Inhibitory effects on esterase enzymes buche and ache in rainbow trout (Oncorhyncus mykiss) produced by the slow release insecticide chitosan diethyl phosphate

The study on the toxicity of chitosan diethyl phosphate (ChDP), a controlled release insecticide, on the activities of butyrylcholinesterase (BuChE) and acetylcholinesterase (AChE) in rainbow trout exposed to this pesticide was carried out. It was found that ChDP reduced BuChE activity in O. mykiss by a factor of eight at 6 days, with high fluctuation to the end of the exposition time at 12 days. The in vitro analysis of brain AChE treated with ChDP and Phenamiphos showed that it was competitively inhibited by both organophosphates. The values obtained for Km and Vmax for the AChE-ChDP (Km: 21.23 microM; Vmax: 43.10 micromol/min/g) and AChE-Phenamiphos (Km: 38.62 microM; Vmax: 38.91 micromol/min/g) systems were relatively low compared to values of the AChE (control) system (Km: 62.99 microM; Vmax: 63.29 micromol/min/g). Results reported in this study confirmed that chitosan diethyl phosphate performs similarly to organophosphate pesticides, producing inhibition in cholinesterases in rainbow trout.     

Molecular docking and dynamics studies of cigarette smoke carcinogens interacting with acetylcholinesterase and butyrylcholinesterase enzymes of the central nervous system

The free radicals produced by cigarette smoking are responsible for tissue damage, heart and lung diseases, and carcinogenesis. The effect of tobacco on the central nervous system (CNS) has received increased attention nowadays in research. Therefore, to explore the molecular interaction of cigarette smoke carcinogens (CSC) 4-(methylnitrosamine)-1-(3-pyridyl)-1-butanol (NNAL), 4-(methylnitrosamine)-1-(3-pyridyl)-1-butanone (NNK), and N′-nitrosonornicotine (NNN) with well-known targets of CNS-related disorders, acetylcholinesterase (AChE), and butyrylcholinesterase (BuChE) enzymes, a cascade of the computational study was conducted including molecular docking and molecular dynamics simulations (MDS). The investigated results of NNAL+AChE_complex, NNK+AChE_complex, and NNK+BuChE_complex based on intermolecular energies (?G) were found to ?8.57 kcal/mol, ?8.21 kcal/mol, and ?8.08 kcal/mol, respectively. MDS deviation and fluctuation plots of the NNAL and NNK interaction with AChE and BuChE have shown significant results. Further, Molecular Mechanics Poisson-Boltzmann Surface Area (MM‐PBSA) results shown the best total binding energy (^Binding?G) ?87.381 (+/?13.119) kJ/mol during NNK interaction with AChE. Our study suggests that CSC is well capable of altering the normal biomolecular mechanism of CNS; thus, obtained data could be useful to design extensive wet laboratory experimentation to know the effects of CSC on human CNS.

Graphical abstract

     

B-type esterases in the snail Xeropicta derbentina: an enzymological analysis to evaluate their use as biomarkers of pesticide exposure

The study was prompted to characterize the B-type esterase activities in the terrestrial snail Xeropicta derbentina and to evaluate its sensitivity to organophosphorus and carbamate pesticides. Specific cholinesterase and carboxylesterase activities were mainly obtained with acetylthiocholine (K_m = 77.2 mM; V_max = 38.2 mU/mg protein) and 1-naphthyl acetate (K_m = 222 mM, V_max = 1095 mU/mg protein) substrates, respectively. Acetylcholinesterase activity was concentration-dependently inhibited by chlorpyrifos-oxon, dichlorvos, carbaryl and carbofuran (IC50 = 1.35 × 10⁻⁵-3.80 × 10⁻⁸ M). The organophosphate-inhibited acetylcholinesterase activity was reactivated in the presence of pyridine-2-aldoxime methochloride. Carboxylesterase activity was inhibited by organophosphorus insecticides (IC50 = 1.20 × 10⁻⁵-2.98 × 10⁻⁸ M) but not by carbamates. B-esterase-specific differences in the inhibition by organophosphates and carbamates are discussed with respect to the buffering capacity of the carboxylesterase to reduce pesticide toxicity. These results suggest that B-type esterases in X. derbentina are suitable biomarkers of pesticide exposure and that this snail could be used as sentinel species in field monitoring of Mediterranean climate regions.     

