Phorate Sulfoxide Research Articles

Evaluation of Organophosphates Residue in Stored Cereals from Some Selected Markets in Jalingo, Nigeria

Cereal grains such rice, sorghum, maize and millet among others are the staple foods in large parts of the world, supplying most of the energy and bulk in diets. Pesticide residue analysis in cereals from the various sampling locations for this dissertation revealed the following organophosphate pesticide residue were present in cereals analyzed Dichlorvos, Diazinon, Phorate sulfon, Malathion, Phorate, Chloropyrifos, Methyl Parathion, Profenofos, Ethion, Dimethoate, Phorate Sulfoxide, Phosalone, Edifenfos, Fenitrothion and Chlorofenvinfos. The presence of pesticide residues is detected in the samples of cereals (Rice, Maize, Millet and sorghum) analyzed. This could be as a result of high utilization of various pesticides during plant, cultivation and storage thus leading to the bioaccumulation of this substance in the individual cereals. It indicates high levels of non-carcinogenic risk associated with the life time consumption of cereals produce and sold within this region. Based on findings from this study’s, I hereby make the following recommendations. Regulatory agencies in Nigeria should step up efforts to ensure compliance with the ban on these chemicals. Farmers and other pesticide users also need to be educated on the dangers of using banned products and on the over application of these pesticides. Furthermore, farmers should be educated on the properly usage of these chemical product, during plant, harvest and storage. Also, manufacturers of these chemicals should produce less toxic pesticide using organic materials in other to prevent the health risk associated with chemical pesticide and their residues in food crops and the environment.

Bioelectrochemical platform with human monooxygenases: FMO1 and CYP3A4 tandem reactions with phorate

It is highly advantageous to devise an in vitro platform that can predict the complexity of an in vivo system. The first step of this process is the identification of a xenobiotic whose monooxygenation is carried out by two sequential enzymatic reactions. Pesticides are a good model for this type of tandem reactions since in specific cases they are initially metabolised by human flavin-containing monooxygenase 1 (hFMO1), followed by cytochrome P450 (CYP). To assess the feasibility of such an in vitro platform, hFMO1 is immobilised on glassy carbon electrodes modified with graphene oxide (GO) and cationic surfactant didecyldimethylammonium bromide (DDAB). UV–vis, contact angle and AFM measurements support the effective decoration of the GO sheets by DDAB which appear as 3 nm thick structures. hFMO1 activity on the bioelectrode versus three pesticides; fenthion, methiocarb and phorate, lead to the expected sulfoxide products with KM values of 29.5 ± 5.1, 38.4 ± 7.5, 29.6 ± 4.1 µM, respectively. Moreover, phorate is subsequently tested in a tandem system with hFMO1 and CYP3A4 resulting in both phorate sulfoxide as well as phoratoxon sulfoxide. The data demonstrate the feasibility of using bioelectrochemical platforms to mimic the complex metabolic reactions of xenobiotics within the human body.

Study on the Remediation of Phorate in Soil by Microbial Consortia

In order to bioremediating of phorate contaminated soil by microbial consortia, three degrading bacteria in different combinations were inoculated into the phorate contaminated soil. The residual phorate and its metabolites were determined. The results showed that in 42 days the degradation rates of phorate by any two bacteria (Brevibacterium frigoritolerans +Bacillus aerophilus, Bacillus aerophilus +Pseudomonas fulva and Brevibacterium frigoritolerans +Pseudomonas fulva) were 94.09%, 97.15% and 97.42%, respectively. However the degradation rate of phorate by three bacteria was 98.31%. The microbial consortia consisted of three degrading bacteria had the lowest content of phorate sulfone and phorate sulfoxide in soil. Therefore, the microbial consortia consisted of three degrading bacteria could significantly reduce the residual phorate and its metabolites in soil.

