Acephate Research Articles

Removal of acephate and methamidophos from water: Coagulation and adsorptive treatment approaches

Pesticides has transformed the agricultural industry, primarily by enhancing productivity. However, the indiscriminate use of such compounds can adversely affect human health and disrupt ecosystem balance. Limited knowledge exists regarding the removal of these compounds from water, particularly for organophosphate pesticides when employing conventional treatment technologies. Therefore, this study aimed to assess the removal of acephate (ACE) and methamidophos (MET) - considered priority pesticides in Brazil - from waters with high and low turbidity during the clarification process carried out with aluminum sulfate (AS) and ferric chloride (FC), either alone or combined with powdered activated carbon (PAC) adsorption. All water samples were submitted to solid phase extraction (SPE C18 cartridges) prior to acephate and methamidophos analysis by HPLC MS/MS. The clarification process with either AS or FC coagulant did not efficiently remove acephate or methamidophos and maximum average removal (27 %) was observed with waters of high turbidity when using ferric chloride as coagulant. Addition of mineral PAC was also ineffective for removing both pesticides. However, the use of vegetable PAC (10 mg/L) resulted in better removal percentages, up to 80%, but only for methamidophos. The limited removal rates were attributed to the high hydrophilicity of acephate and methamidophos, along with their neutral charge at coagulation pH. These factors hinder the interaction of such organophosphorus pesticides with the flocs formed during coagulation as well as with PAC surface.

Effective removal of different species of organophosphorus pesticides (acephate, omthosate, and methyl parathion) using chitosan/Zeolite-A as multifunctional adsorbent

Chitosan/zeolite-A composite (CS/ZA) was synthesized and characterized as a multifunctional, eco-friendly, and enhanced adsorbent for three species of organophosphorus pesticides (acephate (AC), omthosate (OM), and methyl parathion (MP)). The CS/ZA composite achieved maximum capacities of 650.7 mg/g, 506.5 mg/g, and 560.8 mg/g for AC, OM, and MP, respectively. The kinetic and equilibrium inspection validate Pseudo-first order and Langmuir properties for the uptake of the pesticide by CS/ZA. Moreover, the thermodynamic parameters declared the nature of these reactions as spontaneous, favorable, and exothermic processes. The values of Gaussian energy, enthalpy, and free energy suggested a complex uptake mechanism involving chemical and physical reactions for the assessed pesticides. The CS/ZA composite showed promising affinities for the AC, OM, and MP pesticides even in the existence of other inorganic anions or metal ions. The adsorption properties of CS/ZA as a fixed bed (6 cm) in column systems achieved removal percentages of 78% (AC), 57.6% (OM), and 74.3% (MP) considering the selected flow rate (5 mL/min), concentration (25 mg/L), and pH (pH 8). The CS/ZA displayed considerable stability and recyclability during the removal of the three pesticides. • Chitosan/zeolite-A was used in the adsorption of organophosphorous pesticides. • The q max of acephate, omthosate, and methyl parathion are 650, 506, and 560 mg/g. • The uptake behavior of both ions follow Langmuir and Pseudo-First order models. • The uptake of the ions occurred by physical exothermic and spontaneous reactions. • The column tests showed promising removal of the pesticides by the composite bed.

A novel acetylcholinesterase biosensor with dual-recognized strategy based on molecularly imprinted polymer

Biosensors using acetylcholinesterase (AChE) as the recognition element detect both toxicity (AChE inhibition activity) and concentration of organophosphorus pesticides (OPs). However, real application of these biosensors remains a challenge due to their low selectivity and low resistance to sample matrix, interferences and hash analytical conditions. In this study, a novel dual-recognized strategy was established by using molecularly imprinted polymer (MIP) and AChE selective to different moieties of acephate (AP) as affinity molecules simultaneously. Using AP as the model OP, MIP highly selective to certain moieties but not phosphorus of AP was prepared on the surface of microplate by self-polymerization of dopamine. The MIP enriched AP from samples selectively. Then AChE selective to phosphorus of AP quantified the levels of AP captured by MIP. AP captured by MIP still inhibited the activity of AChE because the affinity of AP to AChE was higher than to MIP. By incorporating selective sample pretreatment with AChE inhibition assay in one sensor, the biosensor identified AP from other OPs, carbamates pesticides and interferences commonly found in food and environmental samples. When vegetables with high matrix effect on AChE inhibition assay were analyzed, selective sample pretreatment ensured the biosensor to detect AP more accurately and selectively than classical AChE inhibition assay. The results of the biosensor had no statistical difference compared with those of HPLC-MS/MS. The dual-recognized strategy may provide a new solution to detect target enzyme inhibitors in complicated samples using enzyme-based biosensors selectively and accurately.

