A study of methyl bromide volatilization and fate from a treated agricultural field was conducted... more A study of methyl bromide volatilization and fate from a treated agricultural field was conducted in Monterey County, California, in 1994. Air concentrations were measured above and downwind from the field with the objective of comparing vertical and horizontal flux terms. Another objective was to compare observed downwind concentrations with those predicted by the Industrial Source Complex model, to begin the process of identifying potential sinks which might scavenge methyl bromide from the atmosphere. The final objective was to determine the limit of detection of our analytical method for airborne methyl bromide using field samples representing a wide range of concentrations. A description of the methods and results of the study will be presented, along with a discussion of data quality and interpretation.
Reviews of Environmental Contamination and Toxicology, 2018
Pesticides and other toxicants released into the environment can contaminate air, water, soil, an... more Pesticides and other toxicants released into the environment can contaminate air, water, soil, and biota. This review focuses on sources, exposures, fate, analysis, and trends. The potential for exposures due to atmospheric transport and deposition of pesticides and related contaminants may pose risks to humans and wildlife. Emissions of chemicals to air are related to physicochemical properties (e.g., vapor pressure and chemical stability). Experimental design and computer-based modeling, as related to emissions and dispersion of pesticides along transects downwind from release sources, will be discussed using the example of pesticide volatilization and drift in California agriculture that results in the transport and deposition downwind to the Sierra Nevada mountains, where much work has been done to refine exposure data for use in risk assessment and management. Predictably, those chemicals found frequently in air are those used most extensively, have multiple emission sources, and resist degradation. Yet to be determined are definitive connections with adverse impacts to humans and wildlife, although the accumulating evidence suggests that endocrine disrupting chemicals, ChE inhibitors, and others warrant further attention. Steps that are being taken to limit emissions, such as in pest control and fuel combustion, offer promising opportunities for improving the quality of air and of the overall environment. Chemical degradation rates and products from trace organics in the air merit more attention, as do the potential for activation by photooxidation and bioaccumulation in food chains. The potential effect of climate change, on atmospheric processes affecting contaminant behavior, is an area ripe for further study.
A method for measuring residues of methyl bromide in air entails concentrating the fumigant on ch... more A method for measuring residues of methyl bromide in air entails concentrating the fumigant on charcoal from an airstream at a flowrate of 100 ml/min, desorption of the trapped material with benzyl alcohol solvent in a sealed vial at 60-110{degrees}C for 10-15 min, and then sampling of the equilibrated vapor for gas chromatographic assay using electron-capture detection. The desorbed vapor is chromatographed on a 27 in x 0.32 mm (id) porous-layer open tubular column, on which methyl bromide has a retention time of about 6 min at 90{degrees}C and at a carrier gas flowrate of 3-3.5 ml/min. Using this method, standard curves were linear over at least three orders of magnitude and a practical limit of detection for field air was about 20 ng/m{sup 3} ({approximately}5 ppt). This method has been used in studies concerned with methyl bromide volatilization from fumigated fields and with ambient background levels.
Journal of Environmental Science and Health Part B-pesticides Food Contaminants and Agricultural Wastes, 1986
Abstract XAD‐4 resin accumulative sampling was tested as a means of on‐site extraction of surface... more Abstract XAD‐4 resin accumulative sampling was tested as a means of on‐site extraction of surface waters. Recoveries for most organochlorine, organophosphorus, organonitrogen, chlorophenol, and chlorophenoxy acid pesticides and related pollutants were acceptable (>50%) when spiked at the 10 and 0.1 ppb levels. Detection limits of 1–100 ppt were attainable for most compounds in river water, although lower levels required the use of an HPLC cleanup/fractionation step prior to those GC determinations using electron‐capture detection. XAD‐4 accumulative sampling was competitive with solvent extraction of grab samples in terms of recoveries, and offered advantages in volume of water sampled, detection limits, and sample handling. The wide range of solute applicability combined with the ease of constructing and operating the accumulative sampler recommends it over grab sampling for many types of monitoring applications.
