Microplastic Pollution In Small Waterbodies And Its Toxicity Effects On Aquatic Organisms

Microplastic pollution is gaining attention and a potential risk to human health.To date,microplastic pollution has been well documented in oceans.Although land-based plastic wastes are recognised as sources of microplastics to the oceans,there is still a lack of knowledge about freshwater and terrestrial environments.As plastic production and thus environmental deposition increases,this will also result in greater accumulation,especially in the areas of high human activity.Through stormwater runoff,atmospheric deposition,etc.,larger amounts of microplastics may be ultimately transferred to water bodies such as lakes,rivers and small waterbodies.Small waterbodies are the most numerous freshwater environments globally.However,the distribution and abundance of microplastics in small waterbodies remain unknown.Therefore,we investigated microplastics in small waterbodies and their resident tadpoles and mosquito fish(Gambusia affinis)in China,as well as stormwater ponds in United States.In addition,we also studied the uptake and elimination of microsphere in the tadpoles of Xenopus tropicalis and hazardous effects of microfibers in adult medaka(Oryzias latipes).Firstly,we analyzed the distribution and characteristics of microplastics in 25 small waterbodies from the Shanghai city and Zhejiang provinces,which are the most populous and rapidly developing areas in China,and where production and use of plastics are significant.Microplastics were detected in surface water and sediment with abundances ranging from 0.5 to 21.5 items/L and 35.8 to 3185.3 items/kg,respectively.The dominant shape and polymer of microplastics in water samples was polyester(PES)fibers,and polypropylene(PP)fibers and fragments were dominant in sediment samples.In addition,microplastics that were < 0.5 mm in size were the most abundant in both water and sediment samples,with the number of particles decreasing with increasing size.Secondly,we further investigated the seasonal and spatial patterns of microplastics in stormwater ponds from Durham,where is the fourth largest city in the state of North Carolina,U.S.A.The average abundance of microplastics in surface water(1.7 ± 1.2 items/L)and sediment(274.8 ± 193.5 items/kg)from high density areas were both significantly higher than those in green space areas,where the average abundances of microplastics in surface water and sediment were 0.8 ± 1.0 items/L and 97.5 ± 85.1 items/kg,respectively.The seasonal distributions of microplastics in surface water from high density areas were not significantly different,while the average abundances of microplastics in sediment collected in July were higher than those in April.Additionally,microplastics observed in inlets of planned stormwater ponds were more than those in outlets.Fiber was most abundant in water samples,while fragment was most abundant in sediment.Microplastics less than 0.5 mm and polypropylene were the most abundant in both water and sediment samples.Microplastic pollution in small waterbodies posed a potential threat to their resident organisms,including amphibians,that are vulnerable to environmental pollution.Thirdly,in order to understand microplastic pollution in resident organisms,we also collected the tadpoles and mosquito fish from these 25 small water bodies.The results showed that microplastic abundances in tadpoles and mosquito fish were ranged from 0 to 2.7 items/individual(0 to 168.5 items/g)and 0 to 0.2 items/individual(0 to 1.9 items/g),respectively.The dominant shape and polymer of microplastics in tadpole samples was polyester fibers,and microplastics were primarily < 0.5 mm in length.Tadpole length was positively correlated to the number of microplastics detected.The abundance,shape and polymer distribution of microplastics in tadpoles resembled that of water rather than sediment,suggesting that tadpoles likely take up microplastics from the surrounding water.Our studies demonstrated that microplastics were abundant in these small waterbodies and ingested by resident tadpoles.This might suggest a pathway of microplastics entry into aquatic and terrestrial food webs.Our studies demonstrated that wild tadpoles could ingested microplastics from their surrounding environments.Fourthly,to study the uptake and elimination of microplastics in tadpoles as well as the effects of food on these processes,we exposed Xenopus tropicalis tadpoles to polystyrene(PS)particles in laboratory.PS particles were observed in gills and digestive tract of tadpoles within 1 h after exposure as well as in feces 6 h after exposure.The accumulation of microspheres in the tadpoles were concentration dependent,but no time dependent accumulation of microspheres was observed in tadpoles 48 h after exposure.Most microspheres in the tadpoles were excreded dramatically after 1-d cultivation with clean water.The ingested PS particles in unfed tadpoles were significantly higher than those in the fed tadpoles at 12 and 24 h after exposure.After transfer to clean water,the fed tadpoles showed a significant decrease in the amount of absorbed polystyrene particles,while the unfed tadpoles showed no significant change in the amount of absorbed polystyrene particles.Our results suggested that microspheres were likely to be ingested and egested relatively fast by tadpoles.Our results indicated that aquatic vertebrate organisms might ingest more microplastics if the abundance of microplastics continues to increase while the available food becomes less.Plastic microfibers pollute aquatic environments globally,with polyester(PES)and polypropylene(PP)the most commonly detected of the synthetic fibers.However,little is known about organismal responses.Adult medaka(Oryzias latipes),a laboratory model fish,were used to determine host responses to chronic microfiber exposure.Fish were exposed for 21 days to environmentally relevant,aqueous concentrations(10,000 fibers/L)containing either PES or PP microfibers.Scanning electron microscopy of gills revealed surficial erosions on arches and filaments,fusion of lamellae,and increased mucus.Histologic sections revealed aneurysms,swellings in the branchial chamber walland alterations of epithelium.Uptake and egestion of microfibers by gut was quantified by their abundance in feces,which averaged 1,367 ± 819 for PES and 157 ± 105 for PP per 24 hrs.In sections only PES microfibers were found in buccal cavity,pharynx(near teeth and on branchial arches),branchial cavity,and on gill filaments and intestinal epithelium.Histochemical analyses of gut showed increased mucous cells and secretions on epithelium of foregut.No significant changes occurred in body condition,gonadosomatic-or hepatosomatic indices,and embryonic development.This study provides novel evidence of microfiber toxicity with identification of pathways of concern for both entry and exit.In conclusion,microplastics were ubiquitously detected in surface water,sediment and tadpole samples from small waterbodies.Micropalstic pollution in these small waterbodies were no less than these of other large freshwater systems such as rivers and lakes.The more micropalstics are in freshwater environment,the worse the effects on freshwater organisms become.In addition,their resident organisms highly dependent on the patches of small waterbodies.Once they are polluted,it may pose a greater threat to their entire ecosystem.The current neglect of high microplastic pollution in small waterbodies may underestimate the contribution of land-based pollution to marine microplastic pollution.