Concentrations Of Fenitrothion Research Articles

Effects of physical (hypoxia, hyperoxia) and chemical (potassium dichromate, fenitrothion) stress on antioxidant enzyme activities in Chironomus riparius mg. (diptera, chironomidae) larvae: Potential biomarkers

AbstractEffects of physical (hypoxia, hyperoxia) and chemical (potassium dichromate, fenitrothion) stress on antioxidant enzyme activities and hemoglobin content in Chironomus riparius Mg. (Diptera, Chironomidae) larvae were evaluated under laboratory conditions in order to identify pertinent biomarkers of stress. Hypoxia and hyperoxia caused an increase in Cu,Zn‐superoxide dismutase (SOD) and Mn‐SOD activities and a simultaneous decrease in total peroxidase (Px) and glutathione peroxidase (GSH‐Px) activities. A parallel increase in hemoglobin concentration in the hemolymph was observed. The exposure to sublethal concentrations of both potassium dichromate and fenitrothion led to an increase in Cu,Zn‐SOD and Mn‐SOD activities and to a decrease in GSH‐Px activity. Activation of catalase (CAT) was observed in the larvae exposed to high fenitrothion concentration (20μg/L). The response of SODs was rapid and sensitive to low chemical concentrations, but changes in CAT, Px, and GSH‐Px were more specific and less sensitive.

Comparison of gas chromatography and immunoassay methods in quantifying fenitrothion residues in grape juice processed into alcoholic drinks

Wine and Arak, the national alcoholic drink in Lebanon, were prepared from grape juice fortified with fenitrothion to a concentration of 20ppm. Samples of the 11 fractions produced by the fermentation and distillation steps were analyzed for fenitrothion residues using gas chromatography (GC) and enzyme‐linked immunosorbent assay (ELISA). Results of residue analyses showed that the two techniques were highly correlated (r = 0.978) and indicated that fenitrothion was stable during the fermentation steps but not during distillation. The clarified wine 35 days later contained about 85% (15.3 ppm) of the fenitrothion concentration found in the juice as determined by GC analysis. Arak was prepared by a two‐steps distillation of the clarified wine. The alcohol distillate and undistilled fraction from the first distillation contained 2.5 ppm and 5.8 ppm of fenitrothion, respectively. No fenitrothion residues were detected by both techniques in the four fractions collected from the second distillation step.

Multiroute Exposure Assessment and Excretion of Urinary Metabolites of Fenitrothion During Manual Operations on Treated Ornamental Plants in Greenhouses

The results of environmental and biological (five subjects) monitoring of exposure to fenitrothion during manual operations on treated ornamental plants in greenhouses are reported. Urinary excretion [GM (GSD)] of alkylphosphates [dimethylphosphate (DMP) + dimethylthiophosphate (DMTP)] (nmol/g creat) was 244.8 (1.8), 174.0 (2.0), and 354.4 (1.6) respectively, on the first (Monday), third (Wednesday), and fifth (Friday) days of work. These levels were not significantly higher than those recorded in a control group (21 subjects) in which urinary excretion [GM (GSD)] of DMP + DMTP was 102.8 (4.2) nmol/g creat. Air concentrations of fenitrothion (nmol/m3) ranged from 45.5 to 81.2 on Monday, 17.3 to 27.1 on Wednesday, and 9.7 to 19.1 on Friday. Dose estimates showed that the respiratory-absorbed doses of fenitrothion accounted, on the average (GM), for 94.7%, 93.1%, and 91.5% of the total absorbed dose on Monday, Wednesday, and Friday, respectively. Multiple regression analysis showed a significant correlation (r2 = 0.595) between urinary excretion of DMP + DMTP, respiratory-absorbed dose, and skin-absorbed dose, estimated on Monday and Wednesday. Total estimated absorbed doses did not exceed the acceptable daily intake for fenitrothion. Serum and erythrocyte cholinesterase activities were not significantly different before and after exposure.

