Concentrations Of Methyl Bromide Research Articles

Methyl bromide vacuum fumigation of California USA in-shell walnuts packaged in fiberboard cartons

Postharvest vacuum fumigation with methyl bromide (MB) was approved by Animal and Plant Quarantine Agency (APQA), Republic of Korea, to control codling moth, Cydia pomonella (Lepidoptera, Tortricidae), infesting 23-kg bags of in-shell walnuts (Juglans regia). Consistent with the approved parameters, in-shell walnuts with nut meat temperature (T) of 15.4 ± 0.2 °C (grand mean ± 2 SD; x‾GM± 2spooled) were packaged in sealed fiberboard cartons, loaded to 53% (v/v) chamber capacity, and fumigated in triplicate trials involving a single 63-carton pallet, with each lasting 4 h following the application of 56 mg L−1 MB at ca. 13.3 KPa (100 mmHg). MB concentrations were measured at four different locations over the course of each fumigation, respective Ct exposures were calculated, and the relative distribution of fumigant was evaluated. Exposures were maintained ≥ ca. 75 mg L−1 h in all cases, resulting in Ct exposures sufficient to control codling moth. A single 18-pallet confirmatory trial involving sealed fiberboard cartons was then conducted at a commercial facility, gas measurements were taken as above, and a minimum Ct of 117 mg L−1 h was observed. A kinetic model of MB sorption was used to demonstrate congruence across all trials, thereby supporting the reproducibility, scalability, and efficacy of this treatment, regardless if the in-shell walnuts are packaged in 23-kg bags or sealed fiberboard cartons.

Efficacy of quarantine treatments using reduced methyl bromide concentrations to disinfest Pinus radiata logs from New Zealand

We report here the results of three successive toxicity studies against a selection of forest insect pests, conducted in New Zealand to determine the efficacy of reduced methyl bromide (MB) rates, i.e. rates lower than those currently used, to disinfest export pine logs. First, the relative tolerance to MB among the naked life stages of the golden-haired bark beetle, Hylurgus ligniperda, the black pine bark beetle, Hylastes ater (Coleoptera: Curculionidae) and burnt pine longhorn beetle, Arhopalus ferus (Coleoptera: Cerambycidae) was determined in the laboratory. Then, the most MB-tolerant species and life stage(s) in pine logs was subjected to selected fumigation schedules using reduced concentrations of MB. Finally, the results of the laboratory studies were validated under commercial conditions at the Port of Tauranga, New Zealand, using logs infested with the most tolerant life stage, and log stacks. Our results indicated that either 30 g/m3 MB at >15 °C or 40 g/m3 MB at ≤ 15 °C for 16 h would ensure quarantine security against forest insects in New Zealand export logs. These reduced MB concentrations are approximately 70% and 65%, respectively, lower than 80 g/m3 at >15 °C or 120 g/m3 at ≤15 °C. If implemented by regulatory agencies and accepted by trading partners, these concentrations will provide significant environmental and economic benefits to the New Zealand forest industry and will pave the way for other countries to implement similar approaches to reduce MB usage in accordance to the Montreal Protocol.

Methyl-bromide and asthma emergency department visits in California, USA from 2005 to 2011

