Validation of an SH-SY5Y Cell-Based Acetylcholinesterase Inhibition Assay for Water Quality Assessment.

The acetylcholinesterase (AChE) inhibition assay has been frequently applied for environmental monitoring to capture insecticides such as organothiophosphates (OTPs) and carbamates. However, natural organic matter such as dissolved organic carbon (DOC) co-extracted with solid-phase extraction from environmental samples can produce false-negative AChE inhibition in free enzyme-based AChE assays. We evaluated whether disturbance by DOC can be alleviated in a cell-based AChE assay using differentiated human neuroblastoma SH-SY5Y cells. The exposure duration was set at an optimum of 3 h considering the effects of OTPs and carbamates. Because loss to the airspace was expected for the more volatile OTPs (chlorpyrifos, diazinon, and parathion), the chemical loss in this bioassay setup was investigated using solid-phase microextraction followed by chemical analysis. The three OTPs were relatively well retained (loss <34%) during 3 h of exposure in the 384-well plate, but higher losses occurred on prolonged exposure, accompanied by slight cross-contamination of adjacent wells. Inhibition of AChE by paraoxon-ethyl was not altered in the presence of up to 68 mgc /L Aldrich humic acid used as surrogate for DOC. Binary mixtures of paraoxon-ethyl and water extracts showed concentration-additive effects. These experiments confirmed that the matrix in water extracts does not disturb the assay, unlike purified enzyme-based AChE assays. The cell-based AChE assay proved to be suitable for testing water samples with effect concentrations causing 50% inhibition of AChE at relative enrichments of 0.5-10 in river water samples, which were distinctly lower than corresponding cytotoxicity, confirming the high sensitivity of the cell-based AChE inhibition assay and its relevance for water quality monitoring. Environ Toxicol Chem 2022;41:3046-3057. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Effect of carbendazim on honey bee health: Assessment of survival, pollen consumption, and gut microbiome composition.

Gut microbiota and nutrition play major roles in honey bee health. Recent reports have shown that pesticides can disrupt the gut microbiota and cause malnutrition in honey bees. Carbendazim is the most commonly used fungicide in China, but it is not clear whether carbendazim negatively affects the gut microbes and nutrient intake levels in honey bees. To address this research gap, we assessed the effects of carbendazim on the survival, pollen consumption, and sequenced 16 S rRNA gene to determine the bacterial composition in the midgut and hindgut. Our results suggest that carbendazim exposure does not cause acute death in honey bees even at high concentrations (5000 mg/L), which are extremely unlikely to exist under field conditions. Carbendazim does not disturb the microbiome composition in the gut of young worker bees during gut microbial colonization and adult worker bees with established gut communities in the mid and hindgut. However, carbendazim exposure significantly decreases pollen consumption in honey bees. Thus, exposure of bees to carbendazim can perturb their beneficial nutrition homeostasis, potentially reducing honey bee immunity and increasing their susceptibility to infection by pathogens, which influence effectiveness as pollinators, even colony health.

Biological toxicity assessment of carbamate pesticides using bacterial and plant bioassays: An in-vitro approach.

In recent times, agricultural practices mainly rely on agrochemicals and pesticides to safe-guard edible crops against various pests and to ensure high yields. However, their indiscriminate use may cause severe environmental hazards that directly and negatively affect soil microorganisms and crop productivity. Considering these, present study was aimed to assess the toxicity of carbamate pesticides namely carbamoyl (CBL), methomyl (MML) and carbofuran (CBN) using bacterial and plant (Vigna mungo L.) bioassays. All pesticide doses (25-100 µg mL-1) showed negative effect on bacteria as well as plant. Growth, morphology, survival, cellular respiration and inner membrane permeability of Sinorhizobiumsaheli was hampered when exposed to pesticides. Pesticide induced morphological changes viz. aberrant margins; cellular cracking and distortion/damage in S. saheli were obvious under scanning electron microscope (SEM). The 100 µgCBNmL-1 had maximum inhibitory effect and it reduced survivability of S. saheli by 75%. In addition, biofilm formation ability of S. saheli was inhibited in a pesticides-dose dependent manner and it was statistically (p ≤ 0.05) significant. Pesticides indorsed significant changes in biomarker enzymatic assays and oxidative stress parameters towards S. saheli. Furthermore, at 100 µgCBNmL-1, germination efficiency, root, shoot length, plant survival and tolerance index of V. mungo were decrease by 50, 75, 65, 70 and 66%, respectively over control. Staining of pesticide treated roots with fluorescently labeled dyes propidium iodide (PI) and acridine orange (AO) showed increased oxidative stress, ROS generation and membrane permeability as revealed under confocal laser scanning microscope (CLSM). Furthermore, stressor metabolites and antioxidant enzymes in plant seedlings were progressively enhanced with increasing concentration of pesticides. Conclusively, present finding bestow an insights into a mechanistic approach of carbamate pesticide induced phyto, morpho and cellular toxic effects towards soil bacterium as well as plant with forthcoming implications for designing the pesticides to reduce their toxic/harmful effects.

