Butachlor

Although butachlor is an herbicide, no acute toxicity tests were found with microalgae; however, regarding chronic toxicity, the pesticide exhibited a wide range of values between 0.00065 mg/L with Pseudokirchneriella subcapitata up to 8.61 mg/L with Chlorella vulgaris. This commonly used acetanilide herbicide can cause acute toxicity in Ceriodaphnia dubia, Daphnia carinata, and Daphnia magna at concentrations between 1.02 and 3.4 mg/L. Similar values have been reported for P. promelas, Heteropneustes fossilis, Clarias batrachus, and C. punctatus. Among these organisms, the most sensitive was P. promelas (0.75 mg/L), whose LC50 value is below the HC5 for acute toxicity estimated for this pesticide (1.0672 mg/L).

A selective systemic herbicide, absorbed primarily by the germinating shoots and secondarily by the roots, with translocation throughout the plant, giving higher concentrations in vegetative parts than in reproductive parts. Butachlor acts by inhibiting elongase needed to elongate very long-chain fatty acids and geranylgeranyl pyrophosphate cyclization enzymes needed for terpenoid synthesis, thus inhibiting algae growth.