Objective: Urban monitors of Methyl bromide (MBr), not typically near application sites, are used to investigate the impact of ambient concentrations on asthma Emergency Department (ED) visits.Methods: 4262 ED visits from August to February of 2005 to 2011 in Central and Southern California were selected from California's Office of Statewide Health Planning and Development (OSHPD). A bidirectional-symmetric case-crossover study design using conditional logistic regression model was used to obtain the odds ratio (OR) and 95% confidence interval associated with a 0.01 ppb (interquartile range) increase in MBr.Results: The population sample was comprised of 46.0% male and 53.9% females. Ethnic groups included 32.0% Non-Hispanic White, 23.5% Non-Hispanic Black, and 44.4% Hispanic. Age distribution was between 2 and 5 years old (11.6%), 6 and 18 years old (23.5%), 19 and 40 years old (29.3%), 41 and 64 years old (24.1%), and 65 or older (6.9%). There was a positive association between MBr and asthma ED visits among Non-Hispanic Blacks [OR: 1.065 (95% confidence intervals: 1.019, 1.108)] and Hispanics [OR: 1.107 (95% confidence intervals: 1.043, 1.173)], while Non-Hispanic Whites did not have an association with asthma ED visits. Positive association between MBr and asthma ED visits was found only among 6 to 18 [OR: 1.071 (95% confidence intervals: 1.016, 1.125)] years old.Conclusion: An increase in MBr concentration was found to be associated with an increase of the odds of having asthma ED visits in California among 6 to 18 years old and disproportionately affects Non-Hispanic Blacks and Hispanics over Non-Hispanic Whites.

Monitoring the concentration of methyl bromide in the treated space during commercial fumigation of logs

Development of sciencebased fumigation schedules for phytosanitary treatments relies on an understanding of the factors which influence the effectiveness of a fumigant under different conditions Understanding the sorption characteristics of a fumigant is a critical step in establishing commercial treatment schedules as this process which involves adsorption and absorption of fumigant molecules influences the concentration of the fumigant remaining in the treated space after fumigation and hence the amount of fumigant available to kill insects We monitored the concentration of methyl bromide during commercial fumigation of three log stacks (average volume 4078 m3) with 120 g/m3 methyl bromide for 13 h under a tarpaulin Pine (Pinus radiata D Don) logs were fumigated at South Port Bluff (New Zealand) during April 2015 Gas samples from the treated space were taken at 05 1 2 3 the treated space indicating that the rest of the fumigant was sorbed These data can now be combined with insect toxicity studies to guide the development of improved commercial treatment schedules to treat log exports from New Zealand

Low-dose methyl bromide fumigation as a quarantine disinfestation treatment for nectarines against Queensland fruit fly (Diptera:Tephritidae)

White nectarines (Prunus persica var. nucipersica) were fumigated with methyl bromide (MB) at a nominal treatment dose of 18 g m-3 at 18°C for 5 h and 30 min as a quarantine disinfestation treatment against Bactrocera tryoni, the Queensland fruit fly. Three large scale trials were conducted against each of the four immature lifestages, eggs and first, second and third instars. There were no survivors from the estimated 43,614 eggs, 41,873 first instars, 41,345 second instars and 33,549 third instars treated, thereby resulting in an efficacy of GROTERDAN99.99% mortality at the 95% confidence level for each lifestage. Of the 12 trials reported herein, the highest concentration of MB, sampled from the chamber headspace analysed by gas chromatography, was 18.7 g m-3. The maximum chamber temperature from 5 min readings was 19.7°C and the maximum fruit core temperature was 19.5°C. The treatment time for all trials was exactly 5.5 h. Thus the recommended treatment dose to disinfest nectarines from B. tryoni is 19.0 g m-3 MB at 20.0°C for 5.5 h. Fruit quality trials were conducted on white nectarines at three combinations of treatment parameters: 15 g m-3 MB at 19°C for 5.25 h; 18 g m-3 MB at 19°C for 5.5 h and 21 g m-3 MB at 19°C for 5.5 h. The fruit were stored at 0, 4 and 8 days at 4°C and 8 days at 4°C followed by 4 d at 22°C. They were then were assessed for skin colour, flesh colour, skin defects, flesh defects, fruit weight loss, flesh firmness, total soluble solids, titratable acidity and rots. There was no significant difference between untreated control and MB treated fruits in any of the parameters measured. Thus the treatments did not have adverse effects on fruit quality.