Bioremoval of Acephate by biofilm-forming Enterobacter cloacae – VITDAJ8 in a vertical packed bed biofilm bioreactor

Organophosphorus (OP) pesticides are widely used due to their specific chemical properties and broad spectrum insecticidal activity. Accumulation of OP residues in various targeted and non-targeted environmental sites have increased the risk of biomagnifications thereby rendering serious threat to human health and the environment. Hence, the present study is primarily focused on the effective removal of Acephate (ACP) from aqueous solution. Bacteria isolated from the agricultural field and tannery effluent were screened based on their tolerance against two OP pesticides. The pesticide-resistant strains were further screened for biofilm formation and EPS production under ACP stress. Isolate VITDAJ8 exhibited highest pesticide tolerance against ACP, excellent biofilm formation and EPS production ability. Molecular characterization of VITDAJ8 by 16S rRNA gene sequencing revealed the isolate to be the closest neighbor of Enterobacter cloacae (Accession no. KP305912). A bench-scale vertical packed bed biofilm bioreactor was designed for the bioremoval of OP pesticides. Groundnut shells with a bed height of 10 cm were used as substrate with biofilm formed by VITDAJ8. The biosorption of ACP from the aqueous solution was monitored using UV-Vis spectrophotometer and HPLC and maximum ACP bioremoval up to 86% was achieved within 90 minutes of reaction time. Removal of ACP using groundnut shells without biofilm support was comparatively less efficient. The equilibrium adsorption study revealed the process to be the best fit for Langmuir isotherm modeling with maximum adsorption up to 235 mg L-1 and the kinetics of biosorption was found to be fitting well with the second-order kinetic model.

Manejo de agrotóxicos no cultivo de grãos e sua relação com a saúde e ambiente

Este estudo teve por objetivo identificar como ocorre o manejo de agrotóxicos utilizados no cultivo de grãos e sua relação com a saúde e o ambiente em um município da região da Serra Catarinense. Foram entrevistados 79 agricultores que cultivam grãos (soja, milho e feijão) para coleta de informações sociodemográficas e de suas propriedades, sobre o uso, transporte, armazenamento e descarte das embalagens vazias. Quase metade dos agricultores transporta agrotóxicos em carro fechado, junto com outros produtos e não possui local exclusivo para o armazenamento dos produtos. Além disso, 26,6% deles relataram não receber assistência técnica, 25,3% compram agrotóxico sem receita e 5,1% não realizam logística reversa das embalagens. Foram utilizados 40 tipos de agrotóxicos diferentes no cultivo de grãos, sendo o herbicida glifosato o mais utilizado, seguido fungicida propinebe e o inseticida acefato. Tendo em vista o modelo agrícola baseado no monocultivo, que impõe aos agricultores a utilização dos agrotóxicos, pode-se observar que os resultados obtidos nesse estudo constituem-se em um problema de saúde pública uma vez que o transporte, armazenamento e, principalmente, o descarte inadequado de resíduos e das embalagens vazias, podem ocasionar contaminação nos diversos compartimentos ambientais, bem como, à saúde humana.

Comparative examination on synergistic toxicities of chlorpyrifos, acephate, or tetraconazole mixed with pyrethroid insecticides to honey bees (Apis mellifera L.)