COMPARATIVE EFFECTIVENESS OF ORGANOPHOSPHORUS PROTOXICANT ACTIVATING SYSTEMS IN NEUROBLASTOMA CELLS AND BRAIN HOMOGENATES

The ability of bromine and rat liver microsomes (RLM) to convert organophosphorus (OP) protoxicants to esterase inhibitors was determined by measuring acetylcholinesterase (AChE) and neuropathy target esterase (NTE) inhibition. Species specific differences in susceptibility to esterase inhibition were determined by comparing the extent of esterase inhibition observed in human neuroblastoma cells and hen, bovine, and rodent brain homogenates. OP protoxicants examined included tri-o-tolyl phosphate (TOTP) , O -ethyl O-p -nitrophenyl phenylphosphonothioate (EPN), leptophos, fenitrothion, fenthion, and malathion. Bromine activation resulted in greater AChE inhibition than that produced by RLM activation for equivalent concentrations of fenitrothion, malathion, and EPN. For EPN and leptophos, bromine activation resulted in greater inhibition of NTE than RLM. Only preincubation with RLM activated TOTP; resultant inhibition of AChE was less in hen brain (13 +/- 3%) than in neuroblastoma cells (73 +/- 1%) at 10-6 M . In contrast, 10-6 M RLM-activated TOTP produced more inhibition of hen brain NTE (89 +/- 6%) than NTE of human neuroblastoma cells (72 +/- 7%). Human neuroblastoma cells and brain homogenates from hens, the accepted animal model for study of OPinduced neurotoxicity, were relatively similar in sensitivity to esterase inhibition. Homogenates from hens were more sensitive to NTE inhibition induced by phenyl saligenin phosphate (PSP), an active congener of TOTP, than were homogenates from less susceptible species (mouse, rat, bovine). AChE of hen brain homogenates was also more sensitive than homogenates from other species to malaoxon, the active form of malathion.

In vivo inhibition of AChE activity in the European eel Anguilla anguilla exposed to technical grade fenitrothion

European eel ( Anguilla anguilla) were exposed to sublethal fenitrothion concentrations in a continuous flow-through system for 4 days. Plasma acetylcholinesterase (AChE) activity was evaluated after 2, 8, 12, 24, 32, 48, 56, 72 and 96 h pesticide exposure. AChE activity in the plasma of the eel decreased as concentration of fenitrothion increased. Pesticide induced significant inhibitory effects on the AChE activity of A. anguilla ranging from 51% inhibition at sublethal concentration of 0.02 ppm to 57% inhibition at sublethal concentration of 0.04 ppm. Eel were exposed to both fenitrothion concentrations for 96 h and then allowed a period of recovery in pesticide-free water. Following 1 week of recovery, the AChE activity for those animals previously exposed to fenitrothion was still different from the controls. Animals transferred to clean water showed plasma AChE activities reduced in a 34 and 51% when previously exposed to 0.02 and 0.04 ppm pesticide, respectively. This is probably due because regeneration of the enzyme is mainly by the novo synthesis after exposure to organophosphates and levels need a large extent to recover.

Effects of sublethal exposure to a pesticide on levels of energetic compounds in Anguilla anguilla.

The effect of two sublethal fenitrothion concentrations (0.02 and 0.04 mg/L) on the energy metabolism of the european eel Anguilla anguilla and its recovery from intoxication was investigated. Analysis of various parameters such as glycogen, proteins and total lipids was made on liver and muscle eel tissues after 2, 8, 12, 24, 32, 48, 56, 72 and 96 hr of fenitrothion (0,0‐dimethyl 0–3‐methyl‐4‐nitrophenyl phosphorothioate) exposure. Subsequently, the fish were allowed recovery periods of 8, 12, 24, 48, 72, 96, 144 and 192 hr in clean water, and the same parameters were again evaluated. The results obtained during the exposure to the pesticide as well as during the recovery phase were used to calculate the caloric content in both tissues of A. anguilla. A reduction in energy reserves in the selected tissues was observed after exposure to both fenitrothion concentrations and the caloric content in those animals was lower than in the controls. Most of the metabolic disorders did not persist after allowing recovery in clean water during a week.

Treatment of Wastewater from Seed Disinfection in Raising Rice Seedlings.

水稲の育苗に先立って行う種子消毒の廃液が環境汚染の観点から問題となっている.そこで, 著者らは種子消毒を行ったフェニトロチオン(1000倍液)およびペフラゾエート・オキソリニック酸(200倍液)を含む廃液の希釈率を0, 2, 5, 10, 20倍(対照区は井戸水)として, 育苗箱床土に散布して処理する方法を検討した.出芽ユニットから出した際, 移植の際, およびポットならびに本田で栽培した際の生育と収量に関わる形質を比較したところ, 出芽には何ら影響は認められなかったが, 移植時までの生育において, 特に根の伸長抑制があり, 10倍以上の希釈が必要であった.実際の田植え機利用を考慮すると, 根のマットが十分に形成される20倍以上の希釈が好ましかった.また, 廃液による苗床時の悪影響は移植以降には解消した.さらに, 環境基本法での要監視項目にあるフェニトロチオンの濃度も基準値より十分に低くなることが推察された.

