Study On Water Quality Criterion And Ecological Risk Assessment Of Typical Contaminants In Shaying River Basin

The Shaying River Basin is one of the basins with prominent pollution problems and significant pollution contribution in the upper reaches of the Huaihe River Basin.In the Shaying River Basin,there are composite pollutions in papermaking,fertilizer,food fermentation,ammonia synthesis,brewing,leather and livestock,resulting in a combined pollution in the water environment.There are few studies on the water quality criterion of aquatic organisms in Shaying River Basin and lack of water quality criterion under conditions of water quality characteristics.In addition,there is lack of local biotoxicity data of nitrobenzene in the Shaying River Basin.Therefore,this study selected the typical pollutants cadmium,ammonia and nitrobenzene to derive water quality criterion and conduct ecological risk assessment.The main findings of this paper are as follows:?1?The hardness of water can affect the toxicity of cadmium.This study collected the toxicity data of cadmium on aquatic organisms and all the toxicity data included hardness values,and the acute and chronic toxicity tests of 6 native species in Shaying River under different hardness?H=50 mg/L,H=150 mg/L,H=250 mg/L?were added.The experimental results showed that with the increase of water hardness,the toxic effects of cadmium on organisms are significantly reduced.Under the condition that all toxicity data were standardized to hardness H=100mg/L,the cadmium water environmental reference equation with hardness as the independent variable was established:1)CMC=?1.136672-0.041838×lnH?×exp?1.0585×lnH-3.8234?,2)CCC=?1.101672-0.041838×lnH?×exp?1.0083×lnH-6.1156?.It was found that when the hardness was 100 mg/L,the criteria maximum concentration?CMC?and criteria continuous concentration?CCC?values of cadmium were 2.86 and 0.23?g/L,respectively.At the same time,the risk of cadmium of surface water in the Shaying River Basin was evaluated using the tiered risk assessment method?HQ method,safety threshold method,joint probability curve method?.The HQ method indicated that the hardness value can affect the risk level.Although the concentration of cadmium at the sampling point of the Shaying River during the wet season was generally higher than dry season,the risk level of most of the points was similar by standardizing the exposure concentration of cadmium to the same hardness.The safety threshold method indicated that although the MOS₁₀ in the Shaying River Basin during the wet and dry periods was greater than 1,there were still some areas where the Cd exposure concentration is higher than the water quality criterion,indicating that the Cd in the Shaying River Basin still has potential ecological risk for aquatic organisms.The joint probability curve method showed that the ecological risk of cadmium in the wet season was higher than that in the dry season.The potential risk of damage to more than 5%of aquatic organisms during the wet season was 33.21%and 4.74%for dry season under the long-term exposure of aquatic organisms in the Shaying River Basin.?2?The toxicity of ammonia are affected by temperature and pH,and the fishes are not affected by temperature.This study collected toxicity data of ammonia on aquatic organisms and all the toxicity data included temperature and pH,and the acute and chronic toxicity tests of 3 native species in Shaying River under different pH conditions?pH=7,pH=8,pH=9?were added.The experimental results showed that the toxic effect of ammonia on the organism increases significantly with the increase of pH.The toxicity data were uniformly standardized to pH=7,T=20°C,and the baseline equation of ammonia water environment with temperature and pH as independent variables was established:1)CMC=0.547×[0.0114/(1+10^7.204-pH)+1.6181/(1+10^pH-7.204)]×MIN(44.643,39.122×10^{0.036×?20-T?}),2)CCC=0.659×[0.0278/(1+10^7.688-pH)+1.1994/(1+10^pH-7.688)]×MIN(0.914×10^{0.028×?20-?MAX?T,7?}).It was found that when pH=7,T=20°C,the CMC and CCC values of cadmium were 21.416 mg N/L and 0.602 mg N/L,respectively.At the same time,the risk assessment of the ammonia in the surface waters of the Shaying River Basin was carried out using the tiered risk assessment method.The HQ method showed that there were different degrees of risk for all sampling points indicating that there was severe pollution of ammonia in the Shaying River Basin.Among them,30%of the points were low ecological risk level,and70%of the points were medium risk levels.In addition,small differences in pH can lead to large differences in risk assessment results.The safety threshold method indicated that the MOS₁₀ in the Shaying River Basin was 0.76,which is less than 1.It was inferred that the ammonia in the surface water of Shaying River has caused a certain ecological risks to aquatic organism under the current conditions.This was consistent with HQ method.The joint probability curve method showed that the potential risk of ammonia on aquatic organisms with more than 5%in the dry season was 24.12%.?3?There is lack of the toxicity data of Nitrobenzene on aquatic organisms in Shaying River Basin.This study collected toxicity data of nitrobenzene on aquatic organisms,and supplemented experiments of 4 native species in Shaying River Basin.Using the species sensitivity ranking?SSR?method,the calculated FAV was 0.061 mg/L and the final acute-to-chronic ratio?FACR?was 7.453.Finally,the CMC and CCC were 0.030 mg/L and0.008 mg/L,respectively.In addition,the water quality criterion for nitrobenzene were calculated using the species sensitivity distribution?SSD?and the ETX 2.0 software published by the Dutch RIVM,and the results were higher than SSR method.A stratified risk assessment method was used to assess the risk of nitrobenzene of surface water in the Shaying River Basin.The results of the three methods were consistent with each other,that is,the nitrobenzene in the Shaying River has almost no risk to aquatic organisms.