Degradation of methyl iodide in soil: effects of environmental factors

Sustainable methods for the carboxymethylation and methylation of ursolic acid with dimethyl carbonate under mild and acidic conditions

Ursolic acid is a triterpene plant extract that exhibits significant potential as an anti-cancer, anti-tumour, and anti-inflammatory agent. Its direct use in the pharmaceutical industry is hampered by poor uptake of ursolic acid in the human body coupled with rapid metabolism causing a decrease in bioactivity. Modification of ursolic acid can overcome such issues, however, use of toxic reagents, unsustainable synthetic routes and poor reaction metrics have limited its potential. Herein, we demonstrate the first reported carboxymethylation and/or methylation of ursolic acid with dimethyl carbonate (DMC) as a green solvent and sustainable reagent under acidic conditions. The reaction of DMC with ursolic acid, in the presence of PTSA, ZnCl2, or H2SO4-SiO2 yielded the carboxymethylation product 3β-[[methoxy]carbonyl]oxyurs-12-en-28-oic acid, the methylation product 3β-methoxyurs-12-en-28-oic acid and the dehydration product urs-2,12-dien-28-oic acid. PTSA demonstrated high conversion and selectivity towards the previously unreported carboxymethylation of ursolic acid, while the application of formic acid in the system led to formylation of ursolic acid (3β-formylurs-12-en-28-oic acid) in quantitative yields via esterification, with DMC acting solely as a solvent. Meanwhile, the methylation product of ursolic acid, 3β-methoxyurs-12-en-28-oic acid, was successfully synthesised with FeCl3, demonstrating exceptional conversion and selectivity, >99% and 99%, respectively. Confirmed with the use of qualitative and quantitative green metrics, this result represents a significant improvement in conversion, selectivity, safety, and sustainability over previously reported methods of ursolic acid modification. It was demonstrated that these methods could be applied to other triterpenoids, including corosolic acid. The study also explored the potential pharmaceutical applications of ursolic acid, corosolic acid, and their derivatives, particularly in anti-inflammatory, anti-cancer, and anti-tumour treatments, using molecular ADMET and docking methods. The methods developed in this work have led to the synthesis of novel molecules, thus creating opportunities for the future investigation of biological activity and the modification of a wide range of triterpenoids applying acidic DMC systems to deliver novel active pharmaceutical intermediates.

Dissipation, adsorption-desorption, and potential transformation products of pinoxaden in soil

This study established and validated a simple and sensitive analytical approach for determining pinoxaden residues in soil. The dissipation and adsorption-desorption of pinoxaden in four kinds of Chinese soil were comprehensively investigated for the first time, and the possible metabolic products and pathways were identified. The developed method was successfully applied in dissipation and adsorption-desorption trials. Several influential factors, including temperature, organic matter, and moisture content, affected the dissipation rate of pinoxaden in soil. During the dissipation process, 1 hydrolytic intermediate and 13 possible transformation products were identified, and predicted metabolic pathways were composed of electron rearrangement, oxidation, cyclization, carboxylation, and so on. Both the adsorption and desorption isotherms of pinoxaden in four kinds of Chinese soil followed the Freundlich equation, and the Freundlich K_f values were positively correlated with the soil cation exchange capacity. According to the calculated Gibbs free energies, the adsorption of pinoxaden was an endothermic reaction and mainly a physical process. These results could provide some useful data for the determination of pinoxaden in other matrices and the evaluation of the environmental fate of pinoxaden in soil and other ecosystems.

Soil properties, presence of microorganisms, application dose, soil moisture and temperature influence the degradation rate of Allyl isothiocyanate in soil

Allyl isothiocyanate (AITC) is a soil fumigant derived from plants that can effectively control soil-borne diseases. Fully understanding the impact of various factors on its degradation can contribute to its effectiveness against pests and diseases. First, orthogonal design determined the extraction method of AITC in soil, that is using ethyl acetate as the extraction reagent, vortexing for 1 min as the extraction method and holding for 30 min as the method time. Then we studied the effects of soil texture and environmental factors on the rate and extent of AITC degradation in soil. The half-lives of nine origins soils varied from 12.2 to 71.8 h that were affected by the soil's electrical conductivity, available nitrogen, pH and organic matter content. Biotic degradation of AITC contributed significantly (68%-90%) of the total AITC degradation in six soil types. The degradation rate of AITC decreased as the initial dose of AITC increased. The degradation rate of AITC in Suihua soil generally increased with increasing temperature and soil moisture. The effect of temperature on AITC degradation was more pronounced when the soil was moist, which has practical implications for the control of soil pests and diseases. In agricultural soil, the soil's characteristics and environmental factors should be considered when determining the appropriate AITC dose suitable for soil borne disease while at the same time minimizing emissions and impact on the environment.

