Pesticides are known to transform in the environment, but so far the study of their effects in the environment has concentrated on the parent compounds, thereby neglecting the effects of the degradation products. The embryotoxic, developmental, and teratogenic effects of chloroacetanilide
herbicides and their environmentally stable
aniline degradation products were investigated in this study in view of the massive application of
alachlor and
metolachlor. Embryos at midblastula to early gastrula stages of a locally abundant African clawed frog Xenopus laevis were used as test organisms. The embryos were exposed to the test chemicals for 96 h in each experiment.
Alachlor is more embryotoxic (the concentration causing 50% embryo lethality, 96-h LC50 = 23 microM [6.1 mg/L]) and teratogenic (teratogenic index [TI] = 1.7) than
metolachlor (96-h LC50 = 48 microM [13.6 mg/L], TI = 0.2). The degradation products of
alachlor and
metolachlor, respectively,
2,6-diethylaniline (96-h LC50 = 13 microM [19.4 mg/L], TI = 2.1) and 2-ethyl-6-methyaniline (96-h LC50 = 509 microM [68.8 mg/L], TI = 2.7), are less embryotoxic but more teratogenic than their parent compounds. The most common teratogenic effects observed were
edema for
alachlor as opposed to axial flexures and
eye abnormalities for
2,6-diethylaniline and 2-ethyl-6-methylaniline.
Metolachlor is found to be an example of a nonteratogenic
herbicide that upon degradation loses toxicity but gains teratogenicity, and both the
herbicides,
metolachlor and
alachlor, are potential sources of teratogenic transformation products.