Effects of the pyriproxyfen and fenthion on the gonadal morphology of Nile tilapia (Oreochromis niloticus: Perciformes, Cichlidae)

Commercially available insecticides present acute toxicity to the health of fish and other aquatic organisms, which may impair the local aquaculture. This study evaluated the gonadal morphology of freshwater fish exposed to pyriproxyfen and fenthion. Forty-five juvenile male Nile tilapias (Oreochromis niloticus) were divided into control, pyriproxyfen-exposed (0.01 g/L), and fenthion-exposed (0.001 g/L) groups. They were evaluated in three moments (30, 60, and 90 days). The variables analyzed were the gonadosomatic index (GSI), weight to length ratio, seminiferous tubules morphometry (diameter and height), tissue damage, and immunohistochemical analysis for caspase-3, tumor necrosis factor alpha (TNF-α), and vascular endothelial growth factor (VEGF). Pyriproxyfen and fenthion injured the seminiferous tubule tissue, and the damage progressed according to the exposure time. In addition, the GSI gradually reduced over time in all groups compared with the first moment (30 days), while caspase-3, TNF-α, and VEGF values increased only in the fenthion-exposed group. Therefore, pyriproxyfen and fenthion changed the gonadal morphology of male Oreochromis niloticus, which may affect their reproduction in the wild or captivity.

The cytotoxicity and genotoxicity of single and combined fenthion and terbufos treatments in human liver cells and zebrafish embryos

The mechanism of genotoxicity of the individual and combined pesticides of terbufos and fenthion were evaluated using HepG2 cells and zebrafish embryos. We determined genotoxicity by neutral comet assay and phosphorylation of H₂AX (γH₂AX), which indicated that cells treated with terbufos and/or fenthion caused DNA double-strand breaks (DSBs). The combination of these pesticides at the equimolar concentration (40 μM) exhibited less toxicity, genotoxicity, and did not impact DNA homologous recombination (HR) repair activity compare to terbufos or fenthion alone treatment. In HepG2 cells, terbufos, fenthion and their combination decreased only Xrcc2 expression (one of DNA HR repair genes). Moreover, the combined pesticides decreased Xrcc6 expression (one of DNA non-homologous end joining (NHEJ) repair genes). In addition, only terbufos or fenthion decreased XRCC2 protein expression, while Ku70 was impacted in all of the treated cells irrespective of up or down regulation. In zebrafish embryos, only fenthion impaired HR genes (Rad51 and Rad18) expression at 24 h. After 48 h exposure to pesticides, the combined pesticides elevated HR genes (Rad51 and Xrcc2) expression while terbufos or fenthion inhibited the expression of these four genes (Rad51, Rad18, Xrcc2, Xrcc6). In addition, the hatching rate of zebrafish embryos with fenthion or the combined pesticide at 72 hpf was significantly impaired. Collectively, terbufos and/or fenthion in combining caused DSBs in HepG2 cells and zebrafish embryos. Moreover, the specific mechanism of combined pesticide both HepG2 and zebrafish embryos revealed antagonism interaction.

Evaluation of an acute oral gavage method for assessment of pesticide toxicity in terrestrial amphibians

Development of an acute oral toxicity test with a terrestrial-phase amphibian was considered necessary to remove the uncertainty within the field of agrochemical risk assessments. The bullfrog (Lithobates catesbeianus) was selected for use as it is a representative of the family Ranidae and historically this species has been used as an amphibian test model species. Prior to definitive study, oral gavage methods were developed with fenthion and tetraethyl pyrophosphate. Dimethoate and malathion were subsequently tested with both male and female juvenile bullfrogs in comprehensive acute oral median lethal dose (LD50) studies. Juvenile bullfrogs were administered a single dose of the test article via oral gavage of a single gelatin capsule of dimethoate technical (dimethoate) or neat liquid Fyfanon^® Technical (synonym malathion), returned to their respective aquaria, and monitored for survival for 14 d. The primary endpoint was mortality, whereas behavioral responses, food consumption, body weight, and snout-vent length (SVL) were used to evaluate indications of sublethal toxicity (secondary endpoints). Acute oral LD50 values (95% fiducial interval) for dimethoate were 1459 (1176-1810, males) and 1528 (1275-1831, females), and for malathion they were 1829 (1480-2259, males) and 1672 (1280-2183, females) mg active substance/kg body weight, respectively. Based on the results of these studies, the methodology for the acute oral gavage administration of test items to terrestrial-phase amphibians was demonstrated as being a practical method of providing data for risk assessments. Environ Toxicol Chem 2018;37:436-450. © 2017 SETAC.

Subchronic Exposure to Fenthion Induces Hematological Changes in Liver Tissue of African Catfish Clarias gariepinus

In this study, African Catfish (also known as Sharptooth Catfish) Clarias gariepinus were exposed to sublethal concentrations of fenthion of 2.0, 4.0, and 8.0 mg/L for 21 d and allowed to recover for 7 d to investigate the potential for hematological changes. Whole blood was sampled on days 1, 7, 14, and 21 postexposure and after a 7-d recovery period. During exposure, fenthion caused a reduction in red blood cell counts, hemoglobin concentration, and packed cell volume. There was an increase in white blood cell counts but no significant difference in mean corpuscular hemoglobin concentration, mean corpuscular volume, and mean corpuscular hemoglobin. Both increases and decreases were observed in white blood cell differentials. After the 7-d recovery period, both increases and decreases were observed in the hematological parameters. These results reveal that sublethal concentrations of fenthion can cause hematological alterations in African Catfish and that the substance should be used with caution. Received October 20, 2015; accepted May 4, 2016.

Fenthion, an organophosphorus pesticide, induces alterations in oxidant/antioxidant status and histopathological disorders in cerebrum and cerebellum of suckling rats

Fenthion (FEN) is an organophosphorus pesticide known for its wide toxic manifestations. In this study, the effects of FEN were evaluated on the cerebrum and cerebellum oxidant/antioxidant status and histopathological disorders in the suckling rats. Pregnant rats were divided into two groups: control group received pure water, while FEN group received daily by their drinking water 551 ppm of FEN from the 14th day of pregnancy until day 14 after delivery. Acetylcholine esterase (AChE) activity was inhibited in both the cerebrum and cerebellum of suckling rats whose mothers were treated with FEN. The cerebrum and cerebellum oxidative damage was demonstrated by a significant increase of malondialdehyde (MDA), advanced oxidation protein product and glutathione (GSH) levels and disturbance in the antioxidant enzyme activities. A significant decline of non-protein thiol and vitamin C levels was also observed. These changes were confirmed by histopathological observations which were marked by pyknotic neurons in the cerebrum and apoptotic cells in the cerebellum of FEN-treated rats. In the cerebellum of FEN-treated rats, the most conspicuous damage was the absence of external granular layer, indicating growth retardation. These data suggested that exposure of pregnant and lactating rats to FEN induced oxidative stress and histopathological disorders in the cerebrum and cerebellum of their pups. Thus, the use of FEN must be under strict control, especially for pregnant and lactating mothers.

Effects of the organophosphate fenthion for control of the red-billed quelea Quelea quelea on cholinesterase and haemoglobin concentrations in the blood of target and non-target birds

The red-billed quelea bird Quelea quelea is one of sub-Saharan Africa's most damaging pests, attacking small-grain crops throughout semi-arid zones. It is routinely controlled by spraying its breeding colonies and roosts with organophosphate pesticides, actions often associated with detrimental effects on non-target organisms. Attributions of mortality and morbidity of non-targets to the sprays are difficult to confirm unequivocally but can be achieved by assessing depressions in cholinesterase activities since these are reduced by exposure to organophosphates. Here we report on surveys of birds caught before and after sprays that were examined for their blood cholinesterase activities to assess the extent to which these became depressed. Blood samples from birds were taken before and after sprays with fenthion against red-billed quelea in colonies or roosts, and at other unsprayed sites, in Botswana and Tanzania and analysed for levels of haemoglobin (Hb) and activities of whole blood acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Background activities of AChE, BChE and Hb concentrations varied with bird species, subspecies, mass, age and gender. Contrary to expectation, since avian erythrocytes are often reported to lack cholinesterases, acetylcholinesterase activities in pre-spray samples of adult birds were positively correlated with Hb concentrations. When these factors were taken into account there were highly significant declines (P < 0.0001) in AChE and BChE and increases in Hb after contact with fenthion in both target and non-target birds. BChE generally declined further (up to 87 % depression) from baseline levels than AChE (up to 83 % depression) but did so at a slower rate in a sample of quelea nestlings. Baseline activities of AChE and BChE and levels of Hb were higher in the East African subspecies of the red-billed quelea Q. q. aethiopica than in the southern African subspecies Q. q. lathamii, with the exception of BChE activities for adult males which were equivalent.

