Growth, development and sex ratios of Spotted Marsh Frog (Limnodynastes tasmaniensis) larvae exposed to atrazine and a herbicide mixture

Exposures of Limnodynastes tasmaniensis tadpoles to atrazine (0.1, 1, 3 and 30 μg L^-1), metolachlor (0.1, 1 and 10 μg L^-1) and thiobencarb (90, 180 and 360 μg L^-1) from Gosner stage 28 to 42 under controlled laboratory conditions gave no significant effects on tadpole growth, development and sex ratios. A binary mixture of atrazine and thiobencarb as well as a ternary mixture of all three herbicides also had no significant effects on the developing larvae to show no evidence of interactive toxicity. Abnormal gonad morphology was observed on two occasions; both from 0.1 μg L^-1 atrazine treatments with one tadpole observed with testicular ovarian follicles. The low frequencies of abnormal gonadal morphology and testicular ovarian follicles did not indicate a concentration associated response to herbicide exposure. No significantly unbalanced sex ratios were observed to suggest any evidence of chemically induced feminisation. These observations suggest that environmentally relevant concentrations of atrazine, metolachlor and thiobencarb do not present a significant threat to the normal development of L. tasmaniensis larvae in surface waters of irrigated agricultural areas.