Dissipation,half-lives,and mass spectrometric identification of endosulfan isomers and the sulfate metabolite on three field-grown vegetables

Endosulfan 3 EC, a mixture of α- and β-stereo isomers, was sprayed on field-grown pepper, melon, and sweet potato plants at the recommended rate of 0.44 kg A.I. acre^?1. Plant tissue samples (leaves, fruits, or edible roots) were collected 1 h to 30 days following spraying and analyzed for endosulfan isomers (α- and β-isomers). Analysis of samples was accomplished using a gas chromatograph (GC) equipped with a mass detector in total ion mode. The results indicated the formation of endosulfan sulfate as the major metabolite of endosulfan sulfite and the relatively higher persistence of the β-isomers as compared to the α-isomer. The initial total residues (α- and β-isomers plus endosulfan sulfate) were higher on leaves than on fruits. On pepper and melon fruits, the α-isomer, which is the more toxic to mammals, dissipated faster (T_1/2 = 1.22 and 0.95 d, respectively) than the less toxic β-isomer (T_1/2 = 3.0 and 2.5 d, respectively). These results confirm the greater loss of the α-isomer compared to the β-isomer, which can ultimately impact endosulfan dissipation in the environment. Additionally, the higher initial residues of endosulfan on pepper and sweet potato leaves should be considered of great importance for timing field operations and the safe entry of harvesters due to the high mammalian toxicity of endosulfan.     

Dissipation, half-lives, and mass spectrometric identification of endosulfan isomers and the sulfate metabolite on three field-grown vegetables

Endosulfan 3 EC, a mixture of α- and β-stereo isomers, was sprayed on field-grown pepper, melon, and sweet potato plants at the recommended rate of 0.44 kg A.I. acre(-1). Plant tissue samples (leaves, fruits, or edible roots) were collected 1 h to 30 days following spraying and analyzed for endosulfan isomers (α- and β-isomers). Analysis of samples was accomplished using a gas chromatograph (GC) equipped with a mass detector in total ion mode. The results indicated the formation of endosulfan sulfate as the major metabolite of endosulfan sulfite and the relatively higher persistence of the β-isomers as compared to the α-isomer. The initial total residues (α- and β-isomers plus endosulfan sulfate) were higher on leaves than on fruits. On pepper and melon fruits, the α-isomer, which is the more toxic to mammals, dissipated faster (T(1/2) = 1.22 and 0.95 d, respectively) than the less toxic β-isomer (T(1/2) = 3.0 and 2.5 d, respectively). These results confirm the greater loss of the α-isomer compared to the β-isomer, which can ultimately impact endosulfan dissipation in the environment. Additionally, the higher initial residues of endosulfan on pepper and sweet potato leaves should be considered of great importance for timing field operations and the safe entry of harvesters due to the high mammalian toxicity of endosulfan.     

Methode zum nachweis von rückständen der insektizide acephat, dimethoat, methamidophos und omethoat in kleinen nektarmengen

A gas chromatographic method for the determination of the insecticides acephate, dimethoate, methamidophos and omethoate in small amounts of nectar has been developed. By the use of a miniaturized extraction technique and a nitrogenphosphorus selective detector (NPD) residues down to 0.005 – 0.01 ppm could be detected in a sample size of 1 g. Because of the low content of co-extractives in nectar and the use of a highly selective detector a clean-up of the extracts was not necessary.     

Degradation of disulfoton,oxydemeton‐methyl,methamidophos and demeton in asparagus plant

Abstract

Disulfoton and methamidophos (both at 1.12 kg a.i./ha), oxydemeton‐methyl and demeton, (both at 0.56 kg a.i./ha) were applied as post‐harvest foliar sprays to control the European asparagus aphid, Brachycolus asparagi. Oxidation of disulfoton, oxydemeton‐methyl and demeton to their corresponding sulfoxides and sulfones occurred in asparagus foliage 2 to 5 days after application. The total residues of these three compounds, including their toxic oxidative metabolites declined to less than 0.5 ppm about 47 days after the spray application whereas methamidophos persisted longer; 0.84 ppm of its residue was found even after 85 days. No residue was found above the limit of detection of 0.002 ppm in any asparagus spears which were produced in the following spring; the four compounds were sprayed on the asparagus plants during the previous season at realistic rates for aphid control.     

