Environmental Behavior Of PPGEs In A Tropical Estuary

Platinum group elements(PGEs)include six elements: ruthenium(Ru),rhodium(Rh),palladium(Pd),osmium(Os),iridium(Ir),and platinum(Pt),which are in low abundance in the earth’s crust.Palladium subgroup of PGEs(PPGEs,)which contains Pt,Pd,and Rh,is widely used in automotive exhaust catalytic converters because of its good physicochemical properties.As the number of motor vehicles increases and exhaust emission standards become more stringent,the environmental problems caused by PPGEs are becoming more serious.PPGEs discharged into the environment enter and accumulate in rivers through atmospheric deposition and runoff scouring,leading to an increase in the content of PPGEs in water bodies.Estuaries are the hubs connecting rivers and oceans,with intensive human activities and drastic changes in the water environment,which affect the migration and accumulation of PPGEs.However,current reports on PPGEs have focused on roadside dust,soil,and rivers,and relatively few studies have addressed the environmental behavior of PPGEs in tropical estuaries.In this study,PPGEs were selected as the research subjects,a typical tropical estuary,the Nandu River estuary was used as the research area,and the relationship between the physical chemical properties of water bodies and the distribution of PPGEs was investigated through a comprehensive study of field in situ monitoring,indoor environmental analysis,and numerical simulation.The particle size composition and Total Organic Carbon(TOC)content of the sediment were measured,and the effects of particle size and TOC on the accumulation of PPGEs in sediment were demonstrated;an aquivalence model for the transport of PPGEs in the water was established based on the measured data,and the environmental process flux of PPGEs was calculated by simulating the transport of PPGEs between media in the Nandu River estuary.The potential ecological risk of PPGEs in the surface sediments of the Nandu River estuary was assessed using the geo-accumulation index method,the Nemerow single factor index and the integrated index method.The main conclusions are as follows:The Pd content in the water environment is much higher than Pt and Rh,which is related to the amount of PPGEs used and discharged.The physicochemical properties of water bodies are profoundly influenced by tides and change dramatically.Under the disturbance of water body physicochemical properties,dissolved and suspended PPGEs show different adsorption and desorption characteristics,and dissolved Pt rises significantly in high salinity areas;due to the different elemental properties of PPGEs,the content of particulate Pd and Rh is low in areas with high concentration of suspended matter;conversely,the content of particulate Pd and Rh is high.The content of PPGEs in sediments was higher than that in the crust.The sediment composition and TOC content varied widely among sampling stations,showing a trend of increasing sand content and decreasing TOC content from river to ocean.Sediment grain size is influenced by hydrodynamics,and sand content is high at the mouth of the Henggou River and the Northern Mainstem.TOC is obviously controlled by grain size,and TOC content is high at sampling stations with high clay and silt content,while TOC is lower in areas with high sand content.High levels of PPGEs were found in areas with high TOC,clay and silt content,indicating that PPGEs were influenced by grain size and TOC,but high levels of PPGEs were also found in the sandy sediments of the Henggou River,while this phenomenon was not found in the sandy sediments of the Northern Mainstream,which may be related to the influence of hydrodynamic strength on the accumulation of PPGEs.The main source of PPGEs in the water is inflow water(Pt: 216.43 g/d;Pd:9359.05 g/d;Rh: 238.95 g/d);the main output is sediment burial(Pt: 213.15 g/d;Pd:9359.05 g/d;Rh: 232.13 g/d).The migration process of PPGEs is mainly influenced by suspended sediment deposition and sediment resuspension.During the water-sediment environment,the net transport direction of PPGEs was from water to sediment at the rates of Pt(213.15 g/d),Pd(9104.83 g/d),and Rh(232.13 g/d),which indicated that the sediment phase was the destination of some PPGEs.Influenced by organic matter,the rate of sediment-water interdiffusion was higher than water-sediment diffusion.The transport flux of Pd in environmental processes was much higher than that of Pt and Rh,which was the dominant PGEs pollutant in the Nandu River estuary.The potential ecological risk of PPGEs can be quantified comprehensively and comprehensively using multiple ecological risk evaluation methods.The results of the geo-accumulation index and single factor index evaluation were similarly,and among the 19 sampling stations,Pt was mainly light or moderately polluted,Pd was heavily extremely or heavily polluted,and Rh was also lightly or moderately polluted.The combined index,on the other hand,indicates that PPGEs are heavy pollution.Innovation:1.First investigation of PPGEs in the Nandu River estuary,China.2.The influence of grain size and TOC on PPGEs accumulation in sediments was discussed.3.The environmental behavior of PPGEs in tropical estuary was simulated by using aquivalence model.