Effect of sequential surface irrigations on field-scale emissions of 1,3-dichloropropene

Reducing the discrepancies between the Aerodynamic Gradient Method and other micrometeorological approaches for measuring fumigant emissions

Observations of fumigant and pesticide emissions are needed for multiple public health and environmental protection mandates. The aerodynamic gradient method (ADM) is commonly used to measure fumigant and pesticide emissions. However, the ADM may over estimate emissions compared to other micrometeorological and modeling approaches, which would increase uncertainty over the true flux estimate. Different studies with ADM have also used multiple differing transport functions that relate concentration gradients to emissions. Therefore, we tested different and more recent transport functions to try to correct the anticipated observed higher values with ADM using observations from two sites in California, USA. We evaluated different transport functions against eddy covariance observations and found that using the functions developed by Högström (1996) corrected the ADM values to be in line with other observational methods. For the Fresno experiment, cumulative emission masses from the ADM- Högström functions were within 7% of other approaches while the Pruitt function was >15% higher. Applying the Högström functions to a series of previous fumigation experiments in California saw reductions in the ADM observations of >25% for cumulative mass emissions. The results indicate that the Högström functions should be used for future ADM experiments in the absence of more robust transport factors for local meteorological conditions. The results also illustrate how previous ADM observations could be corrected to reduce uncertainty in flux emissions estimates.

Simulating emissions of 1,3-dichloropropene after soil fumigation under field conditions

Soil fumigation is an important agricultural practice used to produce many vegetable and fruit crops. However, fumigating soil can lead to atmospheric emissions which can increase risks to human and environmental health. A complete understanding of the transport, fate, and emissions of fumigants as impacted by soil and environmental processes is needed to mitigate atmospheric emissions. Five large-scale field experiments were conducted to measure emission rates for 1,3-dichloropropene (1,3-D), a soil fumigant commonly used in California. Numerical simulations of these experiments were conducted in predictive mode (i.e., no calibration) to determine if simulation could be used as a substitute for field experimentation to obtain information needed by regulators. The results show that the magnitude of the volatilization rate and the total emissions could be adequately predicted for these experiments, with the exception of a scenario where the field was periodically irrigated after fumigation. In addition, the timing of the daily peak 1,3-D emissions was not accurately predicted for these experiments due to the peak emission rates occurring during the night or early-morning hours. This study revealed that more comprehensive mathematical models (or adjustments to existing models) are needed to fully describe emissions of soil fumigants from field soils under typical agronomic conditions.

Effect of surface application of ammonium thiosulfate on field-scale emissions of 1,3-dichloropropene

Soil fumigation is important for food production but has the potential to discharge toxic chemicals into the environment, which may adversely affect human and ecosystem health. A field experiment was conducted to evaluate the effect of applying ammonium thiosulfate fertilizer to the soil surface prior to fumigating with 1,3-dichloropropene (1,3-D). The ammonium thiosulfate solution was applied as a spray with minimal water to minimize the effect on emissions from saturating (e.g. sealing) the soil pores with water. Two independent data sets were collected for determining the emission rate. One data set was used with three micrometeorological approaches: aerodynamic, integrated horizontal flux and theoretical profile shape; the other dataset with two indirect, back calculation methods that used the CALPUFF and ISCST3 dispersion models. Using the five methodologies, the 1,3-D emission rate was obtained for 16days. The maximum emission rates ranged from 7 to 20μgm^-2s^-1, the maximum 24-hour averaged emission rates ranged from 5 to 13μgm^-2s^-1, and the total 1,3-D emissions ranged from 12 to 26%. Comparing to fumigation without ammonium thiosulfate spray revealed that emissions were reduced from 3% (CALPUFF) to 29% (ADM). Using a simulation model, ammonium thiosulfate spray would be expected to reduce emissions by almost 21%. These data provide evidence that emissions of 1,3-D can be reduced by spraying ammonium thiosulfate fertilizer on the soil surface prior to soil fumigation, and provides another emission-reduction strategy to those recently reported (e.g., deep injection, water seals and organic amendments).