The effect of pesticides and metals on acetylcholinesterase (AChE) in various tissues of blue mussel (Mytilus trossulus L.) in short-term in vivo exposures at different temperatures

The purpose of the study was to assess the impact of short-term exposure to selected toxicants as well as metal accumulation upon acetylcholinesterase (AChE) in the blue mussel, Mytilus trossulus L., in laboratory in vivo experiments. Mussels were exposed for up to 48 hours to a mixture of copper (Cu^{2 +}, 400 μ g L^?1) and cadmium (Cd^{2 +}, 200 μ g L^?1), to dichlorvos (DDVP, 100 μ g L^?1), and to carbaryl (100 μ g L^?1) at two temperatures: 5°C and 20°C. Samples were collected after 0, 6, 12, 24, and 48 hours of exposure, and AChE activity and metal concentration (where applicable) were analysed in gills, digestive gland, mantle+muscles, and the whole soft tissue. Very strong AChE inhibition was observed in response to the dichlorvos treatment, mainly in gills. Carbaryl and the metals caused a short-term inhibition effect. Considerable differences in AChE activity between the two temperatures were noticed. In particular, the metals were accumulated much faster at 20°C than at 5°C, especially in gills. No correlation between AChE activity and metal concentration was found. Gills turned out to be the optimal tissue for AChE activity analysis in short-term studies.     

黄菖蒲和狭叶香蒲根系对氮磷的吸收动力学

采用改进的常规耗竭法，研究了黄菖蒲（Iris pseudacorus L.）和狭叶香蒲（Typha angustifolia L.）根系对NH₄⁺、NO₃^-和H₂PO₄^-的吸收特征及差异。结果表明，这2种植物根系对NH₄⁺、NO₃^-和H₂PO₄^-的吸收动力学特征均可采用Michaelis-Menten方程描述。2种植物根系对NH₄⁺、NO₃^-和H₂PO₄^-的亲和力（Km）和最大吸收速率（Vmax）有显著差异。吸收H₂PO₄^-时，黄菖蒲根系具有较高的Vmax值和较低的Km值，说明黄菖蒲具有嗜磷特性，并能够适应广范围浓度的H₂PO₄^-环境，适宜用于污染水体磷的去除；吸收NO₃^-时，狭叶香蒲根系具有较高的Vmax值和较低的Km值，表明狭叶香蒲可用于广范围浓度NO₃^-污染的水体修复；吸收NH₄⁺时，黄菖蒲根系具有较低的Vmax值和Km值，而狭叶香蒲根系具有较高的Vmax值和Km值，说明黄菖蒲适宜用于NH₄⁺污染较轻水体的修复，而在NH₄⁺污染较重水体中宜选用狭叶香蒲作为先锋植物。     

Environmental dynamics of phosphate esters. III. Comparison of the bioconcentration of four triaryl phosphates by fish

Uptake, clearance and extent of metabolism of ¹⁴C-labelled t-butylphenyldiphenyl phosphate (t-BPDP), tri-m-cresyl phosphate (mTCP), tri-p-cresyl phosphate (pTCP) and triphenyl phosphate (TPP) were studied in rainbow trout ($\text{Salmo}$$\text{gairdneri}$) and fathead minnows ($\text{Pimephales}$$\text{promelas}$) using short-term static exposures (50 and 5 μmg/L). Bioconcentration factors for pTCP, mTCP, TPP and tBPDP calculated by use of total radioactivity in whole fish were 1420, 784, 573 and 1096 respectively, for rainbow trout and 928, 596, 561 and 1010 respectively, for fathead minnows. Differences in rates of clearance and biotransformation among the four compounds were more closely related to their ease of hydrolysis than to hydrophobicity.     