Dissipation behavior of phorate and its toxic metabolites in the sandy clay loam soil of a tropical sugarcane ecosystem using a single-step sample preparation method and GC-MS

The dissipation of phorate in the sandy clay loam soil of tropical sugarcane ecosystem was studied by employing a single-step sample preparation method and gas chromatography with mass spectrometry. The limit of quantification of the method was 0.01 μg/g. The recoveries of phorate, phorate sulfoxide, phorate sulfone, and phorate oxon were in the range 94.00-98.46% with relative standard deviations of 1.51-3.56% at three levels of fortification between 0.01 and 0.1 μg/g. The Half-life of phorate and the total residues, which include phorate, phorate sulfoxide and phorate sulfone, was 5.5 and 19.8 days, respectively at the recommended dose of insecticide. Phorate rapidly oxidized into its sulfoxide metabolite in the sandy clay loam soil. Phorate sulfoxide alone accounted for more than 20% of the total residues within 2 h post-application and it was more than 50% on the fifth day after treatment irrespective of the doses applied. Phorate sulfoxide and phorate sulfone reached below the detectable level on 105 and 135 days after treatment, respectively as against 45 days after treatment for phorate residues at the recommended dose. Thus, the reasonably prolonged efficacy of phorate against soil pests may be attributed to longer persistence of its more toxic sulfoxide and sulfone metabolites.

QuEChERS method for the simultaneous quantification of phorate and its metabolites in porcine and chicken muscle and table eggs using ultra-high performance liquid chromatography with tandem mass spectrometry.

An analytical method to detect phorate and its metabolites, including phorate sulfone, phorate sulfoxide, phoratoxon, phoratoxon sulfone, and phoratoxon sulfoxide, in porcine and chicken muscles and table eggs was developed and validated. Extraction was performed using a quick, easy, cheap, effective, rugged, and safe method and analysis was conducted using ultra-high performance liquid chromatography-tandem mass spectrometry. Matrix-matched calibrations were linear over the tested concentrations, with determination coefficient ≥ 0.995 for all tested analytes in the different matrices. The limits of detection and quantification were 0.001 and 0.004 mg/kg, respectively. The calculated recovery rates at three fortification levels were satisfactory, with values between 74.22 and 119.89% and relative standard deviations < 10%. The method was applied successfully to commercial samples collected from locations throughout the Korean Peninsula, and none of them showed any traces of the tested analytes. Overall, the developed method is simple and versatile, and can be used for monitoring phorate and its metabolites in animal products rich in protein and fat.

LC-MS/MS를 이용한 축산물 중 Phorate 및 대사산물 5종 동시분석법 개발

A simultaneous official method was developed for the determination of phorate and its metabolites (phorate sulfoxide, phorate sulfone, phorate oxon, phorate oxon sulfoxide, phorate oxon sulfone) in livestock samples. The analytes were quantified and confirmed via liquid chromatograph-tandem mass spectrometer (LC-MS/MS) in positive ion mode using multiple reaction monitoring (MRM). Phorate and its metabolites were extracted from beef and milk samples with acidified acetonitrile (containing 1% acetic acid) and partitioned with anhydrous magnesium sulfate. Then, the extract was purified through primary secondary amine (PSA) and C18 dispersive sorbent. Matrix matched calibration curves were linear over the calibration ranges (0.005-0.5 mg/L) for all the analytes into blank extract with r > 0.996. For validation purposes, recovery studies were carried out at three different concentration levels (beef 0.004, 0.04 and 0.2 mg/kg; milk 0.008, 0.04 and 0.2 mg/kg, n = 5). The recoveries were within 79.2-113.9% with relative standard deviations (RSDs) less than 19.2% for all analytes. All values were consistent with the criteria ranges requested in the Codex guidelines. The limit of quantification was quite lower than the maximum residue limit (MRL) set by the Ministry of Food and Drug Safety (0.05 mg/kg). The proposed analytical method was accurate, effective and sensitive for phorate and its metabolites determination and it will be used to as an official analytical method in Korea.

