Influence of fumigants on sunflower seeds: Characteristics of fumigant desorption and changes in volatile profiles

Coupled use of Fe-impregnated biochar and urea-hydrogen peroxide to simultaneously reduce soil-air emissions of fumigant and improve crop growth

Reducing the emissions of soil fumigants such as 1,3-dichloropropene (1,3-D) is essential to protecting air quality. Although biochar is useful in reducing such emissions, biochar-adsorbed fumigants may desorb and cause secondary air pollution. This study investigated the degradation of 1,3-D on iron (Fe)-impregnated biochar (FBC) amended with urea-hydrogen peroxide (UHP). The results indicated the degradation rate of trans-1,3-D on FBC-UHP was 54-fold higher than that on pristine biochar (PBC). Electron paramagnetic resonance (EPR) combined with other characterization methods revealed that the presence of semiquinone-type radicals in FBC effectively accelerated the Fe(III)/Fe(II) cycleto maintain enough Fe(IIII) for UHP activation and ·OH generation. ·OH, rather than ·O₂^-, was the dominant active oxidant. Soil column tests showed that application of FBC to the soil surface reduced cumulative 1,3-D emissions from 34.80 % (bare soil) to 0.81%. After the column experiment, the mixing of the FBC with UHP resulted in the residual cis-isomers decreasing from 32.5% to 10.5%. Greenhouse bioassays showed that mixing post-1,3-D degradation FBC-UHP with soil significantly promoted lettuce growth relative to PBC. The findings of this study provide a new approach for biochar application, especially for the emission reduction of hazardous volatile organic compounds from soil.

Susceptibility of the Cigarette Beetle Lasioderma serricorne (Fabricius) to Phosphine, Ethyl Formate and Their Combination, and the Sorption and Desorption of Fumigants on Cured Tobacco Leaves

Simple Summary

Lasioderma serricorne (Fabricius) (Coleoptera: Anobiidae) is distributed throughout the world, where it is responsible for large amounts of economic damage to stored products in tropical and subtropical regions. To prevent the damage caused by this insect, the susceptibility of L. serricorne to phosphine (PH₃), ethyl formate (EF), and their combination was evaluated in this study. Eggs, larvae, pupae and adults were subjected to treatment with fumigants to determine the 90% lethal concentration time values. The results show that, through treatment with PH₃ + EF, control can be achieved at lower concentrations than for treatment with EF alone and at lower exposure times than for treatment with PH₃ alone. The sorption rates of the fumigants on cured tobacco leaves were determined for the safety of workers, and EF required a ventilation time of longer than 22 h to desorb from cured tobacco leaves. Therefore, PH₃ + EF can effectively control L. serricorne in cured tobacco leaves, with sufficient ventilation time required after treatment for the safety of workers.

Abstract

The susceptibility of Lasioderma serricorne to phosphine (PH₃), ethyl formate (EF) and their combination (PH₃ + EF) was evaluated in this study. Eggs, larvae, pupae and adults were subjected to treatment with fumigants to determine the 90% lethal concentration time (LCt₉₀) values. Treatment with PH₃ for 20 h resulted in LCt₉₀ values of 1.15, 1.39, 14.97 and 1.78 mg h/L while treatment with EF resulted in values of 157.96, 187.75, 126.06 and 83.10 mg h/L, respectively. By contrast, the combination of PH₃ + EF resulted in LCt₉₀ values of 36.05, 44.41, 187.17 and 35.12 mg h/L after 4 h. These results show that, through treatment with PH₃ + EF, control can be achieved at lower concentrations than for treatment with EF alone and at lower exposure times than for treatment with PH₃ alone. The sorption rates of the fumigants on cured tobacco leaves were determined for filling ratios of 2.5%, 5.0% and 10.0% (w/v). Cured tobacco leaves were treated with either 2 mg/L PH₃, 114 mg/L EF or 0.5 mg/L PH₃ + 109 mg/L EF. Treatment with PH₃ showed sorption rates of 0.0%, 7.1% and 14.3%. EF, however, showed higher sorption rates of 64.9%, 68.5% and 75.5%, respectively, for the indicated filling ratios. When PH₃ and EF were combined, the sorption rate of PH₃ was 0.0%, while the sorption rates of EF were lower (9.1%, 12.0% and 23.2%) than treatment with only EF. EF required a ventilation time of longer than 22 h to desorb from cured tobacco leaves. Therefore, PH₃ + EF can effectively control L. serricorne in cured tobacco leaves, with sufficient ventilation time required after treatment for the safety of workers.

Phosphine fumigation - Time dependent changes in the volatile profile of table grapes

Industrial and agricultural goods are fumigated in transport containers in order to control pest infestations and to avoid the transmission of alien species. Phosphine is increasingly used prior to the export as fumigant for table grapes, fruit cultures and dried fruits to control active table grapevine insect pests. Less knowledge exists for fumigants about the desorption time of toxic gases and factors that affect the composition of the fumigated good. Therefore, red and white table grapes (´Thompson seedless´, ´Scarlotta´ and ´Flame seedless´) were chosen to represent the allowed group of phosphine fumigated foods and were treated with a concentration of 2000 vpm phosphine (PH₃) at different temperatures. In the present study, sorption and desorption behavior of PH₃ by table grapes and possible changes in their VOC (volatile organic compounds) profiles were investigated. The PH₃ concentration was monitored before and after the fumigation process and was determined under the maximum residue level 0.005 ppm after 35 days. The adsorbed amount of PH₃ was not influenced by fumigation parameters. For analysis of the influences on the volatile profile after fumigation, a headspace solid-phase micro-extraction coupled to gas chromatography mass spectrometry (HS-SPME-GC/MS) was used. Small differences in volatile profiles of fumigated and subsequently outgassed table grapes compared to non-fumigated table grapes could be observed. A slight influence on the aldehyde group directly after fumigation could be perceived by a decrease of hex-2-en-1-ol and 1- hexanol in PH₃-treated table grapes. The concentrations of both compounds increase again after completion of the desorption process. On the other hand terpenes are not significantly influenced by the fumigation process. Overall these changes are likely to affect table grape aroma characteristics directly after a treatment with PH₃ and it could be demonstrated that phosphine alters the volatile profile of fumigated table grapes qualitatively and quantitatively.

Physical, chemical and biological behaviour of fumigants on cottonseed

Fumigation is required to protect cottonseed in storage and pre-shipment from insect pests and/or microorganisms. Fumigation of cottonseed with carbon disulphide (CS₂), carbonyl sulphide (COS), ethanedinitrile (C₂N₂), ethyl formate (EF), methyl bromide (MB) and phosphine (PH₃) showed that >85% of the fumigants disappeared within 5 h of exposure. COS maintained >20 mg L^-1 for 24 h. After 1 day of aeration, 75%-85% of the absorbed COS and MB and 20%-40% of the absorbed CS₂, EF and PH₃ were released from treated cottonseed. The fumigant residues were reduced by 80% for COS, 50% for EF or MB and 25% for CS₂ after 1 day of aeration. After 13 days of aeration, fumigant residues were reduced by 95% for MB, 65% for EF, 55% for CS₂ and to natural levels in the COS residue. Carbon disulphide, COS, PH₃, EF and C₂N₂ had no effect on the germination of cottonseed, but germination was reduced to 50% by MB. COS has potential as a fumigant for control of insect pests in cottonseed because it dissipates quickly and does not negatively impact germination. On the other hand, MB appears to strongly absorb and requires an extended period for residues to dissipate, and it negatively impacts germination.