Reactive films for mitigating methyl bromide emissions from fumigated soil

Emissions of methyl bromide (MeBr) from agricultural fumigation can lead to depletion of the stratospheric ozone layer, and so its use is being phased out. However, as MeBr is still widely used under Critical Use Exemptions, strategies are still required to control such emissions. In this work, novel reactive films (RFs) were designed and their efficacy in limiting loss of MeBr from soil was tested. A reactive layer, containing dry ammonium thiosulfate (ATS), was sandwiched between two layers of plastic film, the lower layer being HDPE (high-density polyethylene film, which is permeable to MeBr) and the upper layer HDPE or VIF (virtually impermeable film). MeBr diffusion through, and transformation by, the RFs were tested in a stainless-steel permeability cell. Although ineffective when dry, the RFs substantially depleted MeBr when activated with water to produce ATS solution. MeBr half-life (t(1/2)) was around 9.0 h at 20 °C in the presence of activated RF, and was sensitive to temperature (t(1/2) 15.7 and 2.9 h at 10 and 40 °C, respectively). When the upper film layer was VIF, less than 0.15% of the added MeBr diffused through the film, with the remainder being transformed within the reactive layer. These findings indicate that such films have good potential to reduce MeBr loss from fumigated soils to the atmosphere.     

Effect of surface tarp on emissions and distribution of drip-applied fumigants

Soil fumigants are used to control a wide variety of soil-borne pests in high-cash-value crops. Application of soil fumigants through drip irrigation systems is receiving increasing attention as a method to improve the uniformity of fumigant application. Little information is available on the emissions and soil distribution of fumigants following subsurface drip application, or the effect of plastic tarp on fumigant emissions in these systems. In these experiments, the fumigant compounds 1,3-dichloropropene (1,3-D), Vapam (a methyl isothiocyanate (MITC) precursor), and propargyl bromide (PrBr) were applied to soil beds via drip irrigation at 15 cm depth. Beds were tarped with either standard 1-mil high-density polyethylene (HDPE) or a virtually impermeable film (VIF), leaving the furrows bare. Cumulative emissions of 1,3-D, MITC, and PrBr in these tarped bedded systems was very low, amounting to <10% of the applied mass. These experiments were conducted in the winter months, with average air temperatures of 12-15 degrees C. Cumulative emissions of MITC and 1,3-D from a sandy loam field soil were decreased by > or =80% by tarping the bed with VIF rather than HDPE. A large fraction of the 1,3-D and PrBr flux was from the untarped furrows in VIF-tarped plots, indicating that inhibiting volatilization from the furrow will be important in further reducing emissions in these systems. Monitoring the fumigant distribution in soil indicated that tarping the bed with VIF resulted in a more effective containment of fumigant vapors compared to use of a HDPE tarp.     

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.     

Remediation of methyl iodide in aqueous solution and soils amended with thiourea

Methyl iodide (MeI) is considered a very promising fumigant alternative to methyl bromide (MeBr) for controlling soil-borne pests. Because atmospheric emission of highly volatile fumigants contributes to air pollution, feasible strategies to reduce emissions are urgently needed. In this study, thiourea (a nitrification inhibitor) was shown to accelerate the degradation of MeI in soil and water. In aqueous solution, the reaction between MeI and thiourea was independent of pH, although the rate of MeI hydrolysis increased in alkaline solution. Substantial increases in the rate of MeI dissipation were observed in thiourea-amended soils. Transformation of MeI by thiourea in aqueous solution was by a single chemical reaction process, while MeI degradation in thiourea-amended soil apparently involved a catalytic mechanism. The electron delocalization between the thiourea molecule and the surfaces of soil particles is energetically favorable and would increase the nucleophilic reactivity of the thiono group toward MeI, resulting in an enhancement of the dissipation rate. The soil half-life for MeI was reduced from >300 h for unamended soils to only a few hours in soil or sand amended with thiourea at a 2:1 molar ratio (thiourea:MeI). The MeI transformation rate in thiourea-amended soil increased with increasing soil temperature and decreasing soil moisture. Therefore, spraying thiourea on the soil surface to form a "reactive surface barrier" may be an effective and innovative strategy for controlling fumigant emissions to the atmosphere and for improving environmental protection.     

