Leaching potential of persistent soil fumigant residues

Persistent fumigant residues in soil resulting from agricultural pest-control practices may be released into water and leached to groundwater. In this study, the leaching potential of persistent soil fumigant residues was evaluated, and the effect of dissolved organic matter (DOM) and ammonium thiosulfate (ATS) amendment was investigated. A silt loam soil was incubated separately with the fumigants 1,3-dichloropropene (1,3-D), chloropicrin (CP), and methyl isothiocyanate (MITC) at 240-990 mg kg(-1) for 35 d, followed by 48 h of evaporation. The soil was packed into stainless steel columns (1.4 cm x 10 cm) and leached with water, 5 mM ATS, and DOM solution (DOC 250 mg L(-1)) by gravity. Residues of 1,3-D, CP, and MITC in the evaporated soil were 5.61, 11.38, and 1.83 mg kg(-1), respectively. Concentrations of 1,3-D, CP, and MITC in column effluents ranged from 0.05 to 0.73, 0.16 to 0.81, and 0.05 to 0.27 mg L(-1), respectively, when the soil was leached with 10 pore volumes of water. DOM did not promote the leaching of persistent fumigant residues, and ATS remarkably reduced the amount of 1,3-D and CP yet notably increased MITC recovered in the effluents. The results suggest that the leaching of persistent fumigant residues through soil to water is significant, and movement of fumigants in soil is not facilitated by DOM. Amending soil with ATS through irrigation is an effective method to remove persistent residues of halogenated fumigants. To reduce groundwater pollution risks posed by fumigation, persistent soil fumigant residues have to be considered.     

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.     

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.     

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.     

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.     

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.     

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.     

Identification of volatile/semivolatile products derived from chemical remediation of cis-1,3-dichloropropene by thiosulfate

The prevalent use of soil fumigants has resulted in air pollution in some agricultural regions. Our previous research showed that application of thiosulfate fertilizers at the soil surface may offer an effective and economical approach to reduce the emission of halogenated fumigants via a chemical remediation process. In this fumigant emission-reduction strategy, volatile 1,3-dichloropropene (1,3-D) reacts with thiosulfate to generate a nonvolatile Bunte salt (thiosulfate derivative of 1,3-D). However, the decomposition of the Bunte salt may be associated with the production of perceptible odors. This study investigated the stability of this reaction product in different environmental media. Hydrolysis experiments demonstrated that the thiosulfate derivative was relatively stable in neutral and moderately acidic aqueous solutions. In contrast, the thiosulfate derivative was readily converted to a dialkyl disulfide via a base hydrolysis process in pH 10 buffer solution. In a strongly acidic solution, a mercaptan and a dialkyl disulfide compound were detected as two primary hydrolysis products. In soil, this initial reaction product underwent a series of biotic conversions to generate several volatile or semivolatile organic sulfur compounds. The formation and distribution of four volatile/semivolatile products in the air and soil were detected in different soils treated with the thiosulfate derivative of 1,3-D. This study indicated that odors occurring in soil treated with halogenated fumigants and thiosulfate fertilizers might arise from the generation and release of these and other volatile/semivolatile organic sulfur products. The environmental fate and effects of such volatile/semivolatile sulfur compounds should be considered in the application of sulfur-containing fertilizers in fumigated fields.     

Nitrogen and carbon dioxide adsorption by soils

High-resolution nitrogen (77 K) and carbon dioxide (273 K) adsorption at subatmospheric pressures has been studied for a range of model soils of various origins with different organic matter (OM) contents. It is demonstrated that N2 and CO2 molecules probe different regions of soil particles. Nitrogen is adsorbed primarily on the outer surface of soil particles, while CO2 has a higher affinity to OM domains. Low-pressure nitrogen adsorption reveals that soil particle surfaces consist of clay/mineral domains with discrete patches of OM. A linear correlation has been found between the CO2 uptake and the amount of organic carbon reduced per unit of the external surface area. A new method for discriminating the microporosity of soil particles and accessibility of OM has been proposed.     