Phytotransformation of Phorate by Brassica juncea (Indian Mustard)

Over 5 days, Brassica juncea removed 54% of the highly toxic insecticide phorate from the medium with the formation of phorate sulfoxide in small quantity. The loss of phorate from the medium followed first-order kinetics. The half-life of phorate disappearance from water decreased by ~4.5-fold in the presence of B. juncea. Mild phorate phytotoxicity was evident from the elevated activities of the antioxidative enzymes like glutathione-disulfide reductase, glutathione S-transferase, superoxide dismutase, and catalase in the plants. Nevertheless, the ubiquitous antioxidative peroxidase was not significantly increased, nor the total glutathione content, due to phorate exposure. Phosphotriester bond hydrolysis and glutathione S-transferase-mediated conjugation seemed to be the key reactions for phorate metabolism by B. juncea. From the limited information available, for the first time, a tentative mapping of phytotransformation pathways was performed.

Effect of sonication on eliminating of phorate in apple juice

The degradation of phorate in apple juice by sonication was investigated in the present study. Results showed that sonication was effective in eliminating phorate in apple juice, and the ultrasonic power and sonication time significantly influenced the degradation of phorate ( p < 0.05). The degradation of phorate followed the first-order kinetics model well. Phorate-oxon and phorate sulfoxide were identified as the degradation products of phorate by gas chromatography–mass spectrometry (GC–MS). Moreover, the toxicity of apple juice samples spiked with phorate was significantly reduced by sonication ( p < 0.05). The quality indexes of apple juice including pH, titratable acidity (TA), electrical conductivity (EC), total soluble solids (TSS), and the contents of sucrose, glucose and fructose were not affected by sonication, and no visible difference in color was observed between the sonicated samples and the control.

Hypersalinity acclimation increases the toxicity of the insecticide phorate in coho salmon (Oncorhynchus kisutch).

Previous studies in euryhaline fish have shown that acclimation to hypersaline environments enhances the toxicity of thioether organophosphate and carbamate pesticides. To better understand the potential mechanism of enhanced toxicity, the effects of the organophosphate insecticide phorate were evaluated in coho salmon (Oncorhynchus kisutch) maintained in freshwater (<0.5 g/L salinity) and 32 g/L salinity. The observed 96-h LC50 in freshwater fish (67.34 ± 3.41 μg/L) was significantly reduced to 2.07 ± 0.16 μg/L in hypersaline-acclimated fish. Because organophosphates often require bioactivation to elicit toxicity through acetylcholinesterase (AChE) inhibition, the in vitro biotransformation of phorate was evaluated in coho salmon maintained in different salinities in liver, gills, and olfactory tissues. Phorate sulfoxide was the predominant metabolite in each tissue but rates of formation diminished in a salinity-dependent manner. In contrast, formation of phorate-oxon (gill; olfactory tissues), phorate sulfone (liver), and phorate-oxon sulfoxide (liver; olfactory tissues) was significantly enhanced in fish acclimated to higher salinities. From previous studies, it was expected that phorate and phorate sulfoxide would be less potent AChE inhibitors than phorate-oxon, with phorate-oxon sulfoxide being the most potent of the compounds tested. This trend was confirmed in this study. In summary, these results suggest that differential expression and/or catalytic activities of Phase I enzymes may be involved to enhance phorate oxidative metabolism and subsequent toxicity of phorate to coho salmon under hypersaline conditions. The outcome may be enhanced fish susceptibility to anticholineterase oxon sulfoxides.

