Toxicology Effect Of Oil Spill And Surfactant Composition On Juvenile Sea Cucumber (Stichopus Japonicus)

Along with the development of society and economy, the applications ofsurfactants have been penetrated into all aspects in daily production and life. Their useand consumption will continue to increase, and accompanied by a large number ofproduction and domestic sewage discharged into the environment. In addition, a suddenmassive oil spill accidents occur frequently, also brought serious harms to theenvironment. This paper focuses on the research of effects of common surfactants suchas sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS) and oildispersants to deal with accidents of oil spill in mariculture on juvenile sea cucumber(Stichopus japonicus). The related researches have been carried out with thetoxicological means as follows:To investigate the effects of surfactant pollutants and dispersants to deal with theaccident of oil spill on juvenile sea cucumber, acute toxicity of SDS, SDBS, oildispersant, water accommodated fraction (WAF) of crude oil and chemical enhancedwater accommodated fraction (CEWAF) of crude oil to juvenile sea cucumber wasdetermined respectively. The results showed that72h-LC50and96h-LC50of SDS tojuvenile sea cucumber were15.03and10.89mg·L-1,72h-LC50and96h-LC50of SDBSto juvenile sea cucumber2.50and1.71mg·L-1, and96h-LC50of oil dispersant tojuvenile sea cucumber7498.94mg·L-1. The cute toxicity of SDBS on juvenile seacucumber is stronger than that of SDS, and96h-LC50value of dispersants is far greaterthan SDBS and SDS, i.e. their cute toxicity on juvenile sea cucumber being very small.Increasing doses exposure of crude oil and oil dispersant for96hrs had not made thejuvenile sea cucumber dead, showing small stimulus to juvenile sea cucumber, such asshort time body contraction.96h-LC50of CEWAF to3months and4months oldjuvenile sea cucumber were246.09mg·L-1and399.15mg·L-1respectively.In order to optimize the conditions affected WAF and CEWAF of toxicity testexposed process, total petroleum hydrocarbon (TPH) concentration by determinationUV spectrophotometry, TPH weathering process and component analysis under laboratory conditions have been investigated thoroughly in the present study. Toaccurately measured concentration of TPH in CEWAF, oil plus oil dispersantconcentration-absorbance response curves were used as CEWAF standard curve ofthe total petroleum hydrocarbon concentration determination. Because of white flocformation of oil dispersant in n-hexane solvent, the prepared standard stock solutionshould be kept to stand sufficiently (or centrifugal5min to2000r/min), thenabsorbed the supernatant liquid to be diluted for preparing standard liquid, to avoidbeing brought the floc into the prepared standard solution and interfering absorbancereadings. Under laboratory conditions within80hrs, the total petroleum hydrocarbonconcentration in WAF decreased linearly because of weathering, and its weatheringrate declined continuously over time. Correspondingly, weathering trends of CEWAFwould also have been observed within the120hrs. While at the beginning of12hrsthere have been no changes observed for total petroleum hydrocarbon contents,however decreasing sharp during from time of12o’clock to36, and then trending tobe stable with slight fluctuation after36hrs. To reduce the measurement errors of thetotal petroleum hydrocarbon concentration, some approaches could be used such asreplacing the test liquids frequently to avoid biological degradation, in which WAFtest liquids suggested to be replaced every2~3hrs, and CEWAF test liquids every10~12hrs. As it should be, the total petroleum hydrocarbon concentrations were alsodetermined at the beginning of test.The relative abundance of polycyclic aromatic hydrocarbons in WAF is higherthan n-alkanes, the latter, however, has higher relative contents in the test crude oil andCEWAF. The proportion of n-alkanes in WAF is far less than that in CEWAF, butbeside alkanes of C11, C12, and C15, the contents of the other n-alkanes are relatively lowin the CEWAF. For example, the proportion of pristane in the CEWAF is much lowerthan that in the WAF. While the proportion of total PAHs in the WAF with alkanes of16.16%reaches up to44.44%, it is only10.35%in the CEWAF. Because of oildispersants, the proportion of low molecular