Organic matter chlorination rates in different boreal soils: the role of soil organic matter content

Transformation of chloride (Cl(-)) to organic chlorine (Cl(org)) occurs naturally in soil but it is poorly understood how and why transformation rates vary among environments. There are still few measurements of chlorination rates in soils, even though formation of Cl(org) has been known for two decades. In the present study, we compare organic matter (OM) chlorination rates, measured by (36)Cl tracer experiments, in soils from eleven different locations (coniferous forest soils, pasture soils and agricultural soils) and discuss how various environmental factors effect chlorination. Chlorination rates were highest in the forest soils and strong correlations were seen with environmental variables such as soil OM content and Cl(-) concentration. Data presented support the hypothesis that OM levels give the framework for the soil chlorine cycling and that chlorination in more organic soils over time leads to a larger Cl(org) pool and in turn to a high internal supply of Cl(-) upon dechlorination. This provides unexpected indications that pore water Cl(-) levels may be controlled by supply from dechlorination processes and can explain why soil Cl(-) locally can be more closely related to soil OM content and the amount organically bound chlorine than to Cl(-) deposition.     

Effect of two organic amendments on norflurazon retention and release by soils of different characteristics

The influence of two organic amendments on norflurazon sorption-desorption processes in four soils with very different physicochemical characteristics was studied in laboratory experiments to evaluate the potential leaching of this pesticide through organic fertilized soils. Sorption-desorption experiments were performed on original soils and on a mixture of these soils with urban waste compost (SUW) and a commercial amendment from olive-mill wastes (OW), at a rate of 6.25% (w/w). These mixtures were used immediately after preparation and after aging for 2 months. Norflurazon was analyzed by using a HPLC method. Norflurazon retention in original soils was related not only to the organic matter (OM) content but also to mineral surfaces present in soils. Norflurazon sorption increases largely after amendment in soils with low OM content, but the addition of exogenous OM to soils with medium OM content and/or other available adsorptive surfaces did not significantly affect norflurazon sorption. Even in some cases pesticide sorption decreases, due to the blocking of the mineral and organic soil surfaces with the amendment added. Transformation of exogenous OM during incubation depends both on the amendment added and on the type of soil and can affect sorption-desorption behavior of the soils surfaces in different manner, due to the modification of their hydrophobic-hydrophilic characteristics. Norflurazon desorption from original soils showed hysteresis in all cases, but it was not affected or even decreased in amended soils. It was a nonexpected behavior, especially in sandy soil, since it is generally assumed that a higher sorption always implies a lower mobility in soils. Norflurazon sorption must be taking place on very low affinity sites on exogenous OM through weak bindings, from which the pesticide can be easily desorbed. The application to soils of the organic amendments used in the present study could not be accepted to reduce norflurazon losses due to leaching processes.     

Formation and fate of bound residues from microbial biomass during 2,4-D degradation in soil

During organic contaminant degradation in soil, bound or nonextractable residues (NER) are formed. Part of these residues may be biogenic, because degrading microorganisms assimilate carbon derived from the pollutant and mineralized CO(2) to form cellular components for example, [fatty acids (FA) and amino acids (AA)], which are subsequently stabilized within soil organic matter (SOM). We investigated the formation and fate of FA and AA from biodegradation of (13)C(6)-2,4-D in soil and the incorporation of the (13)C-label into living biomass via (13)CO(2) fixation. After 64 days of incubation, (13)C-AA in SOM indicated that 44% of the initially applied (13)C(6)-2,4-D equivalents had been converted to microbial biomass and finally to biogenic residues. The intermediate maximum of (13)C-FA in SOM indicated a 20% conversion of (13)C(6)-2,4-D to biomass, but (13)C-FA decreased to 50% of that value whereas (13)C-AA in the SOM remained stable. We provide the first evidence that nearly all bound residues from 2,4-D are biogenic, containing natural microbial residues stabilized in SOM. Because of biogenic residue formation, the potential risk of bound residues from readily metabolized xenobiotics in soils is highly overestimated. Hence, the formation of biogenic residues must be considered in general when performing mass balances of pollutant biodegradation in soils.     

THE EFFECT OF FUMIGANTS ON FOOD QUALITY

Fumigants are used to prevent pest infestations in food and other stored commodities. The quality of the commodity may be affected by fumigant treatment in several ways. Residues of unchanged fumigant may remain in the commodity. Reaction of the individual chemical components of the commodity with the fumigant may alter its chemical or physical properties, thus resulting in changes in flavor, taste, odor, nutritional value or processing qualities. Methyl bromide, ethylene dibromide, ethylene dichloride, carbon tetrachloride, phosphine and ethylene oxide are the major fumigants used for treatment of grains, vegetables and fruits. Their effects on food quality and the significance of residues in treated commodities are reviewed.     

