Acute Toxicity Of Chlorpyrifos Research Articles

Biosynthesized CS-MgO/zeolite hybrid material: An efficient adsorbent for chlorpyrifos removal - Kinetic studies and response surface methodology

The prevalence of organophosphate pesticides in aquatic environments raises severe concerns on a global scale. Chlorpyrifos, an insecticide, is included in a class of organophosphate pesticides. It is widely used on agricultural lands to control pests in cotton, fruit, and vegetables. The acute toxicity of chlorpyrifos is still dangerous to all aquatic living organisms. Then the treatment of water contaminated with chlorpyrifos is an important aspect. The recent decade has witnessed adsorption technology emerging as an advanced organophosphate pesticide wastewater treatment with great potential and a grand blueprint, in which the specific surface area and active sites of the adsorbent are considered to be the two most important characteristics largely impacting the adsorption performance. In this study, a CS-MgO/Zeolite composite was prepared by the microbial method as an effective adsorbent for the removal of chlorpyrifos from an aqueous solution. The adsorbent's properties were carefully characterized using X-ray diffraction, scanning electron microscopy, and Fourier-transform infrared spectroscopy. The refinement of experimental conditions, encompassing variations in adsorbent dosage, contact time, and chlorpyrifos concentration at five discrete levels, was systematically undertaken through the utilization of a composite central design rooted in response surface methodology. The solution pH played a key role in chlorpyrifos removal, and a pH of 7.0 was selected according to its high adsorption ability. The highest removal (80.9%) of chlorpyrifos by CS-MgO/Zeolite was obtained at an optimum pH of 7, a contact time of 40 min, an adsorbent dosage of 0.4 g/L, and a chlorpyrifos concentration of 5 mg/L−1. The adsorption results were highly fitted with the Freundlich adsorption isotherm model, and the maximum adsorption was 83.3 mg/g. Kinetic studies indicate that the removal of chlorpyrifos followed the pseudo-second-order model of adsorption (0.994). The thermodynamic parameters indicate the spontaneous and endothermic nature of chlorpyrifos sorption on CS-MgO/Zeolite sorbent. The results revealed that introducing chitosan could improve the adsorption capacity and rate effectively even though it sacrificed part of the specific surface areas of the MgO/Zeolite, indicating that active sites might play a dominant role during chlorpyrifos adsorption. The fabricated CS-MgO/Zeolite adsorbent nanocomposite displayed high reusability based on the elution and simultaneous regeneration ability. Therefore, as a cheap green nanocomposite adsorbent with high adsorption performance for chlorpyrifos, the CS-MgO/Zeolite nanocomposite adsorbent is expected to become one of the best candidate materials for chlorpyrifos removal aqueous solutions.

Acute Toxicity of Chlorpyrifos on the Freshwater Bivalves (Unio Tigridis) and Effects on Bioindicators

A freshwater bivalve plays a crucial function in aquatic habitats as the filtered water and burrowing mussels mix the sediment, thus increasing oxygen content and making the ecosystem healthier. The aim of the study is to see how chlorpyrifos affects biochemical markers in freshwater mussel Unio tigridis. About 180 individuals per taxon and water samples were collected from the Qandil water resource on the Greater Zab River, Erbil Province, Iraq. Once arrived at the lab, the individuals were kept in aquaria with river water and an air-conditioned room Temperature: 25±2 and Light: 12h/12h and acclimatized to laboratory conditions for seven days in aged tap water. The mussel's identification molecularly and the DNA sequence of the mussel includes U. tigridis supplied gene bank accession number ON872361, ON872362, ON872363, and ON872364 nucleotide sequencing. The 96-h toxicity of chlorpyrifos pesticide in the freshwater mussel U. tigridis was investigated using various nominal concentrations, including 50, 100, 200, 300 and 400 ppm. The water quality of the river and aquaria was tested for physicochemical parameters including water temperature, the potential of hydrogen ion pH, electrical conductivity EC, and total dissolved solids TDS, dissolved oxygen, total alkalinity, total hardness, calcium ion, magnesium ion. Water quality results of aquaria revealed that most tested variables were favorable for the breeding of mussels. The mortality of the mussels was observed daily and the 96 h LC50 value for mussels was 157.99 ppm. Within the tissue of the gills, Acetylcholinesterase (AChE), Glutathione S-transferase (GST), Catalase (CAT), and Malondialdehyde (MDA) were determined. The chlorpyrifos exposures caused significant increases in GST, CAT, and MDA. The elevation of oxidative stress biomarkers was inversely related to the AChE inhibition in the examined species. In conclusion water pollution by chlorpyrifos lead to unsafe condition for aquatic taxa.

