Dosages Of Methyl Bromide Research Articles

Sorption and desorption characteristics of methyl bromide during and after fumigation of pine (Pinus radiata D. Don) logs.

The sorption and desorption characteristics of methyl bromide (MB) were determined during and after fumigation of recently harvested pine (Pinus radiata D. Don) logs. The effects of dose (48 or 120 g m-3 ), degree of bark cover (0, 50 or 100%) and end-grain sealing (sealed or unsealed) on sorption and desorption were determined over time. Sorption of MB was proportional to the dose applied and dependent on the amount of end-grain sealed. After 16 h, an average of 70.7 ± 2.5% of the initial concentration remained in the treated space when end-grains were sealed, whereas only 47.3 ± 2.5% remained when unsealed. During aeration, MB was released from logs, initially ranging from 2.8 to 8.8 g · h m-3 , depending on the treatment. The rate of desorption quickly decreased during aeration. The surface area of a log is the most important factor influencing MB sorption and desorption rates, with greater surface area resulting in greater (de)sorption rates. Sorption data can now be combined with insect toxicity data to estimate a minimum effective dose of MB for further evaluation, while desorption data can be combined with fumigant plume modelling to assess worker safety. © 2016 Society of Chemical Industry.

Optimizing postharvest methyl bromide treatments to control spotted wing drosophila, Drosophila suzukii, in sweet cherries from Western USA

Methyl bromide (MB) chamber fumigations were evaluated for postharvest control of spotted wing drosophila (SWD), Drosophila suzukii (Matsumura) (Diptera: Drosophilidae), in fresh sweet cherry exports from Western USA. Sweet cherries were infested with SWD, incubated to maximize numbers of the most MB-tolerant specimens (ca. 60 to 108-h old at fumigation, 88% 3rd & 2nd instars), buried amongst uninfested fruit in bins consistent with commercial practice, cooled to an average pulp temperature ≥ 8.3 °C, and then fumigated in a chamber. Treatment efficacy was diagnosed by the percentage of survivors emerging as adults from fumigated cherries relative to that from non-fumigated control cherries. A kinetic model of sorption was developed based on the measurement of MB and how calculated exposures varied across the fumigation trials. The model describes how to manipulate the applied MB dose, fumigation duration, and the load factor so that the resultant exposure is adequate for SWD control across various pulp temperatures when cherries are fumigated in wooden versus plastic bins. Results are discussed in the context of graduation toward optimized quarantine fumigation schedules for control of SWD, which will promote more strategic technical and economic Quarantine Pre-shipment (QPS) use of MB.

Effects of box liner perforation area on methyl bromide diffusion into table grape packages during fumigation

Plastic liners are used inside boxes of table grapes to retard moisture loss from the grapes and to contain sulfur dioxide gas released inside the packages to control postharvest decay. However, to control organisms of quarantine concern, regulators specify exported packages must be fumigated with methyl bromide (MB), and to enable adequate diffusion of the fumigant into the packages they specify the liners must be perforated. The percentage of the area of the liner that is perforated, formerly stipulated to be not less than 0.3%, was recently increased to not less than 0.9%. Two MB fumigation schedules specified for control of the Chilean mite, Brevipalpus chilensis, were applied to grape packages with a high-density polyethylene liners with perforated areas of 0.9% or with a SO2-releasing liners with perforated areas of 0.3, 0.6, or 0.9%. Package and chamber concentrations were measured repeatedly for up to three hours during MB fumigation at 4.4 or 6.0 °C with a dosage 64 mg L−1 or at 26.7 °C with a dosage 56 mg L−1. Diffusion was similar and rapid into the packages among all perforated areas. MB concentrations inside the packages were not less than 95% of those of the chamber atmosphere within 15 min. After fumigation with an MB dosage 64 mg L−1 at 4.4 °C and subsequent storage at 2.0 °C, mean MB residue content in grapes from most packages 48 h after MB fumigation was below the limit of quantitation of 0.002 mg kg−1. After fumigation with an MB dosage 56 mg L−1 at 26.7 °C and subsequent storage at 2.0 °C, mean MB residue content in grapes from most packages 24 h after MB fumigation was below the limit of quantitation.