weight alkanes has significantly increasedin the water from the oil, while more aromatics dissolved in the water from crude oilowing to mechanically stirring. The level of naphthalene and phenanthrene and theirderivatives in the WAF and CEWAF is fairly high, in which the proportion ofnaphthalene in the hexane extract of WAF reaches up to13.36%.In order to study subacute toxicity of surfactants to juvenile sea cucumber, superoxide dismutase (SOD) and catalase (CAT) was used as biomarkers in the presentwork. Juvenile sea cucumber had been exposed experimentally to a series of solutionsof sodium dodecyl sulfate (SDS) and oil dispersant for7days, and then conducted byimmune recovery for7days in the fresh boiled seawater, during a period of14days.Approaches of hydroxylamine and visible spectrophotometry were used to test andobtain SOD, CAT activity values of perisome muscles and internal organs of juvenilesea cucumber of4months. Results showed that during the period of SDS exposure test,the activity values of SOD and CAT has a similar regularity, which reflects that there isa cooperation relationship between SOD and CAT for oxidative decomposition usingreactive oxygen species (ROS) in the anti-oxidation. Comparing the activity changes ofSOD and CAT of the perisome muscles of juvenile sea cucumber under SDS stress,SDS exposure induced effects on SOD and CAT activity were found to be timedependent. While the induced effects on SOD activity in the internal organs of juvenilesea cucumber also had time dependency, but that on CAT activity has not. Under oildispersant stress, however, there were no obvious time and dose dependence for theactivity values of SOD and CAT in the perisome muscles of juvenile sea cucumber,which is not a regular phenomenon. Considering the dramatic differences between testconcentrations of SDS and oil dispersant, the influence of oil dispersant on juvenile seacucumber is smaller than SDS, while the usage of oil dispersants in an oil spill accidentis usually very large, made a large number of juvenile sea cucumbers to discharge theinternal organs. This phenomenon, therefore, may have far-reaching effects and beworthy of some attention.To investigate the safety of dispersants in processing oil spill, SOD and CAT wereused as biomarkers. Juvenile sea cucumber had been exposed experimentally to a seriesof CEWAF and WAF test solutions for7days, and then conducted by immune recoveryfor7days in the fresh boiled seawater during, during a period of14days. Approachesof hydroxylamine and visible spectrophotometry were used to test and obtain SOD,CAT activity values of perisome muscles and internal organs of juvenile sea cucumber.Results showed that during the period of WAF and CEWAF exposure test, the activityof two antioxidant enzymes in perisome muscles and internal organs was effectedevidently by WAF and CEWAF test solutions. During immune recovery, however, afterbeing exposed to WAF, antioxidant enzyme activities both of perisome muscles andinternal organs of juvenile sea cucumber failed to be back to normality, while after being exposed to CEWAF, contrariwise, the antioxidant enzyme activities both had gota certain degree of recovery. This may imply that the juvenile sea cucumbers exposed tothe WAF had more seriously long-term effects than those exposed to the CEWAF,despite being the higher concentrations of total petroleum hydrocarbons in the CEWAFthan in WAF. GC-MS analysis of the hexane extracts of the CEWAF and WAFrevealed that the components in the two test solutions are much different, in which thetotal PAHs proportion in the WAF reached as high as44.44%, but that in the CEWAFaccounted for only10.35%. On the contrary, total alkane proportion in the CEWAF wasas high as39.37%, but that in the WAF accounted for only16.16%. Some researchthought that PAHs had more biological toxicity to organisms than alkanes. This couldpartly explain the reason why those juvenile sea cucumbers exposed to the WAF havemore serious long-term effects than those exposed to the CEWAF. By comparison, itwas found that the activity level of CAT in the internal organs of juvenile seacucumbers is higher than that in the perisome muscles, implying that for lower animalssuch like juvenile sea cucumbers internal organs may be a more suitable biologicaltissues for determination of antioxidant enzymes.