Comparative Toxicity of Two Different Dimethoate Formulations in the Common Toad (Rhinella arenarum) Tadpoles.

Dimethoate (D) are among the most commonly used organophosphates insecticides in the world. To evaluate the toxicity of two D formulations were selected as test organisms tadpoles of Rhinella arenarum. This toad species has an extensive neotropical distribution and is easy to handle and acclimate to laboratory conditions. The tadpoles were exposed in an acute assay for 48 h to D soluble concentrates (DSC) and emulsifiable concentrates (DEC). The 48 h-LC50 (95% confidence limits) value of DSC was 57.46 mg L-1 (40.52-81.43) and to DEC was 12.76 mg L-1 (10.39-15.68). These differences in toxicity were statistically significant (p < 0.05). In both formulations, acetylcholinesterase), carboxylesterase, and glutathione-S-transferases enzyme activities varied significantly respect to those of control group (p < 0.05). The DEC formulation was the most toxic. These results would allow the assessment and characterization of potential ecological risks following the application of those formulations.

A simple spectroscopic method to determine dimethoate in water samples by complex formation.

A simple and rapid method for the determination of dimethoate in water was developed based on the monitoring of the complex formation between bis 5-phenyldipyrrinate of nickel (II) and the herbicide dimethoate. The method showed a short response time (10 s), high selectivity (very low interference from other sulfate and salts), high sensitivity (limit of detection (LOD) 0.45 µM, limit of quantitation (LOQ) of 1.39 µM), and a Kd of 2.4 µM. Stoichiometry experiments showed that complex formation occurred with a 1:1 relation. The method was applied to different environmental water samples such as lagoon, stream, urban, and groundwater samples. The results indicated that independently from the water source, the method exhibited high precision (0.25-2.47% variation coefficient) and accuracy (84.42-115.68% recovery). In addition, the method was also tested using an effluent from a wastewater treatment plant from Mexico; however, the results indicated that the presence of organic matter had a pronounced effect on the detection.

Sand as a solid support in ultrasound-assisted MSPD: A simple, green and low-cost method for multiresidue pesticide determination in fruits and vegetables.

Sand was studied as a solid support in ultrasound-assisted matrix solid-phase dispersion (UA-MSPD) for the extraction of different pesticide classes, including organophosphates, carbamates, triazoles and pyrethroids from fruits and vegetables, with determination by GC-MS and LC-MS/MS. The performance of sand was compared with that of different types of classic solid supports and alternative natural materials from renewable sources. The best results were obtained using 0.5 g sample, 1 g sand as a solid support, 20 mg activated charcoal and 5 mL ethyl acetate as elution solvent. Recoveries ranged from 55 to 140% with an RSD ≤ 20%. LOQs varied from 0.005 to 0.5 mg kg-1 for all analytes. Thiamethoxam, captan, chlorpyrifos, dimethoate and pyrimethanil were found in strawberry samples at concentrations from 0.01 to 0.06 mg kg-1. Acephate and tebuconazole were found in a tomato sample at concentrations of 0.45 and 0.30 mg kg-1, respectively. The method developed was efficient, simple, cheap, robust, and environmentally friendly.

Chloride anion effect on the advanced oxidation processes of methidathion and dimethoate: role of Cl2(·-) radical.

The reaction of phosphor-containing pesticides such as methidathion (MT) and dimethoate (DM) with dichloride radical anions (Cl(2)(·-)) was investigated. The second order rate constants (1.3 ± 0.4) × 10(8) and (1.1 ± 0.4) × 10(8) M(-1) s(-1) were determined for the reaction of Cl(2)(·-) with MT and DM, respectively. A reaction mechanism involving an initial charge transfer from the sulfide groups of the insecticides to Cl(2)(·-) is proposed and supported by the identified transient intermediates and reaction products. The formation of chlorinated byproducts was determined. The unexpected consequences of an efficient Cl(2)(·-) reactivity towards MT and DM on the degradation capacity by Advanced Oxidation Procedures applied to polluted waters containing the insecticides and Cl(-) anions is discussed.

Vibrational and scaled quantum chemical study of O,O-dimethyl S-methylcarbamoylmethyl phosphorodithioate, dimethoate.

Infrared and Raman spectra of O,O-dimethyl S-methylcarbamoylmethylphosphorodithioate, dimethoate, have been recorded. Density functional theory, DFT, with the B3LYP functional was used for the optimization of the ground state geometry and simulation of the infrared and Raman spectra of this molecule. Calculated geometrical parameters fit very well with the experimental ones. Based on the recorded data, the DFT results and a normal coordinate analysis based on a scaled quantum mechanical (SQM) force field approach, a complete vibrational assignment was made for the first time.