Effect of application rate on chloropicrin half-life and simulated emissions across a range of soil conditions

The volatile release of agricultural fumigants from soil to air is a critical concern in terms of human and environmental health. A major control on the release of fumigants from soil to air is their degradation rate within the soil; however, this is a function of human/soil/environmental conditions and their inter-relationships. For the common fumigant chloropicrin (CP), it is known that application rate has a marked effect on degradation rate, with a potential further influence on CP emissions. We conducted batch degradation studies to better understand how CP degradation rate changes in response to application rate (56, 224, 392kgha^-1) under gradients of soil temperature (10, 25, and 40°C), soil moisture content (1, 8, and 15%), and organic matter content (1, 2, and 3%). A general trend of degradation rate decreasing with increasing application rate was observed across almost all such gradients, which is likely attributable to decreased microbial numbers and activity (i.e., degradation) at high (toxic) application rates. The effects of these ranges in degradation rate on emissions from soil to air were predicted using an analytical solution model, indicating that between the low and high application rates, total emissions percentage increased markedly (increases ranging from 69 to 99.8 percentage points, depending on prevalent conditions). The work will be useful to state and federal regulators in assessing the likely impact of CP use on air quality and human health.

Stimulation of earthworms (Eisenia fetida) on soil microbial communities to promote metolachlor degradation

Degradation of metolachlor in surface soil is extremely important to its potential mobility and overall persistence. In this study, the effects of earthworms (Eisenia fetida) on the degradation of metolachlor at two concentration levels (5 and 20 mg kg^-1) in soil were investigated via the column experiment. The degradation kinetics of metolachlor indicate that addition of earthworms enhances metolachlor degradation significantly (P < 0.05), with the enhanced degradation rate of 30% and 63% in the low and high concentration treatments at the 15th day, respectively. Fungi rather than bacteria are primarily responsible for metolachlor degradation in soil, and earthworms stimulate metolachlor degradation mainly by stimulating the metolachlor-degrading functional microorganisms and improving fungal community structure. Earthworms prefer to promote the possible fungal degraders like order Sordariales, Microascales, Hypocreales and Mortierellales and the possible bacteria genus Rubritalea and strengthen the relationships between these primary fungi. Two metabolites metolachlor oxanilic (MOXA) and moetolachlor ethanesulfonic acid (MESA) are detected in soil and earthworms in the high concentration treatments. Earthworms stimulate the formation of MOXA and yet inhibit the formation of MESA in soil. Another metabolite metolachlor-2-hydroxy (M2H) is also detected in earthworms, which is reported firstly. The study provides an important information for the remediation of metolachlor-polluted soil.

Current advances in the catalytic conversion of carbon dioxide by molecular catalysts: an update

Recent advances (2015–) in the catalytic conversion of CO₂ by metal-based and metal-free systems are discussed.

Methyl Iodide Exposure Presenting as Severe Chemical Burn Injury with Neurological Complications and Prolonged Respiratory Insufficiency

Methyl iodide (iodomethane) is a monohalomethane that is mainly used as an intermediate in the manufacturing of different pharmaceuticals and pesticides. Until now, only 13 cases of methyl iodide poisoning have been described in the literature. The authors present the first case of severe chemical burn injury due to methyl iodide exposure in a 36-year-old Caucasian man who suffered superficial to partial-thickness burn injuries over 75% of his BSA and developed neurological malfunctions and prolonged respiratory insufficiency. Human poisoning with methyl iodide is very rare. In addition to the already described neurological symptoms and respiratory insufficiency, severe chemical burn injury can cause a life-threatening medical emergency.

Effect of application rate on fumigant degradation in five agricultural soils

Soil fumigation is an important pest management tool for many high value crops. To address the knowledge gap of how fumigant concentration in soil impacts dissipation, and thereby efficacy, this research determined the degradation characteristics of four fumigants as affected by application rate. Laboratory incubation experiments were conducted to determine degradation rates of 1,3-dichloropropene (both cis- and trans isomers), chloropicrin (CP), dimethyl disulfide (DMDS), and methyl iodide (MeI) in five agricultural soils. Fitted to pseudo first-order kinetics, the degradation rate constant (k) of CP, DMDS, and MeI decreased significantly as application rate increased while the 1,3-D isomers were the least affected by rate. Half-lives increased 12, 17, and 6-fold for CP, DMDS, and MeI, respectively, from the lowest to the highest application rate. At low application rates, the degradation rate of all fumigants in the Hueneme sandy loam soil was reduced by 50-95% in sterilized soil compared to the biologically active controls. However, this difference became much smaller or disappeared at high application rates indicating that biodegradation dominates at low concentrations but chemical degradation is more important at high concentrations. When co-applied, CP degradation was enhanced with biodegradation remained above 50%, while 1,3-D degradation was either reduced or not changed. Among the fumigants tested, the relative importance of biodegradation was DMDS>CP>MeI>1,3-D. These results are useful for determining effective fumigation rates and for informing regulatory decisions on emission controls under different fumigation scenarios.