Mechanisms for 1,3-Dichloropropene Dissipation in Biochar-Amended Soils

Biochar, which is organic material heated under a limited supply of oxygen, has the potential to reduce fumigant emissions when incorporated in the soil, but the mechanisms are not fully understood. The objective of this study was to determine the effects of biochar properties, amendment rate, soil microbe, moisture, temperature, and soil type on the fate of 1,3-dichloropropene (1,3-D) isomers in laboratory incubation experiments by assessing the 1,3-D degradation rate and adsorption capacity. 1,3-D dissipation rates were significantly reduced due to strong adsorption by biochar, which was also strongly affected by biochar type. Following a 1% biochar amendment, the half-lives of 1,3-D in soil were increased 2.5-35 times. The half-lives of 1,3-D in soil were strongly affected by soil moisture, temperature, and amendment rate. The effects of sterilization on 1,3-D degradation were much smaller in biochar-amended soils than in nonsterilized soils, which suggests the importance of abiotic pathways with biochar's presence. Dissipation of 1,3-D in biochar was divided into adsorption (49-93%) and chemical degradation pathways. Biochar properties, such as specific surface area (SSA), pH, water content, carbon content, and feedstock, all appeared to affect 1,3-D dissipation with potentially complex interactions. The biochar (air-dry) water content was highly correlated with 1,3-D adsorption capacity and thus can serve as an important predictor for fumigant mitigation use. The fate of the adsorbed fumigant onto biochar requires further examination on potential long-term environmental impacts before guidelines for biochar as a field practice to control fumigant emissions can be formulated.

Emissions of 1,3-Dichloropropene and Chloropicrin after Soil Fumigation under Field Conditions

Soil fumigation is an important agronomic practice in the production of many high-value vegetable and fruit crops, but the use of chemical fumigants can lead to excessive atmospheric emissions. A large-scale (2.9 ha) field experiment was conducted to obtain volatilization and cumulative emission rates for two commonly used soil fumigants under typical agronomic practices: 1,3-dichloropropene (1,3-D) and chloropicrin. The aerodynamic method and the indirect back-calculation method using ISCST3 and CALPUFF dispersion models were used to estimate flux loss from the treated field. Over the course of the experiment, the daily peak volatilization rates ranged from 12 to 30 μg m(-2) s(-1) for 1,3-D and from 0.7 to 2.6 μg m(-2) s(-1) for chloropicrin. Depending on the method used for quantification, total emissions of 1,3-D and chloropicrin, respectively, ranged from 16 to 35% and from 0.3 to 1.3% of the applied fumigant. A soil incubation study showed that the low volatilization rates measured for chloropicrin were due to particularly high soil degradation rates observed at this field site. Understanding and quantifying fumigant emissions from agricultural soil will help in developing best management practices to reduce emission losses, reducing adverse impacts to human and ecosystem health, and providing inputs for conducting risk assessments.

Mitigating 1,3-dichloropropene, chloropicrin, and methyl iodide emissions from fumigated soil with reactive film

Implicated as a stratospheric ozone-depleting compound, methyl bromide (MeBr) is being phased out despite being considered to be the most effective soil fumigant. Its alternatives, i.e., 1,3-dichloropropene (1,3-D, which includes cis and trans isomers), chloropicrin (CP), and methyl iodide (MeI), have been widely used. High emissions of MeI from fumigated soil likely put farm workers and other bystanders at risk of adverse health effects. In this study, two types of constructed reactive film were tested for their ability to mitigate emissions of 1,3-D, CP, and MeI using laboratory permeability cells. Before activation, these films act as a physical barrier to trap fumigants leaving soil. After activation of the reactive layer containing ammonium thiosulfate solution, the films also act as a sink for the fumigants. Over 97% of trans-1,3-D and 99% of the cis-1,3-D, CP and MeI were depleted when they passed into the reactive film. Half-lives (t(1/2)) of cis-, trans-1,3-D, CP and MeI under activated reactive film were 1.2, 1.4, 1.6, and 2.0 h respectively at 40 °C.

