyanate and Methyl isocyanate with hydroxyl radicals under static relative rate conditions
Journal of Agricultural and Food Chemistry, 2014Co-Authors: Vincent R. Hebert, Glenn C. MillerAbstract:Gaseous Methyl Isothiocyanate (MITC), the principal breakdown product of the soil fumigant metam sodium (sodium N-Methyldithiocarbamate), is an inhalation exposure concern to persons living near treated areas. Inhalation exposure also involves gaseous Methyl isocyanate (MIC), a highly reactive and toxic transformation product of MITC. In this work, gas-phase hydroxyl (OH) radical reaction rate constants of MITC and MIC have been determined using a static relative rate technique under controlled laboratory conditions. The rate constants obtained are 15.36 × 10–12 cm3 molecule–1 s–1 for MITC and 3.62 × 10–12 cm3 molecule–1 s–1 for MIC. The average half-lives of MITC and MIC in the atmosphere are estimated to be 15.7 and 66.5 h, respectively. The molar conversion of MITC to MIC for OH radical reactions is 67% ± 8%, which indicates that MIC is the primary product of the MITC–OH reaction in the gas phase.
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Comparison of field Methyl Isothiocyanate flux following Pacific Northwest surface-applied and ground-incorporated fumigation practices.
Pest Management Science, 2012Co-Authors: Matt H Littke, Jane T. Lepage, David A. Sullivan, Vincent R. HebertAbstract:Background A fumigant volatilization emission was conducted in Washington State in the fall of 2008 to estimate flux following applications of metam sodium by modified low-boom-height (LBH) center-pivot chemigation and soil-incorporated shank injection. This study was performed in a commercial potato field circle to assess emission rates and total cumulative field loss of Methyl Isothiocyanate (MITC) (the biologically active conversion product of metam sodium) under conditions typical for fall Pacific Northwest potato preplant fumigation. This assessment provides regionally specific MITC emission rate information for modeling appropriate field-edge set-back buffer distances for bystander protection. Results Soil-incorporated shank injection appreciably reduced MITC emissions, with lower periodic flux compared with low-drift surface-applied LBH chemigation during treatment applications and over the 4 day post-fumigation experimental timeframe. The estimated total cumulative fumigant loss was 13% by shank injection compared with 47% by LBH chemigation over the application/post-application monitoring period. Conclusion The greater adoption of shank-injection fumigation will immediately aid in reducing bystander inhalation exposure to MITC, especially in high-soil-fumigation regions existing at the rural–urban interface.© 2012 Society of Chemical Industry
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Methyl Isothiocyanate Residential Community Air Assessment for South Franklin County, Washington
Bulletin of environmental contamination and toxicology, 2007Co-Authors: J. H. Merriman, Vincent R. HebertAbstract:Metam sodium (metam; sodium Methyl-dithiocarbamate) by weight is the most widely used soil fumigant, and the third most used pesticide in the United States (57–62 million lb/year) (USEPA, 2005a). Metam is applied preplant to a wide variety of crops, with potatoes, tomatoes, tobacco, and strawberries receiving more than 1 million pounds annually. Metam rapidly hydrolyzes upon contact with soil moisture to Methyl Isothiocyanate (MITC), the biologically active ingredient. The high vapor pressure of MITC (2.5–2.8 kPa at 20 C) can lead to substantial surface emission and subsequent off-target air mass movement if metam is not properly applied to the soil (Lee et al., 2002; Li et al., 2006; Sullivan et al., 2004). Thus, MITC may present a significant human inhalation exposure pathway in communities at the urban– agricultural interface (USEPA, 2005b). Methyl Isothiocyanate is an acute respiratory irritant (Pruett et al., 2001). Many residential exposure incidences with reported nose irritation, sore throat, nausea, and dizziness from probable MITC exposure have been well documented in California (Thongsinthusak, 2003). Although not classified by the EPA as a hazardous air pollutant, MITC is considered a toxic air contaminant under the Code of California Regulations, Title 3, Section 6890(b). In Washington State, metam is the most widely used fumigant, with more than 20 million pounds applied in 2005 for control of soil-borne nematodes and diseases in large-scale potato production (NASS, 2006). It is typically applied preplant during the fall by center-pivot chemigation (PMSP, 2002). Recent expansion of suburban development