Organophosphate Esters In Marine Environment: Sources,Transport And Air-sea Interface Behavior

Organophosphate esters(OPEs)are a group of phosphoric acid esters in which the hydrogen in phosphate molecule is/are replaced by alkyls,aryls,or chlorinated alkyl groups.OPEs are used as flame retardants and plasticizers which have been widely used for decades in industry production of such as textiles,plastics,electronics,building materials and furniture.Since the international bans and phase-outs of brominated flame retardants(BFRs)in the 2000s,the market share of OPE flame retardants has increased considerably.Due to non-chemical bonding to materials,the release of OPEs by volatilization,leaching or abrasion into different environments can easily happen during their production,usage,and disposal.Their release into marine environment through various pathways is also suggested.Given the emerging persistency and bioaccumulation of organic pollutants(e POPs),OPEs prone to long-range atmospheric transport and are treated as e POPs.Till now,very few studies are available about OPEs in marine environment in large scale.This dissertation presents in-depth research on the sources,transport and air-sea interface behavior of OPEs in marine environment.The surface seawater and aerosol samples were collected in the large area of Pearl River-South China Sea-eastern Indian Ocean.Eleven OPEs were measured by gas chromatography-mass spectrometry including(tris(2-chloroethyl)phosphate(TCEP),tris(1-chloro-2-propyl)phosphate(TCPPs),tris-(1,3-dichloro-2-propyl)phosphate(TDCP),tri-n-butyl phosphate(Tn BP),tri-iso-butyl phosphate(Ti BP),tris-(2-ethylhexyl)phosphate(TEHP),tripentyl phosphate(TPe P),triphenyl phosphate(TPh P),tricresyl phosphate(TCPs),2-Ethylhexyl diphenyl phosphate(EHDPP)and triphenylphosphine oxide(TPPO).The concentration levels and spatial variations of the observed OPEs were obtained.Together with aerosol chemical components,ocean hydrological data and meteorological data,backward trajectory analysis of air masses,gas/particle partitioning model and two-film resistance model were used to investigate the sources,transport and sea-air interface behaviors of OPEs in large-scale marine environment.The main research results and conclusions are summarized as follows:(1)The range concentrations of∑OPEs in dissolved phase and suspended particulate matters samples from Pearl River were 117.5-854.8 ng/L and 0.5-13.3 ng/L,respectively;the surface seawater concentrations of∑OPEs in the northern and western South China Sea(SCS)were 1.3-17.6(mean:6.7±5.2)ng/L and 2.28-24.4(mean:7.58±5.5)ng/L,respectively;chlorinated OPEs were predominant in surface water samples from Pearl River and SCS.The surface runoff input from the northern and western of SCS,coast of Hainan Island and eastern coast of Vietnam were the main sources of OPEs in seawater.An accumulation trend of OPEs was observed in the northern SCS as a result of the transport by water masses and surface currents.The concentration of OPEs were higher in the jet and eddy area due to the OPEs contribution through water mass transport and mixing.Risk assessment of OPEs to aquatic organisms in the Pearl River and SCS indicated that Tn BP,TPh P and TCEP in the Pearl River waters have potential ecological risks.However,OPEs in the seawater of SCS exhibited no ecological risk.(2)The aerosol concentrations of∑OPEs in the western SCS and eastern Indian Ocean were 200-1579(mean:717±318)pg/m~3 and 201-976(mean:517±204)pg/m~3,respectively;chlorinated OPEs were predominant in aerosol samples from the SCS to the eastern Indian Ocean;the ratio of mean concentration of TCEP to TCPP is becoming smaller,indicating that the usage of TCPP in surrounding countries was gradually exceeding TCEP.The level of∑OPEs in marine aerosols were associated with transport of air masses;the OPEs in aerosol particle over western SCS were mainly influenced by the air masses originating from the Indochina Peninsula and Malay Archipelago,while the pollution of OPEs over the eastern Indian Ocean were impacted by the air masses from the Southeast Asia,the Australian and land-based polluted air masses.In addition,the observed latitudinal pattern of OPEs congeners over SCS could be expected to be primarily attributed to the influence of ambient temperature,air masses,the difference of physicochemical properties and particle-gas partitioning.The model and field measurements of atmospheric lifetime of OPEs show that atmospheric residence times of particle-bound OPEs over the eastern Indian Ocean are likely dependent on the factors of such as atmospheric radicals,relative humidity and so on.(3)The dry deposition fluxes of∑OPEs over the SCS and the eastern Indian Ocean were estimated to be 25.3 t/yr and 77.4 t/yr,respectively.The model of gas-particle partitioning could predict the occurrence of alkyl and aryl OPE in gas phase but may not be suitable for the prediction of gaseous chlorinated OPEs.The results of air-seawater exchange in this study indicated that the volatilization fluxes of OPEs from seawater to air over northern SCS were5.6 kg/yr.The diffusion of gaseous OPEs from air into seawater were 105 t/yr over western SCS.The seawater of the SCS was acting as a sink for OPEs in the atmosphere.