Assessment of Carbendazim Residues and Safety in Celery Under Different Cultivation Conditions.

Although the carbendazim is widely used to manage spot blight in celery cultivation, information on residues identified is of interest. In this study, we examined the dissipation and residual amounts of carbendazim in celery and soil under different cultivation methods when using the suggested dose and ten times of that and the bioconcentration factor of carbendazim for celery. The results showed that when celery leaves were sprayed with the suggested dose, the half-lives in a celery field and greenhouse were 2.75 days and 3.29 days, respectively. When the soil matrix was sprayed with the recommended dose before cultivation, the half-lives of carbendazim residues were 16.86 days and 11.97 days. We also conducted a long-term dietary risk assessment using the corresponding criteria. The results showed that, in China, the use of carbendazim at a dose of 0.022 g/m2 is safer and more reasonable when the harvest interval is 28 days.

Degradation of carbendazim in water via photo-Fenton in Raceway Pond Reactor: assessment of acute toxicity and transformation products.

This study aimed at investigating the degradation of fungicide carbendazim (CBZ) via photo-Fenton reactions in artificially and solar irradiated photoreactors at laboratory scale and in a semi-pilot scale Raceway Pond Reactor (RPR), respectively. Acute toxicity was monitored by assessing the sensibility of bioluminescent bacteria (Aliivibrio fischeri) to samples taken during reactions. In addition, by-products formed during solar photo-Fenton were identified by liquid chromatography coupled to mass spectrometry (UFLC-MS). For tests performed in lab-scale, two artificial irradiation sources were compared (UVλ > 254nm and UV-Visλ > 320nm). A complete design of experiments was performed in the semi-pilot scale RPR in order to optimize reaction conditions (Fe2+ and H2O2 concentrations, and water depth). Efficient degradation of carbendazim (> 96%) and toxicity removal were achieved via artificially irradiated photo-Fenton under both irradiation sources. Control experiments (UV photolysis and UV-Vis peroxidation) were also efficient but led to increased acute toxicity. In addition, H2O2/UVλ > 254nm required longer reaction time (60 minutes) when compared to the photo-Fenton process (less than 1 min). While Fenton's reagent achieved high CBZ and acute toxicity removal, its efficiency demands higher concentration of reagents in comparison to irradiated processes. Solar photo-Fenton removed carbendazim within 15 min of reaction (96%, 0.75 kJ L-1), and monocarbomethoxyguanidine, benzimidazole isocyanate, and 2-aminobenzimidazole were identified as transformation products. Results suggest that both solar photo-Fenton and artificially irradiated systems are promising routes for carbendazim degradation.

Assessment of the effects of oxamyl on the bacterial community of an agricultural soil exhibiting enhanced biodegradation.

