Acute and chronic effects of lindane on frog tadpoles native to Saskatchewan
Serben, Kerrie Christine
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The purpose of this research was to determine if exposure to the insecticide, lindane, during the aquatic stage of the amphibian life cycle had any deleterious effects on the normal development of native frog species. Acute high level exposure produced effects on swimming behavior and malformations in wood frogs (Rana sylvatica) and boreal chorus frogs (Pseudacris maculata) that were similar to those caused by other organochlorine insecticides. Overall, these sublethal responses were most often quantified in hatchlings whereas mortality was most common in tadpoles. Wood frogs appeared to be more sensitive than boreal chorus frogs. For example, the 48-hour EC50s (median effective concentrations based on erratic swimming as the end point) were lower in wood frogs (1.82 and 2.13 mg/L) than in chorus frogs (3.37 and 4.04 mg/L) and significant mortality was only observed in the wood frogs. The lowest LC50 obtained was 1.90 mg/L at 72-h exposure with wood frog tadpoles. An outdoor microcosm study assessed the effect of chronic exposure to low concentrations of lindane on the survival, growth, and development of wood frog tadpoles. Groups of 40 tadpoles were exposed to three concentrations of lindane (0.1, 1.0, and 10 µg/L) and two control groups (negative and solvent) from 9-10 days post-hatch to metamorphic climax (MC). Survival was not affected (p = 0.13), and there were no significant treatment effects on time to MC (p = 0.88), fluctuating asymmetry (p > 0.42), or hepatic glycogen concentrations (p = 0.06). However, a possible hormetic effect of lindane was observed, as body condition of the metamorphs was highest at the lowest lindane concentration (0.1 µg/L), and decreased with increasing lindane concentration compared to control levels. Exposure to 0.1 µg/L lindane also affected sex ratios, resulting in 71% males in this treatment (p < 0.005). This effect was not dose-dependent, but, along with the alterations in corticosterone and thyroid hormones, and the possible hormetic effect, indicated a potential disruption of the endocrine system. For example, mean T4 (tetraiodothyronine) to T3 (triiodothyronine) ratio was 43% higher than in the 0.1 µg/L treatment compared to the control group. Further investigation is necessary in order to confirm these results and to determine a mechanism of action.