Distribution Characteristics Of Perfluoroalkyl Substances On Estuarine Microplastics And Gas Distribution Coefficients On Plastics

Persistent organic pollutants?POPs?,such as Perfluoroalkyl substances?PFASs?,owing to its environmental persistence,bioaccumulation property,and ability to transport over long distances,resulting in existing in water,soil,sediment,atmosphere and even polar glaciers.At present,plastics?especially for microplastics?,can adsorb heavy metals and organic pollutants in water environment due to their huge specific surface area and excellent adsorption characteristics.Due to their different shapes and different colors,microplastics can be easily eaten by aquatic organisms.Microplastics and their adsorbed pollutants may pose potential risks to aquatic organisms and ecosystem.In recent years,Wristbands made of plastic have become very popular for monitoring organic pollutants exposed to human bodies.However,at present,there is a lack of research on the distribution mechanisms of organic pollutants between plastics and gas.This paper focused on the contamination level and spatial and temporal variations of microplastics and their adsorbed PFASs in surface water of the eight major outlets in the Pearl River Delta in 2018,and determination on the solid-gas distribution coefficients of PFASs between plastics and gas.The main conclusions are as follows:1.Analysis of microplastics in surface water of the eight major estuaries in the Pearl River Delta shows that microplastics were identified in all samples ranging from0.003–2.09 items m^-3(average 0.106 items m^-3)or 0.001–5.68 mg m^-3(average 0.559 mg m^-3).The Fourier transform infrared spectrometer data of microplastics shows that propylene?PP??43.1%?and polyethylene?PE??39.0%?are the two main types of microplastics.Five types of microplastics with different morphologies were collected,which were categorized as fiber?53.1%?,fragment?21.2%?,film?13.1%?,foam?11.4%?and pellet?1.27%?.Spatial variations show that microplastics concentrations from eastern outlets?HM and HE except for HQ and JM?were generally higher than the western outlets?MD,JT,HT and YM?,which may be attributed to the population density and economic development level of different regions.Temporal variations show that microplastics concentration in the wet season?April,June,August?was significantly higher than that in the dry season?January,November?conducted by paired t-test?two-tails??P<0.05?,which may be attributed to the frequency and intensity of rainfall in different seasons.2.Analysis of 21 individual of PFASs on microplastics in surface water of the eight major estuaries of the Pearl River Delta show that?PFASs concentrations range from 3.11ng g^-1 to 9.07×10³ ng g^-1with an average concentration of 616 ng g^-1over the eight estuaries.The individual PFASs concentration was in the range of<LOQ to 8.24×10³ ng g^-1with an average concentration of 29.3 ng g^-1.The spatial variations of PFASs on microplastics show that?PFASs concentrations vary greatly among eastern and western outlets of the PRD region.The highest PFASs concentration was detected in samples collected from HQ,as HQ receives the inflow of Pearl River and East River,while the lowest concentration of PFASs was detected in samples collected from MD with concentrations from 10.3 to 228 ng g^-1.This may be attributed to MD receives the inflow of East River.Since East River mainly runs through agricultural and forestry land areas with a lack of PFASs sources from daily life and industrial factories.Temporal variations of PFASs on microplastics show that higher?PFASs concentrations were found in January and November,whereas lower?PFASs concentrations were found in August.The lowest concentration of PFASs was found in the wet season(267 ng g^-1),which may be due to the dilution and dispersion effects caused by the greater runoff from land.However,PFASs level on microplastics in the wet season are higher than those in the dry season of samples from the HE,HM,YM and MD,indicating that the discharge of industrial or domestic wastewater containing PFASs has much stronger impact on their levels on microplastics than dilution and dispersion by river for those sampling sites.Especially,8:2 di PAP was detected with the highest frequency of 92.5%in all samples.Furthermore,a positive correlation was found between disubstituted polyfluoroalkyl phosphates?di PAPs?and Perfluorinated carboxylic acids?PFCAs?,suggesting that they might share common sources or transportation routes.The results show that PFOS and PFOA accounting for67.8%–91.8%of?PFASs on average,which indicates that C8 PFASs are still the main compositions of PFASs on microplastics in the PRE region.3.Results of solid-gas partition experiment show that PFASs can achieve distribution equilibrium within 60 minutes for three different plastics?polyethylene?PE?,polyurethane?Polyurethane,PU?,silicone rubber?Silicone??and gas.Temperature and relative humidity?RH?also have significant effects on the solid-gas distribution process of PFASs.The results of the temperature influence on the solid-gas equilibrium distribution coefficient show that the Kpa under 35?of other three PFASs and three plastics are 1–5 times of the Kpa under 45?except for FOSA,while Kpa of FOSA under 35?for three plastics is about 10 times than that of Kpa under 45?.The results of the relative humidity influence on the solid-gas equilibrium distribution coefficient show that several PFASs and three plastics Kpa under 0%RH are 2.5–42 times than that Kpa under 100%RH.Compared with the other three PFASs,FOSA is most likely affected by humidity.In summary,the analysis results show that the lower temperature and the lower humidity,resulting in a greater equilibrium constant for the solid-gas partition experiment of PFASs between different plastics and gas.