Postharvest Treatment of Fresh Fruit From California With Methyl Bromide for Control of Light Brown Apple Moth (Lepidoptera: Tortricidae)

Methyl bromide (MB) chamber fumigations were evaluated for postharvest control of light brown apple moth, Epiphyas postvittana (Walker) (Lepidoptera: Tortricidae), in fresh fruit destined for export from California. To simulate external feeding, larvae were contained in gas-permeable cages and distributed throughout loads of peaches, plums, nectarines (all Prunus spp.), apples (Malus spp.), raspberries (Rubus spp.), or grapes (Vitis spp.). Varying the applied MB dose and the differential sorption of MB by the loads resulted in a range of exposures, expressed as concentration x time cross products (CTs) that were verified by gas-chromatographic quantification of MB in chamber headspace over the course of each fumigation. CTs > or = 60 and > or = 72 mg liter(-1) h at 10.0 +/- 0.5 and 15.6 +/- 0.5 degrees C (x +/- s, average +/- SD), respectively, yielded complete mortality of approximately 6,200 larvae at each temperature. These confirmatory fumigations corroborate E. postvittana mortality data for the first time in relation to measured MB exposures and collectively comprise the largest number of larval specimens tested to date. In addition, akinetic model of MB sorption was developed for the quarantine fumigation of fresh fruit based on the measurement of exposures and how they varied across the fumigation trials. The model describes how to manipulate the applied MB dose, the load factor, and the load geometry for different types of packaged fresh fruit so that the resultant exposure is adequate for insect control.

Methyl bromide fumigation of packed table grapes: Effect of shipping box on gas concentrations and phytotoxicity

Current methyl bromide (MB) schedules for table grapes to control pests of quarantine significance are approved for fruit packed in Toyon Kraft Veneer (TKV) boxes. The question arose concerning equivalence of exposure to MB if an expanded polystyrene (EPS) box was used in lieu of the TKV box for table grapes being shipped to foreign countries. Fumigations of ‘Crimson Seedless’ table grapes packed in either EPS or TKV boxes were conducted for comparison of MB gas concentrations and fruit quality using Australian (AQIS) MB treatment schedules. Methyl bromide exposure expressed as the concentration × time (C × T) product (g h m −3) was the same or higher for the EPS box compared to the TKV box. Methyl bromide gas concentrations were higher for EPS boxes at the start of the fumigation, but lower than TKV boxes at the end of the exposure period (2 h) due to a higher sorption rate of MB into the EPS Styrofoam ® material. Evaluation of fruit quality showed internal browning, a typical characteristic of MB phytotoxicity, was absent or very low (<1.7% of the berries) in table grapes packed in both box types. No other injury attributable to exposure to MB was observed. Since C × T product exposure to MB was equivalent or even higher when EPS boxes were used, EPS boxes should be suitable for shipping table grapes to export markets. However, if the practice of determining exposure to MB continues to be based on readings of gas concentrations at the end of the 2-h exposure period, then data show that an increase in MB dose of 4 g/m 3 is suggested when the EPS box is used in lieu of TKV boxes for shipping table grapes to export markets.