Fenthion and terbufos induce DNA damage, the expression of tumor-related genes, and apoptosis in HEPG2 cells

This study investigates the effects of fenthion and terbufos, two organophosphorous pesticides, on DNA damage, tumor-related gene expression, and apoptosis in HepG2 cells. We found that exposure to concentrations ranging from 50 to 200 μM of fenthion and terbufos for 2 hr caused significant death in HepG2 cells. Both compounds induced DNA damage in a concentration-dependent manner as measured using the alkaline comet assay. Tumor-related genes (jun, myc, and fos) and apoptosis-related genes (socs3, tnfaip3, ppp1r15a, and nr4a1) were up-regulated by both compounds. Finally, both compounds induced apoptosis. The results demonstrate that both terbufos and fenthion induce DNA damage and should be considered potentially hazardous to humans.

Tissue-specific in vivo inhibition of cholinesterases by the organophosphate fenthion in Oreochromis niloticus

This study was designed to elucidate the effect of the organophosphate fenthion exposure on cholinesterase-specific activities in brain, liver, and kidney tissues of juvenile Oreochromis niloticus, and to define the best indicator tissue to fenthion exposure. The 96-h LC(50) value was determined as 2.27 mg/L and fish were exposed to 20% of this concentration for 24-, 48-, and 96-h. Recovery periods in similar durations were provided to evaluate the ChE activities. AChE and BChE activities were determined spectrophotometrically. The activities of these enzymes were significantly inhibited in all the tissues tested, liver was the most and kidney was the least affected tissues. The inhibition percentages of AChE and BChE were at similar levels in the liver while BChE was more affected in kidney. BChE was not detected in the brain. A significant positive correlation in ChE inhibitions was found among tissues, and the effect of fenthion on ChE activities was tissue specific. In general enzymes activities were not significantly recovered in 96-h recovery period; however, an elevation in AChE inhibition was observed in brain. Based on the data of this study, the liver may be suggested as the best indicator tissue especially for phosphorothioate exposure.

Combination larvicidal action of Solanum xanthocarpum extract and certain synthetic insecticides against filarial vector, Culex quinquefasciatus (SAY)

The combination activities of temephos, fenthion and petroleum ether extract of Solanum xanthocarpum were observed for their larvicidal activities against Culex quinquefasciatus. The combination of temephos and S. xanthocarpum was studied at ratios of 1:1, 1:2, and 1:4. Similar ratios were also used for the combination of fenthion and S. xanthocarpum. The temephos/plant extract combination acted antagonistically. The combination of fenthion and plant extract acted synergistically against the target organisms at a ratio of 1:1, which showed the best results of: LC50 0.0144 and 0.0056 ppm and LC90 0.0958 and 0.0209 ppm at 24 and 48 hours, respectively. The present study will be helpful in developing a commercial formulation for effective vector management.

Tissue trace and major element levels in organophosphate insecticide fenthion (Lebaycid) toxicity in rats: prophylactic and therapeutic effect of exogenous melatonin

Organophosphate compounds are very toxic chemicals and used in widespread applications. The present study was designed to examine the role of exogenous melatonin against organophosphate toxicity in tissues (brain, heart, jejunum, kidney, liver, lung, muscle and pancreas) trace and major element levels of rats. Trace and major element concentrations in the tissues were measured in the sham group, the control group, prophylaxis with the melatonin group and therapy with the melatonin group (TM) by inductively coupled plasma-optical emission spectroscopy. Statistically significant differences among the experimental groups were detected for some tissue trace and major element concentrations. In the brain tissue, the Al, Mn and Se concentrations in the sham group were significantly higher than those in the control group (p<0.05). In the heart tissue, the Cu, Mn and Se concentrations in the sham group were significantly increased than those in the control group (p<0.05). In the kidney tissue, trace and major element concentrations in the TM group were significantly lower than those in the sham group (Fe and Mn; p<0.05, Cu, Mo, Ni, Ti, V and Zn; p<0.01). In the liver, Mg, Al, Zn and Ca concentrations in the TM group were significantly higher than those in the fenthion-treated control group (p<0.01). In the muscle tissue, element concentrations in the TM group were significantly lower when compared with the sham groups (Ca and Si; p<0.01). The Al, Cr, Mo, Ni, Si and Zn element concentrations were markedly decreased in the control group as compared with the TM group in the pancreas tissue (p<0.01). In conclusion, according to the results of the present study the major findings are that the fenthion-treated rat's tissue element levels were effected and the melatonin may normalize the altered levels of some trace and major elements of the tissues in organophosphate toxicity.

N-Acetylcysteine provides dose-dependent protection against fenthion toxicity in the brain of Cyprinus carpio L

N-Acetyl-L-cysteine, a low-molecular weight thiol compound, with two different doses was used to prevent fenthion, an organophosphorus insecticide and acaricide, related oxidative stress in the brain of a model organism, Cyprinus carpio. Fish were exposed to sub-lethal and nominal concentration of fenthion after intraperitoneal injection of 0.5 or 400 mg/kg NAC. Brain tissues were then dissected and homogenized to analyse GSH, GSSG, TBARS, and protein contents. Enzymes that constitute the first line antioxidant defence, namely SOD and CAT, GSH-related enzymes, GR and GST, together with AChE activities were also determined spectrophotometrically. Fenthion did not cause any alteration in SOD and CAT activities while increasing GSH content, GSH/GSSG ratio and GST specific enzyme activity and decreasing GSSG, TBARS, and protein contents. Although, the highest induction in SOD and GST enzymes activities and the highest increase in GSH content were observed in the 0.5 mg/kg NAC-injected fish, their protein contents showed a decrease. 400 mg/kg NAC impeded the activation of the GST enzyme and a higher decrease in lipid peroxidation was observed. Fish were also protected against protein depletion by the higher dose NAC application. AChE activity was not influenced by fenthion exposure. Xenobiotic and GSH transporters may cause mild oxidative stress conditions in brain. Cellular redox status could trigger a series of reactions that result in an increase in SOD activity and a decrease in protein content. Based on the present results, it was suggested that the usefulness of NAC against fenthion depends on applied dose and tissue characteristics. Species-specifity and concentration selection should be taken into consideration in studies dealing with anticholinesterases.

Effect of repeated application of fenthion as a mosquito larvicide on Nile tilapia (Oreochromis niloticus) inhabiting selected water canals in Sri Lanka

Health status of feral Nile tilapia following repeated applications of fenthion as a mosquito larvicide to selected water canals in Sri Lanka was assessed. With three spray applications of fenthion to the study sites at weekly intervals at the concentration recommended for mosquito control, condition factor and brain acetylcholinesterase activity of the fish were depressed in a time dependent manner. Prominent histopathological alterations displayed were gill hyperplasia and telangiectasis and vacoulation of hepatocytes. Observed ill health effects of fenthion on the fish demonstrate probable ecological risk to the fish populations inhabiting the water canals which receive repeated inputs of fenthion.

In vivo effects of fenthion on oxidative processes by the modulation of glutathione metabolism in the brain of Oreochromis niloticus

The present study was designed to understand the oxidative stress potential of fenthion, an organophosphate (OP) pesticide and its involvement in glutathione metabolism modulated buthionine sulfoximine (BSO, 50 mg/kg) and N-acetylcysteine (NAC, 100 mg/kg) in the brain of fish, Oreochromis niloticus. A sublethal fenthion concentration (0.45 mg/L) was applied for 24, 48, and 96 h together with injection with BSO or NAC; following treatment, recovery periods for 24, 48, and 96 h were allowed. Total glutathione (tGSH), oxidized glutathione (GSSG), lipid peroxidation, protein level, and GSH-related enzyme activities were analyzed by using spectrophotometric methods. Fenthion in applied concentration did not change GSH levels, but increased GSSG levels. BSO application in fenthion exposure caused a depletion in GSH, while increasing the GSSG levels. Glutathione peroxidase (GPx; EC 1.11.1.9) specific activity increased in fenthion-applied groups at 24-h treatment. gamma-Glutamylcysteinyl synthetase (gamma-GCS; EC 6.3.2.2) was not detected in the brain. NAC injection in fenthion treatment decreased GSH and increased GSSG levels and GST activity. In conclusion, fenthion in sublethal concentration induced an oxidative stress processes in brain. BSO application provided an evidence for the involvement of fenthion in GSH metabolism. NAC elevated the fenthion-induced effects in spite of its antioxidant properties. Recovery period for 96 h was not adequate to eliminate the fenthion-induced changes.