Effect of environmental conditions on the permeability of high density polyethylene film to fumigant vapors

Soil fumigation in greenhouses or agricultural fields often includes tarping the soil surface with polyethylene (PE) films to contain the fumigant in the soil and reduce emissions to the atmosphere. Previous research has demonstrated that PE films are permeable to methyl bromide and other fumigant compounds. In these experiments, the effect of temperature, fumigant mixtures, condensed water, and field aging on the permeability of high-density polyethylene (HDPE) was determined. Mass transfer coefficients (h, a measure of permeability) of the fumigants methyl bromide, 1,3-dichloropropene, propargyl bromide, and chloropicrin across HDPE films were determined. In these studies, temperature and HDPE film type had the largest impact on the h of fumigant compounds across HDPE films. Other factors investigated, including fumigant mixtures, condensed water on the film, and field aging of UV-stabilized film, did not have a significant impact on h. The results of these experiments suggest that the permeability of an intact piece of an agricultural film will increase with increasing temperature but is relatively constant despite changes in other environmental conditions.     

Bioreactors for removing methyl bromide following contained fumigations

Use of methyl bromide (MeBr) as a quarantine, commodity, or structural fumigant is under scrutiny because its release to the atmosphere contributes to the depletion of stratospheric ozone. A closed-system bioreactor consisting of 0.5 L of a growing culture of a previously described bacterium, strain IMB-1, removed MeBr (> 110 micromol L(-1)) from recirculating air. Strain IMB-1 grew slowly to high cell densities in the bioreactor using MeBr as its sole carbon and energy source. Bacterial oxidation of MeBr produced CO2 and hydrobromic acid (HBr), which required continuous neutralization with NaOH for the system to operate effectively. Strain IMB-1 was capable of sustained oxidation of large amounts of MeBr (170 mmol in 46 d). In an open-system bioreactor (10-L fermenter), strain IMB-1 oxidized a continuous supply of MeBr (220 /micromol L(-1) in air). Growth was continuous, and 0.5 mol of MeBr was removed from the air supply in 14 d. The specific rate of MeBr oxidation was 7 x 10(-16) mol cell(-1) h(-1). Bioreactors such as these can therefore be used to remove large quantities of contaminant MeBr, which opens the possibility of biodegradation as a practical means for its disposal.     

METHYL BROMIDE, TIME and TEMPERATURE of EXPOSURE ON APPLE QUALITY

ABSTRACT. The use of methyl bromide (MeBr) as a fumigant to control codling moth in 'Delicious'apples resulted in a loss of firmness, internal color and therefore a reduction in the amount of acceptable fruit. Time and temperature of MeBr exposure were directly related to firmness and internal color loss. As the exposure time was increased beyond 2 h and exposure temperature above 6°C firmness and internal color loss were accelerated. an 8-day ambient storage period exacerbated firmness and internal color loss as time and temperature of MeBr exposure were increased. A fumigation regime of 56 g MeBr/m³ at 6°C for 2 h resulted in acceptable fruit during a 60 day refrigerated storage period. Increased exposure times or temperatures beyond 56 g MeBr/m³ at 6°C for 2 h resulted in unacceptable firmness and internal color loss, coupled with a major loss in acceptable fruit.     

Development of a methyl bromide collection system for fumigated farmland

Recent research has indicated that up to 73% of the methyl bromide (MeBr) applied to agricultural farmland is ultimately emitted to the atmosphere despite the practice of complete coverage of the fields with polyethylene (PE) tarp. To reduce the emission of MeBr, several techniques have been investigated. An alternative that has received little consideration is the collection and recycle or treatment of MeBr emissions. We investigated the potential of using a two-layer tarp system for collecting the MeBr. Laboratory experiments with a small two-layer diffusion reactor were conducted to determine the mass transfer coefficient (K) of MeBr through tarps and to validate a model of the collection system. For PE tarps K was 1.15 x 10(-6) m s-1 at 20 degrees C and 5.2 x 10(-6) m s-1 at 60 degrees C. K for so-called virtually impermeable films ranged from 4.6 x 10(-10) m s-1 to 1.3 x 10(-8) m s-1. The mathematical model was then used to simulate a full scale fumigant field application. Results indicate excellent agreement between the model, laboratory experiments, and previous field studies. Total emission from the field was a function of the air exchange rate through the swept volume between the two layers, the length of time the field is covered by the collection system, and the mass transfer coefficient of MeBr though the tarps. The results indicate that the proposed two-layer system can be very effective in collecting MeBr emissions from fumigated farmland.     

