Separation, bioactivity, and dissipation of enantiomers of the organophosphorus insecticide fenamiphos

Most chiral pesticides are used as racemates despite the fact that the pesticidal activity of the given pesticide is usually the result of the preferential reactivity of only one enantiomer while the other enantiomers may have toxic effects against other nontarget organisms. Accordingly, the enantiomer of fenamiphos, an organophosphorus pesticide, was separated by high-performance liquid chromatography with reverse phase and normal phase on a Pirkle model chiral stationary phase column. It was found that n-hexane/isopropanol (95/5) was the best solvent system for enantiomer resolution of fenamiphos. Chromatographic data including capacity factor (k'), separation factor (alpha), and resolution (Rs) are presented. Inhibitory activity to enzyme butyrylcholinesterase and toxicity to Daphnia of enantiomers and racemic insecticide fenamiphos were also studied. In the toxicity tests of Daphnia, the lethal concentration (LC50) of (+)-fenamiphos, (-)-fenamiphos, and racemate were 0.0016, 0.0061, and 0.0019 microg/mL, respectively. No significant difference of LC50 values between (+)-fenamiphos and racemate were found, but (-)-fenamiphos showed significantly lower toxicity to Daphnia. The inhibitory concentration (IC50) to the cholinesterase were 0.008, 0.15, and 0.46 microg/mL for (+)-fenamiphos, (-)-fenamiphos, and racemate, respectively. Both enantiomers and the racemate showed significant difference in inhibiting the cholinesterase. However, (+)-fenamiphos proved to be about 20 times more toxic to Daphnia and only about four times more inhibitory activity to butyrylcholinesterase than (-)-fenamiphos. The dissipation of (+)-fenamiphos, (-)-fenamiphos, and racemate in selected soils and natural water samples were also studied. The half-life (t(1/2)) of (+)-, (-)-, and racemate in soils showed no related to the soil texture, pH, or organic carbon content. By comparing the residues of (+)-, (-)-, and racemate in the water, it was found that (+)-fenamiphos was degraded faster than the others after 21 days. Briefly, (+)-fenamiphos is more toxic than (-)-fenamiphos to a nontarget organism (Daphnia), but the environmental persistence of the two compounds showed no significant difference.     

Assessing intermittent pesticide exposure from flea control collars containing the organophosphorus insecticide tetrachlorvinphos

Fleas are a persistent problem for pets that require implementation of control measures. Consequently, pesticide use by homeowners for flea control is common and may increase pesticide exposure for adults and children. Fifty-five pet dogs (23 in study 1; 22 in study 2) of different breeds and weights were treated with over-the-counter flea collars containing tetrachlorvinphos (TCVP). During study 1, fur of treated dogs was monitored for transferable TCVP residues using cotton gloves to pet the dogs during 5-min rubbings post-collar application. Plasma cholinesterase (ChE) activity was also measured in treated dogs. Average amounts of TCVP transferred from the fur of the neck (rubbing over the collar) and from the back to gloves at 3 days post-collar application were 23,700+/-2100 and 260+/-50 microg/glove, respectively. No inhibition of plasma ChE was observed. During study 2, transferable TCVP residues to cotton gloves were monitored during 5-min rubbings post-collar application. Transferable residues were also monitored on cotton tee shirts worn by children and in the first morning urine samples obtained from adults and children. Average amounts of TCVP transferred to gloves at 5 days post-collar application from the neck (over the collar) and from the back were 22,400+/-2900 and 80+/-20 microg/glove, respectively. Tee shirts worn by children on days 7-11 contained 1.8+/-0.8 microg TCVP/g shirt. No significant differences were observed between adults and children in urinary 2,4,5-trichloromandelic acid (TCMA) levels; however, all TCMA residues (adults and children) were significantly greater than pretreatment concentrations (alpha=0.05). The lack of ChE inhibition in dogs and the low acute toxicity level of TCVP (rat oral LD(50) of 4-5 g/kg) strongly suggest that TCVP is rapidly detoxified and excreted and therefore poses a very low toxicological risk, despite these high residues.     

Genetic and cytogenetic effects induced in the mouse by an organophosphorus insecticide: Malathion

Male mice (Q strain) received an ip injection of malathion (300 mg/kg). The percentage of chromosome aberrations was not increased in both bone marrow cells and spermatogonia. In a dominant lethal mutation assay, the frequency of pre- and postimplantation fetal lethality was not significantly enhanced over the control level.     