Beneficial effect of N-acetylcysteine against organophosphate toxicity in mice

Recent studies showed that oxidative stress could be an important component of the mechanism of organophosphate (OP) compounds toxicity. The aim of present study was to investigate either prophylactic and therapeutic effects of N-acetylcysteine (NAC) against fenthion-induced oxidative stress in mice. Additionally, the effects on survival rates were investigated. Therefore, we determined the changes of the blood levels of glutathione (GSH), malondialdehyde (MDA), nitrite, and nitrate in blood or serum. Additionally, all animals were observed for 6 h and the survival rates were recorded. It was found that fenthion administration increased the levels of MDA, and decreased the levels of GSH, nitrite and nitrate. On the other hand, both prophylactic and therapeutic NAC treatment decreased the levels of MDA, and increased the levels of GSH, nitrite, and nitrate. The results showed that NAC is able to attenuate the fenthion-induced oxidative stress whereby NAC has not only prophylactic but also therapeutic activity in fenthion poisoning. On the other hand, we found that NAC can clearly improve survival rates in mice administered with an acute high dose of fenthion poisoning. In conclusion, NAC can decrease OP-induced oxidative stress and mortality rate, but the exact mechanism of its NAC protective effect needs to be explored further.

Influence of Different Atropine Therapy Strategies on Fenthion-Induced Organ Dysfunction in Rats

We studied the influence of dose and timing of atropine therapy on fenthion-induced organ dysfunction. Thirty-six rats were randomized into six groups. All rats in the five groups except the control group were intoxicated with fenthion. The high-dose atropine group received 2 mg/kg of atropine, whereas the low-dose group received 100 microg/kg of atropine every hour for 24 hr. One group received 2 mg/kg of atropine in the first 4 hr of intoxication while the other group received 2 mg/kg of atropine in the last 4 hr before killed, which for all rats was 24 hr after intoxication. Pseudocholinesterase and aspartate aminotransferase and alanine aminotransferase levels and histopathological markers of lung, brain and liver were studied. None of our atropine therapy strategies in this study totally prevented harm on the three organs. Although the high dose of atropine administered for 24 hr had the least harmful markers for lung, it also had the most harmful markers for brain and liver. We did not succeed in finding a unique therapy strategy in our models beneficial for all studied organs in fenthion intoxication in rats. Atropine administration strategy should be oriented for the most affected organ pathology in fenthion intoxication.

Toxicity assessment of pesticides to Pseudokirchneriella subcapitata under air-tight test environment

This paper presents the toxicity data of seven pesticides including atrazine, parathion, dichlorvos, malathion, fenthion, 2-methyl-4-chlorophenoxyacetic acid, and pentachlorophenol on Pseudokirchneriella subcapitata based on a new algal toxicity testing technique conducted under air-tight environment. The dissolved oxygen production and the cell density were adopted as the response endpoints. Median effective concentrations (EC50) range from 0.0035 to 3.40 mg/L (DO production) and from 0.0067 to 3.12 mg/L (cell density). No-observed-effect concentration (NOEC) was determined using the Dunnett's test. NOEC values are with in the range of 0.001-1.20 mg/L. In general, the two test endpoints revealed similar sensitivities. From comparisons of literature data also based on Pseudokirchneriella subcapitata, it is clear that conventional batch tests tend to underestimate the toxicity of pesticides due to their open test environment. Closed-system tests, i.e., microplate test, respirometer test, and our BOD-bottle test, generally provide better assessment to the effects of pesticides. Data based on our test method reveals much higher toxicity (3-100 times) than that from the conventional batch tests. Furthermore, for organophosphorus insecticides, results from the present study show that Pseudokirchneriella subcapitata is less sensitive than Daphnia magna and rainbow trout, but is more susceptible than fathead minnow. The closed-system test applied in this study provides more adequate assessment for the toxicity of pesticides than the conventional batch tests.

Ultrastructural studies on the effect of fenthion on pituitary (GTH cells) and testis of Glossogobius giuris. (HAM) during breeding phase

Pesticide (fenthion) which finds its way into water bodies, bring about physiological changes in aquatic animals, via histomorphology and histopathology of various tissues. In fishes, it induces disorders including hyposecretion of gonadotropin in the PPD and regression of gonads. Light microscopic studies were made on control and treated pituitary (gonadotropin secreting cells-GTH) and testis of Glossogobius giuris (HAM) during spawning phase after exposing them to different (0.05 to 0.5 ppm) sub-lethal concentration of fenthion for a short-term period (24 to 96 hrs). The results indicated alteration in normal histology of gonadotropin secreting cells and testis, reduction in number of sperms and degranulation of GTH cells under light microscopy. Degeneration and fragmentation of cytoplasmic organelles was noticed in GTH cells under electron microscope, with the increase in the sub-lethal concentration of fenthion. Significance of the results is discussed in detail in the manuscript.

Whole-body metabolism of the organophosphorus pesticide, fenthion, in goldfish, Carassius auratus

The in vivo metabolism of fenthion, an organophosphorus pesticide, and its sulfoxide (fenthion sulfoxide) was examined in goldfish (Carassius auratus). When goldfish were administered fenthion i.p. at a dose of 100 mg/kg, two metabolites were isolated from the tank water. They were identified as fenthion sulfoxide and fenthion oxon, in which > P = S of fenthion is transformed to > P = O, by comparing their mass and UV spectra, and their behavior in HPLC and TLC, with those of authentic standards. However, fenthion sulfone was not detected as a metabolite. The amounts of fenthion, fenthion sulfoxide and fenthion oxon excreted within 4 days were 2.7, 3.4 and 2.5%, of the initial dose of fenthion, respectively. Unchanged fenthion was detected in the body of the fish to the extent of 42-50% of the dose after 10 days, but fenthion sulfoxide and fenthion oxon showed very low concentrations. When fenthion sulfoxide was administered to the fish, about 70% of the dose was excreted unchanged into the tank water within 24 h, but little of the reduced compound, fenthion, was found. In contrast, fenthion was detected at 2.1% of dose in the body of goldfish as a metabolite of fenthion sulfoxide. The fact that fenthion is metabolized to the toxic oxon form in fish presumably has environmental and health implication for its use as a pesticide.

Effects of aerially applied fenthion on survival and reproduction of the panacea sand fiddler, Uca panacea, in laboratory habitats

Sand fiddler crabs, Uca panacea, were exposed in laboratory habitats to measured concentrations of ULV-grade fenthion via simulated aerial spray at 5% and 50% of field rate application of 6-12 mg fenthion/m(2) (0.05-0.10 lbs fenthion/acre). Two habitats served as controls, and two habitats served as replicates for each of the test exposures. The aerial application was repeated 12 times between July 7, 1997, and August 15, 1997, during the period of the most active larval production of the crabs. The resulting measured concentrations of fenthion at the surface and in the water were consistently lower than what the application rate would have suggested. Statistical analysis of total, daily larval counts showed a periodicity of approximately 14 days that did not appear to be affected by fenthion, at least at the 5% application rate, where a 15% reduction in larval production was noted by the end of the second hatching cycle and a 25% reduction by the end of the third. Larval production in the habitats exposed to the 50% application rate was reduced by 18% at the end of the first hatching cycle, 77% at the end of the second, and 100% at the end of the third hatching cycle. At the end of the third hatching cycle, adult crab mortality observed at the surface was 0%, 3%, and 20% for the control, 5%-, and 50%-exposure habitats, respectively. Three weeks after the final fenthion application, survival of adult crabs was 100% in the control habitats, 75% in the 5%-exposure habitats, and 3% in the 50%-exposure habitats. Survival of unfed first-stage zoeae released during the night following the sprays averaged 4.6 +/- 0.9, 3.7 +/- 0.9 and 1.7 +/- 0.6 days for control, 5%-, and 50%-exposure habitats, respectively. Forty-eight-hour LC-50s (nominal) for fenthion exposure of adult crabs submerged in water and for first-stage zoeae were 215 microg fenthion/L and 0.8 microg fenthion/L, respectively.