Acute Toxicity of Chlorpyrifos on Histological Alterations in the Anomuran Crab, Emerita asiatica (H. Milne Edwards, 1837)

Acute toxicity of Chlorpyrifos on histological alterations in the different organs like gills, hepatopancreas and ovary of anomuran crab, Emerita asiatica was studied. Though Emerita asiatica is not a commercially viable crab, but it plays a vital role in the environment to maintain a stable marine ecosystem. Several steps and precautions measures should be taken to conserve these members of the marine food chain to have a stable ecosystem and also to protect this species from extinction. Thus, it can be concluded that the use of Chlorpyrifos which has been legally banned in India is justified. It has been proved by several workers and has been conformed in present investigation that use of this Chlorpyrifos causes serious damage to the vital organ of sand crabs gill, hepatopancreas and ovary. The application of Chlorpyrifos could be reduced in the agricultural field to nearby coastal regions.

Acute toxicity of atrazine, alachlor, and chlorpyrifos mixtures to honey bees

The acute toxicity of chlorpyrifos and chlorpyrifos-oxon (organophosphorothioate insecticides) was examined alone and in combination with atrazine (triazine herbicide) and alachlor (chloroacetanilide herbicide) to honey bees (Apis mellifera). Atrazine and alachlor were observed to not be acutely toxic to bees at doses up to 10 and 4 μg per bee, respectively. However, atrazine significantly increased chlorpyrifos toxicity by 3-fold while reducing chlorpyrifos-oxon toxicity by 1.8-fold. These changes in toxicity are correlated with significant 1.3- and 1.2-fold inhibition of acetylcholinesterase (AChE) activity in bees exposed to chlorpyrifos and chlorpyrifos-oxon, respectively. Atrazine significantly increased cytochrome P450, general esterase, and glutathione S-transferase (GST) activities by 1.5-, 1.2-, and 1.2- fold respectively, in bees compared to untreated individuals. Alachlor increased chlorpyrifos toxicity by 2.5-fold but did not affect the toxicity of chlorpyrifos-oxon. Exposure to alachlor and chlorpyrifos did not affect AChE compared to chlorpyrifos alone. However, exposure to chlorpyrifos-oxon and alachlor significantly increased acetylcholinesterase (AChE) activity by 1.4-fold. GST activity, but not P450 or general esterases, was significantly increased in bees exposed to alachlor. These data provide evidence that triazine and chloroacetanilide herbicide exposure alters detoxification enzyme activity and, in turn, alters the sensitivity of bees to organophosphorothioate insecticides. Importantly, these data can be used to guide future studies aiming to test safety profiles for pollinators and expand regulatory framework required for pesticide registration.

Acute toxicity of chlorpyrifos and its metabolite 3,5,6-trichloro-2-pyridinol alone and in combination using a battery of bioassays.

