Toxicity of commercial neem extract to earthworms (Pheretima peguana)

Abstract

The LC₅₀ of commercial neem extract (Sadao Thai III containing azadirachtin; NEEM) on filter paper in the earthworm Pheretima peguana at 48 h and 72 h was 3.79 and 3.33 µg cm⁻², respectively. In earthworms exposed to five NEEM concentrations from 0.39 (∼10% of 48-h LC₅₀) to 3.13 (∼80% of 48-h LC₅₀) µg cm⁻², the radial thickness of the epidermis and body wall significantly (P < .05) decreased, and thickness of intestinal epithelium increased but only at high doses, approximately 25-fold above the concentration permitted for use as an insecticide in field applications (0.09 µg cm⁻²). NEEM significantly (P < .05) increased the number of binucleated coelomocytes in the micronucleus test (detects chromosomal aberrations) at 3.13 µg cm⁻², approximately 35-fold higher than the recommended dose, but it did not cause coelomocyte DNA single-strand breaks in the comet assay. Thus, NEEM is cytotoxic (increase in binucleates through the inhibition of cytokinesis) but not genotoxic to earthworm coelomocytes. This study demonstrates that the recommended dosage of commercial neem extract as an insecticide in agricultural practices is safe for earthworms.