Rapid and cost-effective multiparameter toxicity tests for soil microorganisms

Three biochemical parameters, DNA quantification in soil samples and two enzymatic activities, beta-galactosidase and dehydrogenase have been assessed as potential end-points for the use in cost-effective toxicity tests on soil microorganisms. The assessment included the development of a classical dose-response 24-h assay and the incorporation of measurements of the effects on microbial activities in soil column leaching studies and multispecies miniaturised terrestrial systems (MTS). Four different chemicals, copper, a new herbicide, thiabendazole and fenthion were studied. A rapid fluorescence DNA quantification technique did not produce adequate responses. The efforts to quantify DNA after extraction and clean-up procedures failed due to the presence of humic acids. From the protocol of the technique one could see that the technical procedure is time-consuming and expensive and, for this reason, not suitable for use as a parameter in rapid and cost-effective tests. However, the enzymatic activities showed their potential as toxicity end-points. Copper produced a concentration/response inhibition of beta-galactosidase and dehydrogenase with EC50 values of 78.39 and 24.77 mg Cu/kg soil, respectively. In the soil column study, these endpoints allowed the measurement of the microbial activities through the column. The effects of the new herbicide on beta-galactosidase and dehydrogenase activities were statistically significant for the highest application dose (40 g/ha). Thiabendazole affected the microbial activity when mixed within the soil, but no effects were observed when this fungicide was applied on the soil surface. Fenthion produced effects when applied either in the soil or on the soil surface. These results can be explained by the low mobility of thiabendazole. The results show the capabilities of these biochemical parameters to be included as endpoints in cost-effective bioassays.

Chronic fenthion toxicity in laying hens

White leghorn laying hens were exposed to weekly dermal applications of either 1 mg fenthion/kg (FEN; low dose) or 4 mg FEN/kg (high dose) for 24 w with the objective of evaluating chronic FEN toxicity. Four of 24 hens at the high dose exhibited transitory loss of proprioception, perching ability, and righting reflex after 8 to 16 w exposure. All hens receiving the high dose lost the ability or desire to jump from a box during the latter half of the FEN exposure period. Inhibition of serum cholinesterase and brain acetylcholinesterase was greater in the high-dose hens. Brain neuropathy target esterase was not inhibited. Behavioral changes were not correlated with changes in brain concentrations of enzymes or neurotransmitters or their metabolites. Muscle fiber abnormalities were more common in the high-dose hens. Muscle electrical activity was recorded electromyographically via telemetry. Fibrillation (denervation) potentials were absent, but amplitude times duration values for motor unit potentials of the peroneus longus muscle for 5 of the 6 4-w evaluation intervals were higher in the high-dose hens. This EMG response suggested presence of a mild neuropathy which was supported by results of ultrastructural examinations of the sciatic nerve. The low dose initially produced 8% stimulation of egg production while the high dose inhibited egg production 10% during the latter 16 w of the study and reduced body weight 8% during this period.

Environmental hazards of mobile ground spraying with cyanophos and fenthion for quelea control in Senegal

Seven roosts of red-billed quelea, Quelea quelea, in the Senegal River Valley and Delta were visited during and after aerial or terrestrial treatments with either Cyanox (cyanophos 500 g a.i. liter-1, five roosts) or Queletox (fenthion 640 g a.i. liter-1, two roosts). The primary goal of the observations was to provide data on environmental effects of cyanophos after mobile ground spraying operations. Twenty-six species of vertebrates (birds, reptile, fish) were found dead or debilitated near the spray sites. Effects on nontarget fauna were most pronounced among owls (cyanophos and fenthion) and blue-naped mousebirds, Urocolius macrourus (fenthion). Among terrestrial invertebrates ants and carabid, and tenebrionid beetles were the most conspicuously affected. Among aquatic invertebrates affected tadpole shrimps, Triops cancriformis, dominated. Extremely high residues were found immediately after spraying on tree leaves in the spillway of a vehicle-mounted Berthoud Super Puma airblast sprayer (up to 1380 mg kg-1) and on birds found dying under these trees (125-11,277 microg bird-1, average 2720 microg bird-1) in two roosts treated with cyanophos. Blue-naped mousebirds were identified as being particularly at risk. Side effects were not dose related. They were most severe after routinely practiced mobile ground spraying applications which led to overdosing. These application methods impose severe environmental hazards, and should be abandoned.

Possible mechanisms for sensitivity to organophosphorus and carbamate insecticides in eastern screech-owls and American kestrels

Effects of a single dietary exposure to fenthion and carbofuran on the survival, feeding behavior and brain ChE activity of eastern screech-owls, Otus asio and American kestrels, Falco sparverius, were evaluated. Birds were exposed to fenthion (23.6-189.0 ppm) or carbofuran (31.7-253.6 ppm) via meatballs. Carbofuran-exposed owls ate either < or = 10% or > or = 80% of the meatball whereas all kestrels ate < or = 10% of the meatball before exhibiting acute signs of toxicity. Fenthion-exposed owls and kestrels displayed a wide spectrum of meatball consumption (< 10-100%). Significant brain ChE inhibition was observed in dead and surviving kestrels exposed to fenthion and carbofuran and dead owls exposed to fenthion (P < 0.0001). Brain ChE activity of owls exposed to carbofuran that survived was not different from that of controls (P = 0.25). Data suggest: (1) slow feeding on a carbamate-contaminated item may provide limited protection from the toxicity of the chemical at certain rates of exposure; (2) the degree of ChE inhibition at neuromuscular junctions may be critical in determining the sensitivity of a species to a carbamate insecticide; (3) sensitivity may be a function of the ChE affinity for the carbamate inhibitor; and (4) the importance of neuromuscular junction ChE depression in determining the sensitivity of an animal may be species-specific.

Effect of combined fenthion and cimetidine use in rats on lethality, blood cholinesterase activities, and serum cholinesterase isoenzymes

H2-receptor antagonists inhibit cholinesterase (ChE) activity. We examined perturbations in ChE isoenzyme patterns and ChE activities of rats from the combined effects of fenthion (FEN) and cimetidine (CIM). Sixty-four female Sprague-Dawley rats were divided into 8 groups. Four rat groups were given FEN or gum arabic solution and each group divided into 2 small groups according to the CIM or gum arabic administration. FEN was administered po at 12.3 mg/kg (1/20 LD50) or 24.5 mg/kg (1/10 LD50) for 14 days or 49 mg/kg (1/5 LD50) every 4 days. CIM was given po at 1,500 mg/kg from days 7 to 13. Samples were collected 3 h after CIM administration on days 8 and 13. CIM did not influence ChE isoenzyme patterns or ChE activity. FEN inhibited both the ChE isoenzyme patterns and ChE activities without producing clinical signs. Although 1 rat in the 12.5 mg FEN/kg + CIM group died on day 10, all rats in other FEN (24.5 mg/kg or 49 mg/kg) + CIM groups died on days 8-10. Differences in suppression of ChE isoenzyme patterns were detectable between the FEN-dosed and FEN + CIM-dosed groups. There were no differences in ChE activities between the FEN-dosed and FEN + CIM-dosed groups. The i.p. administration of 500 mg CIM/kg (LD50) did not suppress ChE activities.

Effects of fenthion, isoxathion, dichlorvos and propaphos on the serum cholinesterase isoenzyme patterns of dogs

The serum cholinesterase (ChE) isoenzyme patterns consist of 5 bands for normal beagle dogs. We examined the ChE isoenzyme patterns and ChE activities of 4 groups, each of which consisted of 4 dogs, given the organophosphate (OP) compounds fenthion (P = S type), isoxathion (P = S type), dichlorvos (P = O type) or propaphos (P = O type) po at 220, 75, 120 or 90 mg/kg respectively. Blood samples were collected for 30 d after the OP administrations. ChE isoenzyme bands 4 and 5 were inhibited 12 h after fenthion and isoxathion administration; dichlorvos and propaphos produced suppression of main bands 4 and 5 20 min after administration. This change was effective to differentiate the type of OP administered (P = S and P = O), while the main ChE isoenzyme bands of dog serum reflected inhibition of serum ChE activity.