Modern agricultural practices largely rely on pesticides to protect crops against various pests and to ensure high yields. Following their application to crops a large amount of pesticides ends up in soil where they may affect non-target organisms, among which microorganisms. We assessed the effects of the carbamate nematicide oxamyl on the whole bacterial diversity of an agricultural soil exhibiting enhanced biodegradation of oxamyl through 16S rRNA amplicon next generation sequencing (NGS) and on the oxamyl-degrading bacterial community through cehA q-PCR analysis and 14C-oxamyl mineralization assays. Oxamyl was rapidly mineralized by the indigenous microorganisms reaching >70% within a month. Concomitantly, a significant increase in the number of oxamyl-degrading microorganisms was observed. NGS analysis of the total (DNA) and active (RNA) bacterial community showed no changes in α-diversity indices in response to oxamyl exposure. Analysis of the ß-diversity revealed significant changes in the composition of the soil bacterial community after 13 and 30 days of oxamyl exposure only when the active fraction of the bacterial community was considered. These changes were associated with seven OTUs related to Proteobacteria (5), Acidobacteria (1) and Actinobacteria (1). The relative abundance of the dominant bacterial phyla were not affected by oxamyl, except of Bacteroidetes and Gemmatimonadetes which decreased after 13 and 30 days of oxamyl exposure respectively. To conclude, oxamyl induced changes in the abundance of oxamyl-degrading microorganisms and on the diversity of the soil bacterial community. The latter became evident only upon RNA-based NGS analysis emphasizing the utility of such approaches when the effects of pesticides on the soil microbial community are explored.

Mixture toxicity assessment of a biocidal product based on reproduction and avoidance behaviour of the collembolan Folsomia candida.

Biocidal products represent mixtures that might be released into the environment at application and continuously during service life. Concentration addition (CA) has been proposed as default model to calculate theoretical mixture toxicity. However, the suitability of CA for chronic toxicity towards soil organisms has so far rarely been evaluated and therefore needs further experimental evidence. The present study investigated the toxicity of a wood preservative product and the individual active substances (tebuconazole and IPBC) therein with the aim to evaluate the compliance with the CA prediction for the product. Folsomia candida was selected as test organism for this purpose using the endpoints reproduction and avoidance behaviour. Both endpoints were increasingly impacted by increasing concentrations of the wood preservative product as well as its active substances tested individually. The chronic effects of the product could be predicted by CA with less than 4-fold deviation, while the assessment for avoidance behaviour indicated a strong underestimation. This underestimation could not be attributed to the one known formulation additive, an organic solvent. Overall, the present study provides some more evidence that CA could be applied as default model for standard endpoints of soil organisms, but warns against using CA for behavioural responses.

Health risk assessment of selected pesticide residues in green pepper and cucumber.

This report describes levels of 170 pesticide residues in green pepper and cucumber marketed in Turkey. The report also comprises the outcome of the consumer risk assessment of selected pesticides. In total, 725 samples of vegetables were analysed for residues of 170 distinct pesticides by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS). The in-house validation data fulfilled the requirements of the European SANTE/11945/2015 Guideline. The limit of quantifications (LOQs) varied from 0.003 to 0.016 mg kg-1. Recoveries ranged between 80.5 and 118.2%, with inter-day precisions of 0.7-19% relative standard deviation (RSD). The expanded measurement uncertainty for individual pesticides ranged from 10.4 to 42.4%. Overall, 12.9% of green peppers and 13.5% of cucumbers contained at least one detectable residue, but the levels were below the EU legal limits. For adults, the Hazard Quotients (HQs) for identified pesticides in green peppers and cucumbers ranged from 0.0003 to 0.0143%, and from 0.0001 to 0.0103%, respectively. Propamocarb and chlorpyrifos were the major contributors to hazard index (HI) for green pepper and cucumber, respectively. The results showed that there is no reason to be concerned about cumulative exposure to residues from green pepper and cucumbers for Turkish population.

Dietary cumulative acute risk assessment of organophosphorus, carbamates and pyrethroids insecticides for the Brazilian population.

