Non‐invasive electrophysiological monitoring: A sensitive method for detecting sublethal neurotoxicity in earthworms

Abstract

AbstractEarthworms were exposed, by external surface contact, to three chemical pollutants: dieldrin (a known neurotoxicant), dimethyl phthalate and fluorene (a possible neurotoxicant). After 48 h of exposure, LC50 values were determined and compared with concentrations required for sublethal neurotoxic effects on giant nerve fiber conduction velocity and escape reflex function, as assessed by nonin vasive electrophysiological recordings. For dieldrin, sublethal decreases in giant fiber conduction velocity occurred at concentrations as low as 1.4 ppm, whereas much higher concentrations were required for lethality (48‐h LC50 = 8,100 ppm). Other sublethal effects of dieldrin included hyperresponsiveness of giant fibers, reduction in giant fiber‐mediated muscle potentials, tonic spasms of longitudinal shortening and ataxia. For fluorene, sublethal neurophysiological effects, including reduced conduction velocity and occasional “rebound” spiking of giant fibers, were evident at 100 and 250 ppm. By comparison, the 48‐h LC50 for fluorene was 360 ppm. No sublethal neurophysiological effects were evident following treatment with dimethyl phthalate; the 48‐h LC50 was 10,900 ppm. The results indicate that noninvasive electrophysiological recording of earthworm escape reflex function can be used as a sensitive means of detecting potential sublethal neurotoxic effects of pesticides and other environmental pollutants in these nontarget organisms.