一株苯酚降解菌的筛选及降解动力学特性

利用富集驯化的培养方法,从首钢焦化厂废水处理系统中的二沉池出水中,分离筛选出一株能够高效降解苯酚的菌株B3对其16S rDNA序列进行分析,并选择Monod方程和Andrews方程分别研究该菌在不同苯酚浓度条件下的降酚动力学模式。结果表明,B3为蜡状芽孢杆菌(Bacillus cereus);苯酚浓度较低时,苯酚对菌株的生长基本不产生抑制作用,用Monod模型对B3降酚动力学过程进行拟合,其动力学参数V max=0.03 h-1,K s=25.53 mg/L;苯酚浓度较高时,按照Andrews模型对B3降酚动力学过程进行非线性最小二乘曲线拟合,其动力学参数V max=0.08 h-1,K s=147.52 mg/L,K i=384.96 mg/L。根据动力学方程,推论菌株B3降解对于浓度238.30 mg/L的苯酚具有最佳降解效果。     

Lethal and sublethal effects of the pyrethroid,bifenthrin, on grass shrimp (Palaemonetes pugio) and sheepshead minnow (Cyprinodon variegatus)

This study investigated the lethal and sublethal effects of the pyrethroid insecticide bifenthrin on adult and larval grass shrimp, Palaemonetes pugio, and adult sheepshead minnows, Cyprinodon variegatus. The effects were determined by conducting 96-h aqueous static renewal tests and 24-h static tests with sediment. Oxidative stress biomarkers, lipid peroxidation, glutathione, and catalase were also assessed. The 96-h aqueous LC₅₀ value for adult shrimp was 0.020 μ g/L (95% CI: 0.015–0.025 μ g/L) and for larval shrimp was 0.013 μ g/L (95% CI: 0.011–0.016 μ g/L). The 96-h aqueous LC₅₀ for adult sheepshead minnow was 19.806 μ g/L (95% CI: 11.886–47.250 μ g/L). The 24-h sediment LC₅₀ for adult shrimp was 0.339 μ g/L (95% CI: 0.291–0.381 μ g/L) and for larval shrimp was 0.210 μ g/L (95% CI: 0.096–0.393 μ g/L). The oxidative stress assays showed some increasing trends toward physiological stress with increased bifenthrin concentrations but they were largely inconclusive. Given the sensitivity of grass shrimp to this compound in laboratory bioassays, additional work will be needed to determine if these exposure levels are environmentally relevant.     

Environmental dynamics of phosphate esters. II. Uptake and bioaccumulation of 2-ethylhexyl diphenyl phosphate and diphenyl phosphate by fish

Uptake, clearance and disposition of ¹⁴C-labelled 2-ethylhexyl diphenyl phosphate (EHDP) and ¹⁴C-diphenyl phosphate (DPP) by rainbow trout (Salmo gairdneri) were investigated using short-term static exposures. Bioconcentration factors of 1314 and 0.3 were calculated for EHDP and DPP, respectively. Highest levels of radioactivity were found in liver and intestine following exposure to 60 μg/L EHDP. A portion (up to 40%) of the radioactivity in each tissue was in the form of DPP while a similar portion was extractable with methanol but could not be identified.     

Effects of Equilibration Temperature on PM10 Concentrations from the TEOM Method in the Lower Fraser Valley

ABSTRACT

This study investigated the effect of equilibration temperature on PM₁₀ concentrations from the tapered element oscillating microbalance (TEOM) method by operating collocated TEOM monitors at different equilibration temperatures in an airshed (the Lower Fraser Valley, British Columbia). This airshed contained an abundance of par-ticulate semivolatile material (PSVM). For the period when three collocated TEOM monitors were operated, the PM₁₀ from the monitor at an equilibration temperature of 30 ° C was 2.5 μ g/m³ (22%) and 1.7 (17%) μ g/m³ higher, on average, than the PM₁₀ from monitors at 50 and 40 ° C, respectively, and the differences were proportional to the ambient PM₁₀ loading. Greater volatilization of PSVM in the TEOM monitors at higher equilibration temperatures may have been a cause of the differences.     