Cumulative acute dietary risk assessments of organophosphorus (OPs), carbamates (CBs) and pyrethroids (PYs) were conducted for the Brazilian population. Residue data for 30786 samples of 30 foods were obtained from two national monitoring programs and one University laboratory, and consumption data from a national survey conducted among persons 10 years or older. Acephate and methamidophos were used as index compounds (IC) for OPs, oxamyl for CBs and deltamethrin for PYs. Exposures were estimated using the Monte Carlo Risk Assessment (MCRA 8.2) software. Orange and orange juice (mainly containing methidathion), pasta and salted bread (mainly pirimiphos-methyl) contributed most to the OPs intake. Rice accounted for 80% of the CBs intake (teenagers), mainly due to aldicarb. Pasta, salted bread and beans contributed most to the PYs intake (9-14%), mainly due to bifenthrin. The intake did not exceed the ARfD at the 99.9th percentile for OPs, CBs and PYs, and the risks from the exposure were not considered of health concern. When food consumption data become available for children under age 10, studies in the cumulative exposure should be conducted, as this age group is the most critical among the population, mainly due to their higher food consumption per kg body weight.

Assessment of protective potential of Nigella sativa oil against carbendazim- and/or mancozeb-induced hematotoxicity, hepatotoxicity, and genotoxicity.

Nigella sativa oil (NSO) possesses antioxidant activity. However, its protective role against the hazards of fungicides has been poorly studied. Therefore, the present work aimed at determining the ameliorative potential of NSO against hepatotoxicity induced by carbendazim (CBZ) and/or mancozeb (MNZ) in female rats. In the present study, about 120 adult female Sprague-Dawley rats were randomly divided into eight equal groups. One group of animals was kept as a negative control (Gp. 1); groups 2, 3 and 4 orally received CBZ (200 mg/kg body wt) and/or MNZ (300 mg/kg body wt) daily for 2 weeks (positive groups). In order to assess the hepatoprotective potential of NSO, in comparison with NSO-treated rats (Gp. 5), groups 6, 7 and 8 were CBZ- and/or MNZ-exposed groups pre-treated orally with NSO (2 ml/kg body wt) daily for 2 weeks (prophylactic groups). All groups were kept further for 15 days without medications to observe the withdrawal effect. At the end of exposure and withdrawal periods, the body weight of all experimental rats was recorded and blood samples were collected for hematological, clinico-biochemical, and micronucleus assays. The animals were then sacrificed, and the liver and bone marrow were harvested for oxidative stress bioassay, chromosomal aberrations, DNA fragmentation, and histopathological examinations. The results suggested that pre-treatment with NSO remarkably diminished CBZ- and MNZ-induced macrocytic hypochromic anemia, leukocytosis, lymphocytosis, eosinophilia, and neutropenia. Besides, it also minimized the elevated liver enzymes, lipid peroxidation, micronucleus incidence, DNA damage, and chromosomal aberration frequency. Conversely, NSO significantly stimulated the CBZ- and/or MNZ-induced antioxidant system suppression. The NSO also normalized the hepatic structural architecture. As far as withdrawal effect is concerned, there was almost disappearance of the bad effects of these fungicides and the values were close to the normal range especially with the use of NSO. Ultimately, the results revealed that N. sativa oil is an effective hepatoprotective agent due to its genoprotective and free radical scavenging activities.

Assessment of hematological parameters in workers exposed to organophosphorus pesticides, carbamates and pyrethroids in Cundinamarca 2016-2017.

OBJECTIVE: To establish hematotoxic alterations through clinical and paraclinical exploration in workers who are exposed to organophosphorus pesticides, carbamates and pyrethroids (OPCP) due to their work in production, packaging, distribution and fumigation processes in Cundinamarca-Colombia between 2016 and 2017. MATERIALS AND METHODS: A cross-sectional descriptive epidemiological study was carried out on a sample of 92 workers from six companies, mostly aged between 18 and 30 years, of which 61 % were males and 39 % females, and 71 % were workers in the operational area and 29 % in the administrative area. Univariate, bivariate and multivariate analyses were performed. RESULTS: Clinical exploration reported findings in 17 % of the sample group, of which only 2 % presented with erythrocyte cholinesterase outside the reference range. The values of hematological parameters such as peripheral blood smear (PBS) and complete blood count (CBC) were outside the range in 15 % and 47 % of the sample, respectively. DISCUSSION: The results suggest that there are hematological alterations in this group that could possibly be associated with chronic exposure to OPCP.

Binary combinations of organophosphorus and synthetic pyrethroids are more potent acetylcholinesterase inhibitors than organophosphorus and carbamate mixtures: An in vitro assessment.