Isolation and characterization of a phorate degrading bacterium

To study the degradation of phorate by a bacterium isolated from phorate-contaminated sites. Ralstonia eutropha strain AAJ1 isolated from soil was found to degrade phorate (supplied as sole carbon source) upto 85% in 10 days in liquid medium. Half-life (t((1/2))) of phorate in the liquid medium in control (uninoculated) and in experimental (inoculated with R. eutropha, strain AAJ1) samples was recorded as 36.49 and 6.29 days, respectively. Kinetics revealed that phorate degradation depends on time and the reaction follows the first order kinetics. Diethyl dithiophosphate was one of the degradation products, which is markedly less toxic than the parent compound; other degradation products included phorate sulfoxide and phorate sulfone. Release of inorganic phosphates and sulfates indicated the potential of the isolate to further degrade the above-mentioned metabolites to simpler forms. The strain was also found to poses phosphomonoesterase and phosphodiesterase enzymatic activity, which are involved in biodegradation of organophosphorus compounds. Ralstonia eutropha AAJ1 could degrade and detoxify phorate upto 85% in 10 days in laboratory conditions. The isolate has the potential to be utilized for remediation of phorate-contaminated water and soil.

Determination of Low-Level Pesticide Residues in Soft Drinks and Sports Drinks by Liquid Chromatography with Tandem Mass Spectrometry: Collaborative Study

A collaborative study was conducted on a method for the measurement of 11 low-level pesticide residues in soft drinks and sports drinks by liquid chromatography with tandem mass spectrometry. The pesticide residues determined in this study were alachlor, atrazine, butachlor, isoproturon, malaoxon, monocrotophos, methyl paraoxon, phorate, phorate sulfone, phorate sulfoxide, and 2,4-dichlorophenoxyacetic acid (2,4-D). Blind fortification solutions containing 3 different levels of pesticide residues were provided to 9 collaborating laboratories to create test samples at concentrations of 0, 0.1, and 0.5 microg/L with a 10-fold concentration for phorate in a total of 6 matrixes (2 colas, 1 diet cola, 1 clear lemon-lime soft drink, 1 orange soft drink, and 1 sports drink). Good qualitative performance of the method was demonstrated for all pesticide residues. Reproducibility relative standard deviation (RSDR) ranged from 7 to 151% for alachlor, atrazine, butachlor, isoproturon, malaoxon, monocrotophos, methyl paraoxon, phorate, phorate sulfone, phorate sulfoxide, and 2,4-D at the 0.1 microg/L level (1.0 microg/L for phorate). At 0.5 microg/L (5.0 microg/L for phorate), RSDR ranged from 9 to 57% for alachlor, atrazine, butachlor isoproturon, malaoxon, monocrotophos, methyl paraoxon, phorate, phorate sulfone, phorate sulfoxide, and 2,4-D in all matrixes. Repeatability relative standard deviation (RSDr), applicable to the diet cola and sports drink, ranged from 0 to 124% for the 11 pesticide residues at the 0.1 microg/L level (1.0 microg/L for phorate). At 0.5 microg/L (5.0 microg/L for phorate), RSDr ranged from 4 to 26%. Recoveries for the 11 pesticide residues in all matrixes ranged from 84 to 300% at the 0.1 microg/L level (1.0 microg/L for phorate) and from 66 to 127% at the 0.5 microg/L (5.0 microg/L for phorate) level. Coefficients of determination (r2) of the matrix-matched calibration curves were > or = 0.95. It is recommended that the method be accepted by AOAC as Official First Action with a limit of quantification of 0.5 microg/L for alachlor, atrazine, butachlor, isoproturon, malaoxon, methyl paraoxon, monocrotophos, phorate sulfone, phorate sulfoxide, and 2,4-D and 5.0 microg/L for phorate.

