Studies On The Genetic Damage And Antioxidant Enzyme Activity In Zebrafish Treated By Nano-TiO₂ And 1,2,4-TCB

1,2,4-trichlorobenzene (1,2,4-TCB) and nanoscale titanium dioxide (nano-TiO2) are widely used in industry.In recent years, lots of studies have reported on effects of nano materials on health of microorganisms, plants, fish and human beings. But the combined effects of nano-TiO2 and other pollutants are few. This study was proposed that pathological section observation, micronucleus test, comet assay, physiological and biochemical indexes were studied to analysis the effects of single or combined nano-TiO2 and 1,2.4-TCB on gill tissue, genetic toxicity and change of antioxidant enzyme activity.human would have a better understanding of joint toxicity of nano-TiO2 and 1,2,4-TCB, and it would provide theoretical basis for water ecological environment protection and security applications of nano-TiO2 photocatalyst.The main research contents:(1) gill pathological damage in zebrafish treated by nano-TiO2 (40nm) and of 1,2,4-TCB showed toxic effects on zebrafish and phenomenon of the impatient, shifting, nervous motion, violent motion and beating. In addition, some fish was death.Combination of nano-TiO2 and 1,2,4-TCB, at the individual level could cause gill and lungs to swell, curvature of spine and other non lethality and gill swelling rate was higher than that of single nano-TiO2 or 1,2,4-TCB group, and had dose——effect relationship with nano-TiO2 or 1,2,4-TCB. Gill was one of target organs of combined exposure of 1,2,4-TCB and nano-TiO2.In addition, pathological section test showed that combined exposure of nano-TiO2 and 1,2,4-TCB would lead to gill tissue appearing gill lamellae arranged in disorder, epidermal cells faulted, cell column shaped, gill lamellae epithelial cells necrosis and shedding, original structure of the pillar cells disappeared, and gill function damaged.(2) genetic studies on zebrafish treated by nano-TiO2 and 1,2,4-TCB have shown that, at 7 days, zebrafish with nano-TiO2 (1,10,20,30 mg·L-1) did not appeare gill chromosome and DNA damage, so that there was no genetic toxicity of nano-TiO2 in zebrafish.zebrafish with 1,2,4-TCB (5,10,20 mg·L-1) had gill chromosome and DNA damage and they had dose——effect relationship with 1,2,4-TCB, and at 10 mg·L-1,2,4-TCB, chromosome and DNA damage increased significantly.however, gill micronucleus rate,and comet rate, tail DNA rate, tail length, tail moment and olive tail moment of comet assay were increasing with concentrations of 1,2,4-TCB or nano-TiO2 in zebrafish exposed to combination of 1,2,4-TCB and nano-TiO2. and showed a dose——effect relationship. Through analysis of two factors, combination of nano-TiO2 and 1,2,4-TCB had synergistic gene toxicity for zebrafish, that strengthened genetic toxicity for each other. In addition, it was found that the smaller size of nano-TiO2 and the longer exposure time, the more gene damage.(3) antioxidant enzymes in zebrafish treated by combination of nano-TiO2 and 1,2,4-TCB were investigated. The results showed that, at 7 days, SOD and CAT activity were decreased in normal range in zebrafish with alone nano-TiO2 (1,10,20,30 mg·L-1) and did not exist significant differences with control;SOD and CAT activity had dose——response relationship with concentration of 1,2,4-TCB in zebrafish with separate 1,2,4-TCB(5,10,20 mg·L-1), and at 10 mg·L-1,2,4-TCB, SOD and CAT activity decreased significantly.However, SOD and CAT activity decreased significantly with concentration of 1,2,4-TCB or nano-TiO2 increasing in zebrafish with combination of 1,2,4-TCB and nano-TiO2, and showed dose——effect relationship. Through two factorial analysis, combination of nano-TiO2 and 1,2,4-TCB had synergistic effects for SOD and CAT activity in zebrafish.In addition, it also found that SOD and CAT activity increased and then decreased with exposure time increasing at the same concentration.It showed short-term induction and long term inhibition. In addition, the study found that the smaller size of nano-TiO2 and the longer exposure time, effects on SOD and CAT activity was higher in zebrafish.4) In different concentrations, exposure time and particle sizes, gill damage, chromosome and DNA damage induced by nano-TiO2 and 1,2,4-TCB related to the antioxidant enzyme activity decreasing (such as SOD and CAT).