Plastic Pollution Status In The Environmental Media And Common Fish Of The Bohai Sea

The widespread of plastic pollution in the natural environments has attracted much attention from both scholars and general public.And plastic debris has been recognized as a global threat to the environments,together with other environmental problems such as climate change,ocean acidification and habitat destruction.Large plastic items are brittle and tend to break down into small pieces as a result of various physical,chemical and biological processes.According to their size,plastics in the aquatic environments are generally divided into three groups:macroplastics（>25 mm）,mesoplastics（5-25mm）and microplastics（<5 mm）.Large plastics can entangle and injure marine organisms.Particularly,microplastics are readily available for ingestion by biota because they pose high similarity in morphology and size to zooplankton,the prey of many organisms.This would cause physical threats or chemical toxicity to the consumers or predators.Therefore,knowledge about the pollution load,distribution and characteristics of plastics in the environment media and organisms is of great significance to better understanding their occurrence,behavior,and source tracing.Furthermore,the knowledge is essential for assessing the ecological risk of plastic pollution in marine environments.The present study focuses on the investigation of the pollution status of plastics（macro-,meso-and microplastics）in the surface water,sediments and fish in the Bohai Sea（Liaodong Bay,Bohai Bay,Laizhou Bay and Central Bohai Sea）.Based on the data of the abundance,spatial distribution and morphology（shape,color,size and polymer）of the plastics,their transfer behavior and relationship between the two environmental media is investigated.Spatial variation of the plastics is assessed from the perspectives of sources（e.g.,influx）and transfer behavior of the plastics,ocean hydraulic forces and oceanography in the four regions of the Bohai Sea.Plastic pollution in fish is studied from the aspects of pollution load in fish and the ecological factors that may affect their intake of plastics,such as the feeding and living habits of fish.Trophic transfer and bioaccumulation of plastics in the food web is also assessed.The following main conclusions are reached.1.Plastics are widely distributed in the surface water and their abundance of plastics considerably vary in terms of spatial distribution across the sea.The average abundance of plastics in the entire water is 0.93 items m^-3（7953 in total）,and the abundance of microplastics is 0.79 items m^-3（6866 in total）,which is at a moderate level compared with the plastics in other oceans.Both plastics(2.29 items m^-3)and microplastics(1.95 items m^-3)are more abundant and show more diverse characteristics in Liaodong Bay than in the other three regions(0.26-0.59 items m^-3 and 0.26-0.59items m^-3,respectively).Plastic wastes from highly concentrated and developed agricultural,industrial,fishery and ocean engineering activities around Liaodong Bay make large contributions to the microplastics in this region.Additionally,low hydrodynamics and long distances to the Bohai Strait are unfavorable for the diffusion of particles,facilitating the retention of particles and increasing their abundance in this bay.Macroplastics(0.10 items m^-3)and mesoplastics(0.04 items m^-3)are far less abundant and show less diverse characteristics than microplastics but do not significantly differ among the four regions of the sea.Fragments（75.1%）,foams（12.0%）and lines（7.4%）are the dominant shapes among the microplastics.Transparent（36.9%）,white（29.1%）and blue（20.0%）particles dominate among the microplastics.The average size of the microplastics is 1.56 mm（0.31-4.99 mm）with small particles（<1 mm）predominating among the microplastics.Alkyd resin（AR,29.3%）,polyethylene（PE,26.4%）,polystyrene（PS,25.6%）and polypropylene（PP,17.8%）are the predominant polymers in the microplastics.2.The average abundances of plastics and microplastics in the surface sediments of the Bohai Sea are 52.05 items kg^-1 d.w.（141 in total）and 48.88 items kg^-1 d.w.（137in total）,respectively,which are not significantly different among the four regions(41.10-67.73 items kg^-1 d.w.).The abundance of the microplastics near the estuary areas is relatively abundant compared to other regions of the Bohai Sea.The plastic abundance in the surface sediments of the entire area is at a medium-low level in comparison with other oceans.In terms of shape composition of the microplastics,fibers（53.3%）are the most dominant particles,followed by fragments（41.6%）.Blue（26.3%）,transparent（22.6%）,black（17.5%）and white（11.7%）particles are the most common types by color.The average size of microplastics is 0.84 mm（0.03-4.89 mm）,with the particles less than 0.5 mm being the most dominant microplastics.Rayon（RY,37.2%）and cellulose（CE,21.8%）dominate the microplastics particles in the sediments by polymers.The abundance and distribution of microplastics in the sediments are considerably affected by anthropogenic activities,river input and ocean hydraulic forces such as currents and tides in the regions.3.Neither the abundance nor the size of the microplastics is proportionally correlated