Degradation study of selected organophosphorus insecticides in natural waters

The degradation of 15 organophosphorus insecticides was studied in drinking, ground, and surface waters under different laboratory-controlled and environmental conditions. Surface waters originated from rivers Savinja (near the city of Celje) and Kamniska Bistrica (at the spring), which both belong to the Danube river basin. Groundwater was collected from wells (70 m deep) in Ljubljana, which are the direct source of drinking water for the capital. These matrices were selected on the basis of their different chemical composition and microbial activity. Major factors influencing the degradation were determined, such as temperature, oxygen, sunlight, pH, and type of water. The degradation of atrazine, present in many water sources in Slovenija, was followed simultaneously as a reference under the same conditions. The degradation kinetics was followed by gas chromatography with mass-selective detection, which also allowed the identification of some degradation by-products, such as oxon analogues paraoxon, dyfoxon, malaoxon, phenyl-methyl sulfoxide, fenthion sulfone, phorate sulfoxide, and phorate sulfone. The results show that the half-lives of the selected organophosphorus insecticides varied from 4 to 192 days or more, depending on the water source and experimental conditions. As a result, kinetically constants and half-lives were calculated for every tested insecticide, and major degradation products were determined.

Determination of Low-Level Agricultural Residues in Soft Drinks and Sports Drinks by Liquid Chromatography/Tandem Mass Spectrometry: Single-Laboratory Validation

In this study, sponsored by PepsiCo Inc., a method was validated for measurement of 11 pesticide residues in soft drinks and sports drinks. The pesticide residues determined in this validation were alachlor, atrazine, butachlor, isoproturon, malaoxon, monocrotophos, paraoxon-methyl, phorate, phorate sulfone, phorate sulfoxide, and 2,4-dichlorophenoxyacetic acid (2,4-D) when spiked at 0.100 microg/L (1.00 microg/L for phorate). Samples were filtered (if particulate matter was present), degassed (if carbonated), and analyzed using liquid chromatography with tandem mass spectrometry. Quantitation was performed with matrix-matched external standard calibration solutions. The standard curve range for this assay was 0.0750 to 10.0 microg/L. The calibration curves for all agricultural residues had coefficient of determination (r2) values greater than or equal to 0.9900 with the exception of 2 values that were 0.9285 and 0.8514. Fortification spikes at 0.100 microg/L (1.00 microg/L for phorate) over the course of 2 days (n=8 each day) for 3 matrixes (7UP, Gatorade, and Diet Pepsi) yielded average percent recoveries (and percent relative standard deviations) as follows (n=48): 94.4 (15.2) for alachlor, 98.2 (13.5) for atrazine, 83.1 (41.6) for butachlor, 89.6 (24.5) for isoproturon, 87.9 (24.4) for malaoxon, 96.1 (9.26) for monocrotophos, 101 (25.7) for paraoxon-methyl, 86.6 (20.4) for phorate, 101 (16.5) for phorate sulfone, 93.6 (25.5) for phorate sulfoxide, and 98.2 (6.02) for 2,4-D.

A comparative study on the dissipation and microbial metabolism of organophosphate and carbamate insecticides in orchaqualf and fluvaquent soils of West Bengal

An experiment has been conducted under laboratory conditions to investigate the effect of phorate (an organophosphate insecticide) and carbofuran (a carbamate insecticide) at their recommended field rates (1.5 and 1.0 kg a.i. ha −1, respectively) on the growth and multiplication of microorganisms as well as rate of dissipation and persistence of the insecticidal residues including their metabolites in laterite (typic orchaqualf) and alluvial (typic fluvaquent) soils of West Bengal. Application of phorate and carbofuran in general, induced growth and development of bacteria, actinomycetes, fungi, N 2-fixing bacteria and phosphate solubilizing microorganisms in both the soils and the stimulation was more pronounced with phorate as compared to carbofuran. Application of phorate recorded highest stimulation of fungi in laterite and actinomycetes in alluvial soil. Carbofuran on the other hand, augmented fungi and N 2-fixing bacteria in laterite and actinomycetes in alluvial soil. Bacterial population was inhibited due to the application of carbofuran in alluvial soil. Phorate sulfoxide and phorate sulfone, the two metabolites of phorate and 3-hydroxycarbofuran and 3-ketocarbofuran, the two metabolites of carbofuran isolated were less persistent in both the soils. Phorate persisted in laterite and alluvial soils up to 45 and 60 days, respectively depicting the half-life ( T 1/2) 9.7 and 11.5 days, respectively while the T 1/2 of carbofuran for the said soils were 16.9 and 8.8 days, respectively. No metabolite of carbofuran was detected in soils after 30 days of incubation while phorate sulfone persisted in alluvial soil even after 60 days of application of the insecticide.