Residues of dicofol on cucumber grown under plastic covers in jordan

Abstract

Residues of dicofol were determined on cucumber leaves and fruits under plastic house (PH) and plastic tunnels (PT). Five sprays, 8 d apart, were applied at 0.15% concentration. initial deposits on leaves were 48 and 58 ppm under PH and PT, respectively. In the last sampling date of leaves, the amounts of 191 and 135 ppm were detected under both cultures, respectively. There was a continuous increase in the initial residue after each spray. The highest amount of dicofol (401) was determined 1 d after the fifth spray under PH. The exposure to high residues may pose a risk to fieldworkers.

On cucumber fruits, residues of 0.95 and 1.60 ppm were determined 1 d after the fourth spray under PH and PT, respectively. These residues decreased after 4 d to 0.40 and 1.49 ppm, respectively. Almost no detectable residues could be determined 8 d after sprays number 4 and 5 under both cultures. All dicofol residues on the fruits were below the tolerance level of 2 ppm.     

Dissipation,half-lives,and mass spectrometric identification of chlorpyrifos and its two metabolites on field-grown collard and kale

The persistence and fate of chlorpyrifos and its two metabolites, chlorpyrifos-oxon and the 3, 5, 6-trichloro-2-pyridinol (TCP) break-down product were investigated on kale and collard leaves under field conditions. A simultaneous extraction and quantification procedure was developed for chrorpyrifos and its two main metabolites. Residues of chlorpyrifos, chlorpyrifos oxon, and TCP were determined using a gas chromatograph (GC) equipped with an electron capture detector (GC/ECD). Chlorpyrifos metabolites were detectable up to 23 days following application. Residues were confirmed using a GC equipped with a mass selective detector (GC/MSD) in total ion mode. Initial residues of chlorpyrifos were greater on collard (14.5 µg g^?1) than kale (8.2 µg g^?1) corresponding to half-lives (T_1/2) values of 7.4 and 2.2 days, respectively. TCP, the hydrolysis product, was more persistent on collards with an estimated T_1/2 of 6.5 days compared to kale (T_1/2 of 1.9 days).     

Studies of methamidophos-C-14 in Costa Rican vegetables and soils

In order to see the effect of time lapse between the last application of methamidophos and harvesting insecticide was applied on lettuce plants (6,84 μCi in one experiment and 4,03 μCi in the other experiment). Analysis of the crops harvested 3 days after last application showed 9,7 ppm residues on leaves, while crops harvested 1 day after application showed residues of 12,7 ppm (25% more). Treatment of tomato plants (39,65 μCi, 1,01 kg/ha) gave residues in fruits 4,92 ppm after 8 days interval between last application and harvesting. 40 days gap between the last application and harvesting leaved residues of 0,7 ppm in fruits which is much less as recommended by FAO/WHO (1 – 2 ppm).Degradation of this insecticide is dependent on the matrix of the soil, this breakdown is observed in the first ten days and than after it remains constant. C-14 radioactivity extracted from soil and plant analysis was methamidophos (92%)     

Toxicity and metabolism of acephate in adult and larval insects

Abstract

Adult and larval insects from the terrestrial and aquatic environments were exposed to acephate. The chemical was more toxic to adult insects than to larvae, and was a poor insect cholinesterase inhibitor in vitro compared to methamidophos which was a much stronger inhibitor. Both acephate and methamidophos inhibited the adult cholinesterase in vitro much more strongly than they did the larval enzymes. Acephate was metabolized by the insects to methamidophos which did not appear to be the only metabolite, although no other metabolites were looked for. The cholinesterase of insects exposed to sublethal levels of acephate was inhibited, but this inhibition appeared to be due to the combined effect of acephate and methamidophos and not to any hypothetical substance with greater anticholinesterase activity. This was bourne out when acephate was incubated with mixed function oxidases (MFO). No activated product with potent anticholinesterase activity was identified. Methamidophos was not produced by the MFO system but by some other unidentified mechanism.     

