Occurrence,Migration And Transformation Pattern Of Arsenic In Groundwater And Health Risk Evaluation In Zhouzhi And Surrounding Area,China

Arsenic is a metalloid element that exists widely in nature and is also a highly toxic element,known as arsenic trioxide.Long-term consumption of arsenic-contaminated water can lead to chronic arsenic poisoning and symptoms such as anemia,hypertension,diabetes,non-sunken edema of the hands and feet,conjunctival congestion,etc.Serious arsenic poisoning can even lead to skin cancer and lung cancer.The survey showed that the rate of arsenic exceedance in groundwater in Zhouzhi and surrounding areas in Shaanxi is high,which may pose a potential health hazard to humans.Therefore,in this paper,through field investigation and sample collection and testing,combined with indoor experiments and simulation calculations,we reveal the regional groundwater arsenic fugacity,migration and transformation patterns,and evaluate its potential health risk status to human beings.This will not only help to improve our understanding of the formation mechanism and migration transformation pattern of high arsenic groundwater in Zhouzhi and surrounding areas,but also provide a scientific basis for regional groundwater environmental management and drinking water safety.The main insights obtained from the paper are as follows:（1）Based on the analysis of groundwater chemistry characteristics in Zhouzhi and surrounding areas,the mechanism of arsenic fugacity in groundwater was revealed.The high arsenic groundwater chemistry is mainly derived from carbonate weathering and silicate weathering processes,while carbonate weathering has a greater influence on groundwater chemistry in the study area than silicate weathering.The alkaline reducing environment is favorable for arsenic enrichment in groundwater,and reductive dissolution of Fe/Mn oxides and arsenic desorption are the main causes of arsenic enrichment in groundwater.The sulfide formed by desulfurization reacts with Fe-Mn ions to form precipitates,which can adsorb part of the arsenic in groundwater and lead to the reduction of arsenic content in groundwater.In addition,according to the PHREEQC simulation results,the main form of arsenic in groundwater in most of the study area is the pentavalent form HAs O₄^2-,and the trivalent form H₃As O₃ dominates arsenic in groundwater in some areas.Arsenic mainly exists in the pentavalent form in the alkaline oxidizing environment,while it mainly exists in the trivalent form in the acidic reducing environment.（2）Indoor soil column experiments were conducted to investigate the migration and transformation patterns of arsenic under the influence of different factors.The results showed that the concentration of arsenic and the migration rate of arsenic in the leachate increased significantly under the conditions of organic matter input.Under the conditions of high Fe and Mn input,the arsenic concentration in the leachate was always maintained at a low level,indicating that the addition of Fe and Mn ions significantly increased the adsorption of arsenic in the medium and affected the migration of arsenic;the results of p H gradient leaching experiments showed that the acidic environment was not conducive to the desorption and migration of arsenic,and as the p H increased,the concentration of arsenic in the leachate increased and the desorption and migration of arsenic The results of p H gradient drenching experiments showed that the acidic environment was not conducive to the desorption and migration of arsenic.（3）Arsenic,trivalent arsenic and pentavalent arsenic were used as evaluation indicators to evaluate the health risks for children and adults in Zhouzhi and surrounding areas using a Monte Carlo stochastic model.The results of the stochastic health risk evaluation showed that the probability values of exceeding the carcinogenic risk for children for total arsenic and pentavalent arsenic in groundwater reached 47.32%and 45.95%,respectively,and the 95th percentile probabilities of carcinogenic and non-carcinogenic risks for adults and children for trivalent arsenic far exceeded the relevant thresholds,and the differences were found to be small when comparing the calculation results of the deterministic model.Sensitivity analysis showed that contaminant factor levels were the parameters that had the greatest impact on carcinogenic and non-carcinogenic risks for adults and children,with trivalent arsenic concentrations having the greatest impact on carcinogenic and non-carcinogenic risks for adults and children,and being the hazardous substance to focus on in diving in the study area.