接触对硫磷农药工人监测指标研究

目的 探讨接触有机磷农药（OP）对硫磷工人的监测指标。方法 对某农药厂包装车间进行现场调查,并对56名长期对硫磷接触工人（接触组）和120名无对硫磷接触工人（对照组）进行体格检查及血胆碱酯酶（ChE）、血清对氧磷酶（PON）、β-葡萄糖苷酸酶（-βGD）和羧酸酯酶（CaE）活力测定。结果 （1）对照组红细胞AChE、血清PON、CaE和BChE活力呈正态分布,不同年龄、性别4种酯酶活力差异无统计学意义（P〉0.05）。（2）接触组红细胞AChE、血清PON、CaE和BChE活力明显低于对照组,差异有统计学意义（P〈0.001）;血清-βGD活力两组之间的差异无统计学意义（P〉0.05）。（3）接触组工人红细胞AChE活力低于参考值下限的异常率,为5.4%,而血清CaE、BChE活力异常率分别为37.5%和48.2%,明显高于红细胞AChE活力异常率,差异有统计学意义（P〈0.001）。血清PON活力异常率为5.4%,与红细胞AChE活力异常率之间差异无统计学意义（P〉0.05）。结论 长期职业接触OP工人红细胞AChE、血清BChE、CaE、PON 4种酯酶活力均受到抑制,血清CaE可作为反映OP接触的一个新的生物标志物。     

Separation and toxicity of enantiomers of organophosphorus insecticide leptophos

Enantiomers of leptophos were separated by high-performance liquid chromatography with a Whelk-O1 column using 3% dichloromethane in n-hexane as mobile phase. Toxicity tests of leptophos enantiomers and racemate were performed with daphnia. Enzyme inhibition of leptohpos was carried out by using butyryl cholinesterase from horse serum and acetylcholinesterase from housefly heads. From the inhibition test of butyrylcholinesterase, the half-inhibitory concentrations, IC(50), of (+)-leptophos, (-)-leptophos, and (+/-)-leptophos were 0.241, 1.17, and 1.05 gmL(-1), respectively. No significant difference in IC(50) in (-)-leptophos and (+/-)- leptophos was found. However, the IC(50) of (+)-leptophos was significantly different from those of the others. In the inhibition test of acetylcholinesterase, the IC(50) values of (+)-leptophos, (-)-leptophos, and (+/-)-leptophos were 14.01, 24.32, and 13.22 gmL(-1), respectively. There was no significant difference in IC(50) in (+)-leptophos and (+/-)-leptophos, although the IC(50) of (-)-leptophos was significantly different from those of the others. From these results, leptophos-both enantiomers and racemate-seems to have higher neurotoxicity for mammals than for the target insects. In the toxicity test of daphnia, the half-lethal concentrations, LC(50), of (+)-leptophos, (-)-leptophos, and (+/-)-leptophos were 0.0387, 0.802, and 0.0409 gL(-1), respectively. There is no significant difference in LC(50) in (+)-leptophos and (+/-)-leptophos. The LC(50) of (-)-leptophos is significantly higher than those of the others. From these results, (-)-leptophos has lower toxicity to daphnia.     

Cleanup procedure for water,soil, animal and plant extracts for the use of electron-capture detector in the gas chromatographic analysis of organophosphorus insecticide residues

Summary A simple, aqueous acetonitrile partition cleanup method for analyses of some common organophosphorus insecticide residues is described. The procedure described is for cleanup and quantitative recovery of parathion, methyl parathion, diazinon, malathion and thimet from different extracts. Those insecticides in the purified extracts of ground water, grain, soil, plant and animal tissues can be detected quantitatively by gas chromatography with an electron capture-detector at 0.01 ppm. Cleanup is satisfactory for paper and thin-layer chromatography for further identification of individual insecticides in the extracts.Contribution No. 949, Department of Entomology, Kansas Agricultural Experiment Station, Manhattan, Kansas, U. S. A. and Contribution No. 16, Kansas Water Resources Institute, Manhattan, Kansas. This project was partially supported by the U. S. Department of the Interior, Office of Water Resources Research pursuant to the Water Resources Act of 1964 as amended; Project No. B-007-KAN, Agreement No. 14-01-0001-1019; and by cooperative agreement No. 12-14-100-9706(51), with the Market Quality Research Division, Agricultural Research Service, Kansas project 5912. The assistance of Mr. Ted Macy, and Mr. Scott Robinson is greatly appreciated.     

