Distribution Of Microplastics And Their Uptake And Elimination In Zooplankton In The Bo Sea And The Yellow Sea

Microplastics(MPs)are plastics fragments with sizes<5 mm.They are abundant and widespread in the marine environment and have received considerable attention in international environmental fields.Due to the small size and the chitin in the zooplankton,it is difficult to quantify microplastics in zooplankton.Moreover,the kinetics of microplastics uptake and elimination by biota and the biological effects were also limited.In this study,we combines the field investigation with the.laboratory research to investigate the digestion efficiency of zooplankton and the recovery rates of microplastics under different digestion conditions.Besides,zooplankton taxon were collected by vertical trawl to investigate the abundances of MPs in zooplankton.Meanwhile,the uptake and elimination of microplastics by Tigriopus japonicas were investigated by using 10 ?m polystyrene microspheres,and the impacts of polystyrene microspheres on the feeding behavior were also assessed in the present study.(1)To investigate the digestion efficiency,of zooplankton,the T.japonicus and the Artemia parthenogenetica were digested at different digestion conditions(65%nitric acid and heated in a water bath at approximately 70? for 2 hours;65%nitric acid and ultrasonication for 40 minutes;65%nitric acid at room temperature for 96 hours and 5%nitric acid at room temperature for 96 hours.).The results shows the digestion efficiency of T.japonicas and A.parthenogenetica was 74.28%±2.20%and 77.30%±0.46%by using 65%nitric acid at room temperature for 96 hours,respectively.Moreover,there were no significant differences in the quantity and weight of the three kinds of MPs(low density polyethylene,polypropylene,polyvinyl chloride)(P>0.05).Overall,our findings illustrate that 65%nitric acid at room temperature for 96 hours can be used in the detection of MPs in marine zooplankton.(2)The abundances of MPs in zooplankton taxa varied from 0.06 pieces/zooplankton for Tunicata to 4.55 pieces/zooplankton for Copepoda.The encounter rates of the zooplankton are low than 40%.Larval fish had the;highest encounter rate with microplastics(18%-35%),Copepoda had the lowest encounter rate with microplastics(0.15%-0.20%).The sizes of the MPs mainly ranged from 0.30 mm to 1 mm(50.45%),followed by 0.10 mm to 0.30 mm(34.23%).The main shape of the detected MPs is fibers(81.53%),followed by fragments(11.71%),lines(4.95%)and particles(1.81%).And the main components of the MPs are cellulose(52.23%),polyester(27.68%)and polypropylene(12.05%).(3)The results indicate that with the increase of the exposure time the amount of polystyrene microspheres detected in T.japonicus increased.The highest detected level of polystyrene microspheres in T.japonicus was(7.00±2.44)particles/individual(n=3).when exposed to polystyrene microspheres at the nominal concentration of 1×103 particles/mL over 24 h.After 48 h,the amount of ingested polystyrene microspheres decreased to(3.20±1.93)particles/individual(n=3).After the exposure,T.japonicus were transferred to clean seawater.The amount of polystyrene microspheres in T.japonicus decreased dramatically with the increase of the exposure time.The polystyrene microspheres were eliminated quickly with a high clearance percentage of 96.3%±1.18%(n=3)after depuration of 24 h,and we did not find polystyrene microspheres in T.japonicus after depuration of 48 h.Moreover,there were no significant differences for the microalgae ingestion rates in.the presence of 1×103 particles/mL polystyrene microspheres over 24 h and 48 h(P>0.05).The results show that the polystyrene microspheres were ingested and eliminated quickly by T.japonicus,but there were no significant differences for the microalgae ingestion rates when the exposure concentration is about two orders of magnitude higher than the concentration of microplastics in seawaters.