into traditionally agricultural areas now appears to be associated with an increasing number of residential health complaints. Recently, 12 cases of possible or probable acute illnesses related to MITC inhalation exposure have been reported to the Washington State Department of Health (Burgess et al., 2000; Morrissey, 2006). Data on Methyl Isothiocyanate concentration in residential air are lacking for estimation of possible inhalation exposure near potatogrowing regions in Eastern Washington. A few agricultural air monitoring studies have evaluated off-target movement of MITC to residential communities. The majority of these evaluations have been conducted in California near row crop production operations (California Air Resources Board, 1994; California Department of Pesticide Regulations, 2003; Seiber et al., 1999). In particular, Seiber et al. (1999) studied regional off-site movement of MITC to residential areas in Bakersfield, California during the summer fumigation season in this region. The 1-h timeweighted average (TWA) MITC residential outdoor ambient concentrations ranged from 0.3 parts per billion (ppb) to a maximum of 14 ppb. Thongsinthusak (2003) has comprehensively summarized the MITC concentrations found in the California residential studies. Fumigation practices for Pacific Northwest field crops differ appreciably from those used for California row crops. Whereas metam is typically shanked directly into the soil during the spring or summer in California, it is generally applied by center-pivot chemigations in eastern Washington during the cooler fall months of September and October before irrigation districts shut off water supplies. The intensity of J. H. Merriman V. R. Hebert (&) Washington State University Tri-Cities, 2710 University Drive, Richland, WA 99354-1671, USA e-mail: vhebert@tricity.wsu.edu
Glenn C. Miller - One of the best experts on this subject based on the ideXlab platform.
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laboratory measured emission losses of Methyl Isothiocyanate at pacific northwest soil surface fumigation temperatures
Bulletin of Environmental Contamination and Toxicology, 2017Co-Authors: Vincent R. Hebert, Glenn C. MillerAbstract:Temperature is a major environmental factor influencing land surface volatilization at the time of agricultural field fumigation. Cooler fumigation soil temperatures relevant to Pacific Northwest (PNW) application practices with metam sodium/potassium should result in appreciably reduced Methyl Isothiocyanate (MITC) emission rates, thus minimizing off target movement and bystander inhalation exposure. Herein, a series of laboratory controlled flow-through soil column assessments were performed evaluating MITC emissions over the range of cooler temperatures (2–13°C). Assessments were also conducted at the maximum allowed label application temperature of 32°C. All assessments were conducted at registration label-specified field moisture capacity, and no more than 50% cumulative MITC loss was observed over the 2-day post-fumigation timeframe. Three-fold reductions in MITC peak fluxes at cooler PNW application temperatures were observed compared to the label maximum temperature. This study supports current EPA metam sodium/potassium label language that indicates surface fumigations during warmer soil conditions should be discouraged.
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determination of Methyl isocyanate in outdoor residential air near metam sodium soil fumigations
Journal of Agricultural and Food Chemistry, 2014Co-Authors: James E Woodrow, Jane T. Lepage, Glenn C. Miller, Vincent R. HebertAbstract:The soil fumigant metam-sodium (CH3NHCS2Na) produces the bioactive respiratory irritant Methyl Isothiocyanate (MITC). Recent laboratory gas-phase oxidative studies indicate that MITC rapidly transforms to the more toxic Methyl isocyanate (MIC) in the lower atmosphere. Inhalation exposure risks from MITC plus MIC may therefore be an occupational worker and/or bystander health concern. To address this concern, MIC was monitored, along with MITC, in outdoor residential air in Washington state during the peak fall metam fumigation season. XAD-7 cartridges, coated with 1-(2-pyridyl)piperazine, were developed to retain MIC as its stable substituted urea derivative. Of the 68 residential air measurements of MIC, 15 (22%) were observed to be above the California Environmental Protection Agency’s chronic inhalation reference level of 1 μg/m3, with an observed maximum MIC air concentration of 4.4 μg/m3. This study indicates MIC air concentrations can be anticipated along with MITC in residential air where seasonal ...
