Effects of flame retardant tributyl phosphate on early development of zebrafish
[Background]Tributyl phosphate(TBP)is widely used as an organophosphate flame retardant.However,there are limited studies on the toxicity of TBP to aquatic organisms at low levels of exposure.[Objective]To investigate the effects of TBP on early development of zebrafish(Danio rerio).[Methods]Zebrafish embryos were randomly divided into four groups at 2 h post-fertilisation(2 hpf),namely,the 0.01%dimethyl sulfoxide(DMSO)control group and TBP exposure groups(0.02,0.2 and 2 μg·L-1).The exposure time was from 2 hpf to 120 hpf and the hatching rate,mal-formation rate,heart rate and body length of zebrafish embryos at 72 hpf,the frequency of tail curling at 24-29 hpf,the locomotor ability at 96 hpf and the survival rate at 120 hpf were evalu-ated,respectively.The whole-body triiodothyronine(T3)and tetraiodothyronine(T4)levels of ju-venile fish were measured by enzyme immunoassay at the end of the infection,and the expression levels of hypothalamic-pituitary-thyroid axis(HPT)and neurodevelopmental-related genes were detected by quantitative real-time PCR(q-PCR).[Results]The heart rates of zebrafish embryos were significantly decreased in all TBP-treated groups(P<0.001),the survival rates of the 0.02 and 2 μg·L-1 TBP groups were significantly decreased(P<0.05),and the malformation rate of the 2 μg·L-1 treated group was significantly increased(P<0.05),which was mainly manifested by pericardial oedema.The frequency of tail curling of zebrafish embryos in all groups reached the highest at 25 hpf,which was significantly lower(P<0.001)in all exposure groups than in the control group(P<0.001).In the locomotor behaviour experiments,the swimming speed of zebrafish larvae in the dark cycle was significantly decreased in the 0.02 and 0.2 μg·L-1 TBP groups(P<0.05),and similar results were found for the light cycle in the 0.2 and 2 μg·L-1 TBP groups(P<0.05).Compared with the control group,the T3 level of zebrafish juveniles in the 0.2 μg·L-1 TBP group increased significantly(P<0.05).The q-PCR results showed that the expression levels of HTP axis-related genes[thyroid hormone receptors(trα,trβ),thyroglobulin(tg),and sodium/iodide co-transporter(nis)]were significantly down-regulated in the exposure groups,the ex-pression level of transthyretin(ttr)was significantly up-regulated in the 0.02 μg·L-1 TBP group,and the iodothyronine deiodinase 2(dio2)expression level was significantly down-regulated in the 0.02 μg·L-1 TBP group(P<0.05);the neurodevelopment-related gene acetyl-cholinesterase(ache)was significantly down-regulated in the exposure groups,and the expression levels of myelin basic protein(mbp)and Elav like neuron-specific RNA binding protein 3(elavl3)were significantly down-regulated in the 0.02 μg·L-1 TBP group(P<0.05).[Conclusion]TBP exposure can lead to early developmental abnormalities in zebrafish,manifested as developmental toxicity,thyroid en-docrine disruption and neurotoxicity during hatching and early juvenile stages.
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