Anticholinesterase insecticides such as organophosphorous (OP) and carbamates pesticides (CB); and synthetic pyrethroids (SP) pesticides commonly co-occur in the environment. This raises the possibility of antagonistic, additive, or synergistic neurotoxicity in exposed organisms. Acetylcholinesterase (AChE) inhibition has been demonstrated to be useful as a biomarker for exposure to OP and CBs in many environments. This study investigated the response of housefly (Musca domestica) head AChE (HF-AChE) exposed to five OPs; chlorpyrifos (CPF), malathion (MLT), triazophos (TRZ), monocrotophos (MCP) and profenofos (PRF) and two CBs; carbaryl (CRB) and carbofuran (CBF) as individual compounds and as binary mixtures of OPs and CBs under in vitro conditions. In addition, the selected OPs and CBs were evaluated for their toxicity in binary combinations with two SPs; deltamethrin (DLT) and cypermethrin (CYP) at fixed concentrations of 0.1 and 10µg/L. The toxicological interaction of five OPs with two CBs pesticides was evaluated under oxidised and un-oxidised conditions using a toxic unit (TU) approach and a concentration addition (CA) model. Pyrethroid combinations were assessed only under oxidised conditions. Since OPs and CBs act by a similar mechanism of inhibition of AChE, a dose additive effect was expected, but not conclusively found. TRZ with either CBF or CRB exhibited synergism under oxidised and un-oxidised conditions but the degree of synergism was stronger under un-oxidised conditions. Additivity was exhibited by CBF+MCP, CRB+MCP, CRB+MLT and CBF+MCP under un-oxidised conditions and CRB+MCP and CRB+CPF under oxidised conditions. Pyrethorids in combination with OPs (TRZ, MLT and CPF) were highly synergistic. In the present study, we used pure housefly head AChE without any interference of monooxygenase and/or esterase enzyme activities. Therefore these other enzymes were not producing the observed deviations from concentration-addition in the binary combinations between OPs, CBs and SPs. The mechanisms of OP, CB and SP interactions in pesticide mixtures requires further investigation.

Genotoxicity and cytotoxicity assessment of new ethyl-carbamates with ixodicidal activity.

The mammalian erythrocyte micronucleus test was used on the peripheral blood of Wistar rats exposed to two new ethyl-carbamates: ethyl-4-bromophenyl-carbamate (LQM 919) and ethyl-4-chlorophenyl-carbamate (LQM 996) to analyze their genotoxic potential. The mitotic index and cell proliferation kinetics in human lymphocyte cultures in the presence of these ethyl-carbamates were used to evaluate cytotoxicity and cytostaticity respectively. Exposure to greater acute doses (300mg/kg) and to all of the subchronic doses (12.5, 25 and 50mg/kg daily for 90 days) of these ethyl-carbamates induced an increased frequency (p<0.05) of micro-nucleated polychromatic erythrocytes (MN-PCE) compared with rats not exposed to the ethyl-carbamates. Increases in MN-PCE was higher in males than in females exposed to LQM 996 50mg/Kg (p<0.05). All observed changes in rats return 21days after suspending ethyl-carbamate exposure. The highest concentration (0.3mM) of both ethyl-carbamates in lymphocyte cultures increased the percentage of cells in first division metaphase and decreased the percentage of cells in third division metaphase, indicating an increase in cell cycle length or a possible cell cycle arrest in metaphase (cytostatic effect). The results of this study show that the evaluated ethyl-carbamates may induce genotoxic damage in rats and alterations in the human lymphocyte cell cycle.

Design and comparative anticonvulsant activity assessment of CNS-active alkyl-carbamoyl imidazole derivatives.

