Teratological evaluation of the phenoxyacid herbicide MCPA in the regenerating forelimb of the adult newt.

The effects of a commercial formulation of the phenoxyacid herbicide 2-methyl-4-chlorophenoxyacetic acid sodium salt (MCPA) on the regenerating forelimb of the adult crested newt were studied. The animals were exposed percutaneously to 0, 200, 400, or 800 ppm of MCPA for 4 days a week throughout the regeneration period and were sacrificed 11 weeks after amputation. The concentrations tested did not cause histologically detectable toxic lesions of the examined organs. Exposure to MCPA resulted in a significant retardation of the morphogenetic process as evidenced by skeletal examination. At the highest concentration tested, a significant growth delay was also evident during the regeneration period. No significant differences in the frequency of skeletal malformations were observed between control and treated newts, although the frequency was higher in the latter.