In vitro and in vivo induction of heat shock (stress) protein (Hsp) gene expression by selected pesticides

The chloroacetamide insecticide alachlor, polyhalogenated cyclic hydrocarbons endrin and chlordane and the organophosphate pesticides chlorpyrifos and fenthion induce oxidative tissue damaging effects including lipid peroxidation and nuclear DNA-single strand breaks. The mechanism involved in the induction of oxidative stress by these xenobiotics is unknown. No information is available regarding whether these pesticides can induce the expression of heat shock (stress) protein (Hsp) genes as a common protective mechanism against tissue damage. The pesticides were administered p.o. individually to female Sprague-Dawley rats in two 0.25 LD50 doses at 0 h and 21 h. The animals were killed at 24 h, and liver, brain, heart and lung tissues were removed to examine the induction of Hsps by Western and Northern blot analysis. In a separate series of experiments, cultured neuroactive PC-12 cells were treated 24 h with 50, 100 or 200 nM concentrations of these pesticides. Alachlor, endrin, chlorpyrifos and fenthion induced Hsp89 alpha and Hsp89 beta in hepatic and brain tissues, as well as in cultured PC-12 cells. Chlordane induced some expression of Hsp89 alpha but not Hsp89 beta in the hepatic and brain tissues of treated rats. Some expression of Hsp89 beta was observed in lung tissues of endrin and alachlor treated animals. These findings were substantiated by Western blot analysis using Hsp90 antibody. Except chlordane all these pesticides induced enhanced synthesis of Hsp90 in cultured PC-12 cells. The results indicate striking tissue differences in the patterns of the Hsps induced by the pesticides which were used, and demonstrate that these pesticides can induce the expression of Hsp89 alpha and Hsp89 beta genes in various target organs of rats. The results support the hypothesis that these genes may be mechanistically involved in protecting tissues against oxidative stress induced by structurally diverse pesticides.

Effects of selected organophosphate insecticides on serum cholinesterase isoenzyme patterns in the rat

The serum cholinesterase (ChE) isoenzyme in rats shows 6 bands after polyacrylamide gradient gel electrophoresis. The effects of organophosphates (fenthion, chlorpyrifos, diazinon, bromophos, propaphos, haloxon, and DFP) on serum ChE isoenzyme bands were studied in 32 male and 32 female 6-w-old Sprague-Dawley rats. Each organophosphate was randomly administered to 4 male and 4 female rats. Blood samples were collected from the abdominal aorta under halothane anesthesia 6 h after dosing. The isoenzyme patterns were determined simultaneously with erythrocyte and serum ChE activities. Changes were observed in all 6 bands of the serum ChE isoenzymes after administration of fenthion, chlorpyrifos and propaphos. Diazinon had no influence on band 6, and DFP and bromophos had no influence on band 5. Haloxon did not effect any of the serum ChE isoenzyme bands. Serum ChE was most suppressed by fenthion, followed by DFP, bromophos, chlorpyrifos, propaphos and diazinon in that order of effect. Serum ChE activity was not suppressed by haloxon. Erythrocyte ChE activity was suppressed by every organophosphate. This experiment demonstrated a correlation between the organophosphate suppression of serum ChE activity and the concentration of serum ChE isoenzyme band 6.

In vitro and in vivo generation of reactive oxygen species, DNA damage and lactate dehydrogenase leakage by selected pesticides

Reactive oxygen species may be involved in the toxicity of various pesticides and we have, therefore, examined the in vivo effects of structurally dissimilar polyhalogenated cyclic hydrocarbons (PCH), such as endrin and chlordane, chlorinated acetamide herbicides (CAH), such as alachlor, and organophosphate pesticides (OPS), such as chlorpyrifos and fenthion, on the production of hepatic and brain lipid peroxidation and DNA-single strand breaks (SSB), two indices of oxidative stress and oxidative tissue damage. The selected pesticides were administered p.o. to female Sprague-Dawley rats in two 0.25 LD50 doses at 0 h and 21 h and killed at 24 h. In a parallel set of experiments, we have determined the in vitro effects of these pesticides on the DNA-SSB and enhanced lactate dehydrogenase leakage (LDH) from neuroactive PC-12 cells in culture. In vitro production of reactive oxygen species by these pesticides was also assessed by determining the enhanced chemiluminescence responses of hepatic and brain homogenates. Following treatment of rats with endrin, chlordane, alachlor, chlorpyrifos and fenthion, increases of 2.8-, 3.0-, 4.2-, 4.3- and 4.8-fold were observed in hepatic lipid peroxidation, respectively, while at these same doses, increases in lipid peroxidation of 2.4-, 2.1-, 3.6-, 4.6- and 5.3-fold, respectively, were observed in brain homogenates. Increases of 4.4-, 3.9-, 1.6-, 3.0- and 3.5-fold were observed in hepatic DNA-SSB following treatment of the rats with endrin, chlordane, alachlor, chlorpyrifos and fenthion, respectively, while at these same doses, increases of 1.9-, 1.7-, 2.2-, 1.4-, 1.4-fold, respectively, were observed in brain nuclear DNA-SSB. Following in vitro incubation of hepatic and brain tissues with 1 nmol/ml of each of the five pesticides, maximum increases in chemiluminescence occurred within 4-7 min of incubation and persisted for over 10 min. Increases of 3.0-, 2.7-, 3.6-, 4.9- and 4.4-fold were observed in chemiluminescence following in vitro incubation of the liver homogenates with endrin, chlordane, alachlor, chlorpyrifos and fenthion, respectively, while increases of 1.7-, 1.8-, 2.0-, 3.4- and 3.7-fold, respectively, were observed in the brain homogenates. Increases of 2.2-, 2.3-, 2.9-, 2.9- and 3.4-fold were observed in the chemiluminescence responses in the liver homogenates of the animals treated with endrin, chlordane, alachlor, chlorpyrifos and fenthion, respectively, while increases of 1.8-, 2.0-, 3.2-, 2.9- and 2.4-fold, respectively, were observed in the brain homogenates. Cultured neuroactive PC-12 cells were incubated with the pesticides and the release of the enzyme lactate dehydrogenase (LDH) into the media as an indicator of cellular damage and cytotoxicity was examined. Maximal release of LDH from cultured PC-12 cells was observed at 100 nM concentrations of the pesticides. Increases of 2.3-, 2.5-, 2.8-, 3.1 and 3.4-fold were observed in LDH leakage following incubation of the PC-12 cells with endrin, chlordane, alachlor, chlorpyrifos and fenthion, respectively. Following incubation of the cultured PC-12 cells with 100 nM concentrations of these same pesticides, increases in DNA-SSB of 2.5-, 2.2-, 2.1-, 2.4- and 2.5-fold, respectively, were observed. The results clearly demonstrate that these different classes of pesticides induce production of reactive oxygen species and oxidative tissue damage which may contribute to the toxic manifestations of these xenobiotics. Reactive oxygen species may serve as common mediators of programmed cell death (apoptosis) in response to many toxicants and pathological conditions.

An aquatic toxicological evaluation of fenthion in the context of finch control in South Africa

Queletox, containing fenthion as active ingredient, is the avicide formulation used in South Africa to control red-billed finches (Quelea quelea). Control measures involve night spraying of roosting areas with a light aircraft. Since roosting areas often include reedbeds along riversides and on islands, proper control is difficult without exposing the aquatic environment to some risk of contamination. This study tested the acute effects of fenthion, in association with the queletox formulation, on the cladocerans Daphnia pulex and Ceriodaphnia dubia and the fish species Poecilia reticulata, Tilapia rendalli, Cyprinus carpio, and Oreochromis mossambicus. The chronic effects of fenthion on D. pulex were evaluated in a 14-day reproduction test. Mean 48-hr LC50 values estimated for D. pulex and C. dubia were 1.30 and 1.72 micrograms liter-1 respectively. For the fish estimated 96-hr LC50 values were as follows: 2.12 (P. reticulata), 2.53 (C. carpio), 2.92 (T. rendalli) and 1.71 micrograms liter-1 (O. mossambicus). In the chronic test reproduction of the exposed population was stimulated at the lowest two fenthion concentrations (0.1 and 0.6 ng liter-1), while a reproductive impairment was recorded at concentrations varying from 1 to 10 ng liter-1. Concentrations of fenthion measured in dams after spraying are given to indicate the levels of contamination that may occur. QSAR was used to estimate the toxicity of some fenthion metabolites. The results of this study reveal that fenthion, at the concentrations occurring in the environment after aerial spraying, can have marked effects on the survival and reproduction of D. pulex for long periods after spraying.

