Impact Of Microplastics On Degradation Of Di-n-butyl Phthalate In Offshore Sediments

The microplastic(particle size less than 5 mm)has a strong ability to adsorb organic pollutants in the environment,and the hydrophobic organic pollutants are carried and settled in the sediment.Organisms such as microorganisms can grow on the microplastic particles and affect the sediment microbial community structure.In the water environment,there may be different modes of action between microplastics and organic contaminants:exogenous contaminants enter sediments containing microplastics(situation A);microplastics enter contaminated sediments(situation B);microplastics adsorbed the aqueous phase contaminants into the sediments(situation C).In this paper,two common microplastics,polypropylene(PP)and polystyrene(PS),and the typical hydrophobic pollutant,dibutyl phthalate(DBP),were selected to study the effects of different conditions and different concentrations of microplastics on the bioavailability of DBP and biodegradation of DBP in simulated offshore sediments.And the influence of microplastics on microbial community structure in sediments was determined.On this basis,the mechanism of microplastics affecting DBP biodegradation in sediments was discussed.The main conclusions of this study are as follows:(1)The adsorption isotherms of DBP in water by two microplastics(PP and PS)with particle size of 200-250?m accord with Freundlich model(R~2=0.995).The adsorption capacity of PS(log K_F=2.22)is higher than that of PP(2.06),and the adsorption capacity of these two microplastics exceeds that of sediment(1.98).The N values of the two microplastics are around 0.6,indicating that surface adsorption and partitioning contribute to the adsorption of DBP.(2)Adding microplastics to the sediments reduces the bioavailable concentration of DBP in the initial sediments(14.80-86.21%).Among them,different simulations have little effect on DBP bioavailability;the amount of microplastics added has a greater impact;the decrease in the addition of PS treatment group was more significant than that in the addition of PP treatment group.When the addition amount of micro-plastics is 0.2%,the degradation rate of DBP can be increased(4.22-14.94%),but the difference of DBP degradation rate(89.06-90.50%)is not significant under different simulation conditions.The higher micro-plastic addition(2-10%)will inhibit the degradation of DBP(5.09-37.88%).The DBP degradation rate in sediments was significantly positively correlated with the ratio of initial DBP bioavailable concentration.(3)The results of 16s r DNA showed that the addition of microplastics changed the microbial community structure of the sediment.Adding a small amount(0.2%,w/w)of microplastics will increase the relative abundance of aerobic bacteria and the total relative abundance of dominant DBP degrading bacteria,and the effect of situation A is more significant.When the amount of microplastics added is high(2%,5%and 10%),the relative abundance of aerobic bacteria and the total relative abundance of dominant degrading bacteria decreased as the amount of addition increases,and the decrease of PS is more significant than PP.Therefore,the relative abundance of degrading bacteria is the main reason for the increase of DBP degradation rate in the 0.2%addition group,and the decrease in bioavailability and relative abundance of dominant degrading bacteria affects DBP degradation rate in2-10%addition group.