Efficacy of Methyl Bromide for Control of Different Life Stages of Stored-Product Psocids

The psocid species Liposcelis paeta Pearman, Liposcelis entomophila (Enderlein), Liposcelis decolor (Pearman), Liposcelis bostrychophila Badonnel (Psocoptera: Liposcelididae), and Lepinotus reticulatus Enderlein (Psocoptera: Trogiidae) were evaluated in laboratory bioassays to determine their susceptibility to six concentrations of methyl bromide (0.027, 0.113, 0.280, 0.393, 0.452, and 0.616 g/m3) after 48 h of exposure at 27.5°C. The life stages that were evaluated were adults (for all species), nymphs (for all species except Lep. reticulatus), and eggs (for L. entomophila, L. decolor, and L. bostrychophila). Adults and nymphs were very susceptible, and complete mortality was recorded at concentrations between 0.027 and 0.280 g/m3. In contrast, eggs were by far more tolerant than adults and nymphs for all species tested. At 0.027 g/m3, mortality did not exceed 53%, while survival was high even at 0.113 g/m3. Complete (100%) egg mortality was recorded at 0.393 g/m3 for L. decolor and at 0.452 g/m3 for L. entomophila and L. bostrychophila; concentrations estimated to give 99% mortality for eggs of these three species were 0.710, 1.044, and 0.891 g/m3, respectively. These results show that stored-product psocids are susceptible to methyl bromide, but concentrations of ≥0.452 g/m3 should be used to control all life stages.

Activated Carbons from End-Products of Tree Nut and Tree Fruit Production as Sorbents for Removing Methyl Bromide in Ventilation Effluent Following Postharvest Chamber Fumigation

End-products of tree nuts and tree fruits grown in California, USA were evaluated for the ability to remove methyl bromide (MB) from ventilation effluent following postharvest chamber fumigation. Activated carbon sorbents from walnut and almond shells as well as peach and prune pits were prepared using different methods of pyrolysis, activation, and quenching. Each source and preparation was evaluated for yield from starting material (%, m/m) and performance on tests where MB-containing airstreams were directed through a columnar bed of the activated carbon in an experimental apparatus, termed a parallel adsorbent column tester, which was constructed as a scaled-down model of a chamber ventilation system. We report the number of doses needed to first observe the breakthrough of MB downstream of the bed and the capacity of the activated carbon for MB (%, m/m) based on a fractional percentage of MB mass sorbed at breakthrough relative to mass of the bed prior to testing. Results were based on a novel application of solid-phase microextraction with time-weighted averaging sampling of MB concentration in airstreams, which was quantitative across the range of fumigation-relevant conditions and statistically unaffected by relative humidity. Activated carbons from prune pits, prepared either by steam activation or carbon dioxide activation coupled to water quenching, received the greatest number of doses prior to breakthrough and had the highest capacity, approximately 12-14%, outperforming a commercially marketed activated carbon derived from coconut shells. Experimental evidence is presented that links discrepancy in performance to the relative potential for activated carbons to preferentially sorb water vapor relative to MB.

Design and Experiment of Fumigant Gas Trace Detection System Based on Photoionization

To meet the requirements, based on the provision of Administration of Quality Supervision, Inspection and Quarantine (AQSIQ), of gas leakage monitoring inside dosing room of fumigant warehouse at the inspection and quarantine port, a fumigant gas trace detection system (FGTDS) based on photoionization detector (PID) is developed. The principle, structure and characteristic of the system design are especially demonstrated. The test data under different temperature, relative humidity (RH) and methyl bromide concentration demonstrate that the FGTDS based on PID can measure methyl bromide under very low concentration. A conclusion can be drawn that the requirements of gas leakage monitoring inside dosing room of fumigation warehouse at the inspection and quarantine port can be met through further proper design.

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.

Methyl bromide fumigation and delayed mortality: safe trade of live pests?