Residues of dicofol on cucumber grown under plastic covers in Jordan

Residues of dicofol were determined on cucumber leaves and fruits under plastic house (PH) and plastic tunnels (PT). Five sprays, 8 d apart, were applied at 0.15% concentration. Initial deposits on leaves were 48 and 58 ppm under PH and PT, respectively. In the last sampling date of leaves, the amounts of 191 and 135 ppm were detected under both cultures, respectively. There was a continuous increase in the initial residue after each spray. The highest amount of dicofol (401) was determined 1 d after the fifth spray under PH. The exposure to high residues may pose a risk to fieldworkers. On cucumber fruits, residues of 0.95 and 1.60 ppm were determined 1 d after the fourth spray under PH and PT, respectively. These residues decreased after 4 d to 0.40 and 1.49 ppm, respectively. Almost no detectable residues could be determined 8 d after sprays number 4 and 5 under both cultures. All dicofol residues on the fruits were below the tolerance level of 2 ppm.     

Simultaneous determination of fenitrothion and aminocarb in blueberry foliage and fruits: Application to the analysis of residues in field samples

Abstract

Samples of blueberry foliage and fruits were collected from spray blocks in Ontario after aerial application of fenitrothion and aminocarb at dosage rates of 210 g active ingredient (AI)/ha and 70 g AI/ha respectively. Residues were extracted from the samples by homogenizing with ethyl acetate, cleaned up by microcolumn chromatography using alumina as adsorbent, and analyzed by GLC‐AFID with a glass column packed with 1.5% OV‐17 and 1.95% OV‐210 on 80–100 mesh Chromosorb W‐HP. Average recoveries for fenitrothion and aminocarb from foliage at three fortification levels (1.0, 0.10 and 0.01 ppm) were respectively 99 and 96%. The corresponding values for the fruits were 99 and 95%. Foliage samples collected 1 h post‐spray contained on average 1.13 ppm of fe‐nitrothion and 1.14 ppm of aminocarb. However, residue levels reached below the detection limit (<0.01 ppm) in foliage collected 15 d after treatment. In addition, the fruit samples collected after 15 d post‐spray contained extremely low levels (0.03 ppm for fenitrothion and 0.02 ppm for aminocarb) of residues, and were barely above the detection limit.     

Residues and half-lives of pyrethrins on field-grown pepper and tomato

The dried flower heads of Tanacetum cinerariifolium Trev. (Family: Compositae) contain insecticidal compounds collectively called "pyrethrins." Pyrethrins are the subject of intense interest for use in crop protection because their toxicological properties permit control of certain insect species at application rates as low as 5-10 g AI acre(-1). Seedlings of sweet pepper, Capsicum annuum L. cv. Bell Boy Hybrid and tomato, Lycopersicon esculentum Mill. cv. Mountain Spring F1 Hybrid were planted and sprayed with a Multi-Purpose Insecticide formulation that contains 0.2% pyrethrins, 1.0% piperonyl butoxide (PBO), 88% diatomaceous earth, and 10.8% inert ingredients. The formulation was sprayed on pepper and tomato foliage when tomato fruits became red ripe and pepper became mature green at the rate of 6 lbs of formulated product per acre (5.4 and 27.2 g AI of pyrethrins and PBO, respectively). Following spraying, pepper and tomato leaves and fruits were collected at different time intervals for residue analysis using a high performance liquid chromatograph (HPLC) equipped with a UV detector. Residues of pyrethrins and PBO were generally higher on the leaves than fruits. Initial deposits (1 h following spraying) of pyrethrins were significantly higher on pepper than tomato fruits. Half-life (T1/2) values on pepper and tomato fruits did not exceed 2 h. Where concern exists over synthetic pesticide residues on treated crops and in the environment, pyrethrins are suitable alternatives that can be used to reduce the risk of exposure to synthetic pesticide residues.     

