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Alexandria, VA, United States

Sullivan D.A.,Sullivan Environmental Consulting Inc. | Ajwa H.A.,University of California at Davis
Soil Science Society of America Journal | Year: 2011

The exposure to airborne particulates and surface deposition are important pathways for many human health assessments. Our primary focus is on air quality modeling issues associated with the emission of airborne particulates from contaminated surfaces via wind erosion and the subsequent deposition onto other areas. In this context, the analysis is directed at long-term impacts associated with wind-erosion-induced movement from a contaminated area onto residential and other property. For this type of application, detailed inputs on soil moisture, armoring, and other factors are typically not known as a function of time. The defined scope and data limitations generally render more detailed and data-intensive approaches impractical compared with more simplified empirical models. We compare and contrast selected empirical models to show the central tendency as a function of the type of applications (flat-regional and flat-local) as examples. Th is review demonstrates the importance of applying empirical wind erosion equations in a manner that is consistent with their development and with due consideration of sitespecific features and the specific air quality analysis under evaluation. Of importance to this review are: the scale of analysis, flat vs. pile (elevated) sources, and an appropriate representation of uncertainty. Without consideration of such factors within dispersion modeling analyses of airborne particulate concentrations or surface deposition rates, the exposure analysis can be substantially biased. © Soil Science Society of America. Source

Gao S.,U.S. Department of Agriculture | Ajwa H.,University of California at Davis | Qin R.,U.S. Department of Agriculture | Qin R.,University of California at Davis | And 2 more authors.
Environmental Science and Technology | Year: 2013

Tarping fumigated fields with low permeability films such as commercial Totally Impermeable Film (TIF) can significantly reduce emissions, but it can also increase fumigant residence time in the soil such that extended tarp-covering durations may be required to address potential exposure risks during tarp-cutting and removal. In an effort to develop safe practices for using TIF, a large field study was conducted in the San Joaquin Valley of California. Comprehensive data on emissions (measured with dynamic flux chambers), fate, and transport of 1,3-dichloropropene and chloropicrin were collected in a 3.3 ha field fumigated with Pic-Clor 60 via broadcast shank application. Low emission flux (below 15 μg m-2 s-1) was observed from the tarped field throughout the tarp-covering period of 16 days with total emission loss of <8% of total applied for both chemicals. Although substantially higher flux was measured at tarp edges (up to 440 μg m-2 s-1), the flux was reduced to below 0.5 μg m -2 s-1 beyond 2 m of tarp edge where total mass loss was estimated to be ≤1% of total applied to the field. Emission flux increased following tarp-cutting, but was much lower compared to 5 or 6 d tarp-covering periods determined in other fields. This study demonstrated the ability of TIF to significantly reduce fumigant emissions with supporting data on fumigant movement in soil. Proper management on use of the tarp, such as extending tarp-covering period, can reduce negative impact on the environment and help maintain the beneficial use of soil fumigants for agricultural productions. © 2012 American Chemical Society. Source

Chellemi D.O.,U.S. Department of Agriculture | Mirusso J.,Mirusso Enterprises Inc. | Ajwa H.A.,University of California at Los Angeles | Sullivan D.A.,Sullivan Environmental Consulting Inc. | Unruh J.B.,University of West Florida
Crop Protection | Year: 2013