Acute toxicity of chlorpyrifos (CP) and its principal metabolite 3,5,6-trichloro-2-pyridinol (TCP) alone and in combination have been evaluated using a test battery comprising aquatic organisms from different trophic levels: luminescent marine bacteria Aliivibrio fischeri, freshwater unicellular alga Pseudokirchneriella subcapitata, and cladoceran Daphnia magna. As expected, D. magna was the more sensitive organism to the compounds tested, being CP more toxic than its metabolite. On the contrary, TCP was found to be more toxic than its parental compound to A. fischeri and P. subcapitata. In all cases, the mixture of CP and its metabolite was more toxic than the compounds tested separately, multiplying between 5 and 200 times CP toxicity level and up to 15 times TCP toxicity level. These results indicate that the co-existence of parent chemical and its degradation product in the environment can result in a synergic interaction involving high risk to the aquatic ecosystems. Graphical abstract.

Removal of chlorpyrifos, an insecticide using metal free heterogeneous graphitic carbon nitride (g-C3N4) incorporated chitosan as catalyst: Photocatalytic and adsorption studies.

The present study investigates the photocatalytic degradation of an organic pesticide using a metal free heterogeneous graphitic carbon nitride (g-C3N4) incorporated into chitosan as catalyst. Chlorpyrifos (O, O-diethylO-3,5,6-trichloro-2-pyridyl phosphorothioate (CPFS)), an insecticide includes in a class of Organophosphate pesticides with a chemical formula (C9H11Cl3NO3PS). It is widely used in agricultural lands to control pests in cotton, fruit and vegetables. The acute toxicity of chlorpyrifos is still dangerous to all aquatic living organisms. The CS/g-C3N4 materials have been characterized using UV-vis spectrophotometer (UV-vis), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscope (SEM), Energy Dispersive X-ray Analysis (EDX), Thermal analysis (TGA-DSC), Chemical oxygen demand (COD), X-ray diffraction (XRD), Diffuse reflectance spectra (DRS) and Electron spin resonance (ESR). The degradation of pesticide using CS/g-C3N4 showed good efficiency of about 85%. The results suggest that CS/g-C3N4 composite is a good alternative for the treatment of chlorpyrifos in aqueous solution. We have proposed a novel photocatalyst by metal free heterogeneous graphitic carbon using melamine and its recombination effects were minimized by chitosan which act as an electron carrier. The enhanced photocatalytic performance could be attributed to an efficient separation of electron-hole pairs through a Z-scheme mechanism, in which chitosan acted as charge separation carriers.

Acute toxicity of chlorpyrifos and carbosulfan to glochidia of the freshwater mussel Hyriopsis bialata Simpson, 1900.

The acute toxicity of carbosulfan and chlorpyrifos in formulated pesticides to glochidia (larvae) of the freshwater mussel (Hyriopsis bialata Simpson, 1900) was evaluated under static conditions in moderately hard dechlorinated tap water. Measured pesticide concentrations were 26 to 34% lower than nominal concentrations; therefore, all results are expressed in terms of measured active ingredient. Carbosulfan was relatively non-toxic to the mussel larvae with median effective concentrations (EC50) of carbosulfan at 24 and 48h greater than 0.10mg/L. The EC50s of chlorpyrifos at 24 and 48h were 0.083 and 0.078mg/L, respectively (measured concentrations). The 48-h EC50 of a combined exposure to a mixture of chlorpyrifos and carbosulfan at a constant ratio of 2.9:1 was 0.0142:0.049mg CP:CB/L. In a separate experiment, the effect of water hardness on carbosulfan, chlorpyrifos, or a combined exposure was assessed using glochidia exposed to either soft, moderately hard, or hard reconstituted water. There was no effect of water hardness on the survival of glochidia after 24- or 48-h exposure to carbosulfan. The chlorpyrifos 48-h EC50s in soft water, moderately hard water, and hard water were 0.18, 0.11, and 0.16mg/L, respectively. The data indicate that the lowest water hardness resulted in the highest survival of glochidia, whereas an increase to moderate water hardness resulted in significantly decreased survival of glochidia (F=15.5, P<0.05). The EC50s of a combined exposure at 48h in soft water, moderately hard water, and hard water were 0.124:0.044, 0.132:0.047, and 0.064:0.022mg CP:CB/L, respectively. The data indicate that the combined toxicity was lowest at low and moderate water hardness, whereas an increase to high water hardness resulted in a significantly decreased survival of glochidia. After 48h, the toxicity of the combined chlorpyrifos and carbosulfan exposure in soft and hard water was greater than that of chlorpyrifos alone.

