Preparation And Application Of Microplastics In Exposure Experiments

Microplastics have become ubiquitous in marine and freshwater ecosystems.It is an issue of increasing scientific concern because these plastic particles are easily accessible to a wide range of aquatic organisms,due to their small size.Microplastics in nature are a solid contaminant suite made up various particles.Most toxicity experiments simplified microplastics as a single compound.In additional,commercial microbeads with regular shape,precise size,and single polymer type were most used,which were not consistent with microplastics in the real environment.This exposure method ignored the diversity properties of microplastics,leading to the toxicological data could not reflect the real risks.To put forward an exposure test method suitable for microplastics,field investigations and laboratory experiments were carried out in this thesis.Firstly,to get aware of the environmental properties of microplastics,the case study targeted microplastics collected from the Yingtao River in Shanghai.In the Yingtao River,the average abundance of microplastics in the surface water was 4763items/m~3,significantly higher than that in the bottom water(878 items/m~3).The results of 24-hour sampling showed that the abundance of microplastics was in a dynamic change every hour.For instance,abundances of microplastics in the surface water ranged from 380 to 3660 items/m~3during one day.Due to the influence of tidal,this investigation highlighted the highly heterogeneous spatiotemporal distribution of microplastics,which has been confirmed by many field investigations in recent years.Secondly,microplastics were prepared and characterized in the laboratory according to the environmental properties.These prepared microplastics would be applied to the subsequent exposure experiments.Three shapes of beads,fibers,and fragments of microplastics were prepared.Microplastics were divided into different sizes by using sieves and filter membranes with certain pore sizes.The optical microscope was used to characterize the shapes,sizes,and colors of the microplastics.The micro-Fourier transform infrared spectroscopy was used to characterize the polymer types of microplastics.Pure water,alcohol,and sodium iodide were used to prepare solutions with different densities(0.8-1.8 g/cm~3).The density ranges of microplastics were determined by observing the suspension and sedimentation state in the density solutions.Concentrations of these well-defined microplastics were counted.Compared to the Casy flow cytometer and the Flowcam counter,counting under the microscope was regarded as the most reliable method for ensuring the concentration.Thirdly,on the basis of the physical and chemical properties of microplastics,exposure methods were established to study the effects of shape,polymer type,and size on the uptake of microplastics by Asian clam Corbicula fluminea.For different shapes of microplastics,clams were more likely to ingest small-size microbeads(0.5-10.25items/g).The bioavailability of clams was found inversely proportional to the elastic modulus of microplastics.For example,clams tended to uptake polyester(4.1 items/g),which presented the lowest elastic modulus(2.2×10~3Mpa).For different sizes of microplastics,clams consumed the most microplastics in the range of 250-1000μm,consistent with the size range of microplastics found in the field clams.The results showed that the uptake of microplastics was based on the shape,polymer type,and size.The physical and chemical properties should be considered in the exposure test method of microplastics.Fourthly,the exposure test method was established to study the effects of exposure capacity on the uptake of microplastics by zebrafish Danio rerio,in light of environmental factors.Results showed that the uptake of microplastics by fish was positively correlated with the exposure concentration.Compared with concentrations,the amounts played a dominant role in the uptake of microplastics.For example,at the same concentration of 1600 items/L,the amounts of microplastics were different in different exposure capacities.The average abundance was 49.50 items/fish in 16 L,significantly higher than that of zebrafish in 4 L(15.44 items/fish).The exposure capacity was crucial to bioavailability by affecting the exposure amount of microplastics.The external factor of exposure capacity should be considered in the exposure test method of microplastics.Finally,the exposure test method was established to study the effects of aging microplastics on reproductive ability,embryo hatching,and offspring growth of Fathead minnow Pimephales promelas.Compared with cotton fibers,microplastics inhibited the reproduction of eggs.Pristine microplastics showed no significant effect on embryo hatching,survival,growth,and development of juvenile fish.Compared with the pristine microplastics,the aging microplastics inhibited the survival of juvenile fish(mean survival rate 88.9%-95.5%).Aging microplastics resulted in severe pericardial edema and spinal curvature in juvenile fish.The results confirmed that the aging of microplastics plays an important role in biological toxicity.Aging should be considered in the exposure test method of microplastics.“Environmentally relevant properties”were suggested to be considered in the exposure test method of microplastics.“Environmentally relevant properties”mean that microplastics used in the toxicity tests have environmentally relevant concentrations,physical,chemical,and aging properties.Factors like exposure capacity that affect the properties of microplastics are covered in this concept as well.To establish the exposure test method,it is necessary to acquire microplastics information from the field.Then,preparing microplastics to simulate environmental properties.Finally,introducing microplastics with“environmentally relevant properties”into toxicity experiments,yielding ecologically relevant toxicological data.