Toxicity In F1 Offspring Following Maternal Exposure To Tris (2-Butoxyethyl) Phosphate And The Reproductive Impairment In Gravid Female Zebrafish

Tris(2-butoxyethyl)phosphate(TBOEP)is a flame retardant widely used in chemical materials,electronic communications,textiles,furniture and other industries,often detected in water,air,soil and living organisms.Studies have shown that TBOEP can elicit toxic effects on the reproductive,nervous and endocrine systems to aquatic biota through bioaccumulation.It has been reported that more severe toxic effects were found in females than in males after exposure to TBOEP,and the developmental toxicity induced by parental transfer of TBOEP was demonstrated.However,the molecular mechanisms behind it remain unclear.In the previous studies,females and males exposed to TBOEP simultaneously.To explore the role of maternal exposure to TBOEP in the developmental toxicity,four-month-old female zebrafish were exposed to TBOEP(0 μg/L,20 μg/L,100 μg/L and 500 μg/L)for 30 days.After the 30-day exposure experiment of female zebrafish,the eggs were spawned with healthy male zebrafish in clean water.The effect of TBOEP on F0 generation female zebrafish was evaluated by detecting the content of TBOEP and vitellin in the ovary of F0 generation female zebrafish,and observing the changes of ovarian histopathological sections;by detecting the basic indicators of growth and development of the 144 hpf(hour post-fertilization)progeny larvae,the growth and development toxicity of the progeny was evaluated;and through the changes of the diameter of the 2 hpf progeny embryos,the content of TBOEP and vitellin in 2 hpf progeny embryos,as well as the growth hormone/insulin growth factors(GH/IGF)axis and the hypothalamic-pituitary-thyroid(HPT)axis of the 144 hpf progeny larvae to explore the toxicity mechanism of maternal TBOEP exposure to progeny zebrafish.The main results are as follows:1.In the 100 μg/L and 500 μg/L concentration groups,the body weight growth rate of F0 generation female fish decreased significantly,but the body length growth rate did not change;the gonad somatic index(GSI)decreased significantly.The results of the histopathological section of the F0 generation ovary showed: In the 20μg/L,100 μg/L and 500 μg/L concentration groups,the proportion of primary oocytes increased significantly,the proportion of mature oocytes decreased significantly;In the 100 μg/L and 500 μg/L concentration groups,the proportion of vitellogenic oocyte decreased significantly.It indicated that TBOEP delayed the maturation of female zebrafish oocytes.And in all concentration groups,the vitellin content in the ovary of female zebrafish was significantly decreased.2.In the 20 ug/L,100 ug/L and 500 ug/L concentration groups,TBOEP was detected in the F0 generation gonads,and the average concentrations were: 13.12 ±0.69 ng/g wet weight(ww),63.46 ± 11.02 ng/g ww and 132.40 ± 10.28 ng/g ww,respectively;TBOEP was also detected in F1 embryos,the average concentrations were: 8.45 ± 2.28 ng/g ww,13.80 ± 0.95 ng/g ww and 31.48 ± 5.41 ng/g ww,respectively.It indicated that TBOEP could accumulate in the gonads of F0 generation and be transferred to offspring with oocytes.3.After female zebrafish were exposed to TBOEP alone,the growth and development of their offspring larvae were inhibited.In the 20 μg/L,100 μg/L and500 μg/L concentration groups,the body length of the offspring larvae decreased significantly.In the 100 μg/L and 500 μg/L concentration groups,the number of heart rate of the offspring larvae decreased significantly.In the 500 μg/L concentration group,the survival rate of the offspring larvae decreased significantly.In the 20 μg/L,100 μg/L and 500 μg/L concentration groups,the deformity rate of the offspring larvae increased significantly,the deformity rate of the 500 μg/L concentration group has a downward trend compared with the 100 μg/L concentration group,which may be due to the dead deformed zebrafish in the 500 μg/L concentration group are not counted,resulting in a decrease in the deformity rate.In addition,in the 100 μg/L and500 μg/L concentration groups,the diameter of the progeny embryos decreased significantly;the vitellin content in the offspring embryos also decreased significantly,and the expression levels of most genes on the GH/IGF axis and HPT axis of the offspring zebrafish larvae decreased significantly.In conclusion,TBOEP can accumulate in the embryos through maternal transmission,by delaying the maturation of female zebrafish oocytes and reducing the content of vitellin in the ovary to affects the diameter of the offspring embryos,the content of vitellin,and the expression of related genes on the GH/IGF axis and the HPT axis to damages the growth and development of the offspring zebrafish.