Chlorpyrifos and chlorpyrifos oxon impair the transport of membrane bound organelles in rat cortical axons

Chlorpyrifos (CPF) is an extensively used organophosphorus pesticide that has recently come under increasing scrutiny due to environmental health concerns particularly its association with neurodevelopmental defects. While the insecticidal actions and acute toxicity of CPF are attributed to its oxon metabolite (CPO) which potently inhibits the cholinergic enzyme acetylcholinesterase (AChE), there is significant evidence that CPF, CPO, and other organophosphates may affect a variety of neuronal targets and processes that are not directly related to AChE. Previously, in adult rat sciatic nerves ex vivo and postnatal neurons from rats in vitro we observed that CPF and CPO impaired the movements of vesicles and mitochondria in axons. Here, in embryonic neurons from rats in culture, we evaluated 24h exposures to CPF and CPO across picomolar to micromolar concentrations for effects on fast axonal transport of membrane bound organelles (MBOs) that contained the amyloid precursor protein (APP) tagged with the fluorescent marker, Dendra2 (APPDendra2). The most notable observations of this study were concentration-dependent decreases in the velocity and percentage of MBOs moving in the anterograde direction, an increase in the number of stationary MBOs, and an increased frequency of pauses associated with both CPF and CPO. These effects occurred at concentrations that did not significantly inhibit AChE activity, they were not blocked by cholinergic receptor antagonists, and they were not associated with compromised cell viability. These effects of CPF and CPO may be significant given the importance of axonal transport to neuronal development as well the function of fully developed neurons.

Genotoxic Effects of Chlorpyrifos in Freshwater Fish Cirrhinus mrigala Using Micronucleus Assay

The genotoxicity of pesticides is an issue of worldwide concern and chlorpyrifos is one of the largest selling organophosphate agrochemicals that has been widely detected in surface waters of India. The studies on long term genotoxic biomarkers are limited; therefore, present study was carried out to analyze the incidence of nuclear anomalies in the blood cells of fresh water fish Cirrhinus mrigala using micronucleus (MN) assay as a potential tool for assessment of genotoxicity. Acute toxicity of chlorpyrifos was evaluated by exposing fingerlings to different doses of chlorpyrifos (1/20, 1/10, and 1/5 of LC50) and LC50 was calculated as 0.44 mg L−1 using probit analysis. Blood samples were taken on days 2, 4, 8, 12, 21, 28, and 35. In general, significant effects for both concentration and duration of exposure were observed in treated fish. It was found that MN induction was highest on day 14 at 0.08 mg L−1 concentration of chlorpyrifos. It was concluded that chlorpyrifos is genotoxic pesticide causing nuclear anomalies in Cirrhinus mrigala.

Chlorpyrifos-induced biomarkers in Japanese medaka (Oryzias latipes).

