Migration And Distribution In A Simulation Micro-cosmos System And The Toxic Mechanisms Of1,2,4-Trichlorobenzene

1,2,4-trichlorobenzene (1.2,4-TCB), a kind of chlorobenzenes, is widely used in industry. High concentration of1,2,4-TCB residual has been detected in variety of natural waters. Aquatic organisms could concentrate1,2,4-TCB through food chain or directly absorpt it from the environmental media. Therefore, it has great significance to study the behavioral and ecological toxicity of1,2,4-TCB in the environment and understand the distribution and toxicity mechanism in water environment. Simulated aquatic ecosystem, one kind of micro-cosmos, was used to study the behavior of1,2,4-TCB in the aquatic environment and its biological toxic effects on fish and plants. The main content in this study include:1. Behavior of1,2,4-TCB in simulated aquatic systemThe dynamic changes of accumulation, distribution and transmission of1,2,4-TCB in water and organisms (swordfish, Hydrocotyle vulgarisl., prawn) were investigated using micro-cosmos system. Organism samples included different tissues and organs, while environmental samples included different media such as water and air. The results showed that66.7%of1,2,4-TCB volatilized to atmosphere in10days, and the rest transferred to different organisms,18%in plant,22.68%in fish and8.78%in prawn. The further study of the adsorption process in different organisms showed Hydrocotyle vulgarisl. adsorpted it through a physical adsorption process; The content of1,2,4-TCB in Hydrocotyle vulgarisl. reached the highest at10th day and reduced to a stable level after15th day. The concentration of1,2,4-TCB in stem is higher than that in leaf. Prawn and fish showed adsorption to different degree. The adsorption rate is rather high in the first10days, and then maintained a steady state. Concentration of1,2,4-TCB in different tissues ranked as heart>gill>gonads>intestine>muscle, and they were suspected to relate to fat content in various tissues.1,2,4-TCB concentration in prawn increased slower than that in fish in the first10days, and the final content was also lower, possibly due to the protection of shell. In conclusion, bioconcentration of1,2,4-TCB was found to be most severe in fish, then prawn, and finally the plant.2. Biotoxicity of1,2,4-TCB(1)A hydroponic experiment was carried out to study the effect of1.2.4-TCB on physiological characteristics of Hydrocoryle vulgarisl. The changes of chlorophyll, carotenoid. soluble protein and malondialdehyde (MDA) contents were determined, as well as the activities of some antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD). The results showed that the physiological indexes of Hydrocotyle vulgarisl changed in concentration-effect and time-effect manner after low concentrations treatment (5,10mg·L-1). but there was no significant difference between the control group and the treatment groups. The total chlorophyll contents. chlorophyll a/b and the contents of soluble proteins rose first and then fell with treatment time. The content of MDA increased with treatment time and1.2.4-TCB concentration. The activities of antioxidant enzymes (SOD. CAT and POD) first increased and then decreased with Treatment time and1.2.4-TCB concentration. The activities of antioxidant enzvmes reached the maximums at10mg·L-1between4-6d. The activities of antioxidant enzvmes decreased significantly in the leaves of Hydrocotyle vulgarisl. with high concentration treatment (15,20mg·L-1).(2)The toxicity of1,2,4-TCB on adult zebrafish and embryo was studied by semi-static test. Adult zebrafish showed acute toxicities and typical symptoms as jumping, running and tachypnea soon after exposure. The LC50of24,48and72h exposure were4.33,4.26and2.72mg-L-1. Embryo exposed to1,2,4-TCB in vitro or exposed to parent zebrafish showed various toxic symptoms and developmental malformation, including exogastrula, bobtail, edema, spinal curvature, and even death. Different toxicological endpoints could be found in different stages of embryonic development. Fertilization and spawning was influenced by1,2,4-TCB to a certain degree. With the increase of the concentrate of1,2,4-TCB, the spawning number and fertilization rate decreased, while the rate of embryonic mortality and death increased as well. Hatching time (juveniles out of egg membrane) was postponed to later than72h. We also found that embryos were more sensitive to1,2,4-TCB in vitro than adults. (3) The adult zebrafish were exposed to1.2.4-TCB in order to investigate the effects of1,2,4-TCB on SOD, CAT and alkaline phosphatase (AKP) in adult and juvenile, and try to investigate the toxic mechanism of1,2,4-TCB. SOD activities were stressed and higher than control group in all treatment groups at8d post-exposure, then following decrease with the exposure time prolonged. SOD activities were significantly inhibited by16mg·L-1treatment. CAT activities in e treatment groups first increased and then decrease with the exposure time prolonged. The activities of AKP were not significantly activated in all treatment groups expect for2and4mg·L-1groups at8d post-exposure. The activities of AKP in16mg·L exposure were lower than control groups.(4) Protein content of juvenile fish hatching6d from embryos exposed to1,2,4-TCB has significantly difference with the control, but not significantly differed from other treatment groups. The effects of SOD, CAT and AKP in each treatment group had no differences with the control group. The embryos was more sensitive to1,2,4-TCB than adult fish.