Surface Sediment Toxicity Testing In Yangtze Estuary And Its Adjacent Area Based On The Development Of Xenopus Tropicalis Embryos

Similar to many other large estuaries in the world, the Yangtze Estuary has sufferedfrom environmental quality deterioration to some extent as a result of rapid economicdevelopment in the Yangtze River Basin in recent years. The specific environmentalstressors include a variety of pollutants (e.g. organic chemicals, nutrients and heavymetals) discharged from wastewater, overfishing and multiple engineering projects inthe estuary. When pollutants are discharged into the estuary, they are mainly adsorbedon suspended particles and subsequently deposited into sediments. Therefore, sedimentsare considered their mainly environmental fate. With persistent pollutants arecontinuously enriched in the sediments, the Yangtze estuary region is facingunprecedented pressure from the environmental and ecological threats. Contaminants insediments are relatively stable and hardly subject to seasonal effects compared withwater, thus the distribution of contaminants in sediments better reflects the situation inthe region in a longer period, which has significant implications for risk assessment. Itis a big challenge to evaluate environmental quality of the estuary objectively andeffectively. Up to date, the evaluation on sediment quality is primarily focused on riskassessment of individual or some classes of pollutants. However, few studies have beenconducted to evaluate the toxicity of contaminants in sediment on aquatic organisms.Moreover, it is still rare to find studies on comprehensive environmental qualityassessment of the sediments of the entire estuary and the trend of contaminants in thesediments.In this study, we chose the Yangtze Estuary and its adjacent area as the study area,which is one of the world’s largest estuaries affected by human activities intensively. Toilluminate the potentially adverse ecological effects and the environmental health statusof the sediments in the Yangtze Estuary, we collected334samples from the estuary andits adjacent seas and evaluated the quality of surface sediments with a new biologicalmodel-Xenopus Tropicalis.The study not only provides the primary information on for pollution control andregional risk analysis of the sediments in the Yangtze Estuary, but also proposes newideas for monitoring the environmental quality of estuaries and oceans.The main results are listed as below: 1. The use of Xenopus Tropicalis embryos can effectively detect the developmentaltoxicity of sediment extracts: the hatch of embryos percentage of is in good conditionand more than90%of embryos are hatched; the percentages of survival rates in Sites88,99,103and106were less than30%, the minimum percentages were10%,10.5%and10.5%in Sites111,116and117, respectively. Multiple malformations are observed inembryos, including pigment disorders, intestinal undifferentiated, proctodeummalformation, narrow fins and other phenomena. Among these malformationsproctodeum malformations and narrow fins are the major malformations types. Thesediment extracts from some sites malformed embryos completely due to the highertoxicity.2. The higher malformation rate of embryos indicates the overall quality of thesediments from the Yangtze Estuary. The regional distribution of the percentage ofmalformation was different. The sediment quality is the best in the South Passage,followed by the South Channel, the North Passage, and the sea area. There are threehigh-value zones in the coastal waters, located in the east mouth of the Yangtze Estuary,the waters between Qushan and the outside of Shengsi, the northeast of Zhoushan Island.The maximum value reaches to100%; There are two low-value zones, which arelocated at the east of Qidong (about122°45’E) and the east of Nanhui (about123°30’E), respectively.3. The toxicity of the sediments varies in each channel. In the South Channelsection, the toxicity is higher in the north side than in the south side. In the NorthPassage section, the toxicity decreases gradually from the upstream to the downstream.The high toxicity is commonly observed in the front of the area when the river flowchanges its direction. In the South Passage section, the sediment quality was in goodcondition except a few sites, where the toxicity is high. In the mouth area, the sedimentquality is gradually deteriorated from inside to outside, from north to south in moutharea.4. The environmental settings in the estuary are complicated. The distribution ofpollutants is affected by various dynamic processes, including runoff, tide andsuspended sediment. The environmental quality of sediments is related to sedimentparticle size: the sediments with smaller particle size are more likely contaminated. Inaddition, the transport trends of bottom sediment may reflect the distribution of contaminants in the region.The results from this study demonstrate that the overall environmental quality ofsediments is poor and varies to some extent indifferent branch which is resulted fromthe complicated environmental settings in the estuary. The study also corroborate thatFETAX(The frog embryo teratogenesis assay-Xenopus) can effectively detect thedevelopmental toxicity of sediment extracts and characterize the environmental qualityof the estuary.