Toxicity,bioconcentration, and metabolism of the herbicide propanil (3′,4′-dichloropropionanilide) in freshwater fish

Fathead minnows (Pimephales promelas) were exposed to technical grade propanil (3′,4′-dichloropropionanilide) in a flow-through diluter system to determine acute lethality. LC₅₀ values were 11.5, 10.2, 8.6, and 3.4 mg·L^?1 at 24, 48, 96, and 192 hr, respectively. Eggs, newly hatched fry, and juvenile fish of this species were similarly exposed but at lower concentrations and for a period of 58 days. The 58-day “no effect” concentration was between 0.4 and 0.6Μg·L^?1, based upon the physiological parameters of length and dry weight of juvenile fish.¹⁴C-Propanil did not bioconcentrate significantly in fathead minnows (1.6× for parent propanil in whole body). Rainbow trout (Salmo gairdneri) readily metabolized propanil, forming at least ten products. One metabolite recovered from trout bile was identified as either 3′,4′-dichloro-2-hydroxypropionanilide or 3′,4′-dichloro-3-hydroxy-propionanilide. The technical grade propanil also contained 0.67 mg·g^?1 of 3,3′,4,4′-tetrachloroazobenzene as a contaminant.