Potential synergistic toxicity of pesticide mixtures has increasingly become a concern to the health of crop pollinators. The toxicities of individual and mixture of chlorpyrifos (CHL), acephate (ACE), or tetraconazole (TET) with nine pyrethroid insecticides to honey bees (Apis mellifera L.) were evaluated to reveal any aggregated interaction between pesticides. Results from feeding toxicity tests of individual pesticides indicated that organophosphate insecticides CHL and ACE had higher toxicities to honey bees compared to nine pyrethroids. Moreover, different pyrethroids exhibited considerable variation in toxicity with LC50 values ranging from 10.05 (8.60-11.69) to 1125 (922.4-1442)mga.i.L-1 after exposure for 7days. Among the 12 examined pesticides, a relatively low toxicity to A. mellifera was detected from the fungicide TET. All the binary mixtures of ACE or TET in combination with pyrethroids exhibited synergistic effects. However, TET in combination with pyrethroids showed greater synergistic toxicity to A. mellifera than ACE in combination with pyrethroids. Approximately 50% binary mixtures of CHL in combination with pyrethroids also showed synergistic responses in honey bees. In particular, CHL, ACE, or TET in combination with either lambda-cyhalothrin (LCY) or bifenthrin (BIF) showed the strongest synergy in A. mellifera, followed by CHL, ACE, or TET in combination with either zeta-cypermethrin (ZCY) or cypermethrin (CYP). The findings indicated that the co-exposure of various pesticides in natural settings might lead to severe injury to crop pollinators. Therefore, pesticide mixtures should be applied carefully in order to minimize negative effects on honey bees while maintaining effective management against crop pests.

Au-Decorated Dragonfly Wing Bioscaffold Arrays as Flexible Surface-Enhanced Raman Scattering (SERS) Substrate for Simultaneous Determination of Pesticide Residues.

Rapid sampling and multicomponent analysis are vital in pesticide residue detection. In this work, we proposed a SERS platform to detect three kinds of pesticides on apple peels simultaneously by a straightforward “press and peel off” method. The flexible Au/dragonfly wing (Au/DW) substrate was obtained from sputtering Au nanoislands on DW bioscaffold arrays by a simple direct current (DC) magnetron sputtering system. The high-performance substrate exhibited a low limit of detection (LOD) to 4-aminothiophenol (4-ATP) (10−9 M), outstanding reproducibility (less than 12.15%), good stability and suitability in multifold pesticide residues detection. Considering its excellent sample collection efficiency, the Au/DW substrate was employed to solve critical pesticide residue problems for detection of acephate (APT), cypermethrin (CPT), tsumacide (MTMC) and their multiple components on apple peels. The results show that the LOD was 10−3 ng/cm2 for APT obtained on the apple surface with a calculation equation of y = 0.26x + 6.68 and a determination coefficient (R2) of 0.970. Additionally, the LOD values for CPT and MTMC were 10−3 ng/cm2 and 10−4 ng/cm2, respectively. The finding in this work may provide a promising biomimetic SERS platform for on-spot detection of other organic pollutants in the food industry and inenvironmental protection.

Developmental toxicity and neurotoxicity of synthetic organic insecticides in zebrafish (Danio rerio): A comparative study of deltamethrin, acephate, and thiamethoxam

Synthetic organic insecticides, including pyrethroids, organophosphates, neonicotinoids and other types, have the potential to alter the ecosystems and many are harmful to humans. This study examines the developmental toxicity and neurotoxicity of three synthetic organic insecticides, including deltamethrin (DM), acephate (AP), and thiamethoxam (TM), using embryo-larval stages of zebrafish (Danio rerio). Results showed that DM exposure led to embryo development delay and a significant increase in embryo mortality at 24 and 48 h post-fertilization (hpf). DM and AP decreased embryo chorion surface tension at 24 hpf, along with the increase in hatching rate at 72 hpf. Moreover, DM caused ntl, shh, and krox20 misexpression in a dose-dependent manner with morphological deformities of shorter body length, smaller eyes, and larger head-body angles at 10 μg/L. TM did not show significant developmental toxicity. Furthermore, results of larval rest/wake assay indicated that DM (>0.1 μg/L) and AP (0.1 mg/L) increased activity behavior with different patterns. Interestingly, as an insect-specific pesticide, TM still could alter locomotor activity in zebrafish larvae at concentrations as low as 0.1 mg/L. Our results indicate that different types of synthetic organic insecticides could create different toxicity outcomes in zebrafish embryos and larvae.

