Different Nutritional Status Affects Cytotoxicity And Accumulation Of PCBs In Fish

Persistent organic pollutants(POPs)are widely present in nature,and due to their persistence,high toxicity and bioaccumulation,they have various adverse effects on the environment and organisms.Among them,dioxins and PCBs are more toxic.PCBs are more polluted in the water environment.Fish ingest a large amount of PCBs through the water environment and diet,then accumulate in the fish body.As the nutritional level increases,the PCBs accumulated in the fish body will increase,which will have a more serious impact on the fish body.PCBs which accumulated in fish body pass to the human body and accumulates in the human body,then causes toxic effects.At present,many studies have focused on monitoring the deposition of PCBs in the environment and organisms.However,few scholars have studied the impact of changes in biological nutrition on the deposition of PCBs in organisms.Therefore,in this study,tilapia was used as a model to explore the variation of PCB concentration,differences in PCB composition and the deposition rate of PCB in fish after PCB exposure under different nutritional conditions.The main experimental results and conclusions of this study are as follows:1.Effects of PCB exposure at different concentrations on fish cell and live toxicity and PCB deposition in fish.In this study,at the cellular level,we used different concentrations of Aroclor 1254 to expose primary cultured hepatocytes of tilapia,and used different concentrations of DL-PCBs to expose zebrafish hepatocyte lineage.It was found that with the increasing concentration of exposure,the survival rate of liver cells significantly decreased,the LC50 of 12 mixed DL-PCBs for zebrafish hepatocytes at 48 hours was about 1.08 ng/ml.At live level,using low concentration(0.4?g/l water)and high concentration(4?g/l water)of Aroclor 1254 to expose tilapia,it was found that as the exposure concentration increased,the concentration of PCB in the whole tilapia fish significantly increased,the expression of CYP1 A gene was significantly up-regulated,but the indicators of lipid metabolism and oxidative stress had no obvious relationship with the exposure concentration.This shows that there is a dose-dependent effect of PCB on fish.Exposure of PCB will affect the oxidative stress and lipid metabolism of fish,but PCB exposure at different concentrations has no significant difference in oxidative stress and lipid metabolism.2.Relationship between different fat intake levels and PCB deposition in fish during PCB exposure and clearance.PCB is a lipophilic organic pollutant.Previous studies have found that the change of PCB is proportional to the body's fat level.However,preliminary experiments in this laboratory found that the fish body removed the PCB after exposure a period of time.During this process,the PCB concentration in the fish with sufficient food decreased significantly,while the PCB concentration in the fish body under starvation increased significantly,and the PCB concentration was inversely proportional to the fish fat level.In order to further verify whether this rule is true,this experiment was carried out at the cellular level and the living level(water exposed PCB and feed exposed PCB).At the cellular level,after exposing zebrafish hepatocytes with DL-PCBs for a period of time,the PCB in the medium is cleared.In this experimental design,one group of cells continued to be cultured with complete medium,and the other group of cells reduced nutrients and glucose in the medium for starvation treatment.The results showed that the expression of CYP1 A gene in the cells exposed to PCB was higher than that in the cells of the control group.During the clearance process,the expression of CYP1 A gene in the nutrition group decreased significantly,but the expression of CYP1 A in the starvation group increased significantly.At the living level,adding Acrolor 1254 to water to expose tilapia for six weeks and then remove PCB from water and starve fish.It was found that the PCB concentration in the whole tilapia fish during the elimination was significantly higher than that in the whole tilapia fish during the previous exposure,and the activities of SOD and LDH in the serum under starvation conditions were significantly reduced,and the expression of the lipolysis-related gene(PPAR? and PPAR?)increased.Further verification experiments showed that after adding DL-PCBs to the feed to expose the tilapia for four weeks,then a group was fed with clean feed and a group was starved for four weeks.It was also found that during the removal process,the concentration of PCB in different tissues of the tilapia under starvation conditions is significantly higher than under satiety conditions.Based on the above