Develpomental Toxicity Of Oil Pollution On Marine Medaka (Oryzias Melastigma) Embryos Under Different Salinity

With the rapid economic development and the increase in demand for crude oil,oil spills accidents occur frequently,and oil pollution could cause disastrous effect to marine ecosystems and marine organisms.Meanwhile,salinity could affect the distribution and natural fate of oil spills,and the changes in salinity may enhance the toxic effect of oil spills to marine organisms.There are no researches that systematically evaluate the toxicity of oil pollution on aquatic organisms under different salinity conditions to date.Therefore,in the present study,marine medaka(Oryzias melastigma)embryos were semi-statically exposed to water-accommodated fractions(WAF)of Oman crude oil at 30‰(the TPH concentration range was 0.13±0.05 mg·L-1 to 3.02 ± 0.03 mg·L-1)and 0.5‰(the TPH concentration range was 0.14±0.04 mg·L-1 to 4.06±0.04 mg·L-1)salinity for 14 days.For evaluating the developmental toxicity of WAF with 30‰ and 0.5‰ salinity on marine medaka embryos,the general morphological score(GMS)and general teratogenic score(GTS)systems were applied and the lethality,hatching and heart rates were also recorded in the present study.And total petroleum hydrocarbons(TPH)and 16 priority polycyclic aromatic hydrocarbons(PAHs)of WAF at different salinity were measured by ultraviolet spectrometry and gas chromatography-mass spectrometry(GC-MS),respectively,to explore its influence mechanism.Results showed that exposure to WAF at different salinity caused dose-dependent effects on lethality and hatching rate in marine medaka embryos.Lethality induced by WAF increased with dilution ratio.LC20(20%lethal concentration)values were 1.77 mg·L-1 and 1.06 mg·L-1 for WAF at 30‰ salinity and WAF at 0.5‰ salinity,respectively,indicating that WAF at 0.5‰salinity was more lethal to marine medaka embryos than WAF at 30‰ salinity.Hatching rates of marine medaka embryos were affected by WAF exposure,and more severe effect on hatching was observed after WAF at 0.5‰ salinity exposure.By GMS analysis,WAF at different salinities could delay the development of marine medaka embryos to some extent,especially hatching failure,unresorbed yolk sac and non-inflation of the swim bladder.Regarding GTS,results showed that WAF at different salinities caused malformation in a dose-dependent manner,and WAF at 0.5‰ salinity induced more severe malformation than WAF at 30‰ salinity.Meanwhile,WAF at different salinities also affected the heart rate of marine medaka embryos.And WAF at 0.5‰ salinity induced a more pronounced impact on the heart rate than WAF at 30‰ salinity.Moreover,chemical analysis indicated that the contents of TPHs and 2-3 rings PAHs of WAF at 0.5‰ salinity were slightly higher than that WAF at 30‰salinity,and marine medaka at lower salinity could uptake more PAHs due to its hyperosmotic.These maybe the predominant factors that the WAF at lower salinity has a slightly higher developmental toxic effect on marine medaka embryos.All these findings could provide a useful scientific basis for the developmental toxicity of crude oil pollution to aquatic organisms under different exposure conditions and different salinity.