Combate químico de THRIPS TABACI (thysanoptera: thripidae) en el cultivo de cebolla, en Morelos, México

El cultivo de cebolla presenta altas poblaciones del trips (Thrips tabaci Lindeman), lo que ocasiona marchitez prematura, retarda el desarrollo de la hoja y distorsiona los brotes vegetativos. Los agricultores han usado diferentes plaguicidas para el manejo del trips, sin tener en cuenta la rotación de grupos químicos y dosis adecuadas, lo que ocasiona contaminación ambiental por el uso excesivo de agroquímicos. Por lo que el objetivo de este estudio, fue evaluar seis grupos de plaguicidas para el manejo de trips, los cuales fueron rotados durante el ciclo del cultivo, así como también se identificó la especie de trips presente en el cultivo de la cebolla. El estudio inició en octubre de 2013, en un cultivo de cebolla, ubicada en Ayala, Morelos. Cada tratamiento consistió en la aplicación de los siguientes insecticidas: T1: Testigo (sin producto); T2: Movento, Velcefate, Muralla, Tracer; T3: Regent, Muralla, Movento, Seizer+ Agromectin; T4: Tracer, Movento, Curacron, Muralla; T5: Actigard, Tracer, Colt, Agromectin; T6: Evisect-s, Curacron, Tracer, Calypso. Para determinar el control de los insecticidas, se contabilizó el número de ninfas y adultos de trips. Con los datos del número de ninfas y adultos de trips en los diferentes tratamientos, se realizó un análisis de varianza y separación de medias con la prueba Tukey (? 0.05). Para determinar las especies de trips presentes, se tomó una muestra en las hojas de las plantas de cebolla. Los insecticidas que lograron un control de las ninfas de trips en el cultivo de cebolla, fueron el Tracer, Acefate, Curacron y la combinación de Seizer+ Agromectin. Los insecticidas Tracer y Muralla, fueron los que mantuvieron las poblaciones más bajas de adultos de trips en el cultivo de cebolla. La especie de trips predominante en el cultivo de cebolla durante el estudio fue Thrips tabaci L.

Prenatal organophosphates exposure alternates the cleavage plane orientation of apical neural progenitor in developing neocortex.

Prenatal organophosphate exposure elicits long-term brain cytoarchitecture and cognitive function impairments, but the mechanism underlying the onset and development of neural progenitors remain largely unclear. Using precise positioned brain slices, we observed an alternated cleavage plane bias that emerged in the mitotic neural progenitors of embryonal neocortex with diazinion (DZN) and chlorpyrifos (CPF) pretreatment. In comparison with the control, DZN and CPF treatment induced decrease of vertical orientation, increase of oblique orientation, and increase of horizontal orientation. That is, the cleavage plane orientation bias had been rotated from vertical to horizontal after DZN and CPF treatment. Meanwhile, general morphology and mitotic index of the progenitors were unchanged. Acephate (ACP), another common organophosphate, had no significant effects on the cleavage plane orientation, cell morphology and mitotic index. These results represent direct evidence for the toxicity mechanism in onset multiplication of neural progenitors.

Extractive efficacy of microwave synthesized zeolitic material for acephate: Equilibrium and kinetics

Present investigation deals with the utilization of Bagasse fly ash (BFA) a sugar industry waste and Zeolitic material (MZBFA), synthesized from BFA by combined conventional and microwave reflux method as adsorbents for the extraction of Acephate (ACP), an organophosphorus pesticide from aqueous solution. The synthesized adsorbents were characterized using various techniques such as FTIR, PXRD and SEM. The effect of various experimental parameters has been investigated using a batch adsorption technique for the extraction of ACP. The extent of removal is increased with decrease in initial ACP concentration and particle size of the adsorbent. Adsorption was fast and the equilibrium was established within 90 min. Pseudo-first-order, Pseudo-second-order, Bangham and intra-particle particle diffusion models were used to fit the experimental data. Pseudo-second-order rate equation was able to provide realistic description of adsorption kinetics. Equilibrium isotherms were analyzed by Freundlich, Langmuir, Dubinin-Radushkevich and Tempkin isotherm equations. Langmuir equation was found to best represent the equilibrium data. The thermodynamic study showed that adsorption of ACP on MZBFA is higher than that on BFA. The results indicate that such Zeolitic material could be employed as low cost alternatives to Bagasse fly ash in wastewater treatment for the removal of pesticides.