Chlorpyrifos (CHL) is an organophosphate compound that is widely used as an insecticide. Due to its repeated use and high environmental residual property, CHL is frequently passed into aquatic environments by runoff. Consequently, there may be an adverse effect on aquatic vertebrate animals, including fish. Therefore, in this study, we assessed how CHL affected Japanese medaka (Oryzias latipes). The acute toxicity of CHL in adult fish after 96h of exposure was determined to be 212.50, 266.79, and 412.28μgL(-1) (LC25, LC50, and LC95, respectively). Acetylcholinesterase (AChE), glutathione S-transferase (GST), and carboxylesterase (CE) activities were obtained from the livers of dead or surviving fish, and the results showed 4.8-fold lower, 4.5-fold higher, and 18.6-fold lower activities for the AChE, GST, and CE, respectively, for 64-h exposure at a concentration of 400μgL(-1) of CHL. In the embryo toxicity test, curved spines were observed in embryos that were exposed to CHL for 48h in a concentration-dependent manner. With identification of biomarkers for CHL in the fish, two protein peaks, 5550.86 and 5639.79 m/z, were found to be upregulated. These two proteins can be used as protein biomarkers for CHL contamination in aquatic systems. A phosphatidyl choline with an m/z ratio of 556.32 dramatically decreased after CHL exposure in the fish; thus, it may be considered as a lipid biomarker for CHL. It is assumed as the first report to identify a phospholipid biomarker using a lipidomics approach in fish toxicology. Taken together, these results demonstrated the adverse effects of CHL on Japanese medaka and reveal several candidate biomarkers that can be used as diagnostic tools for determining CHL.

Evaluation of the Genotoxicity of Chlorpyrifos in Common Indus Valley Toad, &amp;lt;i&amp;gt;Bufo stomaticus&amp;lt;/i&amp;gt; Using Alkaline Single-Cell Gel Electrophoresis (Comet) Assay

Chlorpyrifos is a commonly used pesticide of organophosphate group, which causes toxicological effects in non-target organisms especially fish and frogs. In the present study, the genotoxicity of sublethal concentrations of chlorpyrifos was observed in the erythrocytes of common Indus valley toad, Bufo stomaticus, using the Alkaline Single-Cell Gel Electrophoresis (Comet) assay. In the first step, acute toxicity of chlorpyrifos was evaluated by exposing the tadpoles to high concentrations of the pesticide. The acute LC50 value of chlorpyrifos, calculated by Trimmed Spearman-Karber (TSK) in static bioassay, was found to be 930.0 μg/L. On the basis of acute LC50 value, the tadpoles were exposed to three sublethal concentrations (155, 233 and 465 μg/L) of chlorpyrifos for 96 h. Blood cells were collected at every 24 h interval and were subjected to the Alkaline Single-Cell Gel Electrophoresis assay. The observed DNA damage was concentration and time-dependent, and those levels of DNA damage in between the tested concentrations and times were significantly different (p Bufo stomaticus.

Effects of chlorpyrifos on the transcription of CYP3A cDNA, activity of acetylcholinesterase, and oxidative stress response of goldfish (Carassius auratus)

Chlorpyrifos (CPF) is the widely used organophosphate pesticide in agriculture throughout the world. It has been found that CPF is relatively safe to human but highly toxic to fish. In this study, acute toxicity of CPF on goldfish was determined and then the transcription of goldfish cytochrome P450 (CYP) 3A was evaluated after 96 h of CPF exposure at concentrations of 15.3 [1/10 50% lethal concentration (LC50 )] or 51 μg L(-1) (1/3 LC50 ) of CPF. Meanwhile, the enzymatic activities of acetylcholinesterase (AChE), superoxide dismutase (SOD), and catalase (CAT), total antioxidant activity (T-AOC), and the contents of malondialdehyde (MDA) in the liver or brain of goldfish were also determined. The results of acute toxicity testing showed that the 96-h LC50 of CPF to the goldfish was 153 μg L(-1) . Moreover, a length sequence of 1243 bp CYP3A cDNA encoding for 413 amino acids from goldfish liver was cloned. Polymerase chain reaction results reveal that CPF exposure downregulates CYP 3A transcription in goldfish liver, suggesting that goldfish CYP 3A may be not involved in CPF bioactivation. Finally, the results of biochemical assays indicate that 96 h of CPF exposure remarkably inhibits AChE activity in fish liver or brain, alters hepatic antioxidant enzyme activities, decreases brain T-AOC, and causes lipid peroxidation in fish liver. These results suggest that oxidative stress might be involved in CPF toxicity on goldfish.