INHIBITION OF CREATINE KINASE ACTIVITY IN RAT BRAIN BY METHYL BROMIDE GAS

Rats were exposed to 290 or 495 ppm methyl bromide gas for 6 h/day, 3 times/wk for 4 to 8 wk. Creatine kinase (CK), aspartate aminotransferase (ASAT), and lactate dehydrogenase (LDH) activities and bromide ion concentrations were measured in eight regions of the brain. Methyl bromide gas inhibited CK activities in all regions of the brain, though the inhibition tended to be smallest in the cerebellum (hemisphere and vermis) and largest in the brainstem (hypothalamus, midbrain, and medulla oblongata). The dose of methyl bromide to inhibit CK activities was lower than that to damage the central nervous system histologically. No inhibition of ASAT or LDH activities was seen except for a slight inhibition of these in striatum. Inhibition of CK activities did not increase clearly on increasing dose (290 to 495 ppm) or on prolonging exposure period (4 to 8 wk). Although 50% recovery of CK activities and the half-life of bromide ion agreed well in the medulla oblongata, changes in CK activities and bromide ion concentrations did not correlate otherwise. Thus, inhibition of CK activities in brain appears to be a sensitive indicator of methyl bromide intoxication, and may be related to genesis of its neurotoxicity. The inhibition seems to be caused by methyl bromide itself rather than by bromide ion. When effects on enzyme activities in brain homogenate were examined in vitro by bubbling with methyl bromide gas, CK inhibition was seen within 15 s of exposure. Dithiothreitol suppressed the CK inhibition, whereas N -acetylcysteine did not. These observations suggest that methyl bromide may attack sites in the CK molecule different from those attacked by ethylene oxide or acrylamide.

Combined Soil Treatments and Sequence of Application in Improving the Control of Soilborne Pathogens

ABSTRACT The effects of reduced doses of methyl bromide (MB) or metham sodium, heating, short solarization, and soil microbial activity, alone or in combination, on survival of soilborne fungal pathogens were tested in a controlled-environment system and field plots. Sublethal doses of heating or MB delayed germination of Sclerotium rolfsii sclerotia. Combining MB and heating treatments was more effective than either treatment alone in controlling S. rolfsii and Fusarium oxysporum f. sp. basilici. The application heating followed by fumigation with MB, was significantly more effective in delaying and reducing germination of S. rolfsii sclerotia and in controlling F. oxysporum f. sp. basilici than the opposite sequence. Further, incubation in soil and exposure to microbial activity of previously heated or MB-treated sclerotia increased the mortality rate, indicating a weakening effect. Similarly, incubation of chlamydospores of F. oxysporum f. sp. melonis and F. oxysporum f. sp. radicis-lycopersici in soil in the field after fumigation further reduced their survival, confirming the laboratory results. In field tests, combining MB or metham sodium at reduced doses with short solarization was more effective in controlling fungal pathogens than either treatment alone. Treatment sequence significantly affected pathogen control in the field, similar to its effect under controlled conditions. This study demonstrates a frequent synergistic effect of combining soil treatments and its potential for improving pathogen control and reducing pesticide dose, especially when an appropriate sequence was followed.

Control of Fusarium oxysporum f. sp. cucumerinum of cucumbers by soil solarization with impermeable plastics and/or reduced doses of methyl bromide

Soil solarization is not broadly adopted as a soil deinfestation method mainly because of its long duration (4–6 weeks). We present evidence showing that the duration of solarization can be reduced to nearly half using impermeable plastics and/or low doses of methyl bromide, while still ensuring effective control of Fusarium oxysporum f. sp. cucumerinum. Chlamydospores of a pathogenic isolate of F. o. cucumerinum, formed in sterile soil, were inserted into nylon mesh envelopes and incorporated into the soil prior to treatment at 20- and 30-cm soil depths. Soil treatments included untreated control, soil solarization with polyethylene or impermeable plastics (LMG), and soil solarization with polyethylene or impermeable plastics plus 20 g m−2 methyl bromide. According to the effects on artificial inocula of F. o. cucumerinum checked at weekly intervals for 4 weeks, soil solarization with impermeable plastics was most effective in destroying pathogen populations even two weeks after soil covering.

