2,4-Dichlorophenoxyacetic acid(2,4-D)is widely used in agriculture as herbicide and plant growth regulator in the past semicentury.It progressively accumulates in the environment,especially in aquatic ecosystem.In the present study,we investigated the developmental toxicity of 2,4-D on zebrafish(Danio rerio)embryo.Acute 2,4-D exposure significantly decreased both the survival rate(LC50 = 56.76 mg/L)and hatching rate(IC50 = 53.05 mg/L)of zebrafish during embryonic development.The most common developmental defect observed in 2,4-D treated embryos was pericardial edema,which occurs in a dose-dependent manner.The heartbeat rate of zebrafish embryos was increased after 2,4-D(25 and 50 mg/L)exposure.Consistently,mRNA expression levels of several cardiac-related genes were affected by 2,4-D(25 and 50 mg/L),suggesting a potential molecular mechanism of 2,4-D-induced cardiac malformation of zebrafish embryo.Moreover,similar to other environmental pollutants,2,4-D(25 and 50 mg/L)exposure resulted in the reduced expression of oxidative stress-related genes.It was also found that 2,4-D(25 and 50 mg/L)significantly increased MDA content.Taken together,our study investigated the toxic effects of 2,4-D on zebrafish embryonic development and its potential molecular mechanisms,shedding light on the full understanding of 2,4-D toxicity.