Gas-phase photolysis of phorate, a phosphorothioate insecticide

Novel methods are described for determining atmospheric photolysis rates for the moderately volatile pesticide, phorate. The gas-phase sunlight photolysis of this substance was determined in three test systems which include: (1) 3-L borosilicate flasks exposed to sunlight and laboratory solar simulation, (2) 100-L Tedlar sunlight exposed air sample bags, and (3) 12,800-L Tedlar sunlight exposed chamber studies using a photochemically stable tracer compound. The kinetic results from all systems indicate rapid gas-phase photolysis under midsummer sunlight conditions with observed half-lives being less than 30 minutes. A pronounced increase in transformation rates with increasing volume to surface area suggests photoreactions occur at more rapid rates in the gas-phase. 14C Radiolabeled phorate irradiations resulted in one conversion product, phorate sulfoxide, and this photoproduct accounted for essentially all of the phorate lost.

Environmental Fate of Phorate and Its Metabolites in Northern Prairie Wetlands

ABSTRACT The environmental fate of the organophosphate insecticide phorate and its metabolites, phorate sulfone and phorate sulfoxide was examined in mesocosms placed in South Dakota wetlands. Three treatment concentrations of phorate (1.2, 2.4, and 4.8 kg/ha) were applied to wetland mesocosms. Phorate, phorate sulfone, and phorate sulfoxide were present in water and sediment during the entire study (28 days) in all treatments. Maximum phorate concentrations in water were measured one day after treatment and decreased significantly during a 28-day period. The metabolites of phorate increased significantly in the water during the study. Phorate was present in higher concentrations in sediments than either phorate sulfone or phorate sulfoxide throughout the study.

Hepatic and extrahepatic microsomal oxidation of phorate by the cytochrome P-450 and FAD-containing monooxygenase systems in the mouse

The relative contribution of the cytochrome P-450-dependent monooxygenase system ( P-450) and the FAD-containing monooxygenase (FMO) in the oxidation of phorate ( O,O-diethyl S-((ethylthio)methyl)phosphorodithioate) was investigated in liver, lung, and kidney microsomes isolated from male and female Dub:ICR mice. Selective inhibition was used to define the role of each enzyme system independent of the other system. Liver microsomes exhibited the greatest sulfoxidase activity, with P-450 responsible for greater than 75% of the activity. Although overall rates of sulfoxidation were much lower in lung and kidney microsomes, the FMO activity, relative to P-450, was greater. In all three organs, FMO activity appeared higher in microsomes isolated from female mice than microsomes from male mice. Phorate sulfoxide was the only metabolite detected during the linear range of the time course incubations. Extended time incubations yielded metabolites in addition to phorate sulfoxide in liver microsomes (phorate sulfone and phorate oxon sulfoxide) and lung microsomes (phorate oxon and phorate oxon sulfoxide), but not in kidney microsomes.

Biochemical and Chemical Transformations of Phorate, Phorate Sulfoxide, and Phorate Sulfone in Natural and Sterile Mineral and Organic Soil

A sandy loam and a muck soil were sterilized by autoclaving, and samples were treated at 10 ppm with phorate, phorate sulfoxide, or phorate sulfone. These were incubated in the dark at 28°C, and samples were removed after 1, 2, 4, 8, 12, and 16 weeks and examined for microbial populations, pH, and insecticide concentrations. These variables also were determined in correspondingly treated natural soils. The three applied insecticides disappeared much more rapidly from the natural soils than from the sterilized soils. Phorate sulfoxide and phorate sulfone were observed as intermediate transformation products. In the sterile soils, phorate oxidation to phorate sulfoxide was the major process observed, and further oxidation of the sulfoxide did not occur. The expected increases in rates and changes in the products formed were observed as the sterile soils became nonsterile in time. Reduction of phorate sulfoxide to phorate was detected as a minor process in these contaminated soils. The results show that biochemical processes are of major importance in the transformation of phorate and its oxidation products in soil. The usefulness of appropriate partial rate constants in describing the processes involved is discussed.