Estimation of the digestible energy of ruminant feedstuffs by the combined bag technique

The combined bag technique was used to estimate digestible energy of ruminant feedstuffs. Samples of corn, barley, and sorghum grains; soybean and sunflower meals; corn and wheat silages; and vetch and wheat hays were incubated in dacron bags in the rumens of dairy cattle for 3 to 72 h. Bags containing residues after 12 h of ruminal incubation were introduced into the duodenum and recovered from feces. Feeds and ruminal and intestinal residues were analyzed for dry matter (DM), organic matter (OM), crude protein (CP), neutral detergent fiber, and nonstructural carbohydrates. The effective ruminal degradability of OM was higher in grains (639 g/kg of DM) and in protein supplements (609 g/kg of DM) than in forages (373 g/kg of DM). For grains and forages, carbohydrates contributed most of the degradable OM in the rumen, but, in protein supplements, about 50% of the ruminally degradable OM originated from carbohydrate. For protein supplements, 54% of the OM that disappeared postruminally was CP, but, in the grains and forage ingredients, CP contributed less than 20% of the postruminal OM that disappeared. In grains and forages, 83% of total tract disappearance of OM was from carbohydrates. For protein supplements, CP contributed 50% to overall OM disappearance. The calculated energy equivalent of digested matter averaged among feeds was 4.71 kcal/g. A high correlation was found between digestible energy estimated by the combined bag technique and the respective National Research Council values. The combined bag technique is a useful tool for the estimation of digestible energy in feedstuffs.     

Efficiency of urease and nitrification inhibitors in reducing ammonia volatilization from diverse nitrogen fertilizers applied to different soil types and wheat straw mulching

BACKGROUND: Some authors suggest that the absence of tillage in agricultural soils might have an influence on the efficiency of nitrogen applied in the soil surface. In this study we investigate the influence of no‐tillage and soil characteristics on the efficiency of a urease inhibitor (N‐(n‐butyl)thiophosphoric triamide, NBPT) and a nitrification inhibitor (diciandiamide, DCD) in decreasing ammonia volatilization from urea and ammonium nitrate (AN), respectively. RESULTS: The results indicate that ammonia volatilization in soils amended with urea was significantly higher than in those fertilized with AN. Likewise, the main soil factors affecting ammonia volatilization from urea are clay and sand soil contents. While clay impedes ammonia volatilization, sand favours it. The presence of organic residues on soil surface (no‐tillage) tends to increase ammonia volatilization from urea, although this fact depended on soil type. The presence of NBPT in urea fertilizer significantly reduced soil ammonia volatilization. This action of NBPT was negatively affected by acid soil pH and favoured by soil clay content. CONCLUSION: The presence of organic residues on soil surface amended with urea increased ammonia volatilization, and was particularly high in sandy compared with clay soils. Application of NBPT reduced ammonia volatilization although its efficiency is reduced in acid soils. Concerning AN fertilization, there were no differences in ammonia volatilization with or without DCD in no‐tillage soils. Copyright © 2011 Society of Chemical Industry     

Understanding the effects of soil characteristics on phytotoxicity and bioavailability of nickel using speciation models

Acidity (pH) has been realized to be the most important soil characteristic that modulates bioavailability of heavy metals by affecting both the chemical speciation of metals in soil and the metal binding to the active sites on biota. In this work, we show that besides soil pH, metal bioavailability also depends to a certain extent on the type of soil. A better understanding of the role of soil type in regulating metal availability can be achieved with the analysis of soil composition and with calculations using chemical speciation models. Results of pot experiments, in which three different soils were spiked with nickel, show that the EC50 of total nickel in decreasing the biomass production of oats varies widely (0.7-22.5 mmol kg(-1) soil, more than 30 times). pH (4.7-7.0) is the most important factor, explaining up to a factor of 14 difference of nickel bioavailability in the soils. The remaining variation is caused by other differences in soil composition (soil type). The bioavailability and toxicity of nickel in the organic matter-rich soil studied is less than half of that in the sandy and clay soil studied at a similar pH. The chemical calculations using a multi-surface speciation model show that soil organic matter binds Ni much stronger than clay silicates and iron (hydr)oxides within the acidic pH range, which supports the experimental findings. In all three soils, the EC50 of Ni expressed in terms of Ni in 0.01 M CaCl2 soil extraction is rather stable (24-58 microM), suggesting the possibility to use this extraction as an estimation of metal availability in soil.     