Fate of Fenitrothion in Eel Gills

Eels of species Anguilla anguilla were exposed to sublethal concentrations of fenitrothion in a flow-through test system. Bioaccumulation and elimination of the toxicant in the branchial tissue of the eels were studied. Steady-state was reached after 48 hr of exposure to 0.02 ppm of toxicant, and earlier (24 hr) exposed to 0.04 ppm. Steady-state was maintained until the end of the exposure in both experiments. The highest bioconcentration factor (BCF) value was calculated in animals exposed to 0.04ppm of toxicant, showing the relationship between the bioconcencentration into gills and the water disponibility. When the animals were transferred to clean water (depuration phase) they showed a rapid tendency to eliminate the pesticide. Pharmaco-kinetics parameters for fenitrothion in eel gills (K 1 , K 1 and T 1 /2) were calculated. They showed relatively low K 2 (0.0014 and 0.029 hr -1 ) and higher half-lives. Paralelly, total protein content in the gills was monitored during exposure and depuration phases. A depletion of total proteins of a 70% was observed in gill tissue at the end of the pesticide exposure. Although a tendency to recover protein levels was observed during the depuration phases, the depletion was maintained until the end of the experiments. The results showed a stress situation as a consequence of fenitrothion exposure which indicates the use of proteins as response to the increased energy requirements in this tissue.

Uptake and elimination kinetics of a pesticide in the liver of the European EEL

This study was undertaken to determine the bioconcentration‐elimination process of fenitrothion in the liver of the european eel (Anguilla anguilla). The animals were exposed to two sublethal fenitrothion concentrations corresponding to 1/5 and 1/10 of LC50 96‐h in a flow‐through test system. Uptake kinetics were determined from liver burdens measured at 2, 8, 24, 48, 56, 72 and 96 hours exposure. After pesticide exposure, animals were transferred to clean water for 72 hours. Fenitrothion elimination was determined after 12, 24, 48 and 72 hours of recovery period. The insecticide showed a high bioconcentration tendency. Steady‐state was reached after 48 hours exposure when the animals where exposed to the lowest concentration. This was followed with a rapid elimination process when the animals were transferred to clean water. Animals exposed to 0.04 ppm showed an early accumulation of the toxicant into the liver, and a steady‐state was reached after 8 hours. The elimination rate constant K2 of 0.0096 h‐1 and 0.06 h‐1 were estimated from the data. The biotransformation rate of fenitrothion in the European eel were low as indicated by a relatively short half‐life (11.55 h) of the insecticide. An increase in the Hepatosomatic Index was observed after 96 hours of exposure, but no significant differences were found between control and exposed animals.

Response and Recovery of Brain Acetylcholinesterase Activity in the European Eel,Anguilla anguilla,Exposed to Fenitrothion

European eel (Anguilla anguilla) were exposed to sublethal fenitrothion concentrations in a continuous flow-through system for 4 days. Brain acetylcholinesterase (AChE) activity was evaluated after 2, 8, 12, 24, 32, 48, 56, 72, and 96 h pesticide exposure. Results indicated that AChE activity in eel brains decreased as the concentration of fenitrothion increased. The pesticide induced significant inhibitory effects on the AChE activity ofA. anguilla,ranging from >40% inhibition at a sublethal concentration of 0.02 ppm to >60% inhibition at a sublethal concentration of 0.04 ppm. Eel were exposed to both fenitrothion concentrations for 96 h and then allowed a period of recovery in pesticide-free water. Samples were removed at 8, 12, 24, 48, 72, 96, 144, and 192 h and eel brain AChE activity was evaluated. Following 1 week of recovery, the AChE activity of those animals previously exposed to 0.02 and 0.04 ppm fenitrothion was still different from that of the controls. So, the AChE activity of eel brains at the end of the recovery phase remained significantly depressed.

Response and recovery of acethylcholinesterase activity in the european eel Anguilla anguilla exposed to fenitrothion.