A novel series of carbamoyl derivatives of alkylimidazole has been designed and their anticonvulsant activity was comparatively evaluated in the mice- and rats-maximal-electroshock (MES), subcutaneous-metrazol (scMet) seizure tests and the mice-6Hz psychomotor (6Hz) models. The ten new designed molecules contain in their chemical structure imidazole, alkyl side-chain and carbamate as three potential active moieties. In spite of the close structural features of the carbamoyl imidazole derivatives only compounds 7, 8, 13 and 16 were active at the MES test with ED50 values ranging from 12 to 20mg/kg coupled with high protective index (PI=TD50/ED50) values of 4.1-7.3 after ip administration to rats. A similar phenomenon was observed in mice where compounds 7, 8, 9, 12 had MES-ED50 values of 14-26mg/kg. Compounds 7 and 13 also demonstrated anticonvulsant activity in the 6Hz model with ED50 values of 32 and 44mg/kg, respectively. As the most active entities, compounds 7, 8 followed by 13 and 16, thus offer an optimal efficacy-safety profile and consequently, might be promising candidates for development as new antiepileptics.

Ex vivo assessment of testicular toxicity induced by carbendazim and iprodione, alone or in a mixture.

To measure the testicular toxicity of two fungicides (carbendazim and iprodione), alone or in a mixture, we used a rat ex vivo model of seminiferous tubules, greatly reducing the number of rodents used, in accordance with the 3R rule (Replacement, Reduction, and Refinement). This model allows the representation of puberty, a critical life period with regard to endocrine disruptors. The cellular modifications were followed for three weeks through transcriptomic and proteomic profiling analysis. A quantitative and comparative method was developed to estimate how known pathways were disturbed by each substance. This pathway-driven analysis revealed a strong alteration of steroidogenesis and an impairment of meiosis in all cases, albeit the initial molecular events were different for both substances. The ex vivo cytogenetic analysis confirmed that both fungicides alter the course of the first meiotic prophase. In addition, the mixture of both substances triggered effects greater than the sum of their cumulative effects and compromised future sperm motility after a shorter time of exposure compared with the fungicides tested separately. The alliance of an ex vivo culture with "omics" strategies complemented with a physiological examination is a powerful combination of tools for testing substances, separately or in a mixture, for their testicular toxicity. In particular, proteomics allowed the identification of systematically differentially expressed proteins in the secretomes of exposed cultures, such as FUCO and PEBP1, two proteins linked with the motility and fertilizing ability of spermatozoa, respectively. These proteins may be potential biomarkers of testicular dysfunction and infertility.

Longitudinal Assessment of Blood Cholinesterase Activities Over 2 Consecutive Years Among Latino Nonfarmworkers and Pesticide-Exposed Farmworkers in North Carolina.

OBJECTIVE: This study (1) describes patterns of whole blood total cholinesterase, acetylcholinesterase, and butyrylcholinesterase activities across the agricultural season, comparing farmworkers and nonfarmworkers; and (2) explores differences between farmworkers' and non-farmworkers' likelihood of cholinesterase depression. METHODS: Blood samples from 210 Latino male farmworkers and 163 Latino workers with no occupational pesticide exposure collected 8 times across 2 agricultural seasons were analyzed. Mean cholinesterase activity levels and depressions 15% or more were compared by month. RESULTS: Farmworkers had significantly lower total cholinesterase and butyrylcholinesterase activities in July and August and lower acetylcholinesterase activity in August. Farmworkers had significantly greater likelihood of cholinesterase depression for each cholinesterase measure across the agricultural season. SIGNIFICANCE: A repeated-measures design across 2 years with a nonexposed control group demonstrated anticholinesterase effects in farmworkers. Current regulations designed to prevent pesticide exposure are not effective.

Assessment of Sublethal and Transgenerational Effects of Pirimicarb on the Wheat Aphids Rhopalosiphum padi and Sitobion avenae.