Chemical fumigants are routinely used for soil disinfestation of high value crops. Good agricultural practices (GAPs) are needed to reduce their human health risks, environmental impacts, and improve their cost-effectiveness. This study investigated the effect of fumigant application methods on soil persistence and emission of 1,3-dichloropropene (1,3-D) and chloropicrin (CP). Field experiments were conducted to measure the individual and combined effects of pre-application tillage practices, fumigant application technology, and plastic films on 1,3-D soil concentrations to obtain a numerical index (CT value) to estimate their potential for pest control efficacy and to compare soil persistence, atmospheric flux rate, and cumulative emission of CP and 1,3-D under two diverse application scenarios. Greater 1,3-D soil vapor concentrations were observed by combining a pre-application soil seal with low soil disturbance application technology when compared to pre-application soil tillage and the use of back-swept application shanks. Under high density polyethylene plastic, the low disturbance scenario resulted in time weighted exposure concentration (CT) values ranging from 6.8 to 12.2 μg h cm-3 of soil as compared to CT values ranging from 2.9 to 5.4 μg h cm-3 under the conventional application scenario. Cumulative atmospheric emission of 1,3-D was decreased by 18% under the low disturbance scenario and atmospheric emission of CP by 21% when compared to a conventional application scenario. This study identified GAPs that can be readily implemented in the field to reduce the human and environmental impacts of soil fumigants and improve their cost-effectiveness under solid-tarp (broadcast) applications. © 2012. Source

Spurlock F.,U.S. Environmental Protection Agency | Johnson B.,U.S. Environmental Protection Agency | Tuli A.,U.S. Environmental Protection Agency | Gao S.,U.S. Department of Agriculture | And 6 more authors.
Vadose Zone Journal | Year: 2013

We evaluated the HYDRUS 2D/3D model for simulating chloropicrin and 1,3-dichloropropene fate and transport in broadcast applications. The calibrated model provided relatively accurate estimates of fumigant soil gas concentrations, and volatilization in two data sets using input data were measured, estimated, or obtained by independent calibration. We evaluated the ability of the HYDRUS 2D/3D model to simulate chloropicrin (CP) and 1,3-dichloropropene (13D) fate, transport, and volatilization. Three fields with similar soil conditions were broadcast fumigated under a totally impermeable film (TIF). One field was used to calibrate HYDRUS by adjusting fumigant degradation rates, soil sorption coefficients, and TIF tarp resistance factors. In comparisons of simulated and measured soil gas concentrations, soil temperature, soil water contents, and inverse-modeled estimates of fumigant volatilization flux, the model accurately simulated the basic individual processes of fumigant partitioning and degradation, heat transport, and soil water dynamics in the calibration field. Subsequent flux simulations of the remaining two fields were performed using only measured, independently estimated or calibrated inputs with no further adjustments. The magnitudes of simulated cumulative fluxes and both pre- and post-tarpcut discrete flux densities were within the estimated range of uncertainty (factor of ~2) of conventional inverse-modeled field-based flux estimates. However, the timing of maximum discrete flux densities was delayed by 1 to 2 d relative to inverse-modeled estimates. While HYDRUS provided reasonably accurate flux estimates, it was also evident that parameterization, particularly for TIF tarp permeability properties, generally requires field-based calibration because of a lack of representative field effective permeability data. © Soil Science Society of America 5585 Guilford Rd., Madison, WI 53711 USA. All rights reserved. Source

Ajwa H.,University of California at Davis | Stanghellini M.S.,TriCal Inc. | Gao S.,U.S. Department of Agriculture | Sullivan D.A.,Sullivan Environmental Consulting Inc. | And 3 more authors.
California Agriculture | Year: 2013

With methyl bromide's phase-out, most growers have turned to alternative fumigants, particularly 1,3-dichloropropene (1,3-D) and chloropicrin. These alternatives are tightly regulated because they are classified as toxic air contaminants and volatile organic compounds; the latter combine with other substances to produce ground-level ozone (smog). Two ambient air monitoring studies were conducted to evaluate the potential of totally impermeable film (TIF) to reduce emissions from shank applications of chloropicrin and 1,3-D. In 2009, a study demonstrated that TIF reduced chloropicrin and 1,3-D peak emissions by 45% and 38%, respectively, but TIF did not reduce total emissions when it was cut after 6 days. In 2011, increasing the tarp period from 5 to 10 days decreased chloropicrin and 1,3-D peak emissions by 88% and 78%, and their total emissions by 64% and 43%, respectively. Concurrent dynamic flux chamber results corroborated the ambient air monitoring data. These studies provide regulatory agencies with mitigation measures that should allow continued fumigant use at efficacious application rates. Source

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