| Yunnan Province is located in a low-latitude inland region and crosses six major river systems including the Yangtze,Pearl,Red River,Lancang River,Nu River,and Yiluo River.Small watersheds are widely distributed in Yunnan Province,and the mining area is highly overlapped with small watersheds.The regional and watershed heavy metal pollution problems caused by high geological background and mining are prominent in some areas of Yunnan,which has become an important problem that troubles the management of soil environment and improvement of soil environmental quality in Yunnan.To address the above challenges,it is urgent to carry out risk management and control work for non-ferrous metal mining and selection in small watersheds,establish methods for analyzing the sources and contributions of heavy metal risk management and control in small watersheds,establish a conceptual model for small watershed risk management,and carry out regional risk assessment,providing technical support for soil pollution prevention and control in Yunnan Province.The following key scientific issues need to be addressed to achieve the above goals: distinguishing the contributions of human activities,such as mining,smelting and so on,and geological high background evels of heavy metals to human health,establishing a population health risk assessment plan for heavy metal pollution exposure scenarios in mining small watersheds and improving the basic data and effective survey methods for dietary exposure assessment of regional populations.Based on the above,this study selected the Mouding copper mine and its related Haojiahe small watershed located in Chuxiong City,Yunnan Province as a typical pollution exposure scenario.The pollution surveys on various environmental media were conducted,and the heavy metal pollution characteristics of typical mining areas and small watersheds were explored around typical pollution areas and main exposure scenarios of populations.The evaluation model for heavy metal intake among populations in small watershed polluted by mining areas was enriched by combining the investigation of residents’ dietary types and dietary intake.The typical health characteristics of residents were identified and the possible factors affecting their health were analyzed.The health risk assessment framework for small watershed polluted by mining areas was constructed,and the risk management strategies to reduce potential health hazards were proposed.The research results mainly include the following points:(1)It was found that by measuring the concentrations of heavy metals in different media:(1)The types of locally exceeding foods were limited and not major dietary items,such as konjac,red pears,and persimmons,generally indicating a relatively safe level.However,the elevated levels of Hg in red chili peppers and Cd in chicken,which are relatively significant foods locally,should be given some attention.The dietary specimens collected for this investigation are primarily local,and the locally raised chickens mainly roam freely consuming local crops and being exposed to the local soil environment,which might indicate the presence of certain Hg and Cd contamination in the area.(2)The concentrations of the six heavy metals in the local drinking water samples were far below the national standards,indicating the safety of local drinking water.Given the current lifestyle of residents,drinking water is not a significant pathway for the intake of the six heavy metals for residents according to the current lifestyle.(3)The concentrations of heavy metals in farmland soil were relatively higher in the middle and upper reaches as well as near the mining areas,while the heavy metal concentrations in the downstream watershed were relatively lower,which was consistent with the primary sources of pollution in the area.(4)The maximum mass load of heavy metal elements in road dust was mainly concentrated in the particle size range <0.075 mm,particularly in the Xinqiao town.Particles of road dust in the <0.075 mm size range are more prone to resuspension in the air and inhalation by humans,indicating a potentially higher heavy metal exposure risk to the surrounding population.(5)The emission of heavy metals from fuel was influenced not only by their concentration but also by factors such as stoves and residents’ operations.Heavy metals tended to distribute in ultrafine particles,which had potential health hazards,especially as the concentrations of heavy metals exposed to residents during cooking were higher than those reported in outdoor environments.(2)By comparing the concentration of heavy metals in various media between the study area and other regions,it was found that:(1)The concentrations of heavy metals in the diet of Haojia River were significantly higher than those in other regions,especially for Hg in vegetables,Cd in meat and eggs.(2)The concentrations of heavy metals in farmland soil in the Haojiahe watershed were much higher than thoset in small watershed farmland soil in other regions,which were several to a hundred times higher than those in small watershed farmland soil in other regions.