Live organisms intercepted from treated commodities during phytosanitary inspections usually arouse suspicions of treatment failure, sub-standard treatment application, or post-treatment infestation. The additional possibility that some treatments could kill slowly, meaning commodities might be inspected before pests have succumbed, is seldom considered for treatments other than irradiation. We used a novel biochemical viability assay to measure delays between methyl bromide fumigation and mortality of dipteran eggs, and evaluated the correspondence between egg viability and egg morphological features. Our experimental conditions simulated shipping of rock melons from Australia to New Zealand by sea and air. No eggs survived fumigation, but they took 3–20 days to die, whereas phytosanitary inspections of rock melons occur within 2–7 days. Delays were not influenced by methyl bromide concentration, but were significantly lengthened by cooler storage temperatures. Methyl bromide’s preservative effects delayed degradation of egg morphology, so the biochemical assay detected mortality long before morphological signs of egg death appeared. The results show that commodities subjected to effective methyl bromide treatments are at risk of being inspected before all pests have either died, or started to exhibit morphological signs of death. This could cause commodities to be unnecessarily rejected by quarantine authorities. Better methods than inspection for live pests are needed to assist authorities to gain assurance that treated commodities have been effectively disinfested. These could be developed by exploiting biochemical responses of pests and commodities to treatments.

Relative methyl bromide tolerances of <i>Arhopalus ferus</i> (Mulsant) <i>Hylurgus ligniperda</i> (F) and <i>Hylastes ater</i> (Paykull) adults

The adult stages of three key New Zealand forest pests burnt pine longhorn beetle (Arhopalus ferus) goldenhaired bark beetle (Hylurgus ligniperda) and black pine bark beetle (Hylastes ater) were fumigated at 10 or 20C for 4 h to determine their mortalities at increasing dosages of methyl bromide as a first step towards developing a new fumigation schedule for New Zealand export logs Hylastes adults were the most methyl bromide tolerant methyl bromide concentration required to control Hylastes adults is much lower than the phytosanitary requirement for export logs to India and China which requires 120 g/m3 for for logs exported from New Zealand but further work on other life stages is required

Purge-and-Trap Gas Chromatography Method for Analysis of Methyl Chloride and Methyl Bromide in Seawater

Purge-and-trap technique coupled with gas chromatography with electron capture detector (GC-ECD) is developed for analyzing the concentrations of methyl chloride (CH3Cl) and methyl bromide (CH3Br) in seawater. The optimum conditions were established as follows: purge time (12 min), purge gas flow rate (50 mL min−1), purge temperature (40°C), desiccant (Mg(ClO4)2), liquid nitrogen trap, boiling water desorption (2 min). The detection limits were 2.7 and 0.3 pM, the precision was < 2% and < 8%, and the recoveries were 89%–97% and 75%–85% for CH3Cl and CH3Br, respectively. Experiments for sample storage were carried out to test the reliability of the storage procedure used in this study, and the results showed that there was no significant change in CH3Cl and CH3Br concentrations in seawater within 24 h using this procedure. Merits of this method are that exact concentrations could be estimated and the analysis could be completed within 6 h in situ. This method was also used to measure in situ concentrations of CH3Cl and CH3Br in the surface seawater of the Jiaozhou Bay, and the results showed that the concentrations of CH3Cl and CH3Br ranged from 130 to 346 pM and 3.90 to 20.7 pM, respectively, which were in good agreement with those values reported in literature in other coastal waters. Our study shows that this method meets the demands of the measurement of in situ concentrations of CH3Cl and CH3Br in seawater.

Distributions and fluxes of methyl chloride and methyl bromide in the East China Sea and the Southern Yellow Sea in autumn

