クルマエビ幼生におけるチオノ型・オキソ型有機燐剤の毒性とアセチルコリンとエステラーゼ阻害性

抄録

A study was made regarding the relationship between the toxicity and acetylcholinesterase (AChE) inhibition of three organophosphorothionates (fenitrothion, FS; diazinon, DIN; phenthoate, PAP) and three oxo-forms (fenitrooxon, FO; diazoxon, DOX; dichlorvos, DDVP) in tiger shrimp Penaeus japonicus at different larval stages. The shrimp larvae at nauplius and zoea stages showed relatively high resistance to FS, DIN and PAP, i.e., the respective 24-h LC₅₀ values were 1.84, 10.5 and 5ppm. However, the toxicity of these thiono-form phosphates increased abruptly with the progress of the larval stages, especially after metamorphosis into the postlarva, resulting in the increase by ca. 2, 600, 1, 200 and 850 times respectively to that of nauplius stage. On the other hand, the toxicity of FO and DDVP to the larvae was almost unchanged throughout these stages, at the levels of ca. 7ppb and 5.6ppm as the 24-h LC₅₀ value, respectively.
The susceptibility of the larval AChE to the tested phosphates was almost unchanged from zoea to postlarva. The concentrations of FO, DDVP, DOX, FS, PAP and DIN producing 50% inhibition (I₅₀) of the AChE activity were approx. 0.015, 0.35, 1.27, 200, 650 and 1, 200μm, respectively. Although FS showed the highest AChE inhibition among the thiono-forms; its oxon (FO) displayed 12, 000 times high AChE inhibition compared to FS. The high AChE inhibition of FO was in good correlation with its high toxicity to the larvae even at the early stage.