To determine genotoxicity to coelomocytes, Pheretima peguana earthworms were exposed in filter paper studies to cadmium (Cd) and lead (Pb) for 48？h, at concentrations less than the LC10—Cd: 0.09, 0.19, 0.38, 0.75, and 1.50？μg cm？2; Pb: 1.65, 3.29, 6.58, 13.16, and 26.32？μg cm？2. For Cd at 0.75？μg cm？2, in the micronucleus test (detects chromosomal aberrations), significant increases ( ) in micronuclei and binucleate cells were observed, and in the comet assay (detects DNA single-strand breaks), tail DNA% was significantly increased. Lead was less toxic with minimal effects on DNA, but the binucleates were significantly increased by Pb at 3.29？μg cm？2. This study shows that Cd is more acutely toxic and sublethally genotoxic than Pb to P. peguana. Cadmium caused chromosomal aberrations and DNA single-strand breaks at 45% of the LC10 concentration. Lead, in contrast, did not induce DNA damage but caused cytokinesis defects. 1. Introduction Earthworms are primary decomposers of soil organic matter and, thus, aid in improving soil quality and fertility. Earthworms are a dominant component of the soil faunal biomass, providing 10–200？g？m？2 [1]. Because of their ecological importance, earthworms are now adopted as an indicator organism for the assessment of potential impact of chemicals to soil organisms. In agricultural operations worldwide, there is increasing concern about widespread soil contamination by chemicals and heavy metals. Cadmium (Cd) and lead (Pb) are two of the more toxic heavy metals released into soil by industrial processes. They are of particular concern because they have no biological function but are toxic to living organisms and pose a risk to human and environmental health. In polluted soil, earthworms are exposed to these pollutants both dermally and through gastrointestinal tract absorption from soil. The earthworm immune system is generally sensitive to heavy metal exposure. Exposure of earthworms to chemicals via the dermal route affects coelomocytes directly and, therefore, have a major influence on the health of earthworms. Therefore, monitoring earthworm immune competence can be regarded as a more sensitive and early-warning biomarker of ecosystem health. Inorganic Pb is classified as a group IIA carcinogen, which is a probable human carcinogen [2]. Cd is classified as a group I human carcinogen [3] and an animal carcinogen [4]. In addition, Cd interferes with DNA repair, which can lead to mutations [5] and eventually carcinogenesis [6]. Therefore, assessment of DNA damage is an important aspect of toxicity testing. Earthworm
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