Study On The Occurrence Form And Potential Migration Risk Of Heavy Metals In Soil Around Water Source

The soil environmental quality of drinking water sources directly affects the water quality safety of the water sources and people’s health,and the occurrence and release risks of pollutants,especially heavy metals,in the soil have complex impacts.Shenzhen has a large population of permanent residents and a large demand for drinking water resources.Centralized drinking water sources are the main water supply sources.The water quality of water sources directly affects the living safety and life health of residents.Behaviour is important.In this paper,three different types of soils（red red soil,red soil,and paddy soil）were taken as the research objects in a first-level protected area of a water source in Shenzhen,and three different soil profiles（leaching layer,sedimentary layer and parent material layer）were investigated by field investigation.,referred to as A,B,C layers)Mn,Zn,Cr,Ni,Cu,Pb,As,Tl,Cd content distribution;assessment of the potential hazard.The influence of different environmental factors（pH value,liquid-solid ratio,ambient temperature）on the release capacity of heavy metals in three soils was studied,and the influence rules of different influencing factors on the release of heavy metals were obtained.Finally,physical simulation experiments were used to explore the effects of surface runoff and soil flow under different rainfall intensities（30,90,150 mm/h）and different ground slopes（5°,15°,25°）by taking red soil as an example.Flow characteristics and dissolution and release rules of heavy metals.The research results can provide a scientific reference for the risk management of soil environment around the water source,which is of great significance to ensure the water quality safety of the water source.The main findings are as follows:（1）The order of heavy metal content in the three soils from high to low is Mn>Cr>Pb>Zn>Cu>Ni>As>Tl>Cd,the contents are 88.45～393.71,56.03-98.46,31.82-80.02,56.03 respectively Between-98.46,21.37-52.68,13.08-26.48,3.69-40.02,0.587-0.967,0.502-0.750 mg/kg,in addition to Zn and Pb,red soil contains Mn,Cr,Ni,Cu,As,Tl and Cd in The total amount of layer C is the highest,and layer B is the lowest;in red soil,except for Ni,the total amount of Mn,Zn,Cr,Cu,Pb,As,Tl,and Cd is layer B > layer A > layer C.,Mn,Zn,Cr,Ni,Cu,Pb,As,Tl,and Cd are the highest in the B layer,and the potential risk index value shows that the potential ecological risk index value of Cd in the three soils is between 91.61 and 166.33,which belongs to the strong The ecological hazard level,the comprehensive potential risks of the three soil heavy metals belong to the medium ecological hazard level.（2）Except for Cu and Cr in the three soils,Mn,Zn,Pb,Ni,As,Cd,and Tl are mainly in the residual state,and the weakly acid-soluble,reducible,and The sum of oxidizable states occupies a higher proportion of the total（37-59%,52-77%,40-72%）,and is more prone to release migration.In red red soil and red soil,the potential migration capacity of soil heavy metals decreased with the increase of soil profile depth,and the potential migration capacity of heavy metals in layer B of paddy soil was the largest.Among the 9 heavy metals,the potential hazards are Cd> Tl> Cu> Pb> Cr> Zn>As> Ni> Mn.（3）When the environmental conditions（pH value,liquid-solid ratio,ambient temperature）changed,the batch experiments on the release of heavy metals from the three surface soils showed that the red soil had the strongest release ability of heavy metals,and the weakest was the paddy soil.Among the three influencing factors,the liquid-solid ratio has the greatest influence.Taking Cd as an example,when the liquidsolid ratio increased from 5:1 to 80:1,the amount of Cd released in red soil increased by 12.59 times.However,when the pH value decreased from 7.0 to 3.0,the amount of Cd released in red soil increased by only 0.57 times;when the ambient temperature increased from 15℃ to 45℃,the amount of Cd released in red soil increased by 1.34 times.Therefore,rainfall is an important environmental factor affecting the release of soil pollutants.（4）Surface runoff is an important way of pollutant migration.The concentrations of heavy metals in surface runoff fluctuated with time under different rainfall intensities.Taking Cd as an example,under the rain intensity of 30 mm/h,the Cd concentration fluctuated within 120 minutes after runoff,and stabilized at 0.373 μg/L after 160 minutes.The concentration of pollutants in the rain is obviously high.When the rainfall intensity increased to 90mm/h and 150mm/h,the stable time of Cd concentration was advanced,which were 100 min and 90 min,respectively,and the stable concentrations were 0.463μg/L and 0.396μg/L,respectively.Under the three rainfall intensities,the generation time of soil interflow significantly lags behind that of surface runoff,which are 89 min,25 min,and 20 min,respectively,the flow rate is 24.39%,18.65%,27.93%of surface runoff,and the Cd concentration is stable at 0.099,0.036,and 0.077 μg /L,far less than the Cd concentration in surface runoff.When the ground slope is different,the pollutant concentration in the surface runoff is different.The greater the slope,the higher the pollutant concentration.Taking Cd as an example,the concentrations were stable at 0.293 μg/L（5°）,0.373 μg/L（15°）and 0.422 μg/L（25°）respectively after longterm rainfall.Under different slopes,the Cd concentration in the soil midflow first increased rapidly and then decreased slowly,and the concentration was much lower than that in the surface runoff.When the slope was 5°,the average Cd concentration in the soil midflow only reached 22.09% of the surface runoff.（5）Using the exponential decay model,the correlation between the release of heavy metals in surface runoff and rainfall was identified,and the correlation model between the release concentration of heavy metals Cv and the rainfall V was established;the release of heavy metals and the weak acid soluble state were comprehensively considered.According to the proportional relationship between the contents,the regression equation was modified,and the correlation between the total amount of heavy metals released Wv,the rainfall V and the weak acid soluble content F1 was obtained,and the release and migration of heavy metals in the red soil surface under different rainfall conditions were proposed.The risk investigation method and evaluation model provide a theoretical reference for the potential migration risk assessment of soil heavy metals around the water source.