Interaction of methyl bromide with soil

Because methyl bromide (CH3Br) is a widely used agricultural fumigant for soil disinfection, it is important to know the chemical behavior and fate of CH3Br as a result of its use for soil treatment. A solid-state 13C NMR study of 13CH3Br-treated soil and soil-component samples shows that methylation of soil organic matter may be the major pathway for degradation of CH3Br in soils. Adsorption of CH3Br on a dried clay like Ca-montmorillonite or kaolinite does not contribute directly to the degradation of CH3Br. The results are interpreted in terms of the chemical structures of separated soil fractions and the nature of the separation procedure.     

Preliminary assessment of imidazolium-based room-temperature ionic liquids for extraction of organic contaminants from soils

Alternative solvents known as room-temperature ionic liquids (RTILs) were considered for extraction of organic soil contaminants. A hydrophobic RTIL, 1-butyl-3-methyl imidazolium hexafluorophosphate ([bmim]PF6), and a hydrophilic RTIL, 1-butyl-3-methyl imidazolium chloride ([bmim]Cl), were selected as representative imidazolium-based RTILs to assess the extraction of several organic contaminants (OCs) from two model soils. The two soils were montmorillonite (clay minerals, high surface area, and no organic matter) and glacial till (organic matter). The soils were spiked separately with DDT, dieldrin, hexachlorobenzene, and pentachlorophenol. With the exception of DDT, extractions of OCs from montmorillonite using [bmim]PF6 (79-92%) were nearly as effective as extractions with acetone and ethanol (85-100%). The extraction of OCs from glacial till with RTILs (15-61%) was less effective than extraction with organic solvents (59-100%). The [bmim]Cl was as efficient as [bmim]PF6 for extraction of OCs from glacial till, while [bmim]PF6 was more efficient than [bmim]Cl for extraction of OCs from montmorillonite. The two RTILs were most effective for the extraction of dieldrin (the heaviest OC) from both soils. The extraction results for glacial till showed dependence of OC extraction on the viscosity and melting point of RTILs.     

Soil tests for available copper and zinc in soils of Western Nigeria

Four soil tests for copper and zinc were evaluated for their ability to predict Cu and Zn uptake by oats (Avena sativa, L., Lodi var.) grown on 28 soils from Western Nigeria. Statistical analyses showed that EDTA was a better extractant for predicting Cu uptake than was DTPA, 0.1 N -HCl or 1 N -HCl. Copper uptake was more strongly correlated with inorganic soil fractions than with organic matter and was not significantly affected by soil pH. The best prediction of Zn uptake was provided by a combination of 0.1 N -HCl extractable Zn, pH, organic matter and the silt plus clay fraction in a multiple regression analysis. All four extractants predicted plant Zn uptake better on soils of pH less than 6.0 than on soils of pH greater than 6.0. A significant amount of Cu and Zn in the soils appeared to be associated with sesquioxides, part of which was available for plant use.     

Distribution of aged 14C-PCB and 14C-PAH residues in particle-size and humic fractions of an agricultural soil

Organic matter is considered to be the single most importantfactor limiting availability and mobility of persistent organic pollutants (POPs) in soil. This study aimed to characterize the distribution of 14C-PCB (congeners 28 and 52) and 14C-PAH (fluoranthene and benzo[a]pyrene) residues in an Orthic Luvisol soil obtained from two lysimeter studies initiated in 1990 at the Agrosphere Institute (Forschungszentrum Jülich GmbH, Germany). The lysimeter soils contained a low-density OM fraction, isolated during soil washing, which contained a significant fraction (3-12%) of the total 14C-activity. Soils were also fractionated according to three particle sizes: >20, 20-2, and <2 microm. Relative affinity values of 14C-activity for the different particle sizes varied in the order 20-2 microm > (<2 microm) approximately (>20 microm) for the PCBs. Relative affinity values of 14C-activity for the different particle sizes varied in the order 20-2 microm > (<2 microm) > (>20 microm) for the PAHs. The distribution of 14C-PCB or 14C-PAH residues in the organic and inorganic matrixes of the particle-size fractions was determined using methyl isobutyl ketone (MIBK). 14C-PCB and 14C-PAH-associated activities were primarily located in the humin fraction of the 20-2 and <2 microm particle-size fractions of the soil. A small fraction was associated with the fulvic and humic acid fractions; these were quantitatively more important for the PAHs than the PCBs. There appeared to be a high degree of association of 14C-activity with the mineral fraction following MIBK separation of the humic fractions, ranging between 8 and 52% for 14C-PCBs and 57-80% for 14C-PAHs. The mineral (inorganic) component of the soils apparently played a significant (previously unreported) role in the sequestration of both PCBs 28 and 52 and the PAHs fluoranthene and benzo[a]pyrene.