We determined the distributions and fluxes of methyl chloride and methyl bromide in the East China Sea (ECS) and the Southern Yellow Sea (SYS) in November 2007. Methyl chloride and methyl bromide concentrations in the surface waters ranged from 47.1 to 163 pmol L − 1 and from 0.70 to 9.82 pmol L − 1 , with average values of 87.6 and 2.97 pmol L − 1 , respectively. The distributions of the two methyl halides were clearly influenced by the Yangtze (Changjiang) River effluent and Kuroshio water, with high concentrations appearing in the coastal zone and low values occurring in the open waters. A positive linear correlation was observed between methyl chloride and methyl bromide concentration anomalies in the surface waters, suggesting that they may share some origins in this coastal area. However, no correlation was found between the two methyl halide concentration anomalies and chlorophyll a in the surface waters. The vertical profiles of the two methyl halides were characterized by the maxima in the upper mixed layer. Both gases were generally supersaturated in the surface seawater, with mean sea-to-air fluxes of methyl chloride and methyl bromide of 391 and 20.0 nmol m − 2 d − 1 , respectively.

Production and air–sea flux of halomethanes in the western subarctic Pacific in relation to phytoplankton pigment concentrations during the iron fertilization experiment (SEEDS II)

Abstract Iron could play a key role in controlling phytoplankton biomass and productivity in high-nutrient, low-chlorophyll regions. As a part of the iron fertilization experiment carried out in the western subarctic Pacific from July to August 2004 (Subarctic Pacific iron Experiment for Ecosystem Dynamics Study II—SEEDS II), we analysed the concentrations of trace gases in the seawater for 12 d following iron fertilization. The mean concentrations of chlorophyll a in the mixed layer (5–30 m depth) increased from 0.94 to 2.81 μg L –1 for 8 d in the iron patch. The mean concentrations of methyl bromide (CH 3 Br; 5–30 m depth) increased from 6.4 to 13.4 pmol L –1 for 11 d; the in-patch concentration increased relative to the out-patch concentration. A linear correlation was observed between the concentrations of 19′-hexanoyloxyfucoxanthin, which is a biomarker of several prymnesiophytes, and CH 3 Br in the seawater. After fertilization, the air–sea flux of CH 3 Br inside the patch changed from influx to efflux from the ocean. There was no clear evidence for the increase in saturation anomaly of methyl chloride (CH 3 Cl) due to iron fertilization. Furthermore, CH 3 Cl fluxes did not show a tendency to increase after fertilization of the patch. In contrast to CH 3 Br, no change was observed in the concentrations of bromoform (in-patch day 11 and out-patch day 11: 1.7 and 1.7 pmol L –1 ), dibromomethane (2.1 and 2.2 pmol L –1 ), and dibromochloromethane (1.0 and 1.2 pmol L –1 , respectively). The concentration of isoprene, which is known to have a relationship with chlorophyll a , did not change in this study. The responses of trace gases during SEEDS II differed from the previous findings ( in situ iron enrichment experiment—EisenEx, Southern Ocean iron experiment—SOFeX, and Subarctic Ecosystem Response to Iron Enrichment Study—SERIES). Thus, in order to estimate the concomitant effect of iron fertilization on the climate, it is important to assess the induction of biological activity and the distributions/air–sea fluxes of trace gases by iron addition.

Emissions and distribution of methyl bromide in field beds applied at two rates and covered with two types of plastic mulches

A field experiment was conducted to compare two plastic mulches and two application rates on surface emissions and subsurface distribution of methyl bromide (MBr) in field beds in Florida. Within 30 minutes after injection of MBr to 30 cm depth, MBr had diffused upward to soil surface in all beds covered with polyethylene film (PE) or virtually impermeable film (VIF) and applied at a high rate (392 kg/ha) and a low rate (196 kg/ha). Due to the highly permeable nature of PE, within 30 minutes after injection, MBr volatilized from the bed surfaces of the two PE-covered beds into the atmosphere. The amount of volatilization was greater for the high rate-treatment bed. On the other hand, volatilization of MBr from the bed surfaces of the two VIF-covered beds were negligible. Volatilization losses occurred from the edges of all the beds covered with PE or VIF and were greater from the high rate-treatment beds. Initial vertical diffusion of MBr in the subsurface of the beds covered with PE or VIF was mainly upward, as large concentrations of MBr were detected from near bed surfaces to 20 cm depth in these beds 30 minutes after injection and little or no MBr was found at 40 cm depth. The two VIF-covered beds exhibited greater MBr concentrations and longer resident times in the root zone (0.5–40 cm depth) than corresponding PE-covered beds. Concentrations of MBr in the root zone of the high rate-treatment beds were 3.6–6.1 times larger than the low rate-treatment beds during the first days after application. In conclusion, VIF promoted retention of MBr in the root zone and, if volatilization loss from bed edges can be blocked, volatilization loss from VIF-covered beds should be negligible.