Cytotoxicity and DNA damage of five organophosphorus pesticides mediated by oxidative stress in PC12 cells and protection by vitamin E

Previous studies have demonstrated that pesticides could induce cytotoxicity and genotoxicity in vivo and in vitro, and that oxidative stress may be an important factor involved. However, investigations comparing the capability of different organophosphorous (OP) compounds to induce cytotoxicity, genotoxicity and oxidative stress are limited. Hence, the aim of this paper was to access the cytotoxic and genotoxic effects of five OPs or metabolites, Acephate (ACE), Methamidophos (MET), Chloramidophos (CHL), Malathion (MAT) and Malaoxon (MAO), and to clarify the role of oxidative stress, using PC12 cells. The results demonstrated that MET, MAT and MAO caused significant inhibition of cell viability and increased DNA damage in PC12 cells at 40 mg L−1. MAO was more toxic than the other OPs. ACE, MET, MAT and MAO increased the levels of intracellular reactive oxygen species (ROS) and malondialdehyde (MDA), and decreased the activity of superoxide dismutase (SOD), catalase (CAT) and glutathione (GSH) at 20 mg L−1 and 40 mg L−1 to different degrees. Pre-treatment with vitamin E(600 μM)caused a significant attenuation in the cytotoxic and genotoxic effect; pre-treatment reversed subsequent OP-induced elevation of peroxidation products and the decline of anti-oxidant enzyme activities. These results indicate that oxidative damage is likely to be an initiating event that contributes to the OP-induced cytotoxicity.

A Distribution-Based Multiple Imputation Method for Handling Bivariate Pesticide Data with Values below the Limit of Detection

BackgroundEnvironmental and biomedical researchers frequently encounter laboratory data constrained by a lower limit of detection (LOD). Commonly used methods to address these left-censored data, such as simple substitution of a constant for all values < LOD, may bias parameter estimation. In contrast, multiple imputation (MI) methods yield valid and robust parameter estimates and explicit imputed values for variables that can be analyzed as outcomes or predictors.ObjectiveIn this article we expand distribution-based MI methods for left-censored data to a bivariate setting, specifically, a longitudinal study with biological measures at two points in time.MethodsWe have presented the likelihood function for a bivariate normal distribution taking into account values < LOD as well as missing data assumed missing at random, and we use the estimated distributional parameters to impute values < LOD and to generate multiple plausible data sets for analysis by standard statistical methods. We conducted a simulation study to evaluate the sampling properties of the estimators, and we illustrate a practical application using data from the Community Participatory Approach to Measuring Farmworker Pesticide Exposure (PACE3) study to estimate associations between urinary acephate (APE) concentrations (indicating pesticide exposure) at two points in time and self-reported symptoms.ResultsSimulation study results demonstrated that imputed and observed values together were consistent with the assumed and estimated underlying distribution. Our analysis of PACE3 data using MI to impute APE values < LOD showed that urinary APE concentration was significantly associated with potential pesticide poisoning symptoms. Results based on simple substitution methods were substantially different from those based on the MI method.ConclusionsThe distribution-based MI method is a valid and feasible approach to analyze bivariate data with values < LOD, especially when explicit values for the nondetections are needed. We recommend the use of this approach in environmental and biomedical research.

Development of a Novel Multi-functional Adsorbent Bearing with Long-Chain Hydrophobic and Anion Exchange Groups for the Simple and Rapid Determination of Residual Acephate in Vegetables

A novel multi-functional adsorbent (RP-SAX adsorbent) bearing hydrophobic and anion exchange groups was synthesized for the simple and rapid determination of residual acephate (AP) in vegetables. Macroporous base resin was obtained by suspension copolymerization with glycidyl methacrylate, stearyl methacrylate and glycerin dimethacrylate, and then ethyldimethylamine was introduced at glycidyl groups on the base resin. The adsorbent was packed into a syringe-type tube and used for extraction of AP. AP in the vegetable extract was quantitatively entrapped on the adsorbent and was completely eluted with 3 mL of 30 mmol/L trisodium phosphate in 50% (v/v) methanol solution. The eluate was directly injected into an HPLC-UV detection system with a reverse-phased column. The recoveries of 5 mg/L AP spiked in vegetable extraction samples ranged from 77% to 100%.