The effect of ultra-rapid chilling and subsequent ageing on the calpain/calpastatin system and myofibrillar degradation in lamb M. longissimus thoracis et lumborum

The effect of ultra-rapid chilling (-20°C) on the proteolytic degradation of myofibrillar proteins during ageing, by the calpain/calpastatin system in lamb was investigated. Carcasses (36) were ultra-rapidly chilled (-20°C for 3.5 h followed by 20.5 h at +4°C) or chilling at +4°C for 24 h. After chilling all carcasses were stored at +4°C for a further 4 days. Samples of M. longissimus thoracis et lumborum were taken for Warner-Bratzler shear force measurement, sarcomere length, SDS-PAGE and enzyme activity analysis. Ultra-rapid chilling (-20°C) had no effect on the proteolytic degradation of myofibrillar proteins by the calpain/calpastatin system compared to conventional chilling (+4°C). However, no difference in tenderness was found between the two chilling regimes at 1 or 5 days postmortem so differences in myofibrillar degradation or enzyme activity would not be expected.     

Soil chamber method for determination of drip-applied fumigant behavior in bed-furrow agriculture: application to chloropicrin

To overcome the environmental impacts of soil fumigant use, emission reduction strategies such as tarping can be adopted. There is a need to experimentally quantify the effectiveness of such strategies, preferably in a low-cost manner. We report the design and initial testing of a laboratory soil chamber approach for quantifying the soil distribution and emissions of fumigants from bed-furrow agricultural systems. As far as possible, field conditions (e.g., soil type, bulk density, moisture content temperature) were maintained in the experiments. In studying the drip application of chloropicrin using this system, very good data reproducibility was observed between replicates, allowing confidence in the experimental design. For control chambers, high emissions, around 60% (of the total added), were observed due to the near-surface (5 cm depth) application. When the soil beds were tarped using high-density polyethylene (HDPE) or semi-impermeable film (SIF), emissions were reduced to around 40% due to an accumulation of chloropicrin below the tarp. The approach offers an inexpensive potential alternative to studying fumigant emissions from bed-furrow systems in the field and suggests that less permeable tarps would be required to drastically reduce chloropicrin emissions.     

Humin as an electron mediator for microbial reductive dehalogenation

We report that humins extracted as the solid fractions from paddy soils or sediment are involved in extracellular electron transfer, coupled with microbial reductive dehalogenation of pentachlorophenol (PCP), by serving as both electron acceptor and electron donor. In our system, humin is requisite for the dechlorination of PCP, and this activity cannot be maintained when humin is replaced with soluble humic substances or related compounds, including 0.1 M NaOH-extracted humic acid from soil, Aldrich humic acid, and anthraquinone-2,6-disulfonate. The function of humins is stable against treatments with H(2)O(2) (30%, 30 min), HCl (0.1 M, 48 h), NH(2)OH · HCl (0.1 M, 48 h), NaBH(4) (0.1 M, 15 h), and heat (121 °C, 30 min). Cyclic voltammograms indicated that humin harbors redox-active moieties, and electron spin resonance suggested that quinone moieties within humin are the redox-active centers. Fourier-transform infrared and nuclear magnetic resonance analyses verified the presence of the aryl carbonyl carbon group in humin. Although the proportion of redox-active carbon is very small, the potential electron-mediating ability is not negligible. The finding that humin, in solid form, is redox active has important implications for in situ bioremediation, given the wide distribution of humin and the diversity and ubiquity of humic substance-utilizing microorganisms.     

Thiosulfate and manure amendment with water application and tarp on 1,3-dichloropropene emission reductions

Reducing fumigant emissions is required for minimizing bystander risk and environmental impact. Effective and economic field management methods including commonly used surface sealing technique and soil amendments are needed for achieving emission reductions. This research determined the effectiveness of ammonium thiosulfate (ATS) and composted manure amendments to surface soil in combination with water application or high density polyethylene (HDPE) tarp on reducing emissions of 1,3-D from soil columns. Surface treatments included an untreated control, water seal (single water application at time of fumigant injection), ATS amendments at 1:1 and 2:1 molar ratio of ATS:fumigant, composted steer manure at 3.5 kg m(-2), and HDPE tarp over 1:1 ATS or the manure amendment. Cumulative 1,3-D emission loss over two weeks was greatest for the control (52% of applied). The HDPE tarp over ATS and manure treatments had the lowest 1,3-D emissions at 24 and 16%, respectively. Treatments with ATS or manure alone reduced 1,3-D emissions (29-39%) more effectively than water seal (43%) and further benefit was gained with the addition of HDPE tarp. Amendment of surface soil with organic materials shows greater potential in minimizing fumigant emissions than with chemicals with the need for a better understanding of the organic-fumigant reaction mechanism.     