Evaluation of soil fumigants on soilborne fungal pathogens in a controlled-environment system and in soil

A controlled-environment system was developed for determining the effects on fungal pathogens of fumigants such as methyl bromide (MB) for various combinations of doses ( C) and exposure time ( T). In this system, sclerotia of Sclerotium rolfsii, added to a sandy soil, were most sensitive to MB when soil moisture was 20% of its water-holding capacity. Extension of the exposure time ( T) to MB enabled a reduction in the dose needed to kill 50% ( CT 50 ) of S. rolfsii sclerotia or macroconidia of Fusarium oxysporum f. sp. basilici. However, killing of S. rolfsii sclerotia was more effective at high doses of MB for short exposures (4–48 h) than at a low dose for longer periods (48–96 h) with the same C×T value. Killing of macroconidia of F. oxysporum f. sp. basilici at high concentrations and short exposures was similar to that at longer exposure to low concentrations, with the same C×T values. Sclerotium rolfsii sclerotia were the least sensitive to MB, relative to chlamydospores of F. oxysporum f. sp. radicis-lycopersici and F. oxysporum f. sp. basilici macroconidia and chlamydospores, the latter being the most sensitive. In field plots, the incidence of propagule mortality was correlated with C×T values.

Dose-morality and large-scale studies for controlling codling moth (Lepidoptera: Tortricidae) eggs on 'd'Agen' plums by using methyl bromide.

Codling moth, Cydia pomonella (L.), eggs on 'd'Agen' cultivar of plums, Prunus salicina Lindl., were treated with methyl bromide to determine if a quarantine treatment could be developed so that the plums could be exported to Japan from the United States. Small-scale tests consisted of treating codling moth eggs on plums with various doses of methyl bromide at 20 degrees C for 2 h. Small-scale tests showed that 0- to 24-h-old eggs of codling moth on the plums were controlled by doses > 22.5 g/m3. Because testing showed that 48 g/m3 had no adverse effect on the quality of plums, this dose was chosen for large-scale testing to establish the quarantine dose. Large-scale tests consisted of treating plums at 18.5 degrees C for 2 h using methyl bromide at a dose of 48 mg/liter. Large-scale tests showed that the dose of 48 g/m3 killed all 0- to 24-h-old codling moth eggs exposed on plums in packing cartons without affecting the quality of the plums.

Laboratory Evaluations of Methyl Bromide and Carbon Dioxide Mixture Against Twospotted Spider Mite, 1996

Abstract The potential of carbon dioxide to reduce the dose of methyl bromide required to kill mites during 3-h fumigations was evaluated. Fumigations were performed in modified 2.5-liter desiccator jars with methyl bromide alone or with 5% carbon dioxide at concentrations of 0, 8, and 24 mg/liter at 27° C and 60% RH. Three to five leaf discs (14 mm diam) infested with eggs, nymphs, and adults were placed in the fumitoria and allowed to acclimate for 4 h after which the appropriate treatment dose was added. Doses were confirmed by gas chromatography. Treatment doses were calculated by averaging the dose at the beginning of the exposure period with that at the end of the exposure period. Two to six replicates were run, each on a different day, during Feb and Mar. Following fumigation, leaf discs were removed from the fumitoria, held in petri dishes for 24 h, and mite mortality was assessed.

Fumigant Action of Acrolein on Stored-Product Insects

Acrolein was investigated as a fumigant for the control of stored-product insects. When exposed in space, confused flour beetle adults, Tribolium confusum Jacqueline duVal, cigarette beetle adults, Lasioderma serricorne (F.), and black carpet beetle larvae, Attagenus unicolor (Brahm), were killed by doses of acrolein that were lower than corresponding doses of methyl bromide. However, experiments done in grain showed that when acrolein was applied in the headspace, high doses were required to kill insects in the geometric canter of the mass. In contrast, when acrolein was applied to the surface and the grain was mixed to distribute the compound, insects exposed in the grain were killed by much lower doses than when the grain was not mixed. Sorption of the acrolein on wheat was also investigated to determine the amount of compound available to insects in the interstitial spaces of the grain during a 24-h treatment. Because of the sorption characteristics of acrolein, it may have only limited use as a fumigant

Response to Methyl Bromide Fumigation of Codling Moth (Lepidoptera: Tortricidae) Eggs on Cherries