Dose-related gene expression changes in forebrain following acute, low-level chlorpyrifos exposure in neonatal rats

Chlorpyrifos (CPF) is a widely used organophosphorus insecticide (OP) and putative developmental neurotoxicant in humans. The acute toxicity of CPF is elicited by acetylcholinesterase (AChE) inhibition. We characterized dose-related (0.1, 0.5, 1 and 2 mg/kg) gene expression profiles and changes in cell signaling pathways 24 h following acute CPF exposure in 7-day-old rats. Microarray experiments indicated that approximately 9% of the 44,000 genes were differentially expressed following either one of the four CPF dosages studied (546, 505, 522, and 3,066 genes with 0.1, 0.5, 1.0 and 2.0 mg/kg CPF). Genes were grouped according to dose-related expression patterns using K-means clustering while gene networks and canonical pathways were evaluated using Ingenuity Pathway Analysis®. Twenty clusters were identified and differential expression of selected genes was verified by RT-PCR. The four largest clusters (each containing from 276 to 905 genes) constituted over 50% of all differentially expressed genes and exhibited up-regulation following exposure to the highest dosage (2 mg/kg CPF). The total number of gene networks affected by CPF also rose sharply with the highest dosage of CPF (18, 16, 18 and 50 with 0.1, 0.5, 1 and 2 mg/kg CPF). Forebrain cholinesterase (ChE) activity was significantly reduced (26%) only in the highest dosage group. Based on magnitude of dose-related changes in differentially expressed genes, relative numbers of gene clusters and signaling networks affected, and forebrain ChE inhibition only at 2 mg/kg CPF, we focused subsequent analyses on this treatment group. Six canonical pathways were identified that were significantly affected by 2 mg/kg CPF (MAPK, oxidative stress, NFΚB, mitochondrial dysfunction, arylhydrocarbon receptor and adrenergic receptor signaling). Evaluation of different cellular functions of the differentially expressed genes suggested changes related to olfactory receptors, cell adhesion/migration, synapse/synaptic transmission and transcription/translation. Nine genes were differentially affected in all four CPF dosing groups. We conclude that the most robust, consistent changes in differential gene expression in neonatal forebrain across a range of acute CPF dosages occurred at an exposure level associated with the classical marker of OP toxicity, AChE inhibition. Disruption of multiple cellular pathways, in particular cell adhesion, may contribute to the developmental neurotoxicity potential of this pesticide.

Genotoxicity evaluation of chlorpyrifos to amphibian Chinese toad (Amphibian: Anura) by Comet assay and Micronucleus test

In the present study, the genotoxicity of chlorpyrifos was evaluated in the Chinese toad by using Comet assay and Micronucleus test (MN), as the potential tools for the assessment of genotoxicity. The first step was determined by the acute toxicity of chlorpyrifos. Tadpoles were exposed to the series of relatively high concentrations of chlorpyrifos for 96 h. LC 50 values at 24, 48, 72, and 96 h were 3.63, 1.17, 0.82, and 0.80 mg l −1, respectively. Secondly, the Micronucleus test was used for detecting chromosome damage in Chinese toad tadpoles exposed to the sublethal concentrations of chlorpyrifos and methyl methane sulfonate (MMS), which indicated that they induced chromosomal lesion in erythrocytes of Bufo bufo gargarizans tadpoles. Thirdly, the significant ( P < 0.05 concentration-dependent increase in DNA damage (as indicated by Tail DNA%, Tail length, Olive tail moment)) were observed in erythrocytes and liver cells of tadpoles exposed to the sublethal concentrations of chlorpyrifos and MMS by Comet assay. To our knowledge, this is the first report to describe the use of B. bufo gargarizans for genotoxicity assessment of chlorpyrifos.