Methyl bromide is used as an agricultural soil fumigant and concern is growing over the role it m... more Methyl bromide is used as an agricultural soil fumigant and concern is growing over the role it may play in the depletion of stratospheric ozone. Methyl bromide is applied using various techniques and little is known about how much of the applied fumigant volatilizes into the atmosphere after application. The post-application volatilization losses of methyl bromide from two fields using different application practices were measured using an aerodynamic-gradient technique. One field was covered with a high-barrier plastic film tarp during application and the other was left uncovered, but the furrows made by the injection shanks were bedded over. The cumulative volatilization losses from the tarped field were 22% of the nominal application within the first 5 days of the experiment and about 32% of the nominal application within 9 days including the one day after the tarp was removed on day 8. The nontarped field lost 89%of the nominal application by volatilization in 5 days. The error associated, with each flux measurement, as well as variations in daily flux losses with differing sampling period lengths show the degree of variability inherent in this type of study.
... and PCBs in snow and surface waters (McConnell et al., in preparation ... vp) 12 Soil flux= f... more ... and PCBs in snow and surface waters (McConnell et al., in preparation ... vp) 12 Soil flux= f (vp/KocxS) 15 Water flux= f (vp/S) 12 vp= vapor pressure; Koc= soil sorption ... Origin and fate of pesticides in air, in: Eighth 1nternational Con-gress of Pesticide Chemistry: Options 2000, NN ...
Atmospheric residues of pesticides originate principally from operations involved in their applic... more Atmospheric residues of pesticides originate principally from operations involved in their application and in post-application weathering of residual deposits. The concentration and form of airborne residues are of concern from the viewpoint of exposures for applicators, farmworkers, and others in the vicinity of treated sites, and the possible damage they might cause to sensitive plants and animals downwind from the treated areas. There is also considerable evidence that the atmosphere may be an important medium for movement of pesticides through the environment, and for break-down processes governing their residence and fate in the environment.
A study of methyl bromide volatilization and fate from a treated agricultural field was conducted... more A study of methyl bromide volatilization and fate from a treated agricultural field was conducted in Monterey County, California, in 1994. Air concentrations were measured above and downwind from the field with the objective of comparing vertical and horizontal flux terms. Another objective was to compare observed downwind concentrations with those predicted by the Industrial Source Complex model, to begin the process of identifying potential sinks which might scavenge methyl bromide from the atmosphere. The final objective was to determine the limit of detection of our analytical method for airborne methyl bromide using field samples representing a wide range of concentrations. A description of the methods and results of the study will be presented, along with a discussion of data quality and interpretation.
Reviews of Environmental Contamination and Toxicology, 2018
Pesticides and other toxicants released into the environment can contaminate air, water, soil, an... more Pesticides and other toxicants released into the environment can contaminate air, water, soil, and biota. This review focuses on sources, exposures, fate, analysis, and trends. The potential for exposures due to atmospheric transport and deposition of pesticides and related contaminants may pose risks to humans and wildlife. Emissions of chemicals to air are related to physicochemical properties (e.g., vapor pressure and chemical stability). Experimental design and computer-based modeling, as related to emissions and dispersion of pesticides along transects downwind from release sources, will be discussed using the example of pesticide volatilization and drift in California agriculture that results in the transport and deposition downwind to the Sierra Nevada mountains, where much work has been done to refine exposure data for use in risk assessment and management. Predictably, those chemicals found frequently in air are those used most extensively, have multiple emission sources, and resist degradation. Yet to be determined are definitive connections with adverse impacts to humans and wildlife, although the accumulating evidence suggests that endocrine disrupting chemicals, ChE inhibitors, and others warrant further attention. Steps that are being taken to limit emissions, such as in pest control and fuel combustion, offer promising opportunities for improving the quality of air and of the overall environment. Chemical degradation rates and products from trace organics in the air merit more attention, as do the potential for activation by photooxidation and bioaccumulation in food chains. The potential effect of climate change, on atmospheric processes affecting contaminant behavior, is an area ripe for further study.
