Water Quality Criteria Establishment And Risk Assessment Of Heavy Metal In Qin River (Jincheng Section)

The deterioration of water ecological environment in watersheds due to the rapid development of urbanization and industrialization has been of great concern to academics at home and abroad,especially heavy metal pollutants,which can enter surface water bodies through various channels and pose a serious threat to the ecological health of watersheds.China’s vast territory and developed water system result in the diversity of aquatic ecology in different regions.Implementing the national unified standard for water quality evaluation will produce certain deviation,which is not conducive to the scientific management of water environment.Therefore,according to the characteristics of water ecological environment in different zones,it is of great significance to construct environmental quality thresholds that fit the local water ecological environment to evaluate the current situation of water ecological environment in a scientific and accurate way.In this paper,taking the Qin River basin in Jincheng City as the research object,through field sampling and field survey,on the basis of understanding the current situation of the water environment quality of Qin River and the distribution of native aquatic organisms,the aquatic biological toxicity data of four heavy metals,cadmium,copper,lead and zinc,were collected through domestic and international websites,and after screening and correcting the toxicity data,the species sensitivity distribution model was used to derive the water quality benchmark values of heavy metals,and the derived water quality benchmark values were used as risk thresholds for risk evaluation.The results are as follows.（1）Among the seven conventional factors in the water body of Qin River,the average values of p H,DO,COD,NH₃-N,TP and TN were 8.21,12.81,14.57,0.44,0.07and 5.64 mg/L,respectively.Among them,TN exceeded the standard more seriously,and the exceedance rate was 100%.The mean values of Cr,Ni,Cu,Zn,As,Cd and Pb were 0.521,2.033,4.281,8.494,2.069,5.627 and 1.945μg/L,and none of the heavy metals exceeded the standard.Compared with the water quality condition of Qin in2012,only two heavy metal concentrations of Zn and Cd were higher than before,and all other indicators were lower than the monitoring data in 2012.（2）A total of 81 species of aquatic organisms were identified in the biological survey of Qin River,including 29 species of 6 phyla of zooplankton,23 species of 4phyla of phytoplankton and 29 species of 3 phyla of benthic animals.There are 9dominant species,including Chlorella vulgaris,Chroomonas acuta,Cryptomonas erosa,Difflugia globulosa,Arcella vulgaris,Chironomus riparius Meigen,Ephemera orientalis,Limnodrilus claparedianus,Corbicula fluminea.（3）A total of 5404,4043,2692 and 4214 pieces of heavy metal Cd,Cu,Pb and Zn toxicity data were retrieved from domestic and foreign websites,and 105,119,76 and86 pieces of data were available for water quality benchmark derivation after screening.The biological toxicity data were calibrated with a gradient of water hardness of 50-450mg/L,and the calibration results were good,with R²in the range of 0.005-0.086.（4）The SSD model was used to derive the water quality benchmarks for the four heavy metals.When the water hardness is 100 mg/L,the short-term water quality benchmark values of heavy metals Cd,Cu,Pb and Zn were 9.87,10.52,141.54 and72.11μg/L,respectively,and the long-term water quality benchmark values were 0.96,3.32,13.16 and 22.05μg/L.In comparison with the current water quality standards,the heavy metals Cu and Zn have a certain“under-protection”phenomenon,need to make appropriate adjustments.（5）Single factor index evaluation results showed that the heavy metals Cu and Zn in some points appear to exceed the standard phenomenon,indicating that Cu and Zn existing water quality standards in the water quality evaluation of the deviation,which was not conducive to reflect the current water quality conditions,and should be adjusted according to the water quality benchmark value.Nemero comprehensive pollution index results showed that most points were in the degree of no pollution;the potential ecological risk index values of the four heavy metals are as follows:Cd>Pb>Cu>Zn,heavy metal Cd ecological risk value was the highest.（6）The results of health risk evaluation showed that the non-carcinogenic degree of 7 heavy metals was ranked as follows:Pb>Cr>As>Cd>Cu>Ni>Zn,the carcinogenic degree of heavy metals Cr>As>Cd,and the total carcinogenic risk value of Cr for adults and children has exceeded the maximum acceptable risk value of 5×10^-5,which should be taken seriously.The total carcinogenic risk of children（2.01E-04）was greater than that of adults（1.50E-04）,and the total non-carcinogenic risk was also greater in children（9.76E-09）than in adults（8.29E-09）.Compared with adults,children were more sensitive to the carcinogenic risk of heavy metals,and more vulnerable to the harm of heavy metals...