In vitro cytotoxicity of fenthion and related metabolites in human neuroblastoma cell lines

The aim of our research was the evaluation in vitro of the neurotoxic effects of fenthion and its metabolites on human neuroblastoma cells, as a model for their toxicity in humans. The results indicate that 24 hours exposure was sufficient to produce dose related effects on SK-N-BE and IMR 32 cell viability causing detachment and loss of cells at the effective doses. In the two cell lines fenthion metabolites display an increased cytotoxicity respect to the parent compound with a distinct pattern of toxicity on neurons. Our data suggest that cultured neuronal cells of human origin are discriminating experimental systems, sensitive to minor differences, of correlating in vivo and in vitro neurotoxicants.

Use of a gene expression system based on potato virus X to rapidly identify and characterize a tomato Pto homolog that controls fenthion sensitivity

A novel transient gene expression system was used to study both the tomato disease resistance gene Pto and a Pto homolog designated Fen. The gene expression system was based on potato virus X (PVX). Tomato plants that were both susceptible to strains of Pseudomonas syringae pv tomato carrying the corresponding avirulence gene avrPto and insensitive to the insecticide fenthion were infected with in vitro-generated transcripts of PVX derivatives containing either Pto or Fen. Expression of the Pto gene from the virus genome failed to elicit P.s. tomato resistance, indicating that the PVX system is not suitable for the study of Pto. However, expression of the Fen gene resulted in sensitivity to fenthion. The utility of the PVX gene expression system was further demonstrated through structure/function studies of the Fen gene. A correlation was shown between Fen protein kinase activity and the ability of this protein to confer fenthion sensitivity to tomato. Furthermore, it was demonstrated that mutation of a putative N-terminal myristoylation site, proposed to be involved in membrane targeting, rendered the Fen protein inactive. Analysis of a Pto-Fen chimeric gene allowed the fenthion sensitivity domain to be localized to the C-terminal part of the Fen protein. Interestingly, expression of the Fen kinase from the PVX genome in Nicotiana spp resulted in a fenthion-independent necrotic response. Our results support the involvement of the Fen gene in a signal transduction pathway(s).

Tomato mutants altered in bacterial disease resistance provide evidence for a new locus controlling pathogen recognition

We have employed a genetic approach to study the resistance of tomato to the phytopathogenic bacterium Pseudomonas syringae pv tomato. Resistance to P. s. tomato depends upon expression of the Pto locus in tomato, which encodes a protein with similarity to serine/threonine protein kinases and recognizes pathogen strains expressing the avirulence gene avrPto. Eleven tomato mutants were isolated with altered resistance to P. s. tomato strains expressing avrPto. We identified mutations both in the Pto resistance locus and in a new locus designated Prf (for Pseudomonas resistance and fenthion sensitivity). The genetic approach allowed us to dissect the roles of these loci in signal transduction in response to pathogen attack. Lines carrying mutations in the Pto locus vary 200-fold in the degree to which they are susceptible to P. s. tomato strains expressing avrPto. The pto mutants retain sensitivity to the organophosphate insecticide fenthion; this trait segregates with Pto in genetic crosses. This result suggested that contrary to previous hypotheses, the Pto locus controls pathogen recognition but not fenthion sensitivity. Interestingly, mutations in the prf locus result in both complete susceptibility to P. s. tomato and insensitivity to fenthion, suggesting that Prf plays a role in tomato signaling in response to both pathogen elicitors and fenthion. Because pto and prf mutations do not alter recognition of Xanthomonas campestris strains expressing avrBsP, an avirulence gene recognized by all tested tomato cultivars, Prf does not play a general role in disease resistance but possibly functions specifically in resistance against P. s. tomato. Genetic analysis of F2 populations from crosses of pto and prf homozygotes indicated that the Pto and Prf loci are tightly linked.

Fenthion produces a persistent decrease in muscarinic receptor function in the adult rat retina

Several reports have suggested that exposure to organophosphate pesticides damages the visual system. The prolonged effects of an acute dose of fenthion (dimethyl 3-methyl-4-methylthiophenyl phosphorothionate) were studied on the cholinergic system of the rat retina. Fenthion was administered in a single dose of 0 or 100 mg/kg (sc, in corn oil) to adult, male, Long-Evans rats. The animals were killed 4, 14, or 56 days after treatment and cholinesterase (ChE) activity as well as muscarinic receptor (mChR) function measured in the retina and frontal cortex. Fenthion produced 89% inhibition of ChE activity in both tissues at 4 days, and, although there was recovery, slight (15%) inhibition of the enzyme activity was still observed at 56 days in both tissues. A long-lasting decrease in carbachol-stimulated inositolphosphate (IP) release was observed following fenthion treatment in the retina: IP release was depressed at 4 days and this depression persisted up to 56 days after dosing. The density of mChR in the retina as well as in the cortex was decreased by 14-20% at 4 days and returned to control levels by 56 days. Fenthion had no effect on the metabolism of phospholipids in the retina following intraocular injections of labeled precursors [3H]myo-inositol, [methyl-14C]choline, or [2-3H]glycerol 4 days after fenthion treatment. These prolonged effects of fenthion on mChR function (signal transduction) appear to be specific to the retina as the cortex showed no change in receptor-stimulated IP release even in the presence of significant mChR down-regulation and ChE inhibition. This dose of fenthion did not produce overt morphological changes in the retina or in the cortex, as observed with light microscopy, although an increase in glial fibrillary acidic protein immunoreactivity (GFAP IR) extending from the internal limiting membrane to the external limiting membrane of the retina was noted. This increase in GFAP IR was observed at 14 days and persisted as long as 56 days post-treatment in the retina, but was not noted in the cortex at any of the time points studied. Thus, this long-lasting perturbation in the retinal cholinergic second messenger system induced by fenthion may occur independently of depressed ChE activity and down-regulation of mChR.

Interlaboratory cholinesterase determinations and the effect on the results of statistical evaluation of cholinesterase inhibition

Cholinesterase activity is often a key parameter in the regulatory assessment of cholinesterase-inhibiting agents such as organophosphorous and carbamate pesticides. Thus, the nature and characteristics of the methodology involved in the measurement of plasma (PChe), erythrocyte (R Che), and brain (BChe) cholinesterase activity takes on a heightened degree of importance. In this study an interlaboratory comparison of cholinesterase activity as determined by various laboratories was conducted in order to assess the influence that different methodologies may have on the results of statistical evaluation of cholinesterase inhibition. RChe, PChe, and BChe from animals exposed to fenthion, a known cholinesterase inhibitor, were determined at 8 different laboratories with experience in cholinesterase determination. Seven different instruments and 5 different assay procedures were employed. Marked differences in both the magnitude of inhibition measured and its designation as a statistically significant difference often occurred between laboratories using both the same as well as different methods of cholinesterase analysis. These findings illustrate the importance of considering not only the sensitivity of a given method of analysis, but also the influence of inter- and intra-laboratory variation on statistically responsive aspects of the data profile itself (i.e., precision, sample size, etc.) when establishing regulatory levels (i.e., Reference Doses (RfDs), Health Advisory Levels (HALs), etc.) on the basis of a cholinesterase no-observed- or lowest-observed-effect level (NOEL, LOEL).

Ocular effects of organophosphates: a historical perspective of Saku disease

Many publications, primarily of work performed in Japan, report findings in human populations of an increased incidence of myopia and of a more advanced visual disease syndrome (Saku disease), which reportedly correlated with increasing use of organophosphate pesticides in agriculture. Follow-up studies in animals performed in Japan using such agents as ethylthiometon, fenthion and fenitrothion demonstrate adverse effects of organophosphates on the visual system. The several ocular effects in question are dose dependent, ranging in severity from lenticular and electro-retinographic changes to the seemingly more serious histophysiological changes in such tissues as the ciliary body and retina. An important question arising from this work is that of the role of cholinesterase inhibition in the etiology of the effects. Studies currently in progress on particular organophosphates being conducted at EPA's research facility and by certain registrants of pesticides, which are in various stages of completion, appear to be substantiating much that has been reported in Japan. While animal studies clearly show that some organophosphates elicit ocular toxicity, there are many knowledge gaps with regard to effects in humans and the ocular toxicity in general, e.g. time and dose dependency, cholinesterase inhibition vs ocular effects and effects of routes of exposure. Consequently, the office is unable at this time to incorporate hazard assessment data with exposure assessment data or to perform risk assessments on organophosphates based on the ocular toxicity potential of this class of chemicals.