Fumigation experiments with methyl bromide (MeBr) were done in New Zealand over the summers at the end of 1987 and 1989. A total of 74,033 freshly laid codling moth, Cydia pomonella (L.), eggs on the cherry cultivars Dawson, Bing, Rainier, Sam, and Lambert were used. We found differences in sorption of methyl bromide between cultivars and between seasons. Large differences in results for ‘Sam’ between the two seasons suggest that the condition of the fruit or another factor associated with season may be more important than cultivar. The logit of mortality induced by treatment varied linearly with a power (≈2) of the concentration-time (c × t) sum. This relationship allowed us to predict accurately the LC50 and LC99 for the c × t sum. The sorption curves of the individual season-cultivar combinations were not relevant to this relationship, which was the same for all cultivars and seasons. We also considered other measures of concentration. A straight-line equation, with a constant term that depends on the cultivar and the season, allowed accurate calibration of c × t sums in relation to the dose levels injected. Lethal dose levels of 99%, although differing among season-cultivar combinations, were all at least 10 g/m3 below the injected dose of methyl bromide (64 g/m3, 2 h, 40% load, 12°C) used in commercial cherry fumigations. The commercial treatment thus affords a high level of security. Our results indicate that log (concentration) should not necessarily be used as the explanatory variable, as has been conventional when data from fumigation experiments are subjected to probit analysis.

Preconditioning Grapefruit Callus Tissue Reduces Methyl Bromide-induced K+ Leakage

Callus tissue grown from `Marsh' grapefruit (Citrus paradisi Macf.) albedo tissue was grown at 30C for ≈ 40 days. Calli were preconditioned in normal air for 5 days at 10 or 30C before being fumigated for 2 hr with 0, 32, or 48 g of methyl bromide (MB)/m 3. Calli were then held at 10C and K+ leakage was measured after 1, 10, 20, and 30 days. The amount of K+ leaked from MB-fumigated calli was greater than that for nonfumigated calli and increased with higher MB dose. Leakage also increased with time following fumigation. Leakage of calli preconditioned at 30C and fumigated with 48 g MB/m3 was 140%, 196%, and 260% greater than leakage from nonfumigated calli 10, 20, and 30 days after fumigation, respectively. Leakage from calli preconditioned at 10C for 5 days before MB fumigation was less than that from calli held at 30C. MB doses of 32 and 48 g·m-3 increased leakage of calli preconditioned at 10C by 6% and 43% and for those preconditioned at 30C by 99% and 140%, respectively, 10 days after fumigation. In addition to K+ leakage, MB induced the development of a tan to orangish-brown discoloration.

Recovery of glutathione levels in susceptible and resistant strains of Sitophilus granarius (L.) (Coleoptera: Curculionidae) following methyl bromide treatment

In confirmation of earlier results, treatment of susceptible and resistant strain of Sitophilus granarius (L.) with methyl bromide caused a reduction in glutathione content. Levels for surviving insects of both strains returned to normal within a few days except in insects treated with dosages of methyl bromide causing high mortality. A higher percentage of susceptible than resistant insects died after the first day following treatment.

Pathological Alterations in Embryos of the Codling Moth (Lepidoptera: Tortricidae) Induced by Methyl Bromide

Effects of methyl bromide applied as a fumigant to the eggs of the codling moth, Cydia pomonella (L.), were assessed using light microscopy and transmission electron microscopy. Cell division stopped within 1 h in nearly all embryos after application of a lethal dose (48 g/m3 for 2 h). A small number of terata were produced, the percentage increasing somewhat at a lower dose of fumigant. Cells in terata induced at early germ band stages showed the general characteristics of neoplastic cells. The severity of initial toxic effects of lethal-dose treatment on early embryonic tissue varied among the embryos and occasionally among cells in individual embryos. Methyl bromide is a general cellular toxin as expected from its action as a methylating agent with little substrate specificity. A lethal dose of methyl bromide generally led to some degree of transient cell swelling followed by severe disruption of the cytoplasm and plasma membrane, and to clumping of nuclear chromatin, followed by contraction, coagulation necrosis, and cell lysis.