Respiratory performance and behavioral responses of the freshwater fish, Cyprinus carpio (Linnaeus) under sublethal exposure to chlorpyrifos

A short-term definitive test by static renewal bioassay method was conducted to determine the acute toxicity (LC50) of an organophosphate insecticide, chlorpyrifos on the fish, Cyprinus carpio. Carp fingerlings were exposed to different concentrations (0.120 to 0.200 mg/L) of chlorpyrifos for 96 h. The acute toxicity of chlorpyrifos was found to be 0.160 m g/L. One-seventh (1/7th, 0.0224 mg/L) and one-fourteenth (1/14th, 0.0112 mg/L) of the acute toxicity value were selected as sublethal concentrations for subchronic studies. The fish were exposed to both the sublethal concentrations for 1, 7, and 14 days and allowed to recover in toxicant-free medium for 7 days. Behavioral responses and respiratory rate were studied in experimental periods. Fish in toxic media exhibited irregular, erratic, and darting swimming movements, hyperexcitability, and loss of equilibrium and sinking to the bottom. Caudal bending was the chief morphological alterations during the exposure tenures. The behavioral and morphologic changes might be due to the inhibition of acetylcholinesterase (AChE) activity. The carp were found under stress but mortality was insignificant at both the sublethal concentrations. Considerable variation in respiratory rates (-71.85 to 119.52%; -75.65 to 17.58%) were observed in the 1/7th and 1/14th of lethal concentration of chlorpyrifos respectively. The alteration in respiratory rate is due to respiratory distress, this may be a consequence of impaired oxidative metabolism and elevated physiological response during chlorpyrifos exposure. The impairments in fish respiratory physiology and behavioral responses even under recovery periods may be due to slow release of sequestered chlorpyrifos from storage tissues.

Toxicity of chlorpyrifos and TCP alone and in combination to Daphnia carinata: The influence of microbial degradation in natural water

The acute toxicity of chlorpyrifos and its principal metabolite 3,5,6-trichloropyridinol (TCP) alone and in combination to a cladoceran, Daphnia carinata, was studied in both cladoceran culture medium and natural water collected from a local suburban stream. TCP was found to be more toxic than its parent chemical chlorpyrifos to Daphnia survival in cladoceran culture medium. However, TCP in natural water was not toxic to D. carinata up to 2 μg L −1. The LC 50 values for chlorpyrifos, TCP and chlorpyrifos+TCP were 0.24, 0.20 and 0.08 μg L −1, respectively, in cladoceran culture medium. Although the parent chemicals and their degradation products co-exist in natural waters, the existing guidelines for water quality are based on individual chemicals. The results of this investigation suggest that chlorpyrifos and TCP can interact synergistically, additively or antagonistically, resulting in an increase or decrease in the overall toxicity of the mixture compared to individual compounds. The indigenous microorganisms in natural water could play a significant role in degradation of these compounds thereby influencing their toxicity in receiving waters. This study clearly suggests that the joint action of pesticides and their degradation products should be considered in the development of water quality guidelines. To our knowledge, this is the first study on the interactive effect of chlorpyrifos and TCP to a cladoceran and suggests that these two compounds are non-toxic when present together at concentrations up to 0.12 μg L −1. However, these compounds together act additively at and above 0.5 μg L −1 to fresh water invertebrates and therefore pollution with these compounds may adversely affect natural ecosystems.

Impact of Atrazine on Chlorpyrifos Toxicity in Four Aquatic Vertebrates

Atrazine has been shown previously to potentiate chlorpyrifos toxicity in selected invertebrates. This study examined interactions of atrazine and chlorpyrifos in four aquatic vertebrates. Organisms were exposed to binary mixtures of atrazine and chlorpyrifos during toxicity bioassays. Inhibition of cholinesterase (ChE) enzyme activity and chlorpyrifos uptake kinetics were also examined with and without atrazine exposure. Atrazine alone did not affect organisms at concentrations up to 5000 microg/L; however, the presence of atrazine at 1000 microg/L did result in a significant increase in the acute toxicity of chlorpyrifos in Xenopus laevis. Mixed results were encountered with Pimephales promelas; some bioassays showed greater than additive toxicity, while others showed an additive response. No effect of atrazine on chlorpyrifos toxicity was observed for Lepomis macrochirus and Rana clamitans. Atrazine did not affect ChE activity or chlorpyrifos uptake rates, indicating that these toxicodynamic and toxicokinetic parameters may not be related to the mechanism of atrazine potentiation of chlorpyrifos toxicity. Based on the results of this study, it does not appear that a mixture toxicity of atrazine and chlorpyrifos at environmentally relevant concentrations presents a risk to the vertebrate organisms examined in this study.