EFFECTS OF METHAMIDOPHOS AND ACEPHATE ON EXPERIMENTAL POPULATION DYNAMICS OF ROTIFER &lt;I&gt;BRACHIONUS CALYCIFLORUS&lt;/I&gt;

Effects of sublethal levels(0.01,0.1,1.0,10.0,100.0,1000.0 and 10000.0 μg/L) of organophosphorus insecticides including methamidophos(O,S-Dimethyl phosphoramidothioate,CAS No.10265-92-6) and acephate(O,S-Dimethyl acetylphosphoramidothioate,CAS No.30560-19-1) on population dynamics of rotifer Brachionus calyciflorus were studied by 3-day population growth test at 25±1℃,in dark,and with 3.0×106 cells/mL of S.obliquus as the rotifers' food.The results showed that both methamidophos and acephate influenced significantly the population growth rate,the ratio mictic females/amictic females and the mictic rate of the rotifers.Methamidophos influenced markedly the carrying-egg females/non-carrying-egg females of the rotifers,but acephate did not.Compared to the controls,100.0 μg/L methamidophos and 1.0—10000.0 μg/L acephate increased significantly the population growth rate,but the reverse was true for 1,000.0 and 10,000.0 μg/L methamidophos.1,000.0 μg/L methamidophos increased significantly the ratio carrying-egg females/non-carrying-egg females.0.1 μg/L methamidophos and 10.0—10000.0 μg/L acephate increased significantly the ratio mictic females/amictic females,and both 0.1 μg/L methamidophos and 10 μg/L acephate increased significantly the mictic rate.10.0—10000.0 μg/L acephate significantly increased the resting egg production.The above-stated results indicated that sublethal levels of methamidophos and acephate influenced significantly the population dynamics of B.calyciflorus.

Urinary elimination kinetics of acephate and its metabolite, methamidophos, in urine after acute ingestion

Acephate (AP) is a widely available organophosphorus (OP) insecticide considered to have low mammalian toxicity. In plants and insects, AP is metabolized extensively to methamidophos (MP), a more potent OP insecticide. The limited mammalian metabolism of AP to MP has been studied in laboratory rat models and suggests that initial formation of MP from AP may inhibit further formation. No case reports of human ingestion with urine AP and MP levels have been previously published. A 4-year-old male being evaluated for altered mental status and head trauma was noted to have muscarinic and nicotinic cholinergic signs. Further history suggested possible ingestion of a commercial AP product at an unknown time. Ingestion of AP was confirmed by the presence of urinary AP and MP and severely depressed red blood cell (RBC) cholinesterase and pseudocholinesterase activity levels. The patient initially received atropine in two 0.02 mg/kg IV boluses, then was started on 0.05 mg/kg IV per hour and titrated accordingly to clinical signs of cholinergic toxicity. Pralidoxime was also given at 20 mg/kg IV bolus, followed by an infusion of 10 mg/kg per hour. The patient required mechanical ventilation for 18 days and atropine infusion for 20 days. After a complicated intensive care unit course, he recovered and was discharged after a total of 32 days of hospitalization. Four urine samples collected at different times were analyzed for AP and MP by using high-performance liquid chromatography-atmospheric pressure chemical ionization tandem mass spectrometry. Kinetic calculations were performed by using standard equations. Suspected ingestion was confirmed by the presence of AP and MP in urine. The amount of MP found in urine suggests some limited human metabolism to this more toxic compound. Urinary elimination kinetics of AP demonstrates low metabolic conversion of AP to MP in humans.