European eel (Anguilla anguilla) were exposed to sublethal fenitrothion concentrations in a continuous flow‐through system for 4 days. Muscle acetylcholinesterase (AChE) activity was evaluated after 2, 8, 12, 24, 32, 48, 56, 72 and 96 hours pesticide exposure. Results showed that AChE activity in eel muscle tissue decreased as concentration of fenitrothion increased. Pesticide induced significant inhibitory effects on the AChE activity of A. anguilla ranging from >35% inhibition at sublethal concentration of 0.02 ppm to > 44% inhibition at sublethal concentration of 0.04 ppm. Eel were exposed to both fenitrothion concentrations for 96 hours and then allowed a period of recovery in pesticide‐free water. Samples were taken out at 8, 12, 24, 48, 72, 96, 144 and 192 hours and eel muscle AChE activity was evaluated. Following 1 week of recovery, the AChE activity for those animals previously exposed to 0.02 and 0.04 ppm fenitrothion was still different from the controls. So, the AChE activity of eel muscle at the end of the recovery phases remained significantly depressed.

Inhibition of Gill Na+,K+-ATPase Activity in the Eel,Anguilla anguilla,by Fenitrothion

European eels (Anguilla anguilla) were exposed to sublethal fenitrothion concentrations (0.02 and 0.04 mg/liter) in a continuous flow-through system for 4 days. Gill Mg2+- and Na+,K+-ATPase activities were evaluated after 2, 8, 12, 24, 32, 48, 56, 72, and 96 h of pesticide exposure. Results indicated that ATPase activity in gill tissue decreased as concentration of fenitrothion increased. Pesticide induced significant inhibitory effects on the Na+,K+-ATPase activity ofA. anguilla,ranging from >56% inhibition at a sublethal concentration of 0.02 ppm to >73% inhibition at a sublethal concentration of 0.04 ppm. Eels were exposed to both fenitrothion concentrations for 96 h and then allowed a period of recovery in pesticide-free water. Samples were removed at 8, 12, 24, 48, 72, 96, 144, and 192 h and eel gill ATPase activity was evaluated. Following 1 week of recovery, the Na+,K+-ATPase activity for those animals previously exposed to 0.04 ppm fenitrothion was still different from that of the controls.

Bioconcentration and excretion of fenitrothion in the brain of the eel (Anguilla anguilla)

The bioconcentration of fenitrothion in the brain of the european eel (Anguilla anguilla) and its posterior elimination have been studied. Animals were exposed to a sublethal concentration of fenitrothion (0.04 mg/L) for 96 hours in a flow‐through test system. After this pesticide exposure, animals were transferred to clean water for 72 hours more. Bioconcentration and elimination processes of fenitrothion were studied in blood and brain. This insecticide showed a strong tendency to bioconcentrate into selected tissues. A steady‐state was observed in blood in few hours. Highest accumulation was detected in brain, where any steady‐state could be observed. Elimination started rapidly from both tissues when a recovery period was allowed. Elimination kinetics were adjusted to one‐compartment model. K2 of 0.015 and 0.044 hr‐1 were calculated for fenitrothion in blood and brain. These K2 values were related with a relatively short half‐live of fenitrothion in the analyzed tissues; probably due to the low biotransformation‐rate of this toxicant in the european eel. That fact would protect the animals against many biotransformation products even more toxics than the parent fenitrothion.

Effect of an organophosphorus insecticide, fenitrothion, on survival and osmoregulation of various developmental stages of the shrimp Penaeus japonicus (Crustacea: Decapoda)