experiments,we can conclude that during the removal process,starvation is not conducive to the metabolism and degradation of PCBs,and PCBs have a greater toxic effect on fish after being concentrated in fish.This study also explored the changes in PCBs deposited in the body of tilapia by artificially changing the level of fat in the feed under PCB exposure conditions.First,at the cellular level,the primary cultured hepatocytes of tilapia were cultured by adding Aroclor 1254 and different concentrations of oleic acid to the culture medium.It was found that the expression of CYP1 A in the cells decreased significantly with the increase of oleic acid concentration.PCB levels in cells have decreased under high-fat conditions.After adding DL-PCBs and 100 mM oleic acid to the medium,it was found that the expression level of CYP1 A in the cells was significantly higher than that in the control group.At the live level,tilapia was fed with low-fat(5%)and high-fat(13%)feed,respectively and add Aroclor 1254 in water.It was found that the fat content in the fish body increased significantly under high-fat conditions,but there is no significant difference in PCB deposition concentration in fish body under different treatments.It can be seen that there is no obvious correlation between the change in dietary fat levels and the deposition of PCBs in fish.Although PCB is a lipophilic pollutant,fat is not the only biochemical indicator that determines the change in PCB content.3.The composition and deposition rate of PCB in fish.In the aforementioned experiment of Aroclor 1254 exposure to tilapia,we calculated the contribution rate of PCB monomers in the whole treatment group of tilapia fish,and found that the contribution rate of pentachloro-substituted PCBs was higher,such as PCB-118 and PCB-101.In addition,we also found that the contribution rate of each PCB homologue in all experimental treatment groups of tilapia was similar in whole fish,and they were all similar to the contribution rate of PCB monomers in the Aroclor 1254 standard product,and there is no significant difference.However,in the experiment of adding DL-PCBs to feed tilapia,we found that the contribution rate of DL-PCBs substituted by tetrachloro and pentachloro was higher.The concentration of each PCB monomer in the mixed standard of DL-PCBs added to the feed was the same.However,after the tilapia ingested the PCB,the contribution rate of the PCB monomer in each tissue of the body was different,and there are inter-tissue differences,and all were different from the contribution rate of the standard product.During the clearance process,the contribution rate of PCB in different tissues also changes to varying degrees.For example,during the exposure process,the contribution rate of PCB-118 in whole fish and muscle is as high as 40%,while the contribution rate of PCB-118 in adipose tissue is below 20%.But during the elimination of starvation,the contribution rate of PCB-118 in whole fish and muscle decreased to about 18%,and the contribution rate of PCB-118 in adipose tissue increased to about 60%.It is concluded that the nutritional status will affect the composition of the PCB and show differences between tissues.In further research,we also detected the concentration of DL-PCB in different tissues in the body after feeding Aroclor 1254 and DL-PCBs to tilapia,and calculated the deposition rate of DL-PCBs from feed in the fish.It was found that the deposition rate of PCB was the highest in the body,followed by muscle tissue,then liver tissue,and the deposition rate was the lowest in adipose tissue.The deposition rate of different PCB monomers is different,but the change rule is the same in body and muscle.The deposition rate of PCB-118 is the highest,followed by PCB-105,and the deposition rate of low-chlorinated PCB is lower.PCB deposition rates also show differences between tissues.The deposition rates of PCB-118 and PCB-105 are significantly higher than other homologues in body and muscle,while in liver and adipose tissue,the deposition rates between each homologue are similar,except that low deposition rate of PCB-118 in adipose tissue.It is concluded that different PCB monomers have different deposition efficiencies and show differences between tissues.Combining all the experiments,this paper shows that there is a significant dosedependent effect of PCB deposition and toxicity in tilapia after PCB exposure.Dietary fat levels have no obvious correlation with PCB deposition in fish,and fat is not the only biochemical indicator that determines the change of PCB content.During the clearance process,starvation is not conducive to the metabolism and degradation of PCB.The composition and deposition rate of different PCB monomers in tilapia are different and show differences between tissues.