The Distribution Characteristics And Risk Assessment Of Microplastics/Phthalate Esters In The Nearshore Coral Reef Ecosystem Of Southern Hainan Island

As a new type of pollutants,the effects of microplastics and phthalate esters on coral reefs are still in the exploratory stage in China.In particular,the occurrence characteristics of phthalate esters in coral reefs have not been reported in China.It is essential to investigate the actual pollution status of microplastics and phthalates in environmental media and assess their ecological risks for the subsequent ecological management and development of relevant management and protection strategies in coral areas.Therefore,this paper selected four coastal reefs in the south of Hainan Island to study the occurrence characteristics and ecological risks of microplastics in environmental media（bottom seawater and surface sediment）and organisms（coral reef,benthic shellfish and rest-dwelling fish）in each reef area.The concentrations of 16phthalate esters（PAEs）in the bottom seawater,surface sediment and coral organisms were analyzed.In addition,the occurrence characteristics of microplastics in the sediments of 12 intertidal zones around the reef area were investigated to comprehensively assess the pollution status of microplastics in the southern coral area of Hainan Island.To explore the effects of microplastics and phthalate esters organic pollutants on coral organisms by measuring photosynthetic efficiency parameters and physiological parameters.The main findings of this paper are as follows:、1.Occurrence characteristics and risk assessment of microplastics in the coastal coral reef ecosystem of southern Hainan Island:（1）Occurrence characteristics and ecological risk assessment of microplastics in coral reef ecosystem environment:The average abundance of microplastics in the bottom seawater and surface sediment of the coastal reef area of southern Hainan Island was 8.82±7.13 n·L^-1 and190±143.15 n·kg^-1.The abundance of microplastics was mainly dominated by particle size<1000μm,fibrous microplastics,transparent microplastics and polyethylene terephthalate（PET）are mainly used.There was no significant correlation between the abundance of microplastics in bottom seawater and p H,salinity,dissolved oxygen（DO）and nutrients（p>0.05）;There was no significant correlation between the abundance of microplastics in the surface sediment and organic carbon（TOC）and total nitrogen（TN）（p>0.05）.The spatial distribution of microplastic pollution in the coral reef area of southern Hainan Island was significantly different.According to the results of risk index and Nemero index,the ecological risk level of microplastics in the bottom seawater and sediment was severely polluted in Yalong Bay reef area,while Nanshan Reef area was the lowest（the bottom seawater was slightly polluted and the surface sediment was slightly polluted）.Based on Shannon index and the composition of different shapes of microplastics,it can be inferred that tourism、daily residents life and fishing activities were the main sources of microplastics in the coastal reef area of southern Hainan Island.（2）Occurrence characteristics of microplastics in coral reef ecosystems:The average abundance of microplastics in coral was（0.361±0.263）n·g^-1,with0.235±0.187 n·g^-1 on the surface and 0.126±0.147n·g^-1 in vivo.Large-size and fibrous microplastics were more likely to be enriched on the surface of corals,while small-size and fragmented microplastics were more likely to be enriched in corals.The abundance of microplastics on coral surface was negatively correlated with Fv/Fm（p<0.05）,but positively correlated with NOS and PO（p<0.05）;The abundance of microplastics in corals was positively correlated with CAT and NOS（p<0.05）.The abundance of microplastics was 1.498±1.226 n·g^-1 in benthic shellfish and2.306±1.925 n·individu^-1 in reef fish.The concentrations of microplastics in organisms in the coral reef area of southern Hainan Island were<1000μm,fibrous microplastics and PET were similar to those of microplastics in environmental media.2.Occurrence characteristics of phthalates esters in coastal coral reef ecosystem in southern Hainan Island:（1）Occurrence characteristics of PAEs in coral reef ecosystem environmentHigh concentrations of∑₁₆PAEs were detected in all coral reef areas,ranging from0.517～75.755μg·L^-1 in bottom seawater and 0.008～0.932μg·g^-1（dw）in surface sediments.There was no significant correlation between∑₁₆PAEs concentration and microplastics abundance in bottom seawater（p>0.05）,while dinoctyl phthalate（Dn OP）was positively correlated with microplastics abundance（p<0.05）;The concentrations of∑₁₆PAEs in sediments were negatively correlated with the abundance of microplastics（p<0.05）.（2）Occurrence characteristics of PAEs in coral reef ecosystem:The concentration of∑₁₆PAEs in coral was 2.077～3.163μg·g^-1（dw）,and the average concentration was 2.415μg·g^-1（dw）.The highest concentration of Dn OP was detected in the four coral reef areas,and the concentration of Dn OP was strong in corals.There was a significant negative correlation between sediment and coral PAEs（p<0.05）.The concentration of∑₁₆PAEs was negatively correlated with NOS（p<0.05）and positively correlated with Caspase-3（p<0.05）.3.The distribution characteristics of microplastics and risk assessment in intertidal sediments of southern bay of Hainan Island:The average abundance of microplastics was 715±135.98 n·kg^-1 in the intertidal sediments of the southern bay of Hainan Island.The abundance of microplastics was positively correlated only with TOC,but not with salinity,water content and p H.The morphology characteristics of microplastics were mainly fibrous and fragmented,and the color was single.The particle size range of microplastics was concentrated between0～1000μm.Eight polymer types were detected,mainly Rayon、polyethylene terephthalate（PET）and polyethylene（PE）,and the spatial distribution of microplastics with different components was different.The pollution level of microplastics in the intertidal sediments of the southern bay of Hainan Island is at a moderate level,and it is speculated that domestic sewage input,tourism and fishery activities are the main sources of microplastics.