The toxicity of mixtures of methyl bromide and methyl chloroform to stored product insects

Work on the efficacy of a suitable replacement for the chronically toxic liquid fumigants currently used in the U.K. is described. The toxicity of a 5% mixture of methyl bromide (MB) in methyl chloroform (MC) to a range of pest species was mostly attributable to the dosage of methyl bromide present. The order of tolerance of species was Trogoderma granarium > Tribolium confusum > T. castaneum > Ephestia elutella > Cryptolestes ferrugineus > Sitophilus oryzae > Rhyzopertha dominica > Sitophilus granarius > Oryzaephilus surinamensis, and in each case diapausing larvae, pupae or older developing larvae were the most tolerant stages. With 1–2% MB in MC some joint action of the two compounds was evident. At 25°C there was an indication that the performance of MB against diapausing larvae of T. granarium was enhanced in the presence of MC. In contrast, the older stages of S. oryzae survived higher dosages of MB when MC was present, indicating a degree of antagonism between the two compounds. Little evidence of either potentiation or antagonism was observed with the 5% mixture at 15 or 20°C. Despite an apparent lack of joint action of MB and MC in the 5% mixture, at 25°C lower than usual concentration levels of MB were fully effective against the different test species in the presence of MC. The results show that the efficacy of mixtures containing at least 5% MB in MC proposed for the treatment of bulk commodities can be assessed on the basis of the dosages of methyl bromide achieved throughout the bulk.

Methyl Bromide Fumigation to Control the Oriental Fruit Moth (Lepidoptera: Tortricidae) in Nectarines

Responses of 24-h-old eggs and first through fifth in stars of the oriental fruit moth (OFM), Grapholita molesta (Busck), in artificially infested nectarines, Prunus persica (L.) Batsch var. nucipersica Schneid, to methyl bromide (MB) fumigation for 2 h at 21°C is reported. Eggs were least susceptible and first in stars were most susceptible when LC50’s and concentrations to cause 100% mortality were compared. A MB dose of 30 g/m3 resulted in 100% egg mortality. A currently used MB quarantine fumigation schedule of 32 g/m3 for 2 h at 16–26°C was determined to be efficacious against OFM in nectarines for export to British Columbia.

Effect of combination treatments of gamma radiation and methyl bromide fumigation on the confused flour beetles, Tribolium confusum Duv.

A laboratory study was carried out in Egypt to determine the effect of combining treatments of gamma radiation and methyl bromide fumigation applied to adults of Tribolium confusum (Duv.). An interaction between irradiation and insecticidal treatment was obvious, with additive effects noted at most combination treatments. When the irradiation treatments were applied first and fumigation were accomplished within 24 hr., the intermediate dosage of irradiation (6 krad) afforded the insects some protection against marginally effective dosages of methyl bromide after 14 days. On the contrary, it is evident that a possible synergistic effect of irradiation pretreatment followed by chemical exposure, after 21 days, where all of irradiation dosages used (2–10 krad) enhanced the fumigant effectiveness. On the other hand, when the irradiation dosages were increased from 5–50 krad and followed by fumigant treatments after 7 days, the trend did continue where all combination treatments killed more insects than did either treatment applied alone. Conversely, when fumigation preceded treatment with irradiation the sublethal methyl bromide fumigation also apparently leaves the surviving insects in a debilitated state and became more radiosensitive. In general, the effects from combination of irradiation and fumigation were more effective than were the effects of either treatment given singly, whether irradiation preceded insecticidal treatment or vice versa.

Effect of post-harvest fumigation on quality of asparagus spears

Abstract Asparagus spears were damaged by post-harvest fumigation treatments using moderate or high doses of methyl bromide. Damage was expressed both as the earlier development of decay during shelf-life evaluation and as a reduction in eating quality of spears which showed no visible damage. Fumigation stimulated both respiration rate and ethylene production by asparagus spears.