Soil Persistence of Triasulfuron Herbicide as Affected by Biotic and Abiotic Factors

Persistence of triasulfuron [3-(6-methoxy-4methyl-1,3,5-triazin-2-yl)-1-{2-(2-chloroethoxy)-phenylsulfonyl}-urea] in soil was studied under wheat crop and laboratory conditions. Field experiment was conducted in the farms of Agronomy Division, Indian Agricultural Research Institute (IARI), New Delhi. Randomized block design (RBD) was followed with four replicates and two rates of treatments along with control and weedy check. Triasulfuron was applied as post-emergent application to wheat crop at two rates of application viz., 15 g and 20 g a.i. ha^?1. Soil samples at 0 (3 h), 1, 3, 5, 7, 10, 15, 20, and 30-day intervals after application were drawn, extracted, cleaned up, and analyzed for herbicide residues by high performance liquid chromatography (HPLC) using C₁₈ column and methanol: water (8:2) as mobile phase at 242 nm wave length. Effect of microbial activity and soil pH was studied under laboratory conditions. Dissipation of triasulfuron followed a first-order-rate kinetics. Residues dissipated from field soil with half-life of 5.8 and 5.9 days at two rates of application. The study indicated biphasic degradation with faster rate initially (t _1/2 = 3.7 days), followed by a slower dissipation rate at the end (t _1/2 = 9.4 days). Similar trend was observed with non-sterile soil in laboratory with a longer half-life. Acidic pH and microbial activity contributed toward the degradation of triasulfuron in soil.     

Monitoring of pesticide residues in a cotton crop soil

Abstract

This paper reports on the residues of methyl parathion (O,O‐dimethyl O‐4‐nitrophenyl phosphorothioate), trifluralin (α, α, α‐trifluoro‐2, 6‐dinitro‐N, N‐dipropyl‐p‐toluidine), endosulfan [(1, 4, 5, 6, 7, 7‐hexachloro‐8, 9, 10‐trinorborn‐5‐en‐2, 3‐ylenebismethylene) sulfite] and dimethoate (O, O‐dimethyl S‐methylcarbamoylmethyl phosphorodithioate) in a cotton crop soil. Soil samples (0–15 cm) were collected at different periods from the cotton crop farm and subjected to Soxhlet extraction. The extracted material was analysed after clean‐up by a HP5890 II gas Chromatograph equipped with a ⁶³Ni electron‐capture detector (ECD‐⁶³Ni) and fitted with a 25m x 0,2mm i.d. fused silica capillary column [Ultra‐2 (5% phenylmethyl polysiloxane)]. The recoveries of the pesticide residues from the spiked control soil were determined after Soxhlet extraction and C₁₈ cartridges clean‐up by using radiotracer techniques with the corresponding ¹⁴C‐pesticides. The results show that in the cotton crop soil the pesticide residues under study were present in the range of 0.1 to 0.4 mg ? kg^‐1. Endosulfan was found to be rapidly degraded in the soil and formed a sulfate metabolite.     

Disappearance of dimethoate,methamidophos and pirimicarb in lettuce

Abstract

Foliar sprays of dimethoate at 150 or 300 g a.i./ha, methamidophos at 450 or 900 g a.i./ha and pirimicarb at 140 or 280 g a.i./ha were applied for control of the green peach aphid, Myzus pericae (Sulzer), and the lettuce aphid, Nasonovia ribisnigri (Mosley), about 2 weeks before the lettuce started heading, and again about 1 week from harvest. In lettuce, dimethoate partially oxidized to its oxon and pirimicarb converted to its methylamino‐ and/or formyl methylamino‐analogues. Most residues were present in the outer leaves which were exposed directly to the sprays; only traces of residues were detected in samples of the inner head leaves. Total residues disappeared rapidly. Pirimicarb was the least persistent and only traces of residues (<0.01 ppm) were detected in marketable heads. Concentrations of dimethoate, including the oxon and of methamidophos were well below their respective tolerances of 2 and 1 ppra respectively.     

