Investigation of dissipation kinetics and half-lives of fipronil and thiamethoxam in soil under various conditions using experimental modeling design by Minitab software.

To determine the extent of pesticide buildup and their environmental contamination, the environmental half-lives of pesticides are examined. The influence of the factors affecting the half-lives of fipronil and thiamethoxam including soil type, sterilization, temperature, and time and their interactions was studied using experimental modeling design by Minitab software. Based on the dissipation kinetics data, fipronil concentrations reduced gradually over 60 days while thiamethoxam concentrations decreased strongly. Also, fipronil and thiamethoxam dissipated more rapidly in calcareous soil than in alluvial soil. Thiamethoxam, however, disappeared more rapidly than fipronil in all treatments. Incubation at 50 °C leads to rapid the pesticide degradation. For prediction of the dissipation rate, model 5 was found to be the best fit, Residue of insecticide (%) = 15.466 - 11.793 Pesticide - 1.579 Soil type + 0.566 Sterilization - 3.120 Temperature, R2 = 0.94 and s = 3.80. Also, the predicted DT50 values were calculated by a model, DT50 (day) = 20.20 - 0.30 Pesticide - 7.97 Soil Type + 0.07 Sterilization - 2.04 Temperature. The shortest experimental and predicted DT50 values were obtained from treatment of thiamethoxam at 50 °C in calcareous soil either sterilized (7.36 and 9.96 days) or non-sterilized (5.92 and 9.82 days), respectively. The experimental DT50 values of fipronil and thiamethoxam ranged from 5.92 to 59.95 days while, the modeled values ranged from 9.82 to 30.58 days. According to the contour plot and response surface plot, temperature and sterilization were the main factors affecting the half-lives of fipronil and thiamethoxam. The DT50 values of fipronil and thiamethoxam increased in alluvial soil and soil with low temperature. In general, there is a high agreement between the experimental results and the modeled results.

Efficacy evaluation of some fumigants against Fusarium oxysporum and enhancement of tomato growth as elicitor-induced defense responses.

Fusarium wilt, the most serious soil-borne pathogen, is a serious problem for tomato production worldwide. The presented study evaluated the antifungal activity against Fusarium oxysporum f. sp. lycopersici in vitro and in vivo for nine fumigants. In addition, the research examined the possibility of enhancing the growth of tomato plants in order to increase resistance against this disease by using four chemical inducers. The results indicated that at 20 mg/L, the radial growth of the pathogen was inhibited 100% by formaldehyde and > 80% by phosphine. Among the essential oils investigated, neem oil was the most effective, however, it only achieved 40.54% at 500 mg/L. The values of EC50 for all fumigants, except dimethyl disulfide (DMDS) and carbon disulfide (CS2), were lower than those for thiophanate-methyl. Phosphine was the highest efficient. The elicitors can be arranged based on their effectiveness, gibberellic acid (GA3) > sorbic acid > cytokinin (6-benzylaminopurine) > indole-3-butyric acid. The change in root length, fresh weight, and dry weight was greater with soil drench than with foliar application. The fumigant generators formaldehyde, phosphine and 1,4-dichlorobenzene and bio-fumigants citrus and neem oils as well as elicitors gibberellic and sorbic acid could be one of the promising alternatives to methyl bromide against Fusarium oxysporum as an important component of integrated management of Fusarium wilt.

Adsorption and thermodynamic parameters of chlorantraniliprole and dinotefuran on clay loam soil with difference in particle size and pH.

The behavior of chlorantraniliprole (CAP) and dinotefuran (DNF) insecticides was investigated in clay loam soil, a common type of the Egyptian soil. Effect of temperature, pH and particle size of the soil on the adsorption process was studied. Adsorption isotherm by bulk soil and its constituents; humic acid (HA), clay, silt and sand fractions was measured using batch equilibration technique. The results showed that the adsorption of the insecticides tested was significantly affected by the temperature and was a spontaneous interfacial process in the soil. Freundlich model accurately predicted the adsorption behavior of both insecticides. The interaction between soil and insecticides was endothermic and the highest adsorption for CAP and DNF was obtained at pH 9. However, the effect of pH on the adsorption of DNF was lower than that of CAP. Sorption of CAP and DNF on HA fraction was significantly greater than on clay fraction and bulk soil. In addition, the adsorption was significantly increased with particle size decrease. It could be inferred that the adsorption of CAP and DNF on clay loam soil was physical in nature and greatly influenced by the soil components, pH and temperature.

Chemical composition of the essential oils isolated from peel of three citrus species and their mosquitocidal activity against Culex pipiens.

