Construction Of Aquatic Food Web Model And Research Food Chain Transmission Mechanism Of Emerging Per/Polyfluoroalkyl Substancess

Per-and polyfluoroalkyl substances（PFASs）are a class of synthetic organic compounds with excellent surface activity,which are widely used in various industrial and commercial products.Due to their extensive use,they are frequently detected in various environmental media,organisms and human serum.However,a large number of studies have found that PFASs exposure can be toxic to the growth and development of organisms and humans.Therefore,the occurrence,distribution and potential health risks of these compounds in the environment have gradually attracted attention and are listed in the Stockholm Convention.Due to the strict regulation of traditional PFASs,many fluorinated alternatives have been developed and used in the global market to meet market demand,including short-chain perfluoroalkyl acids and some new PFASs.In recent years,the production and use of new PFASs have increased rapidly,which have been detected in different environmental media,and a small number of toxicological studies have found that they also have bioaccumulation potential and toxic effects.However,there is a lack of research on the bioaccumulation and amplification of new PFASs in aquatic organisms and the mechanism of food chain transmission,which makes it impossible to assess their potential ecological risks.In addition,limited by the difficulty of obtaining aquatic biological samples and the time-consuming and labor-intensive pretreatment,it also restricts the study of the behavior of new PFASs in aquatic organisms.Based on the water environmental media and aquatic organisms in the Taihu Lake Basin,this study systematically constructed a PFASs enrichment model in the aquatic food web,revealed the bioaccumulation and amplification mechanism of new PFASs,and provided a theoretical basis for accurately assessing their potential ecological risks.The specific research results are as follows:（1）Based on the previous literature survey data,a PFASs enrichment model in aquatic food web was constructed to predict the concentration levels of PFASs in aquatic organisms at different trophic levels and reveal the enrichment mechanism.The results showed that the PFASs enrichment model constructed and optimized based on the protein content of aquatic organisms could well predict the concentration of PFASs in different trophic levels of fish,as well as the bioaccumulation factor（BAF）and trophic magnification factor（TMF）of PFASs in fish.According to the results of the bioconcentration model,the enrichment mechanism of PFASs was studied,and it was found that water and sediment were important exposure sources of PFASs in aquatic organisms.Gill respiration is the main channel for fish to uptake short-chain PFAAs(C_6-8).With the increase of carbon chain length of PFASs,the contribution of gill respiration decreases,while the contribution of dietary intake increases.Short-chain PFAAs(C_6-8)were mainly removed from fish by gill respiration.With the increase of hydrophobicity and molecular weight of PFAAs,the relative contribution of fecal excretion gradually increased,which became the main way to remove long-chain PFAAs(C_9-12).In fish with high protein content,dietary intake and fecal excretion were more obvious for the accumulation of PFASs in fish.Growth dilution is the main way for long-chain PFASs(C_12-16)to be excreted from fish,but its total elimination rate constant is very low（0.010-0.013 1/d）,resulting in higher BAFs and TMFs.PFOS has a high cumulative concentration in fish,mainly due to its high total intake and low total elimination rate,as well as high concentrations in water and sediments.（2）Surface water,sediment and aquatic organisms of different trophic levels were collected in Taihu Lake,China.The concentrations of 31 traditional and novel PFASs were systematically analyzed,and the bioaccumulation and amplification mechanisms of novel PFASs were explored by combining the results of bioaccumulation model simulation and field observation.The results showed that novel PFASs,including fuorotelomer sulfonic acid（FTSs）,hexafluoropropylene oxide acid（HFPOs）and chlorinated polyfluorooctane ether sulfonic acid（Cl-PFESAs）,were widely detected in water,sediments and aquatic organisms,with detection rates of 80.6-100%,83.3-100%and 77.7-96.3%,respectively.The concentrations of hexafluoropropylene oxide trimer acid（HFPO-TA）,4,8-dioxa-3-hydrogen-per-fluorononanoate（ADONA）and FTSs were significantly higher than those previously reported（p>0.05）,indicating that their production and use in the Taihu Lake Basin showed an increasing trend.Compared with perfluoroalkyl acids（PFAAs）with the same perfluorocarbon chain length,the organic carbon standardized water-sediment partition coefficient(log K_oc)of these new PFASs is higher than that of traditional PFAAs with the same carbon chain.HFPOs and Cl-PFESAs were more easily deposited in fish liver than their substitutes PFOA and PFOS,respectively.In the study of enrichment mechanism,both field observation and model simulation showed that HFPO-TA,Cl-PFESAs and 6:2 H-PFESA were biomagnified along the aquatic food chain.The model simulation results showed that the accumulation of novel PFASs in fish was mainly through dietary intake,while gill respiration and fecal excretion promoted their elimination.Compared with traditional PFAAs,metabolic transformation may also contribute to their elimination.Weekly intake model（WI）and hazard ratios model（HR）were used to assess the potential health risks caused by consumption of aquatic products（fish,shrimp and shellfish）in Taihu Lake.The results showed that fish was the main source of exposure.In 19 common edible fish species in Taihu Lake.The dietary intakes of PFOA,PFNA,PFHx S and PFOS exceeded the tolerable weekly intake（TWI,4.4ng/kg bw/week）in anchovies（6.2-6.8 ng/kg bw/week）,fish（5.6-6.0 ng/kg bw/week）,minnows（6.8-7.3 ng/kg bw/week）,fish（10-10.9 ng/kg bw/week）and yellow catfish（4.9-5.4ng/kg bw/week）.It shows that eating high-trophic fish is the main source of potential harm to human health.The HR of the typical new substitute 6:2 Cl-PFCESA in all fish was less than1,indicating that it would not directly cause health risks to local residents.