Effects of surface treatments and application shanks on nematode, pathogen and weed control with 1,3-dichloropropene

BACKGROUND

Preplant fumigation with methyl bromide (MeBr) has been used for control of soilborne pests in high-value annual, perennial and nursery crops, but is being phased out. In 2007 and 2008, research trials were conducted to evaluate the effects of surface treatments and two application shanks on pest control with 1,3-dicloropropene (1,3-D) in perennial crop nurseries.

RESULTS

All 1,3-D treatments controlled nematodes similarly to MeBr. Application of 1,3-D with virtually impermeable film (VIF) reduced Fusarium oxysporum compared with unfumigated plots, but was not as effective as MeBr. Applications of 1,3-D with VIF or 1,3-D followed by metam sodium reduced Pythium spp., but 1,3-D followed by intermittent water seals was comparable with the untreated plots. When sealed with high-density polyethylene (HDPE) film or VIF, 1,3-D generally was as effective as MeBr for reducing weed density and total weed biomass, but weed control was reduced by intermittent water seals and in unsealed plots subsequently re-treated with additional 1,3-D or metam sodium.

CONCLUSION

Applications of 1,3-D sealed with HDPE or VIF film or with intermittent water seals can control nematodes similarly to MeBr. However, additional management practices may be needed for effective pathogen and weed control if plastic film is not used.

Higher-tier assessment of the potential for groundwater issues due to the use of 1,3-D soil fumigant; evaluation of the active ingredient, metabolites and potentially related chlorinated compounds

BACKGROUND

1,3-Dichloropropene (1,3-D, CAS No. 542-75-6) is a broad-spectrum soil fumigant used to control numerous species of soilborne plant-parasitic nematodes. 1,3-D consists of two isomers, (Z)- and (E)-1,3-D. There are a number of low-level chlorinated compounds that could potentially be produced as a part of the 1,3-D manufacturing process. 1,3-D and its metabolites, as well as potentially related chlorinated compounds, represent potential groundwater contaminants.

RESULTS

This study has investigated the hydrolytic stability, under biotic and abiotic conditions in the laboratory, of an extensive representative list of 1,3-D and potentially related chlorinated compounds in order to predict their environmental fate. All of these compounds showed intrinsic hydrolytic instability under both abiotic and biotic test conditions. Furthermore, a monitoring programme was carried out. Twenty-five wells were monitored in five Italian regions characterised by historical and existing use of 1,3-D. The parent compound, its two major metabolites and potentially related chlorinated compounds were not detected in the well water at > 0.1 µg L(-1) at any sampling location.

CONCLUSION

The soil fumigant (E,Z)-1,3-D, its metabolites and potentially related chlorinated compounds constitute a low risk to groundwater.

Managing agricultural emissions to the atmosphere: state of the science, fate and mitigation, and identifying research gaps

The impact of agriculture on regional air quality creates significant challenges to sustainability of food supplies and to the quality of national resources. Agricultural emissions to the atmosphere can lead to many nuisances, such as smog, haze, or offensive odors. They can also create more serious effects on human or environmental health, such as those posed by pesticides and other toxic industrial pollutants. It is recognized that deterioration of the atmosphere is undesirable, but the short- and long-term impacts of specific agricultural activities on air quality are not well known or understood. These concerns led to the organization of the 2009 American Chemical Society Symposium titled . An outcome of this symposium is this special collection of 14 research papers focusing on various issues associated with production agriculture and its effect on air quality. Topics included emissions from animal feeding operations, odors, volatile organic compounds, pesticides, mitigation, modeling, and risk assessment. These papers provide new research insights, identify gaps in current knowledge, and recommend important future research directions. As the scientific community gains a better understanding of the relationships between anthropogenic activities and their effects on environmental systems, technological advances should enable a reduction in adverse consequences on the environment.