Kinetics of phenol biodegradation at high concentration by a metabolically versatile isolated yeast Candida tropicalis PHB5

A highly tolerant phenol-degrading yeast strain PHB5 was isolated from wastewater effluent of a coke oven plant and identified as Candida tropicalis based on phylogenetic analysis. Biodegradation experiments with C. tropicalis PHB5 showed that the strain was able to utilize 99.4 % of 2,400 mg l^?1 phenol as sole source of carbon and energy within 48 h. Strain PHB5 was also observed to grow on 18 various aromatic hydrocarbons. Haldane model was used to fit the exponential growth data and the following kinetic parameters were obtained: μ _max?=?0.3407 h^?1, K _S?=?15.81 mg l^?1, K _i?=?169.0 mg l^?1 (R ²?=?0.9886). The true specific growth rate, calculated from μ _max, was 0.2113. A volumetric phenol degradation rate (V _max) was calculated by fitting the phenol consumption data with Gompertz model and specific degradation rate (q) was calculated from V _max. The q values were fitted with Haldane model, yielding following parameters: q _max?=?0.2766 g g^?1 h^?1, K _S ′?=?2.819 mg l^?1, K _i ′?=?2,093 (R ²?=?0.8176). The yield factor (Y _X/S ) varied between 0.185 to 0.96 g g^?1 for different initial phenol concentrations. Phenol degradation by the strain proceeded through a pathway involving production of intermediates such as catechol and cis,cis-muconic acid which were identified by enzymatic assays and HPLC analysis.     

Trade-offs between elimination and detoxification in rainbow trout and common bivalve molluscs exposed to metal stressors

The purpose of this paper was to examine trade-offs between elimination and detoxification in rainbow trout and three common bivalve molluscs (clam, oyster, and scallop) exposed to cadmium (Cd), copper (Cu), and zinc (Zn) based on recent reported experimental data. We incorporated metal influx threshold with subcellular partitioning to estimate rate constants of detoxification (k_d) and elimination (k₂). We found that the relationships between k₂ and k_d were negative for rainbow trout and positive for bivalve molluscs. However, the relationships between k_d and % metal in metabolically detoxified pool were found positive for rainbow trout and negative for bivalve molluscs. Our results also indicated that rainbow trout had higher accumulation (∼60-90%) in metabolically active pool when exposed to essential metals of Cu and Zn and had only 10-50% accumulation in response to non-essential metal of Cd. Based on a cluster analysis, this study indicated that similarity of physiological regulations among study species was found between Cd and Zn. Our study suggested that detoxification can be predicted by an elimination-detoxification scheme with the known elimination rate constant. We concluded that quantification of trade-offs between subcellular partitioning and detoxification provides valuable insights into the ecotoxicology of aquatic organisms and enhances our understanding of the subcellular biology of trace metals.     

Leaching potential of phenylurea herbicides in a calcareous soil: comparison of column elution and batch studies

The transfer of eleven phenylurea herbicides through soil columns was investigated in laboratory conditions in order to determine leaching properties in a calcareous soil. Elution curves with distilled water were plotted after herbicide application on the soil column. Phenylurea retention by the soil indicating interactions with soil can be classified as follows: fenuron < fluometron ≤ isoproturon = monuron < metoxuron < monolinuron < metobromuron < chlorotoluron < linuron = diuron < chlorbromuron. The number and nature of halogen atoms on the phenyl ring had an important influence on leaching. Retention was higher for molecules with higher number of halogen, and it was also higher for bromine than chlorine. Column elution experiments were compared to batch experiments from which the distribution coefficients K _d were determined. According to Kendall correlation coefficients, parameter m/m _0max from column experiments was relatively well linked to K _d. In case of phenylurea, a linear relationship between K _d and m/m _0max was established.     