with low similarity indexes of the characteristics of microplastics in the surface water and sediments.The similarity indexes of the polymer,shape and color of the microplastics in the two environmental media are 0.16,0.29 and 0.38,respectively.The similarity indexes of microplastics characteristics in the four sea areas are different,which are 0.11-0.22,0.26-0.33 and 0.27-0.77 by polymer,shape and color,respectively.This could be caused by the mismatch in the spatiotemporal distribution and variation in the characteristics,fate and behavior of microplastics in the two media.4.Plastic particles（704 in total）are detected in all the 22 fish species with an average detection rate of 54.7%in the Bohai Sea.Most of the plastics are microplastics（679 in total）with a detection rate of 53.4%.The abundances of plastics and microplastics by individual fish,mass and length of fish are 1.0±1.2 items ind.^-1or 0.9±1.2 items ind.^-1,0.1±0.1 items g^-1or 0.1±0.1 items g^-1,and 0.1±0.1 items cm^-1or0.1±0.1 items cm^-1,respectively.The detection rate（25.0-88.9%）or abundance(0.3-1.8 items ind.^-1)in the fish varies with species.Fibers（82.2%）are the most prevalent microplastics in shape and blue（50.8%）,black（19.4%）and grey（15.6%）particles are the dominant microplastics in color.RY（42.3%）and CE（35.2%）dominate the microplastics by polymer.The average size of the microplastics is 1.08 mm（0.03-4.99mm）with particles<0.5 mm dominating the microplastics.The composition of morphological characteristics or chemical components（polymer）of the microplastics detected in the fish is not consistent with those of the microplastics in the two environmental media.The detection rate of microplastics in the fish range from 51.2%to 60.0%across the four regions.The detection rates of microplastics in the fish in terms of ecological or functional groups are following:pelagic fishes（56.1%）>demersal fishes（51.9%）;feeding fish（55.2%）>fish with empty stomachs（51.7%）;local coastal fish（56.5%）>migratory fishes（49.5%）.However,the above factors（region,living habitat,feeding status and moving habit）do not show statistically significant influences on the detection rate or abundance of the microplastics in the fish.Contrastingly,significant differences in detection rate or abundance of microplastics occur among the fish of different feeding habits,in an order of small and medium pelagic fishes(62.1%or 1.2 items ind.^-1)>large benthic predatory fishes(54.4%or 1.0 items ind.^-1)>small and medium-sized benthic predatory fishes(50.5%or 0.8 items ind.^-1)>large pelagic predatory fishes(40.3%or 0.7 items ind.^-1).Foraging strategy of fish may partly account for the differences in the intake of microplastics by fish of different feeding habits.For instance,pelagic filtering fish usually take the plankton prey by filtering large amount of surface seawater,in which microplastics are commonly more abundant than in other water columns.This could make it possible for the pelagic filtering fish to ingest more microplastics directly from the environments during feeding and breathing than others,leading to higher levels of plastic pollution level in these feeders.The size of the plastics/microplastics in the fish is not significantly correlated with fish length.The abundance of microplastics by individual fish is not significantly correlated with fish length,mass or trophic level,either.And the relative abundance of microplastics by fish mass is not significantly correlated to trophic level.These results indicate that microplastics may not show trophic transfer or bioaccumulation in food chains or webs in the Bohai Sea.In conclusion,plastics are ubiquitous in environmental media and common fish of the Bohai Sea.In the surface water,the abundance of plastics considerably vary in terms of spatial distribution across the sea,and both plastics and microplastics are more abundant and show more diverse characteristics in Liaodong Bay than that in Bohai Bay,Laizhou Bay and Central Bohai Sea.Plastic wastes from agricultural,industrial,fishery and ocean engineering activities around Liaodong Bay make large contributions to the microplastics in this region.In addition,low hydrodynamics and long distances to the Bohai Strait increase the abundance in this bay.In the surface sediments,the average abundances of plastics and microplastics are not significantly different among the four regions,and the abundance of the microplastics near the estuary areas is relatively abundant compared to other regions.The spatial distribution of microplastics in surface water and sediments is relatively low,which is related to the mismatch in the spatiotemporal distribution and variation in the characteristics,fate and behavior of microplastics in the two media.Plastics/microplastics are detected in more than half of fish individuals,and the abundance of microplastics in fish is correlated with their foraging strategies.Microplastics may not show bioaccumulation in food chains or webs in the Bohai Sea.The results are expected to provide knowledge for assessing plastic pollution,tracing sources and understanding the behavior and destiny of plastics in the Bohai Sea,particularly the transfer behavior of microplastics between the two environmental media and organisms.