Improved method for quantitative analysis of methylated phosphatidylethanolamine species and its application for analysis of diabetic-mouse liver samples

N-monomethyl phosphatidylethanolamine (MMPE) and N,N-dimethyl phosphatidylethanolamine (DMPE) species are intermediates of phosphatidylcholine (PC) de-novo biosynthesis through methylation of phosphatidylethanolamine (PE). This synthesis pathway for PC is especially important in the liver when choline is deficient in the diet. Despite some efforts focused on the analysis of MMPE and DMPE species, a cost-effective and high-throughput method for determination of individual MMPE and DMPE species, including their regioisomeric structures, is still missing. Therefore we adopted and improved the "mass-tag" strategy for determining these PE-like species by methylating PE, MMPE, and DMPE molecules with deuterated methyl iodide to generate PC molecules with nine, six, and three deuterium atoms, respectively. On the basis of the principles of multidimensional mass-spectrometry-based shotgun lipidomics we could directly identify and quantify these methylated PE species, including their fatty-acyl chains and regiospecific positions. The method provided remarkable sensitivity, with a limit of detection at 0.5 fmol μL(-1), high specificity, and a broad linear-dynamics range of >2500 folds. By applying this method to liver samples from streptozotocin (STZ)-induced diabetic mice and controls, we found that the levels of PC species tended to decrease and the amounts of PE species tended to increase in the liver of STZ-induced diabetic mice compared with controls, but no significant changes in MMPE and DMPE species were determined. However, remodeling of fatty-acyl chains in the determined lipids was observed in the liver of STZ-induced diabetic mice, with reduction in 16:1 and increases in 18:2, 18:1, and 18:0 acyl chains. These results indicated the improved method to be a powerful tool to reveal the function of the PC de-novo biosynthesis pathway through methylation of PE species in biological systems.

Control of Soilborne Pathogens of Zingiber officinale by Methyl Iodide and Chloropicrin in China

Development of effective alternative soil fumigants is essential to the phasing out of methyl bromide (MeBr) while keeping major soilborne pathogens under control. Here, we report on the laboratory studies and field trials evaluating methyl iodide (MeI) and chloropicrin (Pic) for control of major soilborne ginger (Zingiber officinale) pathogens Ralstonia solanacearum, Pythium spp., Fusarium oxysporum, and Meloidogyne incognita in Shandong province of China. Laboratory studies indicated that MeI at 24 mg/kg of soil was most effective, reducing four pathogens by >90%. Treatments with MeI+Pic at 12 mg/kg (1:3 and 1:5) also reduced these pathogens by >82%. In the field trials, MeI at 30 or 40 g/m² and MeI+Pic (1:3) at 40 g/m² yielded excellent long-term control of all target pathogens. These treatments allowed ginger plants to maintain vigorous growth and produce a greater number of tillers (>12 per plant), and increased ginger yields by >80% compared with the nontreated controls. MeI at a reduced rate of 20 g/m² or Pic at 40 g/m² provided levels of disease control similar to MeBr. These studies demonstrated that injection treatments with MeI at 30 and 40 g/m², and MeI+Pic (1:3) at 40 g/m², followed by covering with virtually impermeable film, are effective alternatives of soil fumigation for control of the major ginger pathogens in Shandong.

Dissipation of soil fumigants from soil following repeated applications

BACKGROUND

The dissipation of pesticides in soil and the occurrence of accelerated degradation following repeated applications are well-known phenomena with many pesticides, but much less so with soil fumigants. The fate of various soil fumigants was studied in different agricultural soils following repeated applications of chloropicrin.

RESULTS

Fumigant dissipation reflected by Σconcentration × time (ΣC × T) and half-life values varied widely among the tested soils. Methyl iodide (MI) had the slowest dissipation rate compared with other fumigants in all tested soils. Elimination of biotic agents by soil sterilization prior to MI application did not affect MI concentration in Oxnard soil. Clay content and fumigant dose (ΣC × T values) of chloropicrin, 1,3-dichloropropene and MI were significantly correlated. No significant correlations were found between soil properties and ΣC × T values following metam sodium and methyl bromide (MBr) application.