INSECTICIDAL ACTIVITY AND PERSISTENCE OF PHORATE, PHORATE SULFOXIDE, AND PHORATE SULFONE IN SOILS

AbstractLaboratory tests indicated that phorate, phorate sulfoxide, and phorate sulfone were toxic contact insecticides with broad spectrum activity. In general, p. sulfoxide was most toxic to insects &gt; p. sulfone &gt; phorate. When compared with other insecticides using 24–48 h old field crickets, Acheta pennsylvanicus (Burmeister), as test insects, the three compounds were less toxic by direct contact than carbofuran and fensulfothion, but as or more toxic than aldrin. P. sulfoxide and p. sulfone were strongly inactivated in moist Plainfield sand and were not as insecticidally active in soil against crickets as phorate. Nevertheless, the sulfoxide arid sulfone in soil were intermediate in toxicity between carbofuran and fensulfothion. The insecticidal activity of phorate, p. sulfoxide, and p. sulfone in soil was influenced by soil type, moisture, and temperature. Fumigant toxicity tests indicated that the three compounds volatilized from soil. Chemical analysis showed p. sulfone was most persistent in sand and muck &gt; p, sulfoxide &gt; phorate. Oxidation was observed to be a major degradation reaction for phorate and p. sulfoxide in both soils. Parallel bioassay tests indicated that, in sand, the biological action of "phorate" was due to the joint action of the three compounds. In a field study phorate EC, applied as a broadcast application at 3.4 kg AI/ha and incorporated into the top 7–8 cm of soil was slightly more persistent in muck than in sand. More than 99% and 98% of the applied phorate and its oxidation products disappeared from the sand and muck, respectively, within a year of treatment, indicating that the residues were only moderately persistent under climatic conditions encountered in southwestern Ontario. Low residues of p. sulfoxide and p. sulfone were detected in radishes grown on both soils in the first year but none were present in the second year. No residues were detected in carrots grown on either soil.

Effects of lake bottom mud on the movement and metabolism of14C‐phorate in a flooded soil‐plant system

Abstract The movement and metabolism of 14C‐phorate were investigated in flooded loam soils deposited on lake mud sediments. A layer of lake mud underlying insecticide‐treated loam soil significantly increased the persistence of phorate and reduced the amounts of 14C‐phorate residues that were released from the sediments into the water. After a 2‐week incubation 62% of the applied phorate was recovered undegraded, 13% as phorate sulfoxide, but no phorate s;ulfone could be detected in the presence of lake mud. When insecticide‐treated loam soil was mixed with lake mud sediments, the metabolism of phorate was further reduced and even less radiocarbon moved into the water. Varying the amount of lake mud or of insecticide‐treated soil did not affect the insecticide distribution in the system, nor its metabolism. The evolution of 14CO2 and the release of volatile lipid‐soluble metabolites were both depressed by underlying lake mud. Studies pertaining to the rate of metabolism and movement of 14C‐phorate in a soil‐lake mud‐water‐plant system during a 2‐week incubation period, indicated a decline in the radiocarbon content of the soil‐lake mud mixture during the first 3 days of incubation, with a concomittant increase of 14C in the water. After that, the amounts of 14C‐compounds remained constant in the soil‐lake mud, decreased in the water and increased steadily in the Elodea plants, which picked up these compounds from the water. Most of the plant associated radiocarbon could not be extracted and was bound to the plant tissue, amounting finally to 81% of all the radiocarbon recovered from the Elodea plants.