Effect of chlorpyrifos and monocrotophos on locomotor behaviour and acetylcholinesterase activity of subterranean termites, Odontotermes obesus

The acute toxicity of chlorpyrifos and monocrotophos to subterranean termites, Odontotermes obesus (Rambur), has been studied by a paper contact method. The LC50 values for chlorpyrifos and monocrotophos were 0.046 and 0.148 microg cm(-2), respectively. Chlorpyrifos was 3.22-fold more toxic than monocrotophos. The effect of the pesticides on locomotor behaviour (velocity) and head acetylcholinesterase (AChE: EC 3.1.1.7) activity was estimated in LC50-exposed termites at intervals of 4, 8, 12, 16, 20 and 24 h. Chlorpyrifos- and monocrotophos-treated termites showed, respectively, 97 and 88% reduction in locomotor behaviour (velocity) after 24 h. At all time intervals the chlorpyrifos-treated termites exhibited more AChE inhibition and showed greater distorted behaviour than those exposed to monocrotophos. In vitro studies indicated that the I50 value (50% inhibition) for chlorpyrifos against AChE was 8.75 times that of monocrotophos.

Acute Toxicity of Chlorpyrifos (Dursban®) to &lt;i&gt;Clarias gariepinus&lt;/i&gt; Juveniles

The acute toxicity of Chlorpyrifos (DURSBANâ), an organophosphate insecticide to Clarias gariepinus juveniles was evaluated in the laboratory, using a 96-hour static-renewal toxicity test method. The 96-hour LC50 for the fish was found to be 3.16 X 10 -7 %, with 95% confidence limit of 1.26 X 10 -4 %. Symptoms of toxicosis observed include hyper-ventilation, irregular and erratic movements with jerks, burst swimming, loss of balance, air gulping, excessive mucus production, opercular haemorrhage, tonic convulsion was observed before death finally occurred. Heavy usage of agricultural insecticides produces detrimental effects on the fishery resources and aquatic environment. To minimize the problem of pollution brought by these chemicals, the use of selected low toxicity pesticides should be encouraged. Key Words: Clarias gariepinus, chlorpyrifos, Dursbanâ, acute toxicity. Trop. Vet. Vol.22: (1) 7-11 (2004)

Toxic effects of chlorpyrifos on morphology and acetylcholinesterase activity in the earthworm, Eisenia foetida

The acute toxicity of chlorpyrifos ( O, O-diethyl- O-(3,5,6-trichloro-2-pyridyl) phosphorothioate) was determined in the earthworm, Eisenia foetida. A 48-h contact test as described by the Organization for Economic Cooperation and Development (OECD) guideline 207 was carried out. The LC 50 of chlorpyrifos was 0.063 μg/cm 2. Inhibition of acetylcholinesterase (AChE: EC 3.1.1.7) activity indicated by in vitro neurotoxic potentiality revealed competitive inhibition and altered K m values widely in a dose-dependent manner. The K i value of chlorpyrifos was 4.20×10 −6 M. AChE activity of LC 50-exposed worms was 62%, 79%, 85%, and 91% inhibited at 12, 24, 36, and 48 h, respectively. Scanning electron microscopic studies revealed the morphological abnormalities in the worms. The present study demonstrates a dose- and time-dependent exposure of chlorpyrifos through skin results, morphological abnormalities, and inhibition of AChE in the earthworm, E. foetida.