Three essential oils (EOs) were isolated from the peel of citrus fruits Citrus reticulata L., Citrus reticulata chinase Blanco and Citrus sinensis (L.) Osbeck (Family: Rutaceae) and evaluated against Culex pipiens L.1758 (Family: Culicidae). Chemical composition indicated that the EOs were rich in essential phytochemicals including hydrocarbons, monoterpenes and sesquiterpenes. These constituents revealed some variability among the oils displaying interesting chemotypes limonene (35-51%), 1R-α-pinene (1.04-2.5%), γ-terpinene (0.46-5.65%) and sabinene (0.51-5.42%). The toxicity proved that C. sinensis oil had more effect than C. reticulata chinase and C. reticulata oils against larvae (LC50 = 15.35, 16.11 and 32.84 mg/L, respectively). However, C. reticulate was the most active as fumigant against adults (LC50 2.74 µL/L air). The in vivo effect on acetylcholine esterase (AChE), carboxyl esterase (CbE), acid phosphatase (ACP), alkaline phosphatase (ALP), adenosine triphosphatase (ATPase) and glutathione-S-transferase (GST) were also demonstrated. To the best of our knowledge, this is the first report about the chemical composition and mosquitocidal activity of C. reticulata chinase essential oils. Conclusively, the tested essential oils could be used as eco-friendly alternatives in mosquitoes control programme.

Sorption-desorption of imidacloprid onto a lacustrine Egyptian soil and its clay and humic acid fractions.

Sorption-desorption of the insecticide imidacloprid 1-[(6-chloro-3-pyridinyl)-methyl]-N-nitro-2-imidazolidinimine onto a lacustrine sandy clay loam Egyptian soil and its clay and humic acid (HA) fractions was investigated in 24-h batch equilibrium experiments. Imidacloprid (IMDA) sorption-desorption isotherms onto the three sorbents were found to belong to a non-linear L-type and were best described by the Freundlich model. The value of the IMDA adsorption distribution coefficient, Kd(ads), varied according to its initial concentration and was ranged 40-84 for HA, 14-58 for clay and 1.85-4.15 for bulk soil. Freundlich sorption coefficient, Kf(ads), values were 63.0, 39.7 and 4.0 for HA, clay and bulk soil, respectively. The normalized soil Koc value for imidacloprid sorption was ∼800 indicating its slight mobility in soils. Nonlinear sorption isotherms were indicated by 1/n(ads) values <1 for all sorbents. Values of the hysteresis index (H) were <1, indicating the irreversibility of imidacloprid sorption process with all tested sorbents. Gibbs free energy (ΔG) values indicated a spontaneous and physicosorption process for IMDA and a more favorable sorption to HA than clay and soil. In conclusion, although the humic acid fraction showed the highest capacity and affinity for imidacloprid sorption, the clay fraction contributed to approximately 95% of soil-sorbed insecticide. Clay and humic acid fractions were found to be the major two factors controlling IMDA sorption in soils. The slight mobility of IMDA in soils and the hysteresis phenomenon associated with the irreversibility of its sorption onto, mainly, clay and organic matter of soils make its leachability unlikely to occur.

Inhibition kinetics of acid and alkaline phosphatases by atrazine and methomyl pesticides.

The main objective of this work was to investigate the kinetic characteristics of acid and alkaline phosphatases isolated from different sources and to study the effects of the herbicide atrazine and insecticide methomyl on the activity and kinetic properties of the enzymes. Acid phosphatase (ACP) was isolated from the tomato plant (Solanum lycopersicum L. var. lycopersicum); alkaline phosphatase (ALP) was isolated from two sources, including mature earthworms (Aporrectodea caliginosa) and larvae of the Egyptian cotton leafworm (Spodoptera littoralis). The specific activities of the enzymes were 33.31, 5.56 and 0.72 mmol substrate hydrolyzed per minute per milligram protein for plant ACP, earthworms ALP and cotton leafworm ALP, respectively. The inhibition kinetics indicated that atrazine and methomyl caused competitive-non-competitive inhibition of the enzymes. The relationships between estimates of K(m) and V(max) calculated from the Michaelis-Menten equation have been explored. The extent of the inhibition was different, as estimated by the values of the inhibition constant Ki that were found to be 3.34 × 10(-3), 1.12 × 10(-2) and 1.07 × 10(-2) mM for plant ACP, earthworms ALP and cotton leafworm ALP, respectively, with methomyl. In the case of atrazine, K(i) were found to be 8.99 × 10(-3), 3.55 × 10(-2) and 1.36 × 10(-2) mM for plant ACP, earthworms ALP and cotton leafworm ALP, respectively.

Chemical composition, antimicrobial and insecticidal activities of the essential oils of Conyza linifolia and Chenopodium ambrosioides.

Two essential oil-containing plants growing wildly in Egypt: Conyza linifolia (Willd.) Täckh. (Asteraceae) and Chenopodium ambrosioides L. (Chenopodiaceae) were subjected to essential oil analysis and biological investigation. The essential oils from both plants were prepared by hydrodistillation, and GC/MS was employed for volatiles profiling. This study is the first to perform GC/MS analysis of C. linifolia essential oil growing in Egypt. C. linifolia essential oil contained mainly sesquiterpenes, while that of C. ambrosioides was rich in monoterpenes. Ascaridole, previously identified as the major component of the latter, was found at much lower levels. In addition, the oils were investigated for their antimicrobial activity against two Gram positive and two Gram negative bacteria, and one fungus. The insecticidal activities of both oils, including mosquitocidal and pesticidal potentials, were also evaluated. The results of biological activities encourage further investigation of the two oils as antimicrobial and insecticidal agents of natural origin.