Effect of organic material on field-scale emissions of 1,3-dichloropropene

Soil fumigation is important for growing many fruits and vegetable crops, but fumigant emissions may contaminate the atmosphere. A large-scale field experiment was initiated to test the hypothesis that adding composted municipal green waste to the soil surface in an agricultural field would reduce atmospheric emissions of the 1,3-dichloropropene (1,3-D) after shank injection at a 133 kg ha(-1) application rate. Three micrometeorological methods were used to obtain fumigant flux density and cumulative emission values. The volatilization rate was measured continuously for 16 d, and the daily peak volatilization rates for the three methods ranged from 12 to 24 μg m(-2) s(-1). The total 1,3-D mass that volatilized to the atmosphere was approximately 14 to 68 kg, or 3 to 8% of the applied active ingredient. This represents an approximately 75 to 90% reduction in the total emissions compared with other recent field, field-plot, and laboratory studies. Significant reductions in the volatilization of 1,3-D may be possible when composted municipal green waste is applied to an agricultural field. This methodology also provides a beneficial use and disposal mechanism for composted vegetative material.

Comparisons of soil surface sealing methods to reduce fumigant emission loss

State and federal regulatory agencies depend on quality field data for determining the effects of agricultural management practices on fumigant emissions to develop sound, science-based policies and regulations on preplant soil fumigants. Field plot tests, using growers' standard field operation procedures, were used to simultaneously determine the effectiveness of several commonly proposed emission reduction methods, in a trial involving shank injection of Telone II [a.i. 1,3-dichloropropnene (1,3-D)] to a sandy loam soil to a target rate of 372 kg ha(-1). The experiment was conducted in late September 2008 in the San Joaquin Valley of California. Fumigant emissions were captured using dynamic flux chambers. The results showed that virtually impermeable film (VIF) reduced emissions >95% when compared to bare soil, and the glue joints in the film did not significantly affect the tarp performance. The VIF also created a more uniform distribution of gaseous fumigant in the soil profile, which would likely benefit pest control efficacy. Standard high-density polyethylene (HDPE) tarp reduced total 1,3-D emissions about 50% (higher than most reported values) in this trial, whereas postfumigation intermittent water treatments (seals) reduced cumulative emission losses by approximately 20%. Adding 49.4 Mg ha (equivalent to 20 tons per acre) of composted dairy manure to surface soils did not reduce 1,3-D emissions during this experiment. Use of VIF was the most promising technique in reducing emissions and has the potential to allow lower application rates while providing satisfactory pest control.

Transport and fate of methyl iodide and its pest control in soils

For fumigants, information on transport and fate as well as pest control is needed to develop management practices with the fewest negative environmental effects while offering sufficient pest control efficacy. For this purpose, a 2-D soil chamber with a surface-mounted flux chamber was designed to determine volatilization, real-time soil gas-phase concentration, degradation, and organism survivability after methyl iodide (MeI) fumigation. Three types of pests were used to give a broad spectrum of pest control information. An infected sandy loam soil with a volumetric water content of 10.6% was packed carefully into the 2-D chamber to a bulk density of 1.34 g cm(-3). After MeI fumigation at a rate of 56.4 kg ha(-1) for 24 h, about 28.9% of MeI was emitted into air, 6.8% remained in the soil, and 43.6% degraded in the soil (based on the residual iodide concentration). The uncertainty in the measured MeI degradation using iodide concentration was thought to mainly contribute to the unrecovered MeI (about 20%). The citrus nematodes [Tylenchulus semipenetrans] were effectively eliminated even at low concentration-time (CT) values (<30 microg h mL(-1)), but all Fusarium oxysporum survived. The response of barnyardgrass seeds [Echinochloa crus-galli] spatially varied with the CT values in the chamber. To fully control barnyardgrass seeds, CT of greater than 300 microg h mL(-1) was required. Using this experimental approach, different fumigant emission reduction strategies can be tested, and mathematical models can be verified to determine which strategies produce the least emission to the atmosphere while maintaining sufficient pest control efficacy.