Effects of organophosphates on the visual system of rats

The possibility that exposure to organophosphate insecticides can lead to ocular damage is suggested by Japanese studies from the 1960s and 1970s indicating that exposed humans developed chronic ocular degeneration, in addition to showing more commonly accepted effects of cholinesterase-inhibiting compounds. Other papers reported ocular lesions in laboratory animals treated with organophosphates. More recently, retinal degeneration following chronic organophosphate treatment has been reported to the Environmental Protection Agency by pesticide manufacturers in studies conducted in compliance with good laboratory practice regulations. Several factors, however, have prompted scepticism regarding organophosphate-induced ocular toxicity, including the widespread use of organophosphate compounds for both agricultural and ophthalmological practices without numerous additional reports of comparable ocular toxicity. We are developing a research program to address these issues involving electrophysiological, biochemical and histological investigations of rats treated with organophosphate insecticides. The research program is young, but early results are available. Notably, retinas from rats treated with a single subcutaneous injection of 100 mg kg-1 fenthion showed decreases in carbachol-stimulated release of inositol phosphate, an indicator of cholinergically-mediated intracellular second messenger systems. These effects persisted at least 56 days after fenthion administration. This could indicate several different toxicological actions, which are currently under investigation. It is concluded that the possible association between exposure to organophosphates and ocular toxicity cannot be dismissed, and that several important research issues need to be resolved.

Inhibitory effect of fenthion and diazinon on the contraction of rat aorta, and its contribution to lethality

Fenthion and diazinon, P = S type organothiophosphates which are precursors of cholinesterase inhibitors, cause remarkable atropine-insensitive hypotension in rats when administered intravenously in lethal doses. We investigated their effects on isolated rat aorta and atria to reveal the site of action. Fenthion and diazinon inhibited both types of contractions induced by high K+ solution and norepinephrine in aortic preparations from which the endothelium was removed. IC50 values (under [Ca2+] = 1.5 mM) were 2 x 10(-5) M and 7 x 10(-5) M, respectively. However, the atrial preparations were relatively resistant, since fenthion showed no effect up to 10(-3) M and diazinon at 10(-4) M exhibited a slight inhibition which was antagonized by atropine. The hypotensive effect of fenthion or diazinon was therefore attributable to the direct inhibiting action on the arterial muscle tone, which may be independent of the activation of muscarinic receptors. The results suggested that fenthion and diazinon affect movement and/or utilization of calcium in the aortic muscle cells, since an increase in the calcium concentration in the bathing solution antagonized their inhibitory effect.

Non-cholinergic mechanisms underlying the acute lethal effects of P = S type organophosphorus insecticides in rats

Intravenous administration of the lethal dose of diazinon or fenthion, P = S type organophosphates, to urethan anesthetized rats induced bradycardia and transient apnea followed by a decline of blood pressure, and death. We investigated the mechanisms of the lethal action of these organophosphates in rats through measurements of blood pressure, heart rate, and respiratory pattern. We compared their cardiorespiratory effects in the five different conditions under anesthesia; 1) normal (without treatment), 2) artificially ventilated, 3) vagotomized, 4) atropinized, 5) pithed, vagotomized and atropinized. It was found that the administration of 200 mg/kg of fenthion and 100 mg/kg of diazinon, caused sudden bradycardia, transient apnea and gradual decline of blood pressure in the anesthetized normal rat, and the rat died. The rats in other conditions also died except the artificially ventilated rats, in which 400 mg/kg of fenthion was administered to cause hypotension and subsequent death. Hypotension was observed consistently even after the cardiac effect such as bradycardia was eliminated by atropine treatment. In the pithed rats which were further vagotomized and atropinized, these organophosphates also caused hypotension. These results may indicate that hypotension is the main cause of death which resulted from intravenous administration of the P = S types. Hypotension may be caused by peripheral cardiovascular effect of the P = S types, which is unrelated to cholinergic mechanisms.

Scientific discourse, in public

The experience of writing for a wider audience has benefits and drawbacks. Attempting to make scientific issues more accessible to non-scientists is no easier than explaining them to peers. Indeed, explaining toxicological data such as solvent measurements from a hazardous waste site can be even more difficult, especially in addressing those living next to the site. Alastair Hay reconsiders his experience in two cases that brought toxicology under public scrutiny.

The neurotoxicity of subchronic acetylcholinesterase (AChE) inhibition in rat hippocampus

The neurotoxic effects of long-term, low-level exposure to the commercially available insecticide, Fenthion, were examined in the present study. Young (2 month) adult, male Long-Evans rats were dermally exposed to Fenthion (25 mg/kg, 3X week) and sampled after 2 and 10 months exposure to assess neurotoxic damage in the hippocampus using morphological and biochemical endpoints. Histopathology, consisting of gliosis, swollen and necrotic neurons, and cell dropout, occurred in the dentate gyrus (DG), CA4 (hilus), and CA3 sectors as early as 2 months postexposure. Acetylcholinesterase (AChE) staining of brain tissues taken at this time was severely reduced in the septal nuclei, the DG molecular layer, the CA4, and the hippocampus proper. After 10 months exposure to Fenthion, cellular necrosis and gliosis intensified in the CA4 and CA3 regions and occasionally involved the CA2. Radiometric assays of AChE activity in the hippocampus indicated a 65 and 85% depression after 2 and 10 months exposure, respectively. Quinuclidinyl benzilate binding for the hippocampal muscarinic receptor was reduced by 6 and 15%, after 2 and 10 months exposure, respectively. A separate group of older (12 month) rats was exposed to the same dosing regimen of Fenthion and examined for neuropathological damage after 2 and 10 months exposure. Aged animals exposed for only 2 months expressed severe hippocampal degeneration in a pattern similar to that seen in the young adult after 10 months exposure (viz., DG, CA4, CA3). Aged animals exposed for 10 months showed more extensive histopathology of the CA4-2 and occasionally CA1. These observations indicate that in both young adult and aged animals, subchronic, low-level exposure to anticholinesterase compounds can result in serious neurotoxic consequences to the mammalian hippocampus.

A simple method for screening assessment of acute toxicity of chemicals

We proposed a simple method for screening assessment of acute oral and dermal toxicity using only three rats and mice of each sex at each dose level. Animals were first treated with chemicals at a dose of 2000 mg/kg and were carefully observed for compound-related morbidity and mortality. If none of the animals died, the following toxicity tests were suspended. If some of the animals died, toxicity tests at doses of 200 and 20 mg/kg were performed. The approximate LD50 values calculated by this method showed little difference between two separate laboratories and were in good agreement with LD50 values reported in the literature. Our toxicological data also showed that LD50 values were about 2-2.5 times the MNLD (maximum non lethal dose) in acute oral and dermal toxicity. This meant that a chemical could be regarded as having an LD50 of about 4000 mg/kg or higher when there was no mortality at the dose of 2000 mg/kg. A chemical with such low toxicity would not require further testing for lethal effects. Therefore, this simple method combining the fixed-dose procedure with the limit test is suitable for determination of approximate LD50 values of chemicals and for screening for necessity for classical full LD50 test using many animals.

Electroretinographic changes induced by organophosphorus pesticides in rats

Electroretinographic changes induced by organophosphorus pesticides (OPs) were studied in rats. Male Wistar rats were intraperitoneally injected with fenthion, chlorpyrifos, fenitrothion, dichlorvos or chlorfenvinphos at doses of 0.01 mmol/kg and/or 0.05 mmol/kg. The electroretinogram (ERG) was recorded at 5 hours and 2 days after the administration, and brain and retinochoroid cholinesterase (ChE) activities was assayed at 3 days after the injections. The brain and retinochoroid ChE activities were reduced in rats treated with the OPs. Notably, the reduction of ChE activities by fenthion, chlorpyrifos and dichlorvos were similar. The administration of OPs induced a change in the ERG, characterized by alteration of the amplitudes of a- and b-waves. Nevertheless the ChE activities in the brain and retinochoroid were inhibited by all of the OPs, the OPs affected the amplitude of ERG differently. Fenthion and chlorpyrifos decreased the amplitudes; dichlorvos and chlorfenvinphos increased; and fenitrothion transiently decreased at 5 hours but increased 2 days after the injection. These results indicate that a factor or factors other than inhibition of ChE activities contributes to the alteration of ERG induced by OPs.