Endosulfan and Quinalphos Residues and Toxicity to Soil Microarthropods after Repeated Applications in a Field Investigation

Endosulfan (1,4,5,6,7,7-hexachloro-8,9,10-trinorborn-5-en-2,3-ylenedimethylsulphite) and quinalphos (O,O-diethyl O-quinoxalin-2-yl phosphorothioate) persistence and their effect on soil microarthropods were studied after repeated applications in cotton fields. Dissipation behavior of insecticides after repeated applications was observed from 78 to 292 days after the first insecticide treatment. At any given time the concentrations of endosulfan β residues were always higher as compared to endosulfan α. From 78 to 85 days, 5.0% and 20.4% decrease in α and β endosulfan residues was observed, respectively. Endosulfan β isomer decreased up to 93.0% in 292 days. Endosulfan sulfate was detected as a major metabolite in the soil samples. Total endosulfan residues decreased by 86.6% from 78 to 292 days. The amounts of quinalphos residues were less as compared to endosulfan at any given time. The residues observed after 78 days of application were 0.88 ng g^?1 d wt. soil. At the end of 145 days, a 35.0% decrease in quinalphos residue was observed, which decreased further by 50.9% in 292 days. Among the soil microarthropods studied, Acarina was more sensitive to the applied insecticides as compared to Collembola. Three days after the last treatment, up to 94.5% (p < 0.01) and 71.2% (p < 0.05) decrease in Acarina population was observed in endosulfan and quinalphos treated fields, respectively, compared to control field. In general, no noticeable change in Collembola population was observed after the insecticide treatments.     

Studies on the toxicity, metabolism, and anticholinesterase properties of acephate and methamidophos

The toxicity of acephate to four species of aquatic insects, as well as the metabolism and cholinesterase-inhibiting properties of the chemical in the rat were studied. The results indicated that mayfly larvae were very sensitive to the toxic effects of acephate, whereas larvae of the stonefly, damselfly and mosquito were much less sensitive. In the rat, orally-administered acephate was rapidly absorbed from the intestines and severely inhibited the cholinesterases in the blood and brain. The enzymes began to recover after 24 hours, while the chemical was completely eliminated within three days. The amount of methamidophos observed in the liver was extremely low. The cholinesterase-inhibiting properties of acephate and methamidophos were compared in vitro to that of paraoxon, a known strong anticholinesterase. Enzymes from four vertebrates were used. In all cases, except one, acephate was found to be six orders of magnitude weaker than paraoxon, whereas methamidophos was three orders weaker. Trout brain cholinesterase was the exception; it was as sensitive to paraoxon as it was to methamidophos. Finally, four cholinesterases were inhibited with methamidophos, and their ability to reactivate spontaneously or to recover by induction with pyridine aldoxime methiodide (PAM) in vitro were determined. The results suggested that methamidophos-inhibited cholinesterases did not reactivate spontaneously; instead the enzymes remained inhibited either in a phosphorylated or an aged state. The significance of these results are discussed in relation to the use of acephate for forest insect pests.     

Pesticide dissipation curves in peach,pear and tomato crops in Uruguay*

Dissipation curves of azoxystrobin and of the neonicotinoids acetamiprid and thiacloprid in peach; azinphos-methyl and carbaryl in pear and azoxystrobin, chlorfenapyr and chlorpyrifos in high-tunnel tomato crops were studied in the Southern region of Uruguay. An analytical methodology based on solid phase extraction (SPE) and detection by High Performance Liquid Chromatography with Diode Array Detector (HPLC/DAD) was used for acetamiprid and thiacloprid. Coupled SPE and detection by Gas Chromatography with Mass Selective Detector (GC/MSD) was used for the detection of azinphos-methyl, azoxystrobin, carbaryl, chlorfenapyr and chlorpyrifos residues. Curves were modeled mathematically with Solver program of Microsoft Excel®. The best fit for acetamiprid and thiacloprid in peach was achieved with the exponential model (r²=0.961 and 0.944, respectively). In the case of peach fruits there is not a Maximum Residue Limit (MRL) for acetamiprid in the Codex Alimentarius, while 0.5 mg/kg is the value rated for thiacloprid. The MRLs accepted by the European Union (EU) are 0.1 mg/kg for acetamiprid and 0.3 mg/kg for thiacloprid. According to the curves determined in these experiments, thiacloprid residues 10 to 12 days after application (daa) were below the MRLs established by both sources. In the case of acetamiprid, 25 daa would be required, according to the exponential mathematical model, to get residues levels below the MRL values established by the EU. For azinphos methyl in pear, the residues detected were mathematically fitted to an exponential model (r²=0.999). According to it, residue levels under the MRL established by the EU (0.05 mg/kg) are gotten in our conditions in 20 daa. In plastic tunnel tomato chlorfenapyr residues were not detected from 16 daa, having the dissipation curve an exponential trend. In the same condition, there was not a decay of the azoxystrobin concentration during a 24-day trial, being it around 0.40 ± 0.05 mg/kg.     

