Environmental Ecological Risk Assessment Of Cadmium In River Sediments Based On Tessier Method

Ecological risk assessment of heavy metals in river sediments is very important for maintaining river ecological safety.This paper takes the heavy metal cadmium in river sediments as the research object.Study ecological risk assessment methods and applications,witch base on the physical state.Through experiments,we determined the parameters required for risk assessment,constructed a risk evaluation model,differentiated risk levels,and use the method to evaluate the risk of sediments in Qingyi River Basin.The research results have enriched river sediment ecological risk assessment methods,and have certain theoretical significance and application value.The main research results are as follows:?1?We got the basic data needed to build the main parameters of the model,through experiments on the interaction of Cd between overlying water and sediments.Through the adsorption study under the condition of p H=4?8,it was found that with the increase of p H,the Cd content in the sediment gradually increased.As the hardness increases,Cd in the deposit decreases.However,the increase in the amount of Cd dissolution caused by the increase in hardness does not increase the risk.?2?Through experiments,it is determined that the applicable environmental range of the model is p H=6?8.The adsorption and desorption processes of different forms of heavy metals are different,and they are expressed by adsorption curves.Model construction is divided into two situations:p H=6 and p H=7?8.Through curve fitting,find out the content of Cd in the sediment when the overlying water reaches the standard of aquatic chronic toxicity water quality,and define it as the protective concentrationC₀ⁱ of Cd in the sediment.Under the condition of p H=7?8,the protective concentrationsC₀¹?C₀⁴are:0.22mg/kg,0.15mg/kg,0.04mg/kg,0.13mg/kg;The adsorption equilibrium constantsK_p¹?K_p⁴are:596.28,412.58,are:0.13mg/kg,0.09mg/kg,0.05mg/kg,The adsorption equilibrium constants K_p¹?K_p³are:343.64,239.23,143.68.?3?Drawing on the results of water quality benchmark research,the risk assessment grades of sediment Cd were classified from the perspective of protecting aquatic organisms.The risk level is divided into four grades,namely:safety?Protect more than 95%of aquatic organisms?;potential risks?protect 70-95%of aquatic organisms?;obvious risks?protection of 50-70%of aquatic organisms?and serious risk?over 50%of aquatic organisms are subject to sediment pollution stress?.The corresponding risk index R_snodes are 1,10.8,34 respectively.?4?Through the investigation of Cd in watershed sediments,the average content of Cd in watershed sediments is 0.192mg/kg,which is about 3 times of the background value of environmental soil in Henan Province,and the Cd content in all sediments exceeds this value.Based on the risk assessment method,the risk assessment of the Qingyi River Basin showed that only five of the 29 points were at the level of potential risk,and the sediments in the basin as a whole were in a safe state.Through the risk assessment,the entire watershed will not cause ecological accidents caused by the release of Cd in sediment.However,the analysis found that some non-residual Cd was introduced at some points in the watershed.This pollution has the characteristics of both point and area sources.