Temporal And Spatial Distribution Of Microplastics And Antibiotics In Taihu Lake And Their Combined Effects On Red Tilapia (Oreochromis Niloticus)

Microplastics(MPs)is the plastic fragments smaller than 5 mm,which is decomposed by plastic wastes in aquatic environments after long-term weathering.Recently,MPs pollution has become a global environmental problem.MPs can adsorb various persistent organic pollutants,such as polycyclic aromatic hydrocarbons,heavy metals and others due to the small partice size,large specific surface-area and hydrophobicity,resulting in becoming the vectors of these toxic and harmful substances.Antibiotics are emerging contaminants widely existing in environment.Although the concentrations of antibiotics in aquatic environment are low,long-term exposure to antibiotics may produce bioaccumulation in non-target aquatic organisms,thus affecting physiological processes at the genetic and molecular levels because of their special pharmacological and physiological functions.Currently,studies on the effects of MPs on aquatic organisms in freshwater environments and the interective effects of MPs and antibiotics on organisms are very limited.Therefore,our study first confirmed the coexistence of MPs and antibiotics in Taihu Lake in China.Then the effects of MPs on freshwater organisms were investigated.The red tilapia(Oreochromis niloticus),a common freshwater fish in China,was employed as the model organism,and Polystyrene Microplastics(PS-MPs)were used as the stress factor.Finally,we also evaluated the effect of MPs on the distribution and bioaccumulation of Roxithromycin(ROX)in fish as well as their interactive biological effects.The contents and main conclusions of the study are summarized as follows:1.The temporal and Spatial Distribution of MPs and antibiotics in Taihu Lake.The temporal and Spatial Distribution of MPs and antibiotics at 20 sites in Taihu Lake was sampled and analyzed.The results show that:(1)The detection frequency of MPs was 100% in 20 sampling sites of Taihu Lake.The average abundance of MPs in each month ranged from 8.9 to 24.4 items/L.Moreover,the types of MPs were mainly fibrous and fragmentary,and the contents of MPs in film and sphere were less.The occurrence level of MPs in Taihu Lake had obvious spatial and temporal differences.The occurrence level of MPs in winter was the highest,and that in North Taihu Lake was significantly higher than other areas.(2)The pollution level of antibiotic in Taihu Lake also had obvious spatial and temporal differences.During March and April in spring and November and December in winter,the concentration of antibiotics in Taihu Lake was higher,and the concentration in the North Taihu Lake was obvious higher than that in the South Taihu Lake;the concentration of antibiotics detected in Taihu Lake had a medium to high environmental risk for algae.2.Biochemical effects of polystyrene microplastics on red tilapiaIn this chapter,red tilapia was exposed to clean water(control group)and PS-MPs(0.1 ?m)(treatment group)with concentrations of 1,10 and 100 ?g/L,respectively.The bioaccumulation and distribution of PS-MPs in various tissues(gut,liver,gills and brain)were investigated.Additionally,a suite of biomarkers at the molecular level in fish tissues was applied to evaluate the biochemical effects of PS-MPs on tilapia.The following results were obtained:(1)PS-MPs could be ingested and accumulated in different tissues of tilapia,and bioaccumulation exhibited obvious concentration-and time-dependent effects;(2)The presence of PS-MPs inhibits the activity of acetylcholinesterase(AChE)in the brain of tilapia,suggesting that PS-MPs can inhibit the catalytic activity of this enzyme,and eventually cause neurotoxicity in the fish;(3)During the exposure periods,both the 7-ethoxyresorufin O-deethylase(EROD)and 7-benzyloxy-4-trifluoromethyl-coumarin O-dibenzyloxylase(BFCOD)activities in the liver showed the temporal variability of an initial decrease followed by a rapid increase,indicating disturbance of the metabolism of tilapia;(4)Increased(antioxidant enzyme)SOD activity coupled with limited effects on the malondialdehyde(MDA)content suggest that under oxidative stress from MPs exposure,the antioxidative enzymatic system in fish could be activated and prevent oxidative damage from occurring.3.Combined effects of polystyrene plastics and roxithromycin on tilapiaIn this chapter,red tilapia was exposed to clear water(control group),ROX(treatment group and co-exposure of PS-MPs and ROX(treatment group),respectively.The main goal of the present study was to evaluate the effect of the presence of MPs on the distribution and bioaccumulation of ROX in fish as well as their joint toxicological effect in fish.The following results were obtained:(1)MPs can be used as the vector of ROX to significantly enhance the bioaccumulation of ROX in various tissues in red tilapia,but MPs will not change ROX bioaccumulation pattern in tilapia tissues;(2)The inhibition of AChE activity caused by ROX was alleviated in the presence of PSMPs;(3)Alterations of the EROD and BFCOD activities exposed to all co-exposure treatment levels show a metabolic disorder in fish,and BFCOD enzyme are more sensitive in the coexposure treatments;(4)The increased SOD activity and decreased MDA content caused by co-exposure to ROX and MPs suggest that the presence of MPs could induce the antioxidative enzymatic system in fish,and consequently mitigate the oxidative damage.This study is helpful to comprehensively understand the complex pollution characteristics of MPs and antibiotics in water environment,and provide necessary theoretical basis and technical support for objectively evaluating the ecological health risks of emerging pollutants in water bodies.