Alkylation of urinary guanine in mice by the organophosphorus insecticide tetrachlorvinphos

The methylating capability of tetrachlorvinphos on urinary guanine in mice has been investigated using an insecticide labeled at both O-CH3 groups. Following intraperitoneal administration of the 14C-labeled insecticide to mice, about 0.57% of the radioactivity in the O- to 24-hr samples was associated with the purine fraction. The amount of [7-14C]methylguanine in 0- to 48-hr urine samples, estimated as fraction of applied dose, was 26-31 X 10(-5). The results obtained indicate possible chemical alkylation of urinary guanine. On the other hand, a considerable portion of radioactivity is probably incorporated via the C-1 pool.     

Acute impact of an organophosphorus insecticide on microbes and small invertebrates of a mangrove estuary

The effects of 24 to 72-hr exposure to fenthion (10¹–10³ ppb) were determined for a fungal community, nitrogen-fixing microbes, and representative meiofaunal and zooplankton invertebrates of a mangrove ecosystem. Also tested were the abilities of a benthic diatom and of fungi to grow in the presence of fenthion. Acute lethal, growth-inhibiting, or processdisrupting effects were not detected for exposures to less than 500 ppb fenthion. Results are compared with the findings of several other investigations of the impact of fenthion and other organophosphorus insecticides on non-target organisms.Contribution of the Rosenstiel School of Marine and Atmospheric Science, University of Miami, and the University of Georgia Marine Institute (No. 418).     

Observations on human exposure to the organophosphorus insecticide fenthion in Nigeria

The search for substitutes for chlorinated hydrocarbon insecticides has led to the trial of organophosphorus compounds. Fenthion is promising as a residual spray in malaria eradication, but information on its human toxicology is scanty. In the work reported in this paper the inhabitants of a Nigerian village have been studied during a trial of fenthion. Moderate depressions of plasma cholinesterase were observed for five weeks after spraying, though there was no effect on red blood cell cholinesterase. A search was also made for other possible effects, including measurements of peak expiratory flow rate. No serious toxic effects were found.     

Acetylcholinesterase inhibition in estuarine fish and invertebrates as an indicator of organophosphorus insecticide exposure and effects

The majority of insecticides currently in use are organophosphorus, carbamate, and synthetic pyrethroid compounds. Organophosphorus insecticides (OPs) produce toxicity by inhibiting the cholinesterase enzymes in the nervous system. Monitoring of acetylcholinesterase (AChE) inhibition has been widely used in terrestrial and freshwater aquatic systems as an indicator of OP exposure and effects. This review describes the use of AChE inhibition as a biomarker in the estuarine environment, discusses the relationship between AChE inhibition and other manifestations of OP toxicity, and highlights areas where additional research is needed. A variety of studies with estuarine fish have suggested that brain AChE inhibition levels of > 70% are associated with mortality in most species. Selected species, however, appear capable of tolerating much higher levels (> 90%) of brain inhibition. Sublethal effects on stamina have been reported for some estuarine fish in association with brain AChE inhibition levels as low as 50%. Most studies suggest, however, that these effects are observed only when brain AChE inhibition is at near-lethal levels. A number of field studies have successfully used AChE inhibition in fish as a biomarker in the estuarine environment. The use of AChE inhibition as a biomarker in estuarine invertebrates has been less well studied. Although AChE inhibition has been measured in the tissues of a variety of invertebrate species following OP exposure, the relationship between AChE inhibition and lethality is less distinct. Additional work is needed in both fish and invertebrates to better explain species-specific differences in the relationship between AChE inhibition and mortality and to investigate other physiological perturbations associated with AChE inhibition.     

Bioconcentration kinetics of the organophosphorus insecticide chlorpyrifos in guppies (Poecilia reticulata).

The bioconcentration kinetics of chlorpyrifos (O,O-diethyl O-3,5,6-trichloro-2-pyridyl phosphorothioate) in guppies (Poecilia reticulata) were investigated. A static exposure was used to study the uptake of the compound. The amount absorbed was calculated from the difference in disappearance rates from the water phase in aquaria with and without fish. The uptake rate was found to be first-order with respect to the exposure concentration, and amounts to ca. 38 ml g-1 (fish) hr-1. The elimination rate was studied in separate experiments. Guppies were first given the opportunity to accumulate chlorpyrifos and, following transfer to clean water, the clearance of the compound was measured by determining the residual chlorpyrifos in the fish. It was found that the elimination rate was first-order with respect to the concentration in fish, but depended slightly on the length of the preexposure period. The half-life of tissue chlorpyrifos varied from 31 to 38 hr. Release of unchanged chlorpyrifos turned out to be negligible relative to the amount eliminated. This indicates that metabolic breakdown is the only pathway for elimination. From the kinetic rate parameters, a bioconcentration factor was calculated of about 1700. This value is very similar to that measured directly after an 8-day semistatic exposure. A two-compartment model is proposed to describe the kinetics of the bioconcentration process. The conditions limiting the applicability of the indirect method for measuring the toxicokinetics of chlorpyrifos are discussed.     