Release and metabolism of dopamine in a clonal line of pheochromocytoma (PC12) cells exposed to fenthion

The effects of an organophosphate (OP) pesticide, fenthion (FEN), on the release and metabolism of dopamine were evaluated in a clonal line of rat pheochromocytoma (PC12) cells. HPLC was used to determine media concentrations of DA and the DA metabolites norepinephrine (NE), 3,4-dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA). The FEN formulation solvent did not significantly affect DA metabolism. In the first study, cultures were treated with 10(-5) or 10(-6) M FEN or 10(-5) M neostigmine, a non-OP acetylcholinesterase inhibitor. Concentrations of both catecholamines were elevated in cultures treated with 10(-5) M FEN by 2.8-fold for DA and 3.5-fold for NE. Neostigmine effects were of smaller magnitude and DA was decreased after 24 hr. Cultures were also treated with depolarizing levels of K+, but the effect of FEN was not altered, suggesting that FEN does not act by increasing DA release. In the second study, the effect of 10(-6) M FEN was evaluated in cultures treated with the DA uptake inhibitor benztropine, the monoamine oxidase (MAO) inhibitor pargyline, or the catechol-O-methyltransferase (COMT) inhibitor tropolone. Inhibitor effects were consistent with their known mechanisms of action. In all cultures treated with FEN, the ratio HVA/DOPAC was decreased after 3 and 6 hr of exposure. A decrease in HVA/DOPAC was also observed in cultures treated with neostigmine and tropolone. In combination with pargyline, FEN decreased DA in contrast to its usual effect of increasing DA. Neither the stimulation of DA release nor the inhibition of DA uptake affected the observed action of FEN in PC12 cultures.(ABSTRACT TRUNCATED AT 250 WORDS)

Toxic effects of organophosphates on nerve cell growth and ultrastructure in culture

Organophosphates (OP) comprise one of the major classes of pesticides in use today. It is well accepted that the primary site of action of the OPs is at cholinergic synapses. However, it has been suggested that OPs may have direct neural effects as well. In this study, cultured chick dorsal root ganglia (DRG) were used to study the effect of fenthion (FEN), an OP pesticide, on isolated nerve cell growth and ultrastructure. Light microscopic evaluation revealed a dose-response relationship between the concentration of FEN (10(-2) M to 10(-5) M) and severity of morphologic changes. Cultured explants were treated with a lower concentration of FEN (10(-6) M) and morphologic alterations were compared to those observed in explants treated with 10(-6) M paraoxon, a more acutely toxic OP, or 10(-6) M neostigmine, a non-OP inhibitor of acetyl-cholinesterase. Based on both light and electron microscopy, neostigmine had no observed effect on cell morphology except for an inhibition of the extension of neurites by DRG cells. In contrast, explants treated with OPs exhibited a significant alteration in cell morphology. Initial lesions were observed first in the neurites and pseudopodia and consisted of vacuolization, loss of tubular structures, retraction of pseudopodia, and cell membrane disruption at the growth cone. Lipid accumulations were observed within the cytoplasm of treated cells. The effects of paraoxon on DRG cell morphology were significantly more severe than the effects of FEN, and lipid vacuoles observed in paraoxon-treated cells were several times larger than those observed in FEN-treated cells (5-10 microns in diameter vs. 0.5-1.0 microns in diameter). Results show that OPs have a direct effect on DRG nerve cells in culture, consistent with an alteration in cell membrane integrity. Cultured DRG cells can be useful in the evaluation of toxicologic effects.

[Inhibition of acetylcholinesterase at pupil-related central nuclei by organophosphorus pesticide (fenthion)--an experimental study]

An organophosphorus pesticide (OP) inhibits acetylcholinesterase (AChE) of various organs, especially in cholinergically innervated organs. Pupil constriction is a major sign of an ocular symptom in the patient with acute OP intoxication, but the etiology is unknown. The present experiments were intended to elucidate a central mechanism of pupil size in which AChE and OP are involved. Fenthion (dimethyl 4-methylthion-m-tolyl phosphorothionate) of 5mg/day body weight) was subcutaneously administered dorsally in Wistar rats for 14 days consecutively in the longest group. Histochemical staining and microspectrophotometry were used to analyze the intensity of the AChE activity in the iris, the pretectal nucleus and Edinger-Westphal (EW) nucleus on the 2nd, 4th, 6th, 10th and 14th day of administration. The pupil was measured after 20 minutes of dark adaptation. The pupil constricted on the 6th day and most remarkably on the 10th day. The AChE activity in the iris decreased remarkably on the 4th day. Miosis was not seen on the 4th day. The AChE activity in the pretectal nucleus decreased remarkably on the 6th day. The AChE activity in the EW nucleus reduced gradually from the 6th day and 62% reduction of initial value was seen on the 14th day. Intense miosis was seen on the 10th day. In conclusion inhibition of AChE activity was detected first in the iris, thereafter in the pretectal nucleus and the EW nucleus in close correlation with the miotic pupil. Therefore, miosis associated with OP intoxicated patients may parallel the central inhibition of AChE in pupil-related centers.

Neuromuscular effects of chronic exposure to fenthion in dogs and predictive value of electromyography

Chronic exposure to organophosphates (OP) can result in nonspecific neurologic signs in both man and animals. Improved methods are needed to predict toxicity and to better characterize neuromuscular effects. In this study, dogs were exposed to an OP (fenthion) by weekly dermal application of a 20% solution at a dosage of 44 mg/kg. This dosage does not produce signs of acute OP toxicity in dogs, although plasma cholinesterase (ChE) levels are significantly decreased. Electromyograms (EMG) were used to monitor motor unit potential (MUP) activity at minimal and submaximal contractile effort in four different muscles. At 1-month intervals, muscle biopsies were obtained and plasma ChE levels were determined. At 3 months, hyperreflexia and/or mild proprioceptive deficits were observed. The dosage was reduced to 22 mg/kg for the remaining 3 months of the study. At the end of this 6-month study, nerve and muscle biopsies were obtained. Mean plasma ChE levels were decreased (preexposure value of 1775 IU/liter to low of 310 IU/liter) and correlated with duration of exposure and change in dosage level. Fourier analysis of EMG indicated some increase in higher frequency components of the power spectrum with time, and analysis of individual MUPs revealed a significant (p less than 0.05) increase in the product of the amplitude times the duration of the potentials in all muscles examined. Biopsy results were supportive of EMG findings of altered neuromuscular function and loss of small motor units. The EMG changes were most consistent in the gastrocnemius muscle and were detected prior to development of clinical signs. These results indicate that EMG can be useful in monitoring OP exposure and predicting toxicity.

Effects of topical fenthion on blood cholinesterase and vagal tone in dogs

A 20% fenthion (0,0-dimethyl-0-(3-methyl-4-(methylthio)-phenyl) phosphorothionate) formulation was applied topically to dogs at 8 mg/kg, 2 treatments at 14-day intervals, and 33 mg/kg, 4 treatments at 7-day intervals. Control dogs received 4 treatments at 7-day intervals of the proprietary vehicle. Following the last dose, the dogs were observed for a 14-day period. Plasma cholinesterase (ChE) exhibited a significant dose-related response with maximum inhibition to 52% and 24% of pre-dose activity occurring 4 days after the final fenthion treatment of 8 and 33 mg/kg, respectively. Erythrocyte ChE activity showed a downward trend to 32% of normal activity measured 9 days following the last treatment of fenthion at 33 mg/kg. No cholinomimetic effects were observed. All dogs were challenged with atropine sulfate (0.02 mg/kg, sc) on the last day of the observation period. A 5 min electrocardiogram was analyzed to estimate V as that portion of the variance in the R-R intervals corresponding with the normal respiratory frequency band for dogs. The mean heart period, mean heart period variance, and mean of V had significant change when measured across time in the atropine challenge (0, 25, 70, and 100 min) with a pronounced decrease at 25 min. An attenuation of the V measure in the fenthion-treated groups indicated an altered muscarinic response to atropine from prior subacute fenthion exposure.