Impact of Pulse Exposure to Methoxychlor on Flagfish (Jordanella floridae) Over One Reproductive Cycle

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Abstract
A 7.5- to 15-min pulse (.simeq. 0.30 mg .cntdot. L-1) of the insecticide methoxychlor is currently used to control larval emergence of the blackfly (Diptera: Simuliidae) in several river systems of western Canada. Our chronic life-cycle study with flagfish (Jordanella floridae) tested whether pulse exposure to methoxychlor would alter either the survival, wet weight gain, and reproduction of first-generation fish, or the survival and wet weight gain of their offspring. Flagfish were pulse exposed for 2 h to 0, 0.25, 0.70, 1.84, or 4.00 mg methoxychlor .cntdot. L-1 either once, at 8 d of age, or twice, at 8 and 71 d of age. While mortality and wet weight gain were inconsistent indicators of methoxychlor impact, reproductive characteristics were highly sensitive. Mean daily egg production, total egg production, and time to steady spawning of first-generation fish, as well as hatchability and incidence of abnormalities in their offspring, were all adversely affected by a single 2-h exposure of 8-d-old juveniles to concentrations of methoxychlor .gtoreq. 0.25 mg .cntdot. L-1 (0.0065 of the 96-h pulse-exposure LC50). Therefore, juvenile fish in methoxychlor-treated rivers are at greater risk than would be indicated by continuous exposure experiments. Estimates of the impacts of short-term high-level pulse exposures extrapolated from continuous exposure studies appear to severely underestimate toxicity.