Improved Gas Chromatographic method for analysis of trichlorfon insecticide in soil and turfgrass thatch

Abstract

An improved Gas Chromatographic method utilizing simple extraction and one‐step purification on solid phase extraction tubes was developed for analysis of trichlorfon as an intact insecticide compound in turfgrass thatch and soil. A Gas Chromatograph/Mass Spectrum (GC/MS) was used for confirmation of trichlorfon structure. The method readily determines trichlorfon in the presence of dichlorvos. Using an electron capture (EC) detector, the detection limits were 0.02 ppm in soil, 0.04 ppm in turfgrass thatch, and 0.09 ppm in soil, and 0.2 ppm in turfgrass thatch using an nitrogen phosphorus (NP) detector.     

Contributions to ecological chemistry CXII balance of conversion of buturon‐14C in wheat under outdoor conditions 1

Abstract

The urea herbicide buturon (N‐[p‐chlorophenyl] ‐N’ ‐methyl‐N’ ‐isobutinyl‐urea), ¹⁴C‐labeled, was sprayed on winter wheat as an aqueous formulation (2.98 kg/ha) under outdoor conditions. Upon harvest (three months after application), a total of 49. 2% of the applied radiocarbon was recovered: 2.0% in the plants, 46.9% in the soil, and 0.3% in the leaching water (depth > 50 cm); less than 0.1% was in the grains (0.464 ppm). Only about half of the radioactivity present in plants could be recovered under mild extraction conditions; about half of this was unchanged buturon. In straw and husk extracts, the following metabolites were identified by gaschromatography/mass spectrometry: N‐(p‐chlorophenyl)‐N‐methyl‐O‐methyl‐carbamate (metabolite I), N‐phenyl‐N’ ‐formyl‐urea (metabolite II), two unstable metabolites giving (p‐chlorophenyl)‐isocyanate upon purification (metabolites III and IV), N‐(p‐chlorophenyl)‐N’ ‐methyl‐N’ ‐isobutenylol‐urea (metabolite V), p‐chloroformanilide (metabolite VI) and biologically bound p‐chloroaniline (metabolite VII). In the root and basal stem extract, the following metabolites were identified by gas chromatography/mass spectrometry: N‐(p‐chlorophenyl)‐O‐methyl‐carbamate (metabolite VIII) and N‐(p‐chlorophenyl)‐N’ ‐methyl‐urea (metabolite IX).     

Residual behaviour and risk assessment of flubendiamide on chickpea (Cicer arietinum L.)

The study was undertaken to determine the disappearance trends of flubendiamide residues on chickpea under field conditions and thereby, ensure consumer safety. Average initial deposits of flubendiamide on chickpea pods were found to be 0.68 and 1.17 mg kg⁻¹, respectively, following three applications of flubendiamide 480SC @ 48 and 96 g a.i. ha⁻¹ at 7 d intervals. Half-life of flubendiamide on chickpea pods was observed to be 1.39 and 1.44 d, respectively, at single and double dosages whereas with respect to chickpea leaves, these values were found to be 0.77 and 0.86 d. Desiodo flubendiamide was not detected at 0.05 mg kg⁻¹ level on chickpea samples collected at different intervals. Theoretical maximum residue contribution (TMRC) for flubendiamide was calculated and found to be well below the maximum permissible intake (MPI) on chickpea pods and leaves at 0-day (1 h after spraying) for the both dosages. Thus, the application of flubendiamide at the recommended dose on chickpea presents no human health risks and is safe to the consumers.