Stem injection of insecticides to control herbivorous insects on &lt;i&gt;Eucalyptus nitens&lt;/i&gt;

To minimise environmental impact in urban and recreational environments insecticides may be injected directly into the vascular system of trees rather than by conventional foliar spray application In previous stem injection trials the majority of injected insecticides did not provide effective control of herbivorous insects This was largely because of the insolubility of the formulated insecticide products available in New Zealand Three water soluble insecticides acephate imidacloprid and emamectin benzoate were injected directly into the xylem of Eucalyptus nitens In subsequent laboratory bioassays the effect of these insecticides were assessed on two leaf feeding insects Uraba lugens (gum leaf skeletoniser) and Trachymela sloanei (a eucalyptus tortoise beetle) The results indicate that acephate may be a suitable candidate for protecting trees using stem injection of insecticides but in this study imidacloprid and emamectin benzoate were not effective

Toxicity of Organophosphates on Morphology and Locomotor Behavior in Brine Shrimp, Artemia salina

The acute toxicity and hatching success of four organophosphorus insecticides--acephate (ACEP), chlorpyrifos (CPP), monocrotophos (MCP), and profenofos (PF)--was studied in a short-term bioassay using brine shrimp, Artemia salina. Fifty percent hatchability inhibition concentration and median lethal concentration (LC(50)) values were calculated after probit transformation of the resulting data. Among the insecticides tested, CPP is found to be the most toxic and also to inhibit hatching success of A. salina cysts in a concentration-dependent manner. In addition, the effect of these pesticides on locomotor behavior (swimming speed) and morphologic differences were studied in LC(50)-exposed nauplii after 24 hours. The in vivo effect of these insecticides on acetylcholinesterase (Enzyme commission number (EC 3.1.1.7) activity was also determined in LC(50)-exposed nauplii after 24 hours. Maximum percent decrease in their swimming speed and significant morphologic alterations were noticed in CPP-exposed brine shrimps. The order of toxicity was CPP > PF > MCP > ACEP in all the parameters studied.

Relative safety of combination products of insecticides to Tytthus parviceps (Reuter), a predator of planthoppers and leafhoppers in rice.

Safety of four combination products of insecticides and two single Compound insecticides to adults of brown mirid bug Tyttus parviceps , a predator of rice planthoppers was assessed under greenhouse conditions. Two combination products viz chlorpyriphos (50%.) + cypermethrin (5%,) (at 344 ppm.) and acephate (45%) + cypermethrin (5%) (at 500 ppm) were relatively safer than other two combination products, but less safe than acephate (750 ppm) or monocrotophos (500 ppm). In general, all the products were safer to nymphs of T . parviceps than to adults.

Analysis of functional effects of a mixture of five pesticides using a ray design

The protection of human health from the adverse effects of cumulative environmental exposure to chemical mixtures is an important issue. Of particular interest is the detection and characterization of interaction among chemicals in complex mixtures. Response surface methodology, often supported by factorial designs, is the classical statistical experimental approach. Fixed-ratio ray designs, which may include the use of single chemical data in addition to data along mixture ray(s), have been proposed as an alternative approach. Such designs permit a reduction in the amount of experimental effort when the region of interest can be restricted to exposure-relevant mixing ratios. A ‘single chemicals required’ (SCR) approach and a ‘single chemicals not required’ (SCNR) approach are both described. The methods are illustrated with a five-chemical mixture of organophosphorus pesticides—acephate (ACE), diazinon (DIA), chlorpyrifos (CPF), malathion (MAL) and dimethoate (DIM). Their relative proportions in the mixture were based on the relative dietary human exposure estimates of each chemical as projected by the U.S. EPA Dietary Exposure Evaluation Model (DEEM). Use of the SCR and SCNR methods for binary endpoints are demonstrated using a dichotomized gait score as an indication of toxicity. For both methods, the overall hypothesis of additivity was rejected, indicating significant departure from additivity when the five pesticides were combined at the specified mixing ratio. By comparison of the predicted response under additivity to the modeled response of the experimental mixture data this departure from additivity was characterized as synergy (greater than additive toxicity). To examine the influence of malathion in the mixture, it was removed from the five-pesticide mixture (full ray) and the remaining four chemicals (reduced ray) were combined at the same relative proportions used in the full fixed-ratio ray There was not a significant departure from additivity along the ray with the four remaining pesticides omitting malathion. Thus, although malathion was not dose-responsive alone, it significantly interacted with the other pesticides.