title: Binary combinations of organophosphorus pesticides exhibit differential toxicity under oxidised and un-oxidised conditions.
abstract: 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.
authors: ICAR-National Centre for Integrated Pest Management, PUSA Campus, New Delhi 12, India; Land and Water, CSIRO, Waite Campus, Urrbrae, South Australia 5064, Australia. Electronic address: sumitraarora@hotmail.com.
authors: Sumitra
authors: S
authors: Arora
authors: Land and Water, CSIRO, Waite Campus, Urrbrae, South Australia 5064, Australia. Electronic address: anupama.kumar@csiro.au.
authors: Anu
authors: A
authors: Kumar
mesh_terms: D000110:Acetylcholinesterase; D000818:Animals; D004390:Chlorpyrifos / Q000633:toxicity; D002800:Cholinesterase Inhibitors / Q000633:toxicity; D004785:Environmental Pollutants / Q000633:toxicity*; D006793:Houseflies / Q000201:enzymology; D007306:Insecticides / Q000633:toxicity*; D008294:Malathion / Q000633:toxicity; D008999:Monocrotophos / Q000633:toxicity; D063086:Organothiophosphates / Q000633:toxicity; D016877:Oxidants; D010084:Oxidation-Reduction; D014230:Triazoles / Q000633:toxicity
chemical_list: D002800:Cholinesterase Inhibitors; D004785:Environmental Pollutants; D007306:Insecticides; D063086:Organothiophosphates; D016877:Oxidants; D014230:Triazoles; C012584:triazophos; D008999:Monocrotophos; C024273:profenofos; D000110:Acetylcholinesterase; D004390:Chlorpyrifos; D008294:Malathion
keywords: Antagonism; Combination index–isobologram; Concentration addition model; Housefly acetylcholinesterase; Synergism; Toxic unit