Effect Of DL-PCBs In Zhanjiang Sea Offshore Sediment On Zebrafish Immune Function

Dioxin-like polychlorinated biphenyls(DL-PCBs)are persistent organic pollutants that are spread throughout the world.They belong to polychlorinated biphenyl(PCB)class of chemicals and hence the chemical properties are similar to PCBs.They are lipophilic,cannot be easily degraded in the environment and hence can easily bioaccumulate in organisms especially in tissues with a high fat content.PCBs can cause a variety of disorders including reproductive toxicity,developmental toxicity,skin toxicity,and immunotoxicity.DL-PCBs are migratory and therefore widely exist in the air,water,soil,and sediments including river,lake,and marine sediments.DL-PCBs in marine sediments enter through water bodies.In the ocean,it poses a threat to aquatic plants and organisms including fish,shrimp,shellfish and other aquatic species.The food resources in the ocean are abundant,and aquatic species including fish,shell fish are important sources of raw material for fishmeal.If animal feeds contain DL-PCBs,it may accumulate and cause harm to aquaculture species,farm animals and humans.The immune system is the most important line of defense to prevent disease and thereby maintain health.Damage to the immune system can result in a variety of diseases and impair human and animal health.In this study,zebrafish was used as a model organism to investigate the DL-PCB pollution of the Zhanjiang offshore area and examine the effects of the DL-PCBs extracted from the offshore sediments on the immune function of zebrafish.The main contents of this study are:(1)Extraction of DL-PCBs: The sediments were collected from 6 sampling points in the Zhanjiang offshore area and subjected to ultrasonic-assisted extraction using potassium sulfate and potassium permanganate in combination with Flori column purification pretreatment,and the type and concentration of DL-PCBs measured using gas chromatography-mass spectrometry(GC-MS).(2)Study of DL-PCBs on immune organs in zebrafish: Adult zebrafish were used as the animal model.Experimental animals consisted of a control group,positive control group,low-and a high-dose DL-PCBs.DL-PCBs were added to the water and zebrafish were exposed to DL-PCBs in the water for 28 days.The effects of DL-PCBson immune organs(spleen,kidney)of adult zebrafish was investigated.(3)Study of DL-PCBs on immune cells of zebrafish: The effect of DL-PCBs on adult zebrafish immune cel s(erythrocytes,white blood cel s)was determined.(4)Study of DL-PCBs on immune factors in zebrafish: The effect of DL-PCBs on adult zebrafish immune factors(serum lysozyme,mucin immunoglobulin,and mucin lysozyme)was also determined.The results of these experiments are summarized below:(1)DL-PCBs in sediments: The GC-MS detected several types of PCBs in the sediments.PCB81 was detected in the sediments of Jinsha Bay 6 sampling sites and the mean concentrations was 29.0 ?g/kg.PCB118 was detected in sediments of Lingang industrial district with a mean concentration of 35.0 ?g/kg.DL-PCBs were not detected in the remaining sampling points(Binhu Park,Tiaoshun Island,Yugang Park and Haibin Park).(2)Effect of DL-PCBs on immune organs in zebrafish: Compared with the control group,the spleen index of the zebrafish in the positive control group and the high-dose group was significantly lower(P<0.05)on day 14,and in the low-dose group,a significant decrease(P<0.05)was observed on day 28.The c hange in kidney index was the reverse.Histopathological examination of the tissues showed accumulation of a large amount of hemosiderin in the zebrafish spleen,a decrease in the number of lymphocyte and also lymphocyte damage from day 14 in the low-dose DL-PCB group.These changes were more marked in the DL-PCB high dose group.In the kidney,the renal tubular epithelial cells of the zebrafish head kidney in the positive control group and the high dose group were swollen with shedding of some cells result ing in expansion of the lumen,renal interstitial edema in the low-dose group as early as day 21 but definitely on day 28.These changes were most marked in zebrafish in the high dose group.(3)Effect of DL-PCBs on immune cells of zebrafish: The number of erythrocytes of zebrafish in the positive control group and the high-dose group decreased significantly(P<0.05)from day 7 onwards but a significant effect on the low-dose group(P<0.05)was evident only from day 21 onwards The number of white blood ce lls in zebrafish increased significantly(P<0.05)from day 7 onwards day in the positive control group and the high-dose group.In the low-dose group,a significant increase in white blood cells(P<0.05)was evident only from day 21 onwards.The leukocyte phagocytosis index in the positive control group and the high-dose group decreased significantly from day 14 onwards.A similar effect was observed in the low-dose group but was significant(P<0.05)only on day 28.(4)Effect of DL-PCBs on immune factors in zebrafish: The zebrafish serum lysozyme concentration in the positive control group and high-dose group decreased significantly(P<0.05)from day 21 onwards.No significant change in serum lysozyme activity(P>0.05)was evident in the low-dose group.The surface mucin lysozyme activity and immunoglobulin concentration in the positive control group and high dose group decreased significantly(P<0.05)from day 14 onwards.In the low-dose group a significant decrease in serum lysozyme activity(P>0.05)was observed on day 28(P<0.05).