Evaluation of the permeability of agricultural films to various fumigants

A variety of agricultural films are commercially available for managing emissions and enhancing pest control during soil fumigation. These films are manufactured using different materials and processes which can ultimately result in different permeability to fumigants. A systematic laboratory study of the permeability of the agricultural films to nine fumigants was conducted to evaluate the performance of commonly used film products, including polyethylene, metalized, and high-barrier films. The permeability, as expressed by mass transfer coefficient (cm/h), of 27 different films from 13 manufacturers ranged from below 1 × 10(-4) cm/h to above 10 cm/h at 25 °C under ambient relative humidity test conditions. The wide range in permeability of commercially available films demonstrates the need to use films which are appropriate for the fumigation application. The effects of environmental factors, such as temperature and humidity, on the film permeability were also investigated. It was found that high relative humidity could drastically increase the permeability of the high-barrier films. The permeability of some high-barrier films was increased by 2-3 orders of magnitude when the films were tested at high relative humidity. Increasing the temperature from 25 to 40 °C increased the permeability for some high-barrier films up to 10 times more than the permeability at 25 °C, although the effect was minimal for several of these films. Analysis of the distribution of the permeability of the films under ambient humidity conditions to nine fumigants indicated that the 27 films largely followed the material type, although the permeability varied considerably among the films of similar material.     

Surface irrigation reduces the emission of volatile 1,3-dichloropropene from agricultural soils

Low-cost, practicable techniques are required to limit the release of volatile organic compound-containing fumigants such as 1,3-D to the atmosphere. In this study, we aimed to quantify 1,3-D diffusion and emission from laboratory soil columns maintained under realistic conditions and thereby assess the efficacy of soil irrigation as a technique for reducing emissions. In two soils (one relatively high, and one relatively low, in organic matter), irrigation led to a limiting of upward diffusion of the fumigant and to the maintenance of higher soil gas concentrations. Therefore, rather than being emitted from the column, the 1,3-D was maintained in the soil where it was ultimately degraded. As a consequence, emission of 1,3-D from the irrigated columns was around half of thatfrom the nonirrigated columns. It is concluded that surface irrigation represents an effective, low-cost, and readily practicable approach to lessening the environmental impact of 1,3-D fumigant use. In addition, the higher organic matter soil exhibited emissions of around one-fifth of the lower organic matter soil in both irrigated and nonirrigated treatments, due to markedly enhanced degradation of the fumigant. Organic matter amendment of soils may, therefore, also represent an extremely effective, relatively low-cost approach to reducing 1,3-D emissions.     

Effect of application variables on emissions and distribution of fumigants applied via subsurface drip irrigation

Soil fumigation is useful for controlling soil-borne pests and diseases in high-cash-value crops. Fumigants are highly volatile, and approaches to reduce atmospheric emissions are required to protect human and environmental health. Application of fumigants through drip irrigation has been proposed as a means to decrease fumigant emissions, improve fumigant distribution in soil, and minimize worker exposure. These experiments were conducted to investigate the effect of the configuration of the drip system on the volatilization and distribution of the fumigants 1,3-dichloropropene (1,3-D), propargyl bromide (PrBr), and methyl isothiocyanate (MITC) in bedded systems. Results indicated that changing the drip emitter spacing and using multiple drip lines in each bed had little effect on the emissions and distribution of any fumigant. Increasing the depth of application from 15 to 30 cm reduced volatilization of MITC by approximately 20 to >90%; emissions were reduced due to a decrease in the flux from the bed top, and deeper injection did not change the amount of fumigant volatilized from the bed side slope and furrow. Increasing the application depth resulted in a slight decrease in the rate of fumigant dissipation in soil, indicating the potential for some improvement in pest-control efficacy with deeper application.     