Bioactive paper sensor based on the acetylcholinesterase for the rapid detection of organophosphate and carbamate pesticides.

In many countries, people are becoming more concerned about pesticide residues which are present in or on food and feed products. For this reason, several methods have been developed to monitor the pesticide residue levels in food samples. In this study, a bioactive paper-based sensor was developed for detection of acetylcholinesterase (AChE) inhibitors including organophosphate and carbamate pesticides. Based on the Ellman colorimetric assay, the assay strip is composed of a paper support (1 × 10 cm), onto which a biopolymer chitosan gel immobilized in crosslinking by glutaraldehyde with AChE and 5,5'-dithiobis(2-nitrobenzoic) acid (DTNB) and uses acetylthiocholine iodide (ATChI) as an outside reagent. The assay protocol involves introducing the sample to sensing zone via dipping of a pesticide-containing solution. Following an incubation period, the paper is placed into ATChI solution to initiate enzyme catalyzed hydrolysis of the substrate, causing a yellow color change. The absence or decrease of the yellow color indicates the levels of the AChE inhibitors. The biosensor is able to detect organophosphate and carbamate pesticides with good detection limits (methomyl = 6.16 × 10(-4) mM and profenofos = 0.27 mM) and rapid response times (~5 min). The results show that the paper-based biosensor is rapid, sensitive, inexpensive, portable, disposable, and easy-to-use.

Assessment of reproductive toxicity of orally administered technical dimethoate in male mice.

The effect of organophosphate insecticide dimethoate at three dosage levels (7, 15, and 28 mg/kg/day) on male reproduction in mice was studied. Dimethoate was given orally by gavage to male mice for 20 days before mating with untreated females. Signs of cholinergic effects were observed in the 15 and 28 mg/kg/day treated groups. Brain and skeletal muscle acetylcholinesterase activities were inhibited in both the middle and high dose groups. Dimethoate was associated with a decreased number of implantations and live fetuses, and an increased number of dead and early resorptions at 28 mg/kg/day treated group. The percent morphologically normal spermatozoa were unaffected in any of dose groups. However, sperm production and percent motile sperm were decreased in the 15 and 28 mg/kg/day treated groups compared to the control. Histological changes in testis were observed in the middle and high treated groups. The current study demonstrated the adverse effects of dimethoate on the reproductive performance of male mice and pregnancy outcomes following mating with untreated female mice at dose levels of 15 and 28 mg/kg/day. The No Observed Effect Level (NOEL) in the present study for reproductive performance was 7 mg/kg/day.

Feeding deterrent and growth inhibitory properties of limonoids from Khaya senegalensis against the cotton leafworm, Spodoptera littoralis.

Three rearranged phragmalin-type limonoids, khayanolide A, khayanolide B and 1-O-acetylkhayanolide B, and a mexicanolide-type limonoid, khayalactol, have been isolated from the stem bark of Khaya senegalensis (Desr) A Juss (Meliaceae). The antifeedant and growth-inhibitory activities of the isolated compounds were evaluated on Spodoptera littoralis (Boisduval). When added to an artificial diet, khayanolide A, khayanolide B and 1-O-acetylkhayanolide B showed antifeedant activity in a concentration-dependent manner. Khayalactol exhibited strong antifeedant activity without significant differences at all of the tested concentrations (7.5-100 mg kg(-1)). Khayanolide B was the most potent antifeedant with an ECso of 2.19 mg kg(-1). The results also revealed that the isolated compounds caused marked larval growth inhibition on S littoralis after 7 days of feeding on treated diet; this effect was concentration-dependent. Khayanolide B was the most active growth inhibitor among the isolated compounds, with an EC50 of 6.96 mg kg(-1).

Molluscicidal and anti-feedant activities of diterpenes from Euphorbia paralias L.

Nine known diterpene polyesters of segetanes, jatrophenes and paralianes have been isolated from the aerial parts of Euphorbia paralias L. The molluscicidal activity of isolated compounds was evaluated on Biomphalaria alexandrina (Ehrenberg). Paraliane diterpene, (2S,3S,4R,5R,6R,8R,12S,13S,14R,15R)-5,8,14-triacetoxy-3-benzoyloxy-15- hydroxy-9-oxo-paraliane, was the most potent compound against the snail. Anti-feedant activity was tested by a conventional leaf disc method against third-instar larvae of Spodoptera littoralis (Boisd). Jatrophene diterpene, (2R,3R,4S,5R,7S,8R,13R,15R)-2,3,5,7,15-pentaacetoxy-8-angeloyloxy-14,15- dioxojatropha-6(17)-11E-diene, had the highest anti-feedant activity among the compounds tested.