An evaluation of the cytochrome P450 inhibition potential of selected pesticides in human hepatic microsomes

The goal of this work was to study the ability of 18 pesticides to inhibit selective model activities for all major xenobiotic-metabolizing enzymes, namely CYP1A1/2, 2A6, 2B6, 2C8, 2C9, 2C19, 2D6, 2E1 and 3A4. Generally organophosphorus insecticides were the most potent and extensive inhibitors, especially towards CYP1A1/2 (IC₅₀ values of chlorpyrifos, fenitrothion and profenofos ～3 μ M), CYP2B6 (IC₅₀ values of chlorpyrifos and fenitrothion 2.5 μ M), CYP2C8 (fenitrothion 4.3 μ M), CYP2C9 (fenitrothion and malathion 4.8 and 2.5 μ M, respectively), CYP2D6 (chlorpyrifos and phenthoate ～ 3 μ M) and CYP3A4 (chlorpyrifos, fenitrothion and phenthoate 3–4 μ M). Otherwise there were quite considerable differences in potency and extent of inhibition between different organophosphates. Pyrethroids were in general very weak or inactive. Deltamethrin and fenvalerate were potent inhibitors of CYP2D6 (IC₅₀ values of ～ 3 μ M) while lambda-cyhalothrin potently inhibited both CYP2D6 and CYP3A4-mediated activities (IC₅₀'s about 3–4 μ M). Some pesticides caused relatively potent inhibitions sporadically (carbendazim, CYP2D6, IC₅₀ = 12 μ M; atrazine, CYP3A4, IC₅₀ = 2.8 μ M; glyphosate, CYP2C9, IC₅₀ = 3.7 μ M; hexaflumuron, IC₅₀ = 6.0 μ M). With the exceptions of alpha-cypermethrin, cypermethrin, isoproturon, carbaryl and abamectin, most pesticides inhibited relatively potently at least one CYP-selective activity, which may have relevance for potential interactions in occupational exposures and for further studies on the CYP-associated metabolism of respective pesticides.     

Particulate Air Pollution in Mexico City: A Collaborative Research Project

ABSTRACT

PM₁₀, PM₂₅, precursor gas, and upper-air meteorological measurements were taken in Mexico City, Mexico, from February 23 to March 22, 1997, to understand concentrations and chemical compositions of the city's particulate matter (PM). Average 24-hr PM₁₀ concentrations over the period of study at the core sites in the city were 75 H g/m³. The 24-hr standard of 150 μ g/m³ was exceeded for seven samples taken during the study period; the maximum 24-hr concentration measured was 542 μ g/m³. Nearly half of the PM₁₀ was composed of fugitive dust from roadways, construction, and bare land. About 50% of the PM₁₀ consisted of PM_2.5, with higher percentages during the morning hours. Organic and black carbon constituted up to half of the PM_2.5. PM concentrations were highest during the early morning and after sunset, when the mixed layers were shallow. Meteorological measurements taken during the field campaign show that on most days air was transported out of the Mexico City basin during the afternoon with little day-to-day carryover.     

多层生物滤塔净化硫化氢废气研究

以木屑为填料,采用多层生物滤塔净化H2S气体,研究其适宜的工艺条件及生物降解宏观动力学.结果表明,填料分层可提高H2S去除率,当进气容积负荷＜153.2 g H2S/(m3·d)时,H2S的去除率保持在90%以上;进气浓度低于70 mg/m3,下层200mm填料对H2S总去除率的贡献在50%以上;填料含水率为50%～6...     

