Multi-media Fate Simulation And Risk Assessment Of Organotin In The Water Environment Under Dynamic Water Level In The TGRA

Tributyltin（TBT）and triphenyltin（TPhT）are widely used as fungicides and marine antifouling paints,and are endocrine disruptors with high toxicity and durability（>30 years）.Studies have shown that organotin pollution exists in the water environment of waterworks,sewage treatment plant and surface waters in the Three Gorges Reservoir Area（TGRA）over the years.At the same time,the operation mode of the Three Gorges Reservoir（TGR）has an impact on the migration and distribution of organotin in different water environments in the reservoir area.In order to comprehensively simulate the environmental behavior and pollution level of organotin in the TGRA and evaluate its hazard,this thesis takes TBT and TPhT as the research object,firstly constructs an organotin multi-media fugacity model which is suitable for the TGRA,and then applies the model to the dynamic water level.The organotin in the water environment of the TGRA before and after the ban of organotin was used to carry out multi-media fate simulation.Finally,based on the predicted concentration of TBT and TPhT before and after the ban of organotin,the risk assessment of organotin to the aquatic organisms in the reservoir area and surrounding population was carried out.The research work and main conclusions of this thesis are as follows:1)This paper constructs a multi-media fugacity model for organotin in the water environment under the dynamic water level in the TGRA,and evaluates the model performance using Theil inequality coefficient（TIC）and percent deviation（PBIAS）.The results show that the TIC of organotin is 0.05⁰.18,and the PBIAS index ranges from+8.56%to+26.79%.The model satisfies TIC<0.5 and PBIAS∈[-70%,+70%],and the model performance is good.Sensitivity factor method was used to analyze the sensitivity all raw parameters of the model.The results show that the predicted values of TBT and TPhT in the four environmental phases are two parameters of the influent concentration（Cow）and the inflow rate（Gow）of the water phase,which is very sensitive（sensitivity coefficient SC>0.5）and has a positive correlation.2)Applying the model to carry out the multi-media fate simulation of organotin under dynamic water level.The simulation results of organotin concentration（C）,migration flux（N）and mass flux（m）show that:（1）During different water level period,only the proportion of C distribution in the water and sediment phases of TBT changed little:low water level>high water level,and the ratios of TBT in water phase and TPhT in fish phase were always the highest;（2）The organotin N-value of all environment processes shows the relationship:N-value of low water level is more than the N-value of high water level;advection inflow and outflow process(N_OW,N_WO)and the diffusion process between fish and waterh phase(N_WF,N_FW)are important multi-media environmental processes of TBT and TPhT;the total input and output migration flux（N⁺,N^-）percentage of each environmental phase is constant,and the N⁺and N^-percentage of the water phase are always the highest of the four phases.3)Applying the model to carry out the multi-media fate simulation of TBT and TPhT before and after the ban of organotin.The simulation results of organotin concentration（C）,migration flux（N）and mass flux（m）show that:（1）After the ban of organotin ship antifouling paint,the decrease of C value of TBT（28.3%³3.5%）in each environmental phase during the year was higher than that of TPhT（9.57%¹6.62%）;the ratio of TPhT concentration in fish phase to water phase after the ban（47.45）was greater than that before disapproval（41.74）,the biological enrichment factor（BCF）of the fish phase is higher after the ban;（2）The TBT and TPhT N value of all environmental processes and the total input and output migration flux（N⁺,N^-）of the four environmental phases after the ban were decreased and the degree of declining of N,N⁺and N^-values of TPhT is lower than that of TBT.Before and after the ban,TBT mainly occurs in the low water level period and TPhT mainly appears in the water storage period.It is estimated that TBT is mainly affected by the warehousing flow and temperature,while TPhT is greatly affected by fish biomass in the reservoir area.4)The ecological risk assessment of aquatic organisms in the reservoir area under acute and chronic exposure of organotin showed that:（1）During the simulation period,the risk quotient（RQ）of organotin to aquatic organisms in the reservoir area decreased and the RQ value of the low water level period was greater than high water level;（2）Based on the lowest PNEC value in the existing standards,TBT caused significant acute risk（RQmax=78.36）and chronic risk（RQmax=391.78）for aquatic organisms in the reservoir area during the simulation period,and TPhT only caused significant chronic ecological risk（RQmax=16.79）in the reservoir area.Based on the highest PNEC values,TBT and TPhT still have significant or potential chronic risks to aquatic organisms in the reservoir area.5)The results of health risk assessment of organotins in the reservoir area indicated that the main exposure pathways of TBT and TPhT into the human body were skin infiltration and fish intake;the health index（HI）of TPhT to the reservoir population was significantly higher than that of TBT.However,both TBT and TPhT HI values are lower than 1,that is,the health risk of organotin to the population of the reservoir area is low.6)The tolerable average residual levels（TARL）of TBT and TPhT in fish before and after the ban of organotin in the TGRA were 79.50 ng Sn/g and 134.28 ng Sn/g,respectively.The predicted concentration of TBT before and after the ban of organotin was much lower than its TARL value,while the maximum predicted concentration of TPhT（136.92 ng Sn/g）exceeded its TARL value.It is speculated that TPhT in fish in the TGRA may cause health effects to the fish population.