Enantioselective acetylcholinesterase inhibition of the organophosphorous insecticides profenofos, fonofos, and crotoxyphos

A large number of organophosphorous insecticides (OPs) are chiral compounds, and yet enantioselectivity in their environmental fate and effects is rarely addressed. In the present study, we isolated individual enantiomers of three OPs, profenofos, fonofos, and crotoxyphos, and evaluated enantioselectivity in their inhibition of acetylcholinesterase (AChE). Acetylcholinesterase inhibition by the enantiomers and racemates was determined in vivo in the aquatic invertebrate Daphnia magna and in Japanese medaka (Oryzias latipes) as well as in vitro with electric eel (Electrophorus electricus) and human recombinant AChEs. The overall results showed variable sensitivity between AChE enzymes from different species as well as variable magnitude of enantioselectivity in enzyme inhibition. The (-)-enantiomer of profenofos was 4.3- to 8.5-fold more inhibitory to AChE in vivo, whereas (-)-fonofos was 2.3- to 29-fold more potent than the corresponding (+)-enantiomer. The (+)-enantiomer of crotoxyphos was 1.1- to 11-fold more inhibitory to AChE than the (-)-enantiomer. In contrast, the in vitro results showed (+)-profenofos to be 2.6- to 71.8-fold more inhibitory than the (-)-enantiomer and (-)-crotoxyphos to be 1.6- to 1.9-fold more active than the (+)-enantiomer. The reversed direction of enantioselectivity observed between the in vivo and in vitro assays suggests enantioselectivity within toxicodynamic processes such as uptake, biotransformation, or elimination. Findings from the present study provide evidence of enantioselectivity in the AChE inhibition of chiral OPs in nontarget organisms and indicate the need to consider enantiomers individually when assessing environmental risk of these chiral pesticides.     

2种有机磷类杀蚊幼剂现场灭蚊幼实验研究

目的了解甲基嘧啶磷、毒死蜱在灭蚊幼中的效果及持效期,为今后防治蚊幼提供依据。方法选择试验现场后测量水体体积,分别施药,并在施药前后用勺捕法进行密度测定,评价效果。结果分别施于污水沟、苇塘剂量为0.2、0.4 g/m3的甲基嘧啶磷对蚊幼杀灭率达75%,可分别维持13、28 d;施于苇塘剂量分别为0.5、1 g/m3的毒死蜱对蚊幼杀灭率达100%,可分别维持66、69 d;使用后者剂量施于污水坑,在投药后1~68 d、70 d其杀灭率分别为95.34%~100%、79.91%。结论实验初步验证毒死蜱对蚊幼杀灭效果及持效期优于甲基嘧啶磷。两者均为优良的杀幼剂。在实际现场灭蚊幼中可根据环境、特点、水体污染状况等选择适宜的杀虫药剂和使用剂量。     

Inter and intraindividual variations in plasma cholinesterase activity and substance concentration in employees of an organophosphorus insecticide factory

During a period of 10 months, inter and intraindividual variations in plasma cholinesterase (ChE) activity were studied in 331 employees of an organophosphorus insecticide factory, and in 193 healthy volunteers without occupational exposure to known ChE inhibitors. Repeated (n = 6) measurements of ChE activity and ChE substance concentration were performed in 410 subjects. The study showed substantial intraindividual variations of ChE activity and ChE substance concentration (up to 40%) in the employees and in the reference group. When effects due to sex, ChE-1 phenotype, body weight, and height were considered, one subgroup of employees of the organophosphorus insecticide factory showed a significantly lower average ChE activity than other subgroups; as ChE substance concentrations were found to be proportionally decreased, it was concluded that the low ChE activity was unrelated to occupational exposure. A combined determination of ChE activity and ChE substance concentration is recommended as a rational diagnostic tool when an unexpected decrease of plasma ChE activity is registered in people joining organophosphorus insecticide health surveillance programmes.