Hydrolysis of di-n-butyl phthalate, butylbenzyl phthalate and di(2-ethylhexyl) phthalate in human liver microsomes

Diester phthalates are industrial chemicals used primarily as plasticizers to import flexibility to polyvinylchloride plastics. In this study, we examined the hydrolysis of di-n-butyl phthalate (DBP), butylbenzyl phthalate (BBzP) and di(2-ethylhexyl) phthalate (DEHP) in human liver microsomes. These diester phthalates were hydrolyzed to monoester phthalates (mono-n-butyl phthalate (MBP) from DBP, mono-n-butyl phthalate (MBP) and monobenzyl phthalate (MBzP) from BBzP, and mono(2-ethylhexyl) phthalate (MEHP)) by human liver microsomes. DBP, BBzP and DEHP hydrolysis showed sigmoidal kinetics in V-[S] plots, and the Hill coefficient (n) ranged 1.37-1.96. The S₅₀, V_max and CL_max values for DBP hydrolysis to MBP were 99.7 μM, 17.2 nmol min⁻¹ mg⁻¹ protein and 85.6 μL min⁻¹ mg⁻¹ protein, respectively. In BBzP hydrolysis, the values of S₅₀ (71.7 μM), V_max (13.0 nmol min⁻¹ mg⁻¹ protein) and CL_max (91.3 μL min⁻¹ mg⁻¹ protein) for MBzP formation were comparable to those of DBP hydrolysis. Although the S₅₀ value for MBP formation was comparable to that of MBzP formation, the V_max and CL_max values were markedly lower (<3%) than those for MBzP formation. The S₅₀, V_max and CL_max values for DEHP hydrolysis were 8.40 μM, 0.43 nmol min⁻¹ mg⁻¹ protein and 27.5 μL min⁻¹ mg⁻¹ protein, respectively. The S₅₀ value was about 10% of DBP and BBzP hydrolysis, and the V_max value was also markedly lower (<3%) than those for DBP hydrolysis and MBzP formation for BBzP hydrolysis. The ranking order of CL_max values for monoester phthalate formation in DBP, BBzP and DEHP hydrolysis was BBzP to MBzP ? DBP to MBP > DEHP to MEHP > BBzP to MBP. These findings suggest that the hydrolysis activities of diester phthalates by human liver microsomes depend on the chemical structure, and that the metabolism profile may relate to diester phthalate toxicities, such as hormone disruption and reproductive effects.     

Monitoring Deposition of Nitrogen-Containing Compounds in a High-Elevation Forest Canopy

Measurements of airborne (gaseous and aerosol), cloud water, and precipitation concentrations of nitrogen compounds were made at Mt. Mitchell State Park (Mt. Gibbs, ~2006 m MSL), North Carolina, during May through September of 1988 and 1989, An annular denuder system was used to ascertain gaseous (nitric acid, nitrous acid, and ammonia) and particulate (nitrate and ammonium) nitrogen species, and a chemiluminescence nitrogen oxides analyzer was used to measure nitric oxide and nitrogen dioxide. Measurements of NO₃ ^? and NH₄ ⁺ ions in cloud and rain water samples were made during the same time period. Mean concentrations of gaseous nitric acid, nitrous acid, and ammonia were 1.14 μg/m³, 0.3 μg/m³, and 0.62 μg/m³ for 1988, and 1.40 μg/m³,0.3 μg/m³, and 1.47 μg/m³ for 1989, respectively. Fine particulate nitrate and ammonium ranged from 0.02 to 0.21 μg/m³ and 0.01 to 4.72 μg/m³ for 1988, and 0.1 to 0.78 μg/m³ and 0.24 to 2.32 μg/m³ for 1989, respectively. The fine aerosol fraction was dominated by ammonium sulfate particles. Mean concentrations of nitrate and ammonium ions in cloud water samples were 238 and 214 μmol/l in 1988, and 135 and 147 μmol/l in 1989, respectively. Similarly, the concentrations of NO₃ and NH₄ ⁺ in precipitation were 26.4 and 14.0 μmol/l in 1988, and 16.6 and 15.2 μmol/l in 1989, respectively. The mean total nitrogen deposition due to wet, dry, and cloud deposition processes was estimated as ~30 and ~40 kg N/ha/year (i.e., ~10 and ~13 kg N/ha/growing season) for 1988 and 1989. Based on an analytical analysis, deposition to the forest canopy due to cloud interception, precipitation, and dry deposition processes was found to contribute ~60, ~20, and ~20 percent, respectively, of the total nitrogen deposition.     