Gas-phase distribution and emission of chloropicrin applied in gelatin capsules to soil columns

Chloropicrin (CP) is highly volatile and may pose strong exposure risks for humans and the environment. A gelatin capsule formulation was developed to reduce atmospheric CP emissions and to improve application safety. The objective of this study was to determine the distribution, atmospheric emissions, and soil residual of CP after application in gelatin capsules to soil columns. Two treatments were studied: (i) CP liquid injection with polyethylene film and (ii) CP gelatin capsules with polyethylene film. For the CP liquid injection treatment, the concentration of CP peaked (120.7 microg cm(-3)) at the 20-cm depth 1 h after fumigant injection and decreased with time; at other depths, the CP concentration increased initially and decreased after a typical diffusion-dispersion process. For the gelatin capsule treatment, concentrations of CP at 20 cm depth increased slowly and peaked at 30.04 microg cm(-3) 264 h after application, indicating a slow CP release through the gelatin capsule shells. The results indicate that a rapid breakdown of gelatin capsules occurred between 11 and 12 d after application. The application of CP gelatin capsules reduced total CP emission by approximately 3 times compared with liquid injection with film cover. Similar residual soil CP was found between the liquid injection and the two gelatin capsule treatments. Chloropicrin gelatin capsules could be a promising new technology for reducing environmental emissions and potential human exposure.

1,3-dichloropropene distribution and emission after gelatin capsule formulation application

The gelatin capsule (gel cap) formulation of 1,3-dichloropropene (1,3-D) was developed as a potential means of reducing 1,3-D emissions. The objective of this study was to determine the distribution, emission, and leaching of 1,3-D after applying the gel cap in soil columns. Comparable 1,3-D soil gas concentrations were obtained between a conventional liquid injection control and the gel cap application with film treatment. When the soil surface was irrigated with 39.6 mm water per day during the first 4 days, 1,3-D soil gas concentration was higher than the film treatments at depths below 20 cm, but lower concentrations were observed at 0-15 cm depth. The application of 1,3-D gel cap relatively reduced total 1,3-D emission by about 41% compared to liquid injection with film cover, and total 1,3-D emission was only 0.13% for 1,3-D gel cap application with 4 days of irrigation without a tarp. The results indicated that 1,3-D gel cap could be a promising new technology for reducing environmental emissions and potential human exposure.

Spot fumigation: fumigant gas dispersion and emission characteristics

Reducing emissions of volatile organic compounds (VOCs) from fumigant pesticides is mandatory in California, especially in "nonattainment areas" like the San Joaquin Valley that do not meet federal air quality standards. A two-year field study was conducted to examine the feasibility of site-specific fumigant application only at future tree sites with dramatically reduced amounts of fumigant chemicals on an orchard basis. Soil gas distribution and atmospheric emission of 1,3-dichloropropene and chloropicrin were measured after applying InLine using subsurface drip irrigation. It was predicted that except in the surface 20 cm of soil, satisfactory pest control could be achieved within a 15 cm radius from the injection point. Also, at radial distances of 15-51 cm from the point of fumigant injection, effective nematode control may be achieved. Cumulative atmospheric emission of the fumigants was estimated to be 18-23% of the applied active ingredients in plots that had been cover cropped with Sudan grass and 2-6% in plots that had remained bare for several months before treatment. Considering the significantly small amount of fumigant used on an orchard basis, the spot drip fumigation may achieve a 10-fold reduction in atmospheric VOCs load from fumigant pesticides.

Laboratory assessment of emission reduction strategies for the agricultural fumigants 1,3-dichloropropene and chloropicrin

With the increased use of the agricultural fumigants 1,3-dichloropropene (1,3-D) and chloropicrin (CP), it is important that strategies to reduce emissions of these fumigant from soil to the air are assessed to protect air quality. Using an established soil column approach, the following emission reduction strategies were compared to a control: (1) spray application of ammonium thiosulfate to the soil surface; (2) deep injection at 46 cm depth; (3) high density polyethylene sealed over the soil surface; (4) virtually impermeable film sealed over the soil surface; and (5) irrigation with ammonium thiosulfate solution. Relative to the control, 1,3-D emissions were reduced by 26.1, 1.0, 0.01, 94.2, and 42.5%, for treatments 1 through 5, respectively. For CP the reductions were 41.6, 23.3, 94.6, 99.9, and 87.5% for treatments 1 through 5, respectively. Virtually impermeable film gave the greatest reductions for both fumigants, while HDPE was very effective only for CP. Despite offering less significant emission reductions, the lower cost alternatives to tarping, particularly irrigation with ATS solution, may offer substantial benefitwhere tarping is not economically viable.