METHYL BROMIDE RATE REDUCTION AND MULCH EFFECT ON NUTSEDGE CONTROL

In Florida, nutsedge (Cyperus spp.) is a major weed problem in mulched-vegetable production. As methyl bromide (MBr) is phased out, alternatives are essential for growers. However, because of critical use exemptions, growers will still be able to use restricted amounts of MBr. Therefore, using highly-retentive mulch, such as virtually impermeable film (VIF), can reduce fumigant loss and may allow rate reduction without compromising efficacy. Preliminary studies have shown that metalized mulches can be an alternative to VIF. However, further studies are needed to compare MBr retention properties and nutsedge control of high density polyethylene (HDPE) mulch, VIF, and metalized mulch. Two field studies were conducted in spring 2005, in Ruskin, Florida. Metalized and HDPE mulches, and VIF were combined with the following rates of MBr + chloropicrin (Pic) (67/33, w/w): 175 and 350 lb/acre. Methyl bromide retention was evaluated in soil air samples at 1, 2, 4, and 6 days after treatment (DAT). Nutsedge plants were counted at 2, 4, 7, 9, and 12 weeks after treatment (WAT). Data were examined with regression analysis to establish the relationship between the time and both MBr concentration and nutsedge densities. Concentration of MBr + Pic under either the metalized mulch or VIF was about 6 times higher than under HDPE at 5 DAT, regardless of the MBr + Pic rate. At 12 WAT, nutsedge population was &lt;1 plant/50 ft row with metalized and VIF and 175 lb/acre of MBr + Pic, whereas about 25 plants/50 ft row were present with 350 lb/acre of the fumigant and HPDE. The weed population reached &gt;100 plants/50 ft row with 175 lb/acre of MBr + Pic. These findings demonstrate that metalized and VIF mulches can provide effective control of nutsedge with one-half of the commercially used MBr + Pic rate.

Evaluation of natural products as possible alternatives to methyl bromide in soil fumigation

Methyl bromide (CH 3 Br) is a widely used fumigant in crop production and commodity preservation worldwide. It escapes to the stratosphere and releases bromine atom (Br), which contributes to significant destruction of ozone (O 3 ) layer. It is therefore necessary to explore alternatives to CH3Br that are environmentally safe and economically viable. We present the results of the inhibitory activity of crude extracts from some Kenyan medicinal plants against the soil pathogens, Fusarium oxysporum, Alternaria passiflorae , and Aspergillus niger . Crude organic extracts from Warburgia ugandensis Sprague, Azadirachta indica A. Juss and Tagetes minuta were active against the test soil pathogens while those from Urtica massaica were not. Chromatographic purification of the crude extract from W. ugandensis provided two pure compounds, muzigadial and muzigadiolide. The minimum inhibitory concentration (MIC) for muzigadial ranged from 5 to 100 µg/ml for the different soil pathogens. Muzigadiolide was not active at concentrations tested. Greenhouse tests of W. ugandensis extracts against F. oxysporum pathogen showed the most effective inhibitory concentration to be at least 5 mg/ml. Keywords : methyl bromide, ozone layer, soil fumigation, plant extracts, soil pathogens, and inhibitory concentration Journal of Agriculture, Science and Technology Vol. 7(1) 2005: 41-52

A seasonal study of methyl bromide concentrations in the North Atlantic (35°–60°N)

