Occurrence Characteristics And Transport Modeling Of Trace Organic Contaminants In Typical Estuary Reservoirs

Due to pollution-induced water shortage,estuary reservoir is an import drinking water source to the metropolis nearby.However,the rapid urbanization and population explosion in the downstream area of the Yangtze Basin keep surging the amount of anthropogenic organic chemicals used in industry,daily life,and agriculture.These contaminants are ubiquitous in surface water with a low concentration and may pose a potential risk to the aquatic organism.The contaminants also could pose a risk of endocrine disorder or cancer to human through drinking water.However,pollution in the estuary reservoir is more complicated than an inland reservoir because estuary water quality is influenced by both upstream and saltwater intrusion.Meanwhile,the estuary environment is different from each other.To better monitor and control the trace organic contaminants in the estuary reservoir,we should study more on temporal variation pattern,fate and transport of the contaminants.In the support of the international collaboration project E2S2 between Singapore and China,Qingcaosha Reservoir in Yangtze Estuary in Shanghai and Marina Reservoir in Marina Bay in Singapore were selected to compare the occurrence of the trace organic contaminants.The comparison results could help us to understand the characteristics of the contaminants in different water bodies.Moreover,Delft3 D software suite was used to build the three dimensional hydrodynamic and water quality model of the contaminants in Qingcaosha Reservoir,in order to understand the fate and transport of these contaminants in the estuary reservoir.The major results are listed as follows.(1)Based on the year-long detection results of the 5 PPCPs and 9 pesticides in Qingcaosha Reservoir,the concentrations of the contaminants were found at a low level,all below 100 ng L-1 and 10 ng dryg-1 in surface water and sediment,respectively.The detection results in Qingcaosha Reservoir were then compared with Marina Reservoir.The comparison results showed popular PPCPs,such as caffeine,DEET and BPA were frequently detected and their concentrations were higher than others in both reservoir.The fate and transport processes of BPA in both reservoirs were similar based on the simulation results by Delft3 D.However,the concentration level of the contaminants is also influenced by the size of the water body.The concentration of some PPCPs in Marina Reservoir was almost 10 times higher than Qingcaosha Reservoir.The comparison results exhibited the concentration of trace organic contaminants in sediment is decided by both their usage and Kow value.(2)Both PPCPs and pesticides exhibited different seasonal trends.PPCPs were detected highest in summer while lowest in autumn.Pesticides were detected higher in winter and spring.Although environmental water quality parameters had an influence on the biodegradation of PPCPs,the concentration of PPCPs is determined by their usage and efficiencies of WWTPs based on the correlation analysis results between the PPCPs and water quality paraments with regard to pollution load.Thus,PPCPs were found highest in summer due to the high usage and low efficiencies of WWTPs caused by the heavy rain.PPCPs and pesticides exhibited different relationships with the water quality parameters with regard to pollution load due to their different source.Economic parameters linked with the usage of the contaminants exhibited the positive correlations.It also showed the variation of PPCPs in the sediment is linked with their concentrations in the source water while of pesticides is linked with TOC value of the sediment.(3)The Risk Quotient(RQ)and Hazard Quotient(HQ)were used in this study for ecological risk and human health risk,respectively.The results of the risk assessment estimated by RQs showed that caffeine,bisphenol A,estrone,and simazine were at a high-risk level in the reservoir water.Most herbicides and pirimicarb showed the medium risk while the fungicides and other PPCPs exhibited low risk to the aquatic ecosystem.The HQ results showed all of the emerging contaminants detected posed a low risk to human health through drinking water.However,ethoxyquin needs to further study because the risk was higher than others in drinking water while the risk in surface water was very low.(4)The integrated model was built by Delft3 D suite,a fully integrated multidimensional modeling software.The hydrodynamic model was built by Delft3D-FLOW module and then calibrated and validated against observations from 2011 to 2015.Our results show that the model is capable of describing the hydraulic transport and the spatial and temporal patterns of water temperature,salinity in the reservoir,which is the foundation to build the integrated contaminants model.(5)The coupling of hydrodynamic and water quality model was set by Delft3D-WAQ module.The integrated model was calibrated against observations from 2014 to 2015 and then applied to explore the potential risk of high atrazine concentrations in the reservoir.Our results show that the model is capable of describing the dynamic distributions of two representative emerging contaminants(atrazine and BPA)in the reservoir.The physical and biodegradation processes in this study were found to play a crucial role in determining the fate and transport of atrazine and BPA in the reservoir,which is similar with modeling results of BPA in Marina Reservoir.Wet deposition is also an important pathway for half-volatile contaminants,like atrazine.The model also provides an insight into the potential risk of atrazine and the possible mitigation threshold of 63 ng L-1.The results above are useful to the policy-makers for the future management of Qingcaosha Reservoir.