| Microplastics(less than 5 mm in diameter)are widely present in the marine environment and can enter the Antarctic region through human activities,atmospheric and oceanic circulation,or biological transport.It has been reported that presence of microplastic enrichment which it’s from low trophic level invertebrates to high trophic level marine mammals exists in the Antarctic region.Antarctic seals,as top predators in the Antarctic ecosystem,are facing increasing pressure to survive with marine pollution becoming more severe.The placenta plays an important role in mammals and its ability to block pollutants has become a research hotspot in recent years.Research on human placental microplastics is rapidly developing,but few studies involving other mammalian placental microplastics,especially in Antarctic marine mammals.Based on the CHINARE-34,this study analyzed the placenta collected from seals in the Rathman Hills area in the southern part of Prydz Bay,using DNA barcoding technology to identify seal species,and then studied the distribution characteristics of microplastics in the placenta to analyze its possible sources and assess the hazard risks.The main conclusion of this thesis are as follows.1.By amplifying,sequencing and comparing the COI sequences of seal placenta,and combining the NJ tree and barcoding gap,the seal placenta collected from Prydz Bay was finally determined to belong to one seal species,namely Weddell seal(Leptonychotes weddellii).Meanwhile,the results support that the seal family is sympatric development,which is consistent with previous studies,and also confirm that DNA barcoding technology can play an important role in the identification of Antarctic marine mammal species.2.The average abundance of microplastics in the placenta of Weddell seals was0.046±0.018 items/g(wet weight).In terms of shape,the highest percentage was fibrous(73 %),followed by thin film(18 %)and the lowest percentage was fragments(9 %);in terms of color,the highest percentage was red(61 %),followed by blue(24 %)and black(12 %),and the lowest percentage was green;in terms of particle size,the average particle size was482.09±329.24 μm,with the highest percentage of microplastics in the range of 400-600 μm.In terms of chemical composition,acrylic had the highest percentage of 51.5 %,followed by polyester(PES),polypropylene(PP),polyurethane(PA)and polyethylene terephthalate(PET).The size of microplastics on the fetal side,maternal side and amniotic membrane showed significant variability,as evidenced by the fact that the particle size level on the maternal side was greater than that on the fetal side and amniotic membrane,but the differences in abundance,color,composition and shape were not significant.In terms of source,fibres may come from sewage or surface runoff,films may come from plastic bags or packaging,and fragments are caused by fiber flaking or breaking.3.The level of microplastic contamination in placenta of Weddell seals was low globally.Compared with human placenta,the abundance of microplastics in Weddell seal placenta was low,and the chemical composition was similar to human placenta,but the size range was larger than human placenta,and the difference in placental barrier capacity due to species characteristics may be the most important reason for this result.The results of the microplastic risk assessment showed that the microplastic contamination level in the placenta of Weddell seals was low. |
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