The toxicity of fenitrothion was determined in larvae (nauplii, Zoeae 1 to 3, Mysis 1 to 3), postlarvae (PL stages) and juvenile shrimp (Penaeus japonicus Bate), in two media, seawater (SW) and diluted seawater (DSW) (1100 and 550 mosM kg−1, ≃ 37 and 19‰ S). The effects of fenitrothion on the osmoregulatory capacities (OC) of juveniles were recorded. A gill and epipodite histopathological study was also conducted. For larvae in seawater, 24 and 48 h LC50s ranged from 32.9 μg l−1 (Zoeae 2) to 10.7 μg l−1 (Mysis 3), and from 3.9 μg l−1 (Zoeae 3) to 2.0 μg l−1 (Mysis 3), respectively; 48 and 96 h LC50s in postlarvae (PL) at the same salinity ranged from 1.8 μg l−1 (PL1) to 0.6 μg l−1 (PL5), and from 0.3 μg l−1 (PL7) to 0.4 μg l−1 (PL15). In juveniles, 96 h LC50s were 0.8 μg l−1 in seawater and 1.5 μg l−1 in diluted seawater. From hatching to juvenile stages, the overall trend was a rapid decrease (from nauplii to PL5–PL7) followed by a slight increase (from PL7 to PL15 and juveniles) in the shrimp's ability to tolerate the insecticide. In juveniles kept in seawater and in diluted seawater, fenitrothion decreased the osmoregulatory capacity (OC = difference between the hemolymph osmotic pressure and the osmotic pressure of the medium) at both lethal and sublethal concentrations. This effect was time- and dose-dependent. In SW, the decrease in hypo-OC was ˜ 25% at sublethal concentrations and ˜ 35% at the 96 h LC50. In DSW, the decrease in hyper-OC was ˜ 10 to 15% at sublethal concentrations. In SW, shrimp were able to recover their OC in less than 48 h when transferred to water free of pesticide. In DSW, recovery at 48 h was only possible after exposure to the lowest tested sublethal concentration. Haemocytic congestions (thrombosis) of the gills, lamellae necrosis and other alterations of gills and epipodites (breakage of the cuticle, reduction of the hemolymph lacunae) were noted in juveniles exposed to lethal and sublethal concentrations of fenitrothion.

Pesticide Residue Flux from Rainwater into Lake Nakanuma in the Rainy Season.

Pesticide residues in rainwater were investigated for the estimation of pesticide flux into a lake in Ibaraki Prefecture during the 1990 rainy season. The maximum concentration of oxiadiazon in the rainwater was 4.2μg l-1. The maximum concentrations of fenobucarb, fenitrothion and edifenphos in the rainwater were 0.58, 0.53 and 0.36μg l-1, respectively. The annual ratio of fenitrothion redeposition by rainfall was estimated at 1.5% of the total shipping amount in Ibaraki Prefecture. There was no significant difference between redepositions of pesticides by rainfall and shipping amounts in the prefecture (α= 0.05). Pesticide residues in lake water were investigated in Lake Nakanuma, Ibaraki Prefecture, from March to December 1990. The concentrations of molinate, simetryn, iprobenfos, and thiobencarb in irrigation canal water were in the high range (>1.2μg l-1). The concentrations of diazinon, malathion, and fenthion in the water were at a lower level (<0.2μg l-1). The maximum concentration of simetryn in the lake was 0.91μg l-1. Except for chlornitrofen, the maximum concentration of pesticide in the lake (<1.0μg l-1) was about one-tenths in that of irrigation canals. The amount of pesticide from rainfall was a major factor from the viewpoint of estimating the environmental viability of the lake.

Chronic Toxicity of Fenitrothion to an Algae (Nannochloris oculata), a Rotifer (Brachionus calyciflorus), and the Cladoceran (Daphnia magna)

Chronic toxicity studies were conducted with an algae (Nannochloris oculata), a rotifer (Brachionus calyciflorus), and a cladoceran (Daphnia magna) to determine their relative sensitivities to the organophosphorus insecticide fenitrothion. The cladoceranD. magnawas the most sensitive of the three species. The no observed effect concentrations (NOECs) for the study with the algae (1.0 mg/liter) and for the rotifer (1.0 mg/liter) were higher than the NOEC (0.009 μg/liter) and the LC50of 24 hr (0.067 μg/liter) forD. magna. Most of the algal populations were not initially affected by exposure to fenitrothion. Pesticide concentrations higher than 1.0 mg/liter significantly reduced algal densities after 72 hr exposure. The effects of chronic exposure of the rotiferB. calyciflorusto fenitrothion were evaluated using some demographic parameters: intrinsic rate of natural increase (r), generation time, net reproductive rate, and life expectancy. All the parameters studied decreased with increasing toxicant concentrations. The parameters used to determine the effect of the pesticide onD. magnareproduction were mean total young per female, mean brood size, mean time to first reproduction, andr. Therand the rest of the studied parameters were affected at 0.011-μg/liter and higher fenitrothion concentrations. Growth, as measured by body length, was only depressed significantly at 0.011 μg/liter pesticide.

