monocrotophos and triazophos

Acetylcholinesterase (AChE) inhibition has been demonstrated to be useful as a biomarker for exposure to organophosphorus (OP) insecticides in many environments. The objective of this study was to investigate the response of housefly (Musca domestica) head AChE (HF-AChE) exposed to five OPs as individual compounds and their binary mixtures under in vitro conditions. To examine the effects of oxidation on OP potency in the HF-AChE system, bromine water was used as an oxidisng agent. With oxidation, the sensitivity of HF-AChE to chlorpyrifos (CPF), malathion (MLT) and triazophos (TRZ) increased significantly. Monocrotophos (MCP) and profenofos (PRF) did not exhibit any significant differences in toxicity under oxidised and un-oxidised conditions. The toxicological interaction of five organophosphorus pesticides was evaluated using the concentration addition model, the combination index-isobologram equation and the toxic unit approach. All three models provided similar predictions for the 10 binary combinations of OPs under oxidised and un-oxidised conditions. In the present study, the antagonistic effects of the binary combination of OPs (CPF+PRF, CPF+MLT, MCP+MLT, PRF+MLT, MLT+TRZ and PRF+TRZ) were observed under oxidised conditions. This may be due to dispositional and/or receptor antagonism. Most of the binary combinations assayed under un-oxidised conditions exhibited synergistic responses. Triazophos showed very strong synergism in binary combinations with CPF, MCP and PRF un-oxidised conditions. In contrast, under oxidised conditions, only CPF+TRZ exhibited synergism. The results obtained indicate differential toxicity of binary combinations of OPs under oxidised and un-oxidised conditions. This information could be a valuable tool in understanding the mechanisms of OPs interactions and the interpretation of future in vivo studies with mixtures of OP insecticides.

Topics: Acetylcholinesterase; Animals; Chlorpyrifos; Cholinesterase Inhibitors; Environmental Pollutants; Houseflies; Insecticides; Malathion; Monocrotophos; Organothiophosphates; Oxidants; Oxidation-Reduction; Triazoles

A crop protection system consisting of sequential treatments by six insecticides--dimethoate, monocrotophos, deltamethrin, endosulfan, cypermethrin, and triazophos--at recommended dosages in cotton fields in Punjab, India was investigated for its effects on nontarget soil microorganisms and their activities. Successive applications of the insecticides caused only short-lived adverse effects on the soil microorganisms. None of the insecticides used had any adverse effects on soil fungi as reflected by their total numbers. Significant change in Azotobacter numbers were observed after dimethoate, triazophos, and endosulfan treatment in 1998 soil. An increase of up to 71% in actinomycetes numbers was observed after deltamethrin treatment in the treated fields in 1995. Few short-term changes in iron-reduction capacity were observed after endosulfan and cypermethrin treatments. No adverse effect was observed on the soil respiration during all the experimental periods. The amount of residues detected in soil ranged from 8.5 to 42.0 ng g(-1)dry wt. soil for organophosphorus insecticides and from nondetectable to 5.55 ng g (-1)dry wt. soil for synthetic pyrethroids. It ranged between 7.3 and 35.6 ng g(-1)dry wt. soil for endosulfan. On many occasions two or three insecticide residues were detected together; therefore, the effect observed on soil microorganisms and their activities was a multiresidue effect. In 1998, crop soil amounts of insecticide residues were generally more than those in 1995 and 1996. Persistence and dissipation patterns in soils with a history of exposure to the insecticides compared to the non-history soils were similar.

Topics: Agriculture; Bacteria; Carbon Dioxide; Colony Count, Microbial; Dimethoate; Endosulfan; Fungi; Gossypium; Insecticides; Iron; Monocrotophos; Nitriles; Organothiophosphates; Pesticide Residues; Pyrethrins; Soil Microbiology; Soil Pollutants; Triazoles