Methyl bromide concentrations in and over the North Atlantic were examined during spring, summer, and fall 2003. The results demonstrate that seasonality plays a great role in controlling methyl bromide fluxes from and into the ocean in this area. The North Atlantic acted as a sink of the atmospheric gas during the spring, a source during the summer, and a weak sink during the fall. The annual air‐sea flux of methyl bromide from the North Atlantic area between 30°N and 60°N (approximately 15.4 × 106 km2) was estimated to be in the range of −0.3 to −0.6 Gg y−1, with the methyl bromide flux varying between −4.0 × 106 ± 1 × 106 g d−1, 1.6 × 106 ± 0.6 × 106 g d−1, and −0.6 × 106 ± 0.4 × 106 g d−1 in spring, summer, and fall, respectively. Methyl bromide production necessary to balance air‐sea exchange with oceanic losses was greater in the southern part than in the northern part of the studied area; no oceanic production was necessary to balance methyl bromide loss from the Arctic waters around 60°N. While the regional contribution to the methyl bromide global oceanic flux is small, it is also complex and dynamic. Our data suggest that in this part of the ocean the flux is not so much dependent on sea surface temperature as it is on other, still unknown environmental variables.

Effects of Methyl Bromide Concentration, Fumigation Time, and Fumigation Temperature on Mediterranean and Oriental Fruit Fly (Diptera: Tephritidae) Egg and Larval Survival

The effects of methyl bromide (MB) concentration (16, 32,48, or 64 g/m3), fumigation temperature (15, 20, 25, or 30 degrees C), and fumigation time interactions on the survival of Mediterranean fruit fly, Ceratitis capitata (Wiedemann), and oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), eggs and first and third instars were recorded. Increasing the fumigation temperature from 15 to 20 degrees C or from 20 to 25 degrees C resulted in a significant reduction in fumigation time required for equivalent egg and larval mortalities at all studied MB concentrations; no further reductions in fumigation time resulted from increasing the temperature from 25 to 30 degrees C. Conversely, increasing temperature and time allowed for a reduction in MB concentration to obtain equivalent mortality. Thus, the optimum fumigation temperature for Mediterranean and oriental fruit fly eggs and larvae was 25 degrees C. Reducing MB concentrations required for phytosanitary fumigations would save time and expense, and reduce the amount of MB released into the atmosphere during aeration. Mediterranean fruit fly was as or more tolerant to MB than oriental fruit fly in MB tolerance for eggs and first instars. The egg stage was generally more tolerant to MB regardless of concentration. However, Mediterranean fruit fly eggs showed similar tolerance to first instars at 25 degrees C for the three highest concentrations and to third instars at 25 and 30 degrees C for the highest concentration, with no significant difference between them. Therefore, eggs alone can be used to obtain MB fumigation efficacy and quarantine security data at fumigation temperatures between 15 and 30 degrees C for Mediterranean and oriental fruit fly.

Empirical Relationship between Use, Area, and Ambient Air Concentration of Methyl Bromide

Methyl bromide (MeBr) is one of the most widely used soil fumigants. Human exposure to MeBr above threshold values can cause serious health problems. The exposure assessment of MeBr depends on estimation or measurement of its air concentrations. This study proposed a methodology for systematically exploring the empirical relationship between MeBr use intensity and ambient air concentrations. Monitored air concentrations were regressed to MeBr use over various spatiotemporal scales that step-wise increased around the monitoring site and monitoring period. The results showed that the goodness-of-fit varied with the spatiotemporal scale of MeBr use. The best fit was Y = 0.46 + 0.00120X (R2 = 0.95, n = 11), where Y was the 8-wk average ambient air concentration (microg/m3), and X was the weekly average use (kg/wk) over an area of 11.3 x 11.3 km (7 x 7 mi). The model was calibrated with air-monitoring data and use data of 2000, and verified with the same type data of 2001. The model estimated subchronic air concentration with reasonable accuracy.