(3)The concentrations of heavy metals in road dust in Xinqiao Town were higher than those in other regions both domestically and internationally,and can even reach tens of times.The smelting of non-ferrous metals and high background levels in the Haojiahe watershed may be the main reasons for the high concentration of the above media after analysis.(3)The multi medium risk assessment models were been developed based on multivariate random processes,mainly including surface water quality module,soil quality module,and road dust exposure module.Based on the measured concentration data of this study,the statistical correlation of pollutant concentration distribution between different media was modeled for estimation of pollutant distribution in different media,and the performance of the multi media models were evaluated by testing the fit goodness of the models.Overall,the relevant models can better reflect the typical distribution characteristics of spatial pollutants.Based on the multi medium migration flux of heavy metals obtained from observational data and surveys or simulations,the heavy metal pollution migration model for farmland soil in the Haojiahe watershed was constructed.The contribution of farmland irrigation and slope soil loss input were two orders of magnitude higher than those of dust and manure input,and they were the main sources of heavy metal input in farmland soil.In addition,the overall output effect of heavy metals in rice fields was better than that in corn fields,suggesting the better improvement of heavy metal pollution.The predicted values of this flux model were not significantly different from the actual values,and can accurately predict the migration of heavy metals in various media in the Haojiahe watershed.(4)Results of hazard quotient(HQ)calculations indicated that As,Cd,Pb,and Hg may pose certain health risks to local residents,with the proportion of HQ > 1 for these four elements ranging from 88.4% to 92.8%,21.9% to 37.4%,20.1% to 49.2%,and 1.0% to 11.8% across different age groups,respectively.The risks were relatively higher for children and the elderly.The As exposure mainly came from cereals;Cd came from cereals,vegetables,and animal meats;Pb came from cereals,animal meats,vegetables,potatoes,and eggs.Therefore,reducing As,Cd,and Pb pollution in cereals and vegetables was significantly important for controlling heavy metal intake in the Haojia River watershed population.The overall HQ of daily average metal intake by residents in the Haojiahe region through drinking water,dermal contact with road dust,and inhalation was generally extremely low,and the percentage of HQ values greater than 1 was close to zero.There was no non-carcinogenic risk for the Haojia River basin population through hand-to-mouth contact with road dust.However,for some individuals,HQ values for As and Pb were greater than 1,indicating a low level of non-carcinogenic risk that should be noted.(5)Epidemiological investigations of the basin’s population revealed that the age distribution was primarily skewed towards the elderly,with a median age(25th-75 th percentile)of 57(48-67)years.Approximately 75% of the local population suffered from different types of chronic diseases,which was related to the predominance of elderly residents.Active smoking was a major risk factor for several chronic diseases,especially hypertension.Poor sleep quality was associated with various diseases,including hypertension,diabetes,heart disease risk,and fever frequency,indicating that attention should be paid to the sleep issues among the elderly.Additionally,attention should be paid to mood depression in the local population,as about 4% of the population frequently experiences mood depression.This was associated with anxiety caused by increased income among the surrounding population and increased frequency of staying up late.Analysis revealed that smoking,moderate alcohol consumption,and increased physical exercise can effectively reduce the frequency of mood depression.Overall,the incidence rates of typical chronic diseases,as well as blood pressure,heart rate,and other indicators in the Haojia River basin population,were relatively normal compared to the general population,lacking typical features of endemic diseases.Based on the above results,this study suggested as follows:(1)The primary source of heavy metal intake for residents in the Haojia River basin was through dietary pathways.The exposure risks of As,Cd,and Pb deserved further attention,and it was recommended to conduct exposure interventions focusing on cereal and vegetable consumption.Exposure levels through straw burning,inhalation of road dust,and local drinking water pathways can be considered negligible compared to dietary exposure.(2)The health status of residents in the Haojia River basin was not significantly different from that of the general population domestically and internationally.The heavy metal pollution in the mining area did not led to noticeable occurrences of endemic diseases.(3)The integrated conceptual model for environmental risk assessment was established based on pathways of human-related heavy metal exposure,which can identify the main exposure pathways and elements of concern,laying demonstrative significance for assessing health risks in small watershed populations. |
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