Synergistic effects caused by atrazine and terbuthylazine on chlorpyrifos toxicity to early-life stages of the zebrafish Danio rerio

This study examined the effects of three widely used pesticides that have been previously detected in aquatic systems neighbouring agricultural fields on the early-life stages of the zebrafish Danio rerio. Tests involving single exposures and binary combinations of the s-triazine herbicides (atrazine and terbuthylazine) and the organophosphate insecticide chlorpyrifos were performed. Several endpoints, such as swimming behaviour, morphological abnormalities and mortality, were studied. In addition, the inhibition of acetylcholinesterase (AChE) activity was investigated in order to evaluate the mode of action and toxicity of chlorpyrifos in the presence of these herbicides. Results indicate that both binary mixtures elicited synergistic responses on the swimming behaviour of zebrafish larvae. Moreover, although the herbicides were not effective inhibitors of the AChE on their own, a synergistic inhibition of the enzyme activity was obtained by exposure to mixtures with chlorpyrifos. We observed a correlation between impairment of swimming behaviour of the larvae and inhibition of AChE activity. This study supports previous studies concerning the risk assessment of mixtures since the toxicity may be underestimated when looking only at the single toxicants and not their mixtures.

This study was supported by a PhD grant (SFRH/BD/62818/2009) attributed to Joanne Rodríguez Pérez and by the Pos-Doc grants attributed to Marta Monteiro (SFRH/BPD/45911/ 2008) and Inês Domingues (SFRH/PPD/31752/2006) by the Portuguese Science and Technology Foundation (FCT), funding by FEDER through COMPETE e Programa Operacional Factores de Competitividade and by National funding through Fundação para a Ciência e Tecnologia (FCT), within the research project FUTRICA—Chemical Flow in an Aquatic TRophic Chain (FCOMP-01-0124-FEDER008600; Ref. FCT PTDC/AAC-AMB/104666/2008). Theauthors would like to acknowledge Ana Catarina Bastos for the revision of the English language.

published