A method for measuring residues of methyl bromide in air entails concentrating the fumigant on ch... more A method for measuring residues of methyl bromide in air entails concentrating the fumigant on charcoal from an airstream at a flowrate of 100 ml/min, desorption of the trapped material with benzyl alcohol solvent in a sealed vial at 60-110{degrees}C for 10-15 min, and then sampling of the equilibrated vapor for gas chromatographic assay using electron-capture detection. The desorbed vapor is chromatographed on a 27 in x 0.32 mm (id) porous-layer open tubular column, on which methyl bromide has a retention time of about 6 min at 90{degrees}C and at a carrier gas flowrate of 3-3.5 ml/min. Using this method, standard curves were linear over at least three orders of magnitude and a practical limit of detection for field air was about 20 ng/m{sup 3} ({approximately}5 ppt). This method has been used in studies concerned with methyl bromide volatilization from fumigated fields and with ambient background levels.
Journal of Environmental Science and Health Part B-pesticides Food Contaminants and Agricultural Wastes, 1986
Abstract XAD‐4 resin accumulative sampling was tested as a means of on‐site extraction of surface... more Abstract XAD‐4 resin accumulative sampling was tested as a means of on‐site extraction of surface waters. Recoveries for most organochlorine, organophosphorus, organonitrogen, chlorophenol, and chlorophenoxy acid pesticides and related pollutants were acceptable (>50%) when spiked at the 10 and 0.1 ppb levels. Detection limits of 1–100 ppt were attainable for most compounds in river water, although lower levels required the use of an HPLC cleanup/fractionation step prior to those GC determinations using electron‐capture detection. XAD‐4 accumulative sampling was competitive with solvent extraction of grab samples in terms of recoveries, and offered advantages in volume of water sampled, detection limits, and sample handling. The wide range of solute applicability combined with the ease of constructing and operating the accumulative sampler recommends it over grab sampling for many types of monitoring applications.
Methyl bromide is used as an agricultural soil fumigant and concern is growing over the role it m... more Methyl bromide is used as an agricultural soil fumigant and concern is growing over the role it may play in the depletion of stratospheric ozone. Methyl bromide is applied using various techniques and little is known about how much of the applied fumigant volatilizes into the atmosphere after application. The post-application volatilization losses of methyl bromide from two fields using different application practices were measured using an aerodynamic-gradient technique. One field was covered with a high-barrier plastic film tarp during application and the other was left uncovered, but the furrows made by the injection shanks were bedded over. The cumulative volatilization losses from the tarped field were 22% of the nominal application within the first 5 days of the experiment and about 32% of the nominal application within 9 days including the one day after the tarp was removed on day 8. The nontarped field lost 89%of the nominal application by volatilization in 5 days. The error associated, with each flux measurement, as well as variations in daily flux losses with differing sampling period lengths show the degree of variability inherent in this type of study.
... and PCBs in snow and surface waters (McConnell et al., in preparation ... vp) 12 Soil flux= f... more ... and PCBs in snow and surface waters (McConnell et al., in preparation ... vp) 12 Soil flux= f (vp/KocxS) 15 Water flux= f (vp/S) 12 vp= vapor pressure; Koc= soil sorption ... Origin and fate of pesticides in air, in: Eighth 1nternational Con-gress of Pesticide Chemistry: Options 2000, NN ...
Atmospheric residues of pesticides originate principally from operations involved in their applic... more Atmospheric residues of pesticides originate principally from operations involved in their application and in post-application weathering of residual deposits. The concentration and form of airborne residues are of concern from the viewpoint of exposures for applicators, farmworkers, and others in the vicinity of treated sites, and the possible damage they might cause to sensitive plants and animals downwind from the treated areas. There is also considerable evidence that the atmosphere may be an important medium for movement of pesticides through the environment, and for break-down processes governing their residence and fate in the environment.
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