CONCLUSION

The fate of the tested soil fumigants is highly dependent on and specific to the fumigant, previous fumigant application and soil type. This study suggests that biotic factors are more essential in the dissipation of metam sodium and MBr than abiotic factors. By contrast, MI dissipation from the tested soils is affected more by abiotic factors than by biotic activities.

Coupling of soil solarization and reduced rate fumigation: effects on methyl iodide emissions from raised beds under field conditions

Using field plots, we studied the effect on methyl iodide (MeI) emissions of coupling soil solarization (passive and active) and reduced rate fumigation (70% of a standard fumigation) in raised beds under virtually impermeable film (VIF). The results showed that for the standard fumigation and the passive solarization + fumigation treatments, emissions from the nontarped furrow were very high (∼50%). Emissions from the bed top and sidewall of these treatments were relatively low but were increased in the latter due to the longer environmental exposure of the VIF covering with the coupled approach (increased tarp permeability). Overall, this approach offered no advantage over fumigation-only in terms of emission reduction. With active solarization + fumigation, the large application of hot water during solarization apparently led to severely limited diffusion causing very low total emissions (<1%). Although this suggests a benefit in terms of air quality, a lack of diffusion could limit the pesticidal efficacy of the treatment.

Mitigating iodomethane emissions and iodide residues in fumigated soils

Although long-regarded as an excellent soil fumigant for killing plant pests, methyl bromide (MeBr) was phased out in 2005 in the USA, because it can deplete the stratospheric ozone layer. Iodomethane (MeI) has been identified as an effective alternative to MeBr and is used in a number of countries for preplant pest control. However, MeI is highly volatile and potentially carcinogenic to humans if inhaled. In addition, iodide anions, a breakdown product of MeI, can build up in fumigated soils and potentially cause plant toxicity and contaminate groundwater via leaching. In order to overcome the above two obstacles in MeI application, a method is proposed to place reactive bags containing ammonium hydroxide solution (NH4OH) on the soil surface underneath an impermeable plastic film covering the fumigated area. Our research showed that using this approach, over 99% of the applied MeI was quantitatively transferred to iodide. Of all the resulting iodide, only 2.7% remained in the fumigated soil, and 97.3% was contained in the reactive bag that can be easily removed after fumigation.

Phase partitioning, retention kinetics, and leaching of fumigant methyl iodide in agricultural soils

Although it is not currently being sold in the USA, the recent US registration of the fumigant methyl iodide has led to an increased interest in its environmental fate and transport. Although some work has now considered its volatile emissions from soil, there remains a lack of experimental data regarding its ability to be retained in soil and ultimately become transported with irrigation/rain waters. Using laboratory batch and soil column experiments, we aimed to better understand the phase partitioning of MeI, the ability of soils to retain MeI on the solid phase, and the potential for leaching of MeI and its primary degradation product, iodide, down a soil profile. Results indicated that MeI was retained by the solid phase of soil, being protected from volatilization and degradation, particularly in the presence of elevated organic matter. Retention was greater at lower moisture content, and maximum retention occurred after 56 days of incubation. At higher moisture content, the liquid phase also became important in retaining MeI within soil. Together with low observed K(D) values (0.10 to 0.57 mL g(-1)), these data suggest that MeI may be prone to leaching. Indeed, in a steady-state soil column study, initially retained MeI was transported with interstitial water. The MeI degradation product, iodide, was also readily transported in this manner. The data highlight a potentially significant process by which MeI fate and transport within the environment may be impacted.

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.

Irrigation, organic matter addition, and tarping as methods of reducing emissions of methyl iodide from agricultural soil

Methyl iodide (MeI) is increasingly being used as a highly effective alternative to the soil fumigant methyl bromide. Due to its volatile and toxic nature, MeI draws wide attention on its potential atmospheric emission following field fumigation treatment. Using soil columns that make it possible to determine emissions and gas phase distribution of soil fumigants, we studied MeI behavior in two soils differing in organic matter content. Additionally, the effectiveness of surface irrigation and tarping with virtually impermeable film (VIF) was assessed. In the lower organic matter, bare soil (control), emissions of MeI were rapid and high (83% of total). Although the peak emission flux was reduced by irrigation, the total loss was very similar to the control (82%). Tarping with VIF dramatically reduced emissions (0.04% total emissions). In the higher organic matter soil, degradation rate of MeI was increased around 4-fold, leading to a significant reduction in emissions (63% total emissions). The work suggests that surface tarping with VIF would be highly effective as an emissions reduction strategy and would also result in the maintenance of high soil gas concentrations (important for pest control). Ripping of the tarp after two weeks led to an immediate spike release of MeI, but, even so, the flux rate at this time was almost 20 times lower than the peak flux rate in the control. Even with tarp ripping, the total emission loss from the VIF treatment remained low (6%).

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.