Comparative neurotoxicity of two energetic compounds, hexanitrohexaazaisowurtzitane and hexahydro-1,3,5-trinitro-1,3,5-triazine, in the earthworm Eisenia fetida.

Hexanitrohexaazaisowurtzitane (CL-20) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), both energetic compounds, share some degree of structural similarity. A noninvasive electrophysiological technique was employed to assess the impacts of acute sublethal exposures on impulse conduction in medial (MGF) and lateral (LGF) giant nerve fiber pathways of the earthworm Eisenia fetida and to evaluate the reversibility of neurotoxic effects. Earthworms were exposed to either 0.02 to 2.15 microg/cm2 of CL-20 or 0.04 to 5.35 microg/cm2 of RDX, for 1 to 14 d, on moistened filter paper. Conduction velocities of MGF and LGF were recorded on a digital oscilloscope before and after exposure. Results indicate that at exposure levels as low as 0.02 microg/cm2 of CL-20 or 0.21 microg/cm2 of RDX, worms exhibited physiological impacts such as retardation, stiffness, and body shrink. Both MGF and LGF conduction velocities were negatively correlated with increasing doses of CL-20 or RDX. However, such neurotoxic effects were alleviated or even eliminated within a few days after exposed worms were transferred to an uncontaminated environment, indicating that the neurotoxicity is reversible even after 6-d exposure. The CL-20 is more potent than RDX, which is consistent with previous studies on lethality, growth, and reproduction endpoints in soil oligochaetes.