QUALITY CHARACTERISTICS OF 'BING' AND 'RAINIER' SWEET CHERRIES TREATED WITH GIBBERELLIC ACID, FOLLOWING FUMIGATION WITH METHYL BROMIDE

Methyl bromide (MeBr) fumigation did not significantly influence weight loss, fruit color or soluble solids of either ‘Bing’ or ‘Rainier’ sweet cherries. MeBr increased pitting and reduced objective and subjective stem color of both cultivars. There was a slight advantage in quality (bruising, pitting and stem color) for the 48g/m³ at 12°C over the 64g/m³ at 6°C MeBr treatment. As fumigation temperature increased, bruising and pitting increased and stem color decreased. Use of gibberellic acid resulted in increased firmness for ‘Bing’ cherries and superior fruit and stem color with less pitting for both ‘Bing’ and ‘Rainier’ cherries.     

Formation and extraction of persistent fumigant residues in soils

Fumigants are commonly thought to be short-lived in soil, but residues have been found in soils years following application. In this study, formation and extraction of persistent soil fumigant residues were investigated. Fumigants 1,3-dichloropropene (1,3-D), chloropicrin (CP), and methyl isothiocyanate (MITC) were spiked into Arlington, Glenelg, and Hagerstown soils and incubated for 30 d under controlled conditions. The incubated soils were evaporated for 20 h prior to extraction with a variety of organic solvents at different temperatures. Extraction with acetonitrile in sealed vials at 80 degrees C for 24 h was the most efficient method to recover persistent soil fumigant residues. At application rates of 1000-1700 mg (kg of soil)(-1), persistent residues of 1,3-D, CP, and MITC in the three soils ranged from 5 to 67 mg kg(-1). The residue content increased with application rate, correlated positively with soil silt content, decreased dramatically as indigenous organic matter (OM) was removed, and changed little with external OM addition. Adsorption to clay surfaces was not important in fumigant retention, while pulverization of soil aggregates significantly decreased persistent fumigant residues. The results suggest that persistent fumigant residues are retained in soil intra-aggregate micropores resulting from binding clay flocs and silt particles by humic substances.     

Reducing 1,3-dichloropropene emissions from soil columns amended with thiourea

Soil fumigants are becoming an important source of volatile organic compounds (VOCs) in air, especially in some agricultural areas. In this study, we used thiourea to construct a reactive surface barrier (RSB) at the soil surface for reducing 1,3-dichloropropene (1,3-D) volatilization. The agrochemical thiourea could rapidly transform volatile 1,3-D to nonvolatile products via an SN2 nucleophilic substitution reaction. A catalytic mechanism in thiourea-amended soil facilitated the conversion process. A packed soil column system was employed to investigate the emissions and distribution of 1,3-D and optimize the original fumigant emission-reduction strategy. Volatilization of 1,3-D from the soil surface was significantly reduced in columns amended with a thiourea RSB compared with that of bare soil. Volatilization flux and cumulative emissions decreased with increasing thiourea application rate and increasing fumigation depth in packed soil columns. Surface amendment with the RSB did not affect the subsurface distribution of 1,3-D in the soil profile. Combined application of a thiourea RSB and plastic tarps had a synergetic effect in emission control and could eliminate the relatively high fumigant flux that occurs upon tarp disruption. Therefore, this reduced-risk practice was very effective in reducing atmospheric emissions of VOCs from soil treatment with halogenated fumigants.     

聚乙烯醇/壳聚糖/芒果皮提取物复合膜的制备与表征

为了探究芒果皮废弃物的高值化利用,采用微波工艺制备了芒果皮提取物（MPE）。壳聚糖（CS）使用冰醋酸（AAG）或柠檬酸（CA）溶解后,将MPE与聚乙烯醇（PVA）、CS共混,采用溶液浇铸法制备了PVA/CS/MPE复合膜。利用UV、FT-IR、SEM和TG对复合膜的结构、形貌和热性能进行表征分析,对复合膜的力学性能、耐水性、抗菌性、抗氧化性和降解性能进行了测定。实验结果表明:相比于普通搅拌提取（35 °C,500 r/min,4 h,产率13.86%）,微波工艺（35 °C,300 r/min,1 h）下MPE的产率提升至38.26%;复合薄膜各组分之间主要通过氢键作用结合,相容性较好,无明显的相分离;复合膜均表现出良好的抗菌活性和可降解性;CA体系的复合膜拉断伸长率较纯PVA膜提升近一倍,添加MPE后拉断伸长率更高;而MPE能显著改善AAG体系复合膜的耐水性,同时,MPE提高了复合膜的抗紫外、抗氧化能力。因此,所制备的PVA/CS/MPE复合薄膜在医药、食品包装等行业有着广泛的应用前景。