The wheat aphids, Rhopalosiphum padi (Linnaeus) and Sitobion avenae (Fabricius), are key pests on wheat crops worldwide. Management practices rely primarily on insecticides. The pirimicarb (carbamate) is used extensively as an effective insecticide to control these two aphids. In addition to the mortality caused by pirimicarb, various sublethal effects may occur in aphids when exposed to low lethal or sublethal doses. Understanding the general effect of pirimicarb on aphids could help increasing rational use of this insecticide. Under laboratory conditions, we assessed the sublethal effects of a low lethal concentration of pirimicarb (LC25) on biological traits and acetylcholinesterase (AChE) activity of R. padi and S. avenae. Both direct and transgenerational effects, i.e. on parent and the F1 generations were assessed, respectively. We found that R. padi and S. avenae responded differentially to the LC25 of pirimicarb. The parent generation of R. padi showed a 39% decrease in fecundity and multiple transgenerational effects were observed in the F1 generation; overall juvenile development, reproductive period, adult longevity and lifespan were longer than those of the control group. By contrast, LC25 of pirimicarb showed almost no effects on S. avenae biological traits in both the parent and F1 generations; only the pre-reproductive duration was reduced in F1 generations. Demographic parameter estimates (e.g. rm) showed similar trend, i.e. significant negative effect on R. padi population growth and no effect on S. avenae. However, AChE activity decreased in both R. padi and S. avenae treated by the LC25 of pirimicarb. We demonstrated sublethal and transgenerational effects of pirimicarb in the two wheat aphid species; it hinted at the importance of considering sublethal effects (including hormesis) of pirimicarb for optimizing Integrated Pest Management (IPM) of wheat aphids.

Assessment of a twice dosing regimen both before and after partial hepatectomy in the rat liver micronucleus test.

The liver micronucleus test is an important method to detect in vivo genotoxicants, especially those that require metabolic activation for their genotoxicity. We have already reported that structural or numerical chromosome aberration inducers have to be given before or after partial hepatectomy, respectively, to detect their genotoxicity in the liver of rats. In the present study, we assessed a twice dosing regimen, in which the genotoxicant is dosed both before and after partial hepatectomy, using the four chromosome aberration inducers used in the previous study. Two structural chromosome aberration inducers (diethylnitrosamine and 1,2-dimethylhydrazine) and two numerical chromosome aberration inducers (colchicine and carbendazim) were used. The genotoxicant was administered to 8-week old male F344 rats one day before and again one day after the partial hepatectomy and hepatocytes were isolated 3 days after second dosing (4 days after the partial hepatectomy). As a result, all genotoxicants (structural or numerical chromosome aberration inducers) caused a dose-dependent statistically significant increase in the incidence of micronucleated hepatocytes when given both before and after partial hepatectomy. No marked difference was observed in general toxicity, relative liver weight and cell classification between single dosing regimens and twice dosing regimen of the genotoxicants. These results confirm that the twice dosing regimen, in which the test compound is dosed both before and after partial hepatectomy, can detect in vivo induction of micronucleated hepatocytes by structural or numerical chromosome aberration inducers qualitatively similar to their appropriate regimen in which the test compound is administered either before or after partial hepatectomy.

The combined toxicity assessment of carp (Cyprinus carpio) acetylcholinesterase activity by binary mixtures of chlorpyrifos and four other insecticides.

Mixtures of organophosphate (OP) and carbamate (CB) insecticides are commonly detected in freshwater habitats. These insecticides inhibit the activity of acetylcholinesterase (AChE) and have potential to interfere with behaviors that may be essential for survival of species. Although the effects of individual anticholinesterase insecticides on aquatic species have been studied for decades, the combined toxicity of mixtures is still poorly understood. In the present study, we assessed whether pesticides in a mixture act in isolation (resulting in additive AChE inhibition) or whether components interact to produce either antagonistic or synergistic toxicity. Brain AChE inhibition in carp (Cyprinus carpio L.) exposed to a series of concentrations of the OP (chlorpyrifos, malathion and triazophos) as well as the CB (fenobucarb and carbosulfan) were measured. The concentration addition (CA) model and the isobole method were used to determine whether toxicological responses to binary mixtures of pesticides. In 50:50 % effect mixtures, the observed combined toxicity of chlorpyrifos and malathion was significantly higher than observed and was considered as synergistic. For equivalent dose mixtures, when chlorpyrifos mixed with fenobucarb or malathion, the observed toxicities were significantly higher than predicted, suggesting synergistic joint actions. The rest five binary combinations exhibited concentration additive or slight antagonistic joint actions. The CA model and the isobole method provided estimates of mixture toxicity that did not markedly underestimate the measured toxicity, therefore these methods are suitable to use in ecological risk assessments of pesticide mixtures.