The Amazonian fish Colossoma macropomum (tambaqui) is farmed intensively in rice paddies around the São Francisco River delta in northeast Brazil, where the herbicide trifluralin is regularly used. The aims of this study were to evaluate the inhibitory effects of trifluralin on acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) of brain and muscle from C. macropomum in order to assess the value of this species as a sentinel for herbicide contamination. Trifluralin was highly toxic to fingerlings in vivo (96 h-LC 50 = 0.42 mg L-1). Cholinesterase activity in cell-free extracts of brain was associated with two isoforms, AChE and BChE, although the former predominated. The specific activity of brain AChE was reduced significantly (p < 0.05) following 96.h exposure of fingerlings to trifluralin at 0.5 and 0.75 mg L-1 , but increased by 30% after exposure to 1.0 mg L-1 of herbicide. Muscle AChE was not affected by exposure to trifluralin. and values of brain AChE were 0.043 ±.0.015 mmol L-1 and 0.301.±.0.014 mmol min-1 mg-1 protein, respectively. Brain AChE was moderately sensitive to trifluralin (IC 50 = 0.78 mg L-1), but was very sensitive to the anticholinesterase agent eserine (IC 50 = 0.043 mg L-1). AChE inhibition in C. macropomum may be employed as a biomarker for biomonitoring trifluralin contamination in water bodies.

The herbicide trifluralin is one of the most widely herbicides used in weed control. This study aims to evaluate the genotoxic potential of the trifluralin herbicide on the Colossoma macropomum (tambaqui) using a multi-biomarker approach. The C. macropomum is highly adapted and predominant species in a variety of water bodies in the delta region of the São Francisco River and other river systems in Brazil. The mutagenic and the genotoxic effects of different trifluralin concentrations (0.25, 0.5, 0.75, 1.0 mg L-1) in peripheral erythrocytes of C. macropomum were investigated using micronucleus (MN), comet assay and apoptosis test. After an exposure period of 96 h, the results showed a significant rate of micronuclei and nuclear abnormalities in erythrocytes of C. macropomum exposed to 0.5, 0.75, 1.0 mg L-1 of trifluralin. Compared to controls, the genetic damage index (GDI) showed significant variations (**p < 0.01 and ***p < 0.001) for all the trifluralin concentrations tested. The genotoxicity of trifluralin herbicide on C. macropomum was confirmed by the micronucleus test and comet assay.