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gas phase reaction of Methyl Isothiocyanate and Methyl isocyanate with hydroxyl radicals under static relative rate conditions
Journal of Agricultural and Food Chemistry, 2014Co-Authors: Vincent R. Hebert, Glenn C. MillerAbstract:Gaseous Methyl Isothiocyanate (MITC), the principal breakdown product of the soil fumigant metam sodium (sodium N-Methyldithiocarbamate), is an inhalation exposure concern to persons living near treated areas. Inhalation exposure also involves gaseous Methyl isocyanate (MIC), a highly reactive and toxic transformation product of MITC. In this work, gas-phase hydroxyl (OH) radical reaction rate constants of MITC and MIC have been determined using a static relative rate technique under controlled laboratory conditions. The rate constants obtained are 15.36 × 10–12 cm3 molecule–1 s–1 for MITC and 3.62 × 10–12 cm3 molecule–1 s–1 for MIC. The average half-lives of MITC and MIC in the atmosphere are estimated to be 15.7 and 66.5 h, respectively. The molar conversion of MITC to MIC for OH radical reactions is 67% ± 8%, which indicates that MIC is the primary product of the MITC–OH reaction in the gas phase.
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microbial ecology toxicology and chemical fate of Methyl Isothiocyanate in riparian soils from the upper sacramento river
Environmental Toxicology and Chemistry, 1996Co-Authors: George E Taylor, Kastli B Schaller, Jason D Geddes, Mae Sexauer Gustin, Gwen B Lorson, Glenn C. MillerAbstract:On July 14, 1991, 72,000 L of the pesticide Metam (active ingredient, Methyl Isothiocyanate) was accidentally released into the Upper Sacramento River. We hypothesized that the spill affected streamside microbial communities and that the effects were persistent. To address this hypothesis, we sampled river soils a year later from sites above and below the spill as well as from an agricultural area and determined soil carbon dioxide efflux (as a measure of soil respiration) in response to Methyl Isothiocyanate in controlled-environment microcosms, resulting in estimates of the EC50 and soil degradation rates of Methyl Isothiocyanate. The soil respiration EC50s for the river soils ranged from 13.2 to 51.4 μg/g Methyl Isothiocyanate, whereas that of the agricultural soil was 72.2 μg/g. Thus, the soils from the Upper Sacramento River were more sensitive to the toxicologic effects of Methyl Isothiocyanate than was the agricultural soil. Soils from below the spill site also showed higher (factor two or more) EC50s than soils from reference locations above the spill site. The half-life of Methyl Isothiocyanate in soils ranged from 2.7 to 6.9 days and was longer by a factor of two in the river soils. These degradation rates are controlled by both biotic (microbial) and abiotic processes. The presence of a microbial community accelerated the degradation rate by a factor of two. The pattern of EC50 data demonstrates that changes in the microbial community in the river soils were persistent a full year after the spill and that the stress elicited responses that were indicative of physiologic accommodation or selection for resistance at the population, species, and/or community level.
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gas phase photolysis of Methyl Isothiocyanate
Environmental Science & Technology, 1995Co-Authors: Jason D Geddes, Glenn C. Miller, George E TaylorAbstract:Methyl Isothiocyanate (MITC) is the major volatile transformation product of the fumigant metam sodium. The objectives of these studies were to determine both the products and the kinetics of photolysis of MITC in the gas phase in order to better understand its transformation in the atmosphere. The gas phase photolysis of MITC was examined using Tedlar, borosilicate, and quartz chambers. Since sorption of MITC on the walls of the reactors is potentially important, these studies used a ratioing technique that relates sorption of MITC to two other photostable compounds of similar vapor pressure. These experiments showed that MITC undergoes photolysis in the gas phase with a half-life of 10 ± 3 h under xenon arc irradiation and slightly greaterthan 1 day of late summer sunlight. Photolysis products were determined using GC-NPD/FPD and GC/MS. Products observed include Methyl isocyanate, Methyl isocyanide, sulfur dioxide, hydrogen sulfide, carbonyl sulfide, N-Methylformamide, and Methylamine. These data have implications on the risk assessment of metam sodium on human health and environmental receptors.