Nerve conduction velocity as a non-destructive biomarker in the earthworm Aporrectodea caliginosa exposed to insecticides

摘要

Earthworms are important and useful soil organisms, but in agricultural soils, they are potentially exposed to a wide variety of pesticides. Insecticides represent the highest threat to earthworms and many are neurotoxic. There is a need for a reliable, relevant, simple biomarker to assess the sub-lethal effects of neurotoxic insecticides on earthworms under laboratory or field conditions. The Aporrectodea caliginosa earthworms were exposed to 0 (control), 0.5x, 1x (normal field application rate), and 5x concentrations of a carbamate (PirimorA (R)) and an organophosphate (LorsbanA (R)) insecticides. The nerve conduction velocity (NCV) of the medial giant fibers of A. caliginosa earthworm was recorded on days 0, 1, 2, 3, 4, and 7 to quantify sub-lethal neurotoxic effects. Acetylcholinesterase (AChE) enzyme activity of A. caliginosa homogenates was measured at the conclusion of the experiment. PirimorA (R) but not LorsbanA (R) induced a significant decrease in NCV on days 3, 4, and 7 at 1x and 5x doses. A significant dose-dependent decrease was observed on AChE activity to PirimorA (R) at the doses used but not LorsbanA (R). A clear relationship is observed between AChE activity and NCV in the case of PirimorA (R). This study showed that NCV is a sensitive biomarker that correlates well with classical biomarker measurements such as AChE enzyme activity. This technique could be used to study the impact of insecticides on earthworms and also their recovery.