Cytogenetic effects of cypermethrin and fenvalerate on the root meristem cells of Allium cepa

Cytogenetic effects of two commercial formulations of alpha-cyano pyrethroi d insecticides viz. cypermethrin (cyperkill 25% EC; CYP) and fenvalerate (S umicidin 20% EC: FEN) were evaluated in the root meristem cells of Allium c epa. The test concentrations of compounds were selected by determining EC50 (CYP.10 mg 1(-1); FEN 14.25 mg 1(-1)) of the Allium root growth. Both the compounds significantly and dose-dependently inhibited the mitotic index (M I) and induced chromosome (CA) and mitotic aberrations (MA) at 6 or 24 h tr eatment. The root meristem cells exposed to 6 or 24 h and analysed at 24 h post exposure, revealed a considerable frequency of aberrant cells despite substantial recovery. The types of aberrations induced by both the compound s were quite similar, except the induction of unequal distribution of chrom osomes and micronucleated cells obtained with CYP. Furthermore, CYP was fou nd to be more toxic as the frequency of aberrant cells was much higher in C YP treated cells than that of FEN. These observations, consistent with earl ier reports, indicate that spindle poisoning is the primary mechanism of ge notoxic action of these alpha-cyano pyrethroid insecticides, however, mild percentage of chromosome breaks indicate the clastogenic potential of these compounds. (C) 1999 Elsevier Science B.V. All rights reserved.