Measurement of cholinesterase activity inhibition for the detection of organophosphorus and carbamate pesticides in water

We measured the cholinesterase activity inhibition to determine concentrations of asulam and fenitrothion in soil, surface runoff and subsurface drainage, following simulated rainfall applied 1, 7 and 19 days after application of the pesticides to sloping pasture plots with downslope buffer strips. In the soil and surface runoff, both asulam and fenitrothion levels dropped below detection limits by day 19; in subsurface drainage, neither pesticide was detected at any stage. Whilst the reductions in pesticide concentrations in surface runoff with respect to applied concentrations were considerable, we cannot be certain that this was due to the action of the buffer strips.

HPLC Quantitation Of Fenitrothion and 3-Methyl-4-Nitrophenol in Biological Fluids After Prepacked Cartridge Extraction and Its Application to a Poisoning Case

Abstract We describe here the simultaneous determination of fenitrothion and its metabolite, 3-methyl-4-nitrophenol (MNP), in biological fluids by HPLC after SepPakC18 cartridge extraction and its application to a human poisoning case. One ml of serum or urine mixed with an equal volume of 0.1 N HCl was applied to the SepPakC18 cartridge, which was preactivated using methanol (5 ml), hexane/isopropanol (9/1 v/v, 10 ml), methanol (5 ml) and distilled water (5 ml). After washing by 0.1N HCl(5 ml), the eluate with 5 ml of hexane/isopropanol (9/1 v/v) was concentrated, and the residue was dissolved in 100 μl of methanol containing methaqualone (internal standard, 30 μg/ml). A 20 μ of the aliquot was injected into the HPLC. Recovery yields of fenitrothion and MNP from serum and urine ranged from 78.5–93.3%. Linear calibration curves for fenitrothion and MNP were in the range 0.1 – 10 μg/ml. In a human poisoning case at 18.5 hrs after ingestion of Sumithion, concentrations of fenitrothion and MNP in serum were 11.8 and 3.9 μg/ml and those in urine were less than 0.01 μg/ml and 2.8 μg/ml, respectively.

Predicting algal sensitivity to a pesticide stress

AbstractTwelve freshwater phytoplankton species were used to investigate the factors affecting the toxicity of the organo‐phosphorus insecticide fenitrothion (O,O‐dimethyl‐O‐nitro‐m‐tolyl phosphorothioate) to algae. The unicellular chlorophytesAnkistrodesmus falcatus, Chlamydomonas segnis, Chlamydomonas reinhardtii, Chlorella pyrenoidosa, Chlorella vulgaris, Cosmariumsp.,Pediastrumsp.,Scenedesmus obliquus, Selenastrum capricornutum, and Staurastrumsp.; the bacillariophyteNaviculasp.; and the cyanophyteAnabaenasp. were exposed to three concentrations (0.1, 1.0, and 10.0 mg/L) of fenitrothion. Differential growth effects were observed among the species exposed to fenitrothion over short (96 h) and long‐term (14 d) durations. Fenitrothion concentrations eliciting a 50% growth reduction over 96 h (EC50) ranged from 0.8 to 24.4 mg/L. Selected properties of the test algae (cell size, lipid content, and bioconcentration capacity) were measured and examined for their relationship to fenitrothion sensitivity. Strong correlations were obtained between fenitrothion sensitivity and cell surface area/volume (S/V) ratios, cell lipid content, and fenitrothion bioconcentration capacity of the cells, suggesting that these attributes may be useful predictors of differential sensitivity to lipophilic xenobiotics in unicellular phytoplankton. A positive relationship observed between cell S/V ratio and the bioconcentration of fenitrothion further implicates algal cell size as a significant factor in alga/pesticide interaction and subsequent vulnerability to lipophilic xenobiotics.

Rapid Degradation of Fenitrothion in Estuarine Waters

The degradation of fenitrothion under real environmental conditions was studied. Fenitrothion was applied in the irrigation ditches of the Ebre Delta (Tarragona, Catalonia) at an estimated concentration of 200 (situation 1) and 20 μg/L (situation 2) in order to eliminate the american crab (Procamburus clarkii). The evolution of the levels of fenitrothion and the formation of transformation products (TPs) were recorded during the 4 days after application. The TPs formed were 3-methyl-4-nitrophenol, fenitrooxon, and 5-methyl isomer of fenitrothion. The concentration of fenitrothion decayed sharply in 2 h with 6% and 0.3% of the initial concentrations in situations 1 and 2, respectively, and reached a steady state within 10 h with a concentration of 4 and 0.01 μg/L, respectively, which was constant for the 4 days the experiment lasted