In this paper, several studies were conducted to evaluate the genotoxicity
of two pesticides, Imidacloprid and RH-5849, for earthworm (Eisenia fetida)
. Earthworms were exposed in different exposure systems to evaluate their a
cute toxicity and the geno toxicity of the two pesticides was evaluated by
using the method of sperm deformity assessment, micronucleus test of root t
ip cells in Vicia faba, a mouse bone-marrow micronucleus test, and comet as
say. LC50 (interpolated concentration at which 50% mortality of test popula
tion occurs) for earthworms varied in different exposure systems. The resul
ts indicated that Imidacloprid was consistently more toxic than RH-5849 in
all exposure systems. In this study, sperm deformity test was used to detec
t the potential adverse influences of pesticides on the reproduction of ear
thworms. The results demonstrated that significant induction of sperm defor
mity (p < 0.01) and a dose-effect relationship displayed at Imidacloprid co
ncentrations higher than 0.5 mg/kg dry soil. However, the sperm deformity f
requency of groups exposed to RH-5849 did not show significant difference (
p>0.05) from the control until the dose reached 100 mg/kg dry soil. The res
ults of the V.faba micronucleus tests showed that micronuclei frequency of
the exposed group did not show significant difference (p > 0.05) from the c
ontrol until the concentration of Imidacloprid and RH-5849 reached 100 mg/m
l. The results of the mouse bone-marrow micronuclei test also indicate that
two pesticides did not show significant effects (p > 0.05) on the micronuc
lei frequency in mice bone-marrow cells until the dose reached 100 mg/kg fo
r Imidacloprid and 300 mg/kg for RH-5849 (2/3 LD50). Although no genotoxici
ty was detected by using the micronucleus tests, the results of the comet a
ssay showed that the two pesticides induce significant DNA damage (p < 0.01
) in earthworms and dose-effect relationships were displayed. The 'earthwor
m comet assay' is a rapid and sensitive way to screen chemicals or terrestr
ial environments for their DNA-damaging properties. (C) 2000 Elsevier Scien
ce Ltd. All rights reserved.