Free Fatty Acids and Sterols in Swine Manure

Free fatty acids and sterols were assessed in fresh manure and anaerobic lagoon sludge from swine production facilities in North Carolina. Eight free fatty acids and five sterols were identified and quantified in both manure and sludge samples. Compound identification was performed by gas chromatography/mass spectroscopy (GC-MS), and compound quantities were determined by gas chromatography after solid phase extraction with a 50:50 mixture of diethyl ether and hexane. The free fatty acids occurring in greatest abundance in both fresh manure and lagoon sludge were palmitic, oleic, and stearic. Free fatty acid content in fresh manure ranged from approximately 3 μ g g^?1 dry weight (dw) to over 45 μ g g^?1 dw. In lagoon sludge, free fatty acid content ranged from about 0.8 μ g g^?1 dw to nearly 4 μ g g^?1 dw. Coprostanol and epicoprostanol were the sterols in largest concentrations in fresh manure and lagoon sludge samples. Total sterol content ranged from approximately 0.5 μ g g^?1 dw to around 11 μ g g^?1 dw in fresh manure and from 3.5 μ g g^?1 dw to almost 9 μ g g^?1 dw in lagoon sludge. Fresh manure and lagoon sludge both had high levels of inorganic cations (e.g., Ca, Mg, Fe) capable of binding free fatty acids and forming insoluble complexes, thereby potentially reducing fatty acid biodegradation. In anaerobic lagoons, sterols are an organic fraction of sludge that are resistant to bacterial degradation. In the case of fresh manure, fatty acids could represent a potential source of energy via the manufacture of biodiesel fuel, if efficient means for their extraction and transesterification can be devised.     

Toxicity of the pyrethroid pesticide fenvalerate to freshwater catfish clarias gariepinus: Lethality,biochemical effects and role of dietary ascorbic acid

Static bioassays were made in the laboratory to determine lethal concentration of the pyrethroid pesticide fenvalerate [(RS)-alpha-cyano-3-phenoxybenzyl (RS)-2-(4-chlorophenyl)-3-methylbutyrate] for the freshwater catfish Clarias gariepinus and effects of sublethal concentrations of the pesticide on some biochemical parameters of the fish. For exposure periods of 24 to 96 h, LC₅₀ values of fenvalerate ranged from 5.83–4.76 μ g/L and 4.24–2.94 μ g/L, respectively for water and acetone soluble fenvalerate. Two sublethal concentrations of fenvalerate were used in the bioassays for biochemical parameters: 2.1 μ g/L for 24 h and 1.4 μ g/L for 96 h exposure, both concentrations representing 50% of LC₅₀ value of acetone soluble fenvalerate for the respective exposure period. Hepatosomatic index, liver glycogen, alkaline phosphatase of liver and ascorbic acid of blood, liver, and kidney decreased while haemoglobin (Hb) %, plasma glucose levels and acid phosphatase level of liver increased after 24 h exposure to 2.1 μ g/L fenvalerate. Longer exposure (96 h) to even a lower concentration (1.4 μ g/L) of fenvalerate resulted in reduction of all the parameters (except Hb %) tested as compared with control. Fish previously fed for 60 days with a diet supplemented by a high level of ascorbic acid (100 mg/100 g diet) could reverse most of the effects caused by 24 h exposure to 2.1 μ g/L fenvalerate. A lower level of ascorbic acid (50 mg/ 100 g diet) supplement could not influence these effects of fenvalerate. Even the higher dose of ascorbic acid supplementation (100 mg/100 g diet) could not relieve the stress parameters, except for Hb% and HSI, when the pesticide was applied at 1.4 μ g/L for a longer time period (96 h).