Toxicity, Uptake, and Elimination of the Herbicides Alachlor and Dinoseb in Freshwater Fish

Abstract

Abstract Fathead minnows ( Pimephales promelas ) 30 d of age were exposed to technical grade alachlor [2‐chloro‐2′ ,6′‐diethyl‐ N ‐(methoxymethyl)acetanilide] and dinoseb (2‐ sec ‐butyl‐4,6‐dinitrophenol) in flow‐through tests to determine acute toxicity. Median lethal concentrations (LC 50 values) for alachlor were 9.9, 6.6, 5.0, and 3.0 mg L −1 at 24, 48, 96, and 192 h, respectively; and for dinoseb were 0.8, 0.7, 0.7, and 0.5 mg L −1 , respectively. Early life‐stages of the fathead minnow (embryos, fry, and juveniles) were exposed to lower concentrations of each compound for a total of 64 d. The “no effect” concentration was estimated to lie between 0.52 and 1.10 mg L −1 for alachlor and between 14.5 and 48.5 µ g L −1 for dinoseb. Neither herbicide was appreciably accumulated in fish tissue. Whole body bioconcentration factors for parent 14 C‐alachlor and 14 C‐dinoseb were 6.0 and 1.4, respectively. Rainbow trout ( Salmo gairdneri ) injected with radiolabeled herbicides eliminated ≥ 83% of the radioactivity within 24 h as a combination of parent compound and metabolites. These laboratory studies suggest that the accumulation of alachlor and dinoseb residues and the toxicity of alachlor do not present great environmental risks to fish. However, the toxicity of dinoseb may pose some risk.