Chronic toxicity of technical atrazine to the fathead minnow (Pimephales promelas) during a full life-cycle exposure and an evaluation of the consistency of responses.

Fathead minnows (Pimephales promelas) were continuously exposed to the herbicide atrazine (0.15, 0.25, 0.46, 0.99, and 2.0 mg a.i./L, plus dilution water and solvent controls) for a complete life cycle (274 days). Concentrations of atrazine up to 2.0 mg a.i./L did not significantly reduce hatching success, larval survival at 30 or 60 days post-hatch, or reproduction (eggs/spawn, total eggs, spawns/female, or eggs/female) in the F0 generation. However, at 60 days of exposure, total length and total survival to study completion were significantly reduced in ≥0.46 mg a.i./L and ≥ 0.99 mg a.i./L treatments, respectively. In the F1 generation, hatchability of embryos at ≥0.25 mg a.i./L (range 74-82%) was significantly less than that of pooled control organisms (86%). Following 30 days' post-hatch exposure, F1 survival was not significantly different from pooled control for any treatment. Finally, tissues representing major life stages had bioconcentration factors ranging from 3.7× (F1 embryos, <24 h) to 8.5× (F0 adults), indicating little to no evidence of bioconcentration. We developed a series of questions to assess the consistency of observed responses in order to place the data in context with the wider available and relevant literature (e.g., Observed between studies? Observed between species? Observed at lower levels of biological organization?). The analysis for consistency supports the conclusion that atrazine does not pose a significant chronic risk to freshwater fish in terms of growth, reproduction, or survivorship at concentrations of up to at least 100 μg/L.