Geochemical Baselines Study And Pollution Assessment Of Main Toxic Heavy Metals Of Soil In Daqing City

City is important residential environment for human, but as the acceleration of industrialization process, urban environment has become more and more deteriorated, especially the soil heavy metal pollution. As, Hg, Cd, Pb of the heavy metal have strong toxicity, which tend to be uptaken by oronasals and skin exposure contact, thus they are of great harm to human beings and urban environment. So it is useful to develop pollution assessment of toxic heavy metal of soil and parse pollution souce.An environmental geochemical baseline provides comparison and discrimination of disturbance standard of man-made or nature-made, which is the deep understanding of the first environment (natural environment) and the second environment (disturbed natural environment) by human. An geochemical baseline exploes present environmental states and supplies comparison standards of future environmental disturbance by human or nature. So study on geochemical baseline in city has important theoretical significance.Daqing is both an important petroleum base and a new resource city.Resource-development economical pattern results in soil quality problem that restricts Daqing's society and economic development. Studying on geochemical baseline, we carry out pollution assessment of main toxic heavy metals of soil in Daqing city, which has great significance to promote Daqing's sustainable developmentParticipating in advisor's research project"Urban eco-environment geochemistry assessment in Harbin, Daqing, Qiqihar city", the paper choose main toxic heavy metals—As, Hg, Cd and Pb of soil in Daqing city for study object, use technology of Arc GIS, SPSS and Google Earth, apply theory of urban environmental geochemistry, pollution assessment of heavy metal in soil and heavy metal health risk assessment, then carry out studies about following aspects:Firstly, we determine the geochemical baselines of As, Hg, Cd and Pb of soil in Daqing city based on relative accumulative frequency, which are all in the range of background value of these heavy metals in Son-nen Plain. By statistical analysis for toxic heavy metal content characteristics using SPSS, we conclude: the variation ranges of Hg, Cd and Pb are great, which of As is little. Content difference for Pb in sampling points is great, then As, which are little for Hg and Cd. There have been some anthropogenic input source effects on As, Hg, Cd and Pb. The statistical characteristics indicate that the length and strength of human activity history are also important reasons that affect accumulation degree of urban soil heavy metal.Through Kriging interpolation and contour funtions in Arc GIS, we carry out spatial distribution analyse of main toxic heavy metals of soil in Daqing city, and obtain basic trend of superficial value and spatial distribution law: Contents of As, Hg, Cd and Pb in Daqing's surface soil decline from the city center (high concentration) to surroundings. The content distribution of As in Daqing's surface soil is continuous, and the concentration variation tendency is consistent with dominant wind direction—west wind. The content distribution of Hg is discontinuous and like a isolated island, high concentration of which locates near Binzhou railway and Rangtong railway. The content distribution of Cd increase from the west to east, which is consistent with dominant wind direction, but it has a high concentration island in the center of Ranghulu. The content distribution of Pb is basically continuous, in the juncture of Binzhou railway and Rangtong railway, there is a high concentration anomaly area. The spatial concentration analyse results are consistent with statistical characteristics.Secondly, determining geo-accumulation index according to geochemical baseline, fixing the pollution states by 5 degrades using A classification method, it shows that Daqing's soil contaminated by As, Hg, Cd and Pb moderately and more moderately reach to 74.4%, 31.6%, 72.5% and 48.2%, the order of soil pollution degree of heavy metal is As>Cd>Pb>Hg. The pollution degrades of As, Hg, Cd and Pb are dominated by first grade and second grade, which belong to nonpollution to slight pollution and moderate pollution. The pollution degrades of As and Pb are few the third degrade, which belong to moderate to strong pollution. The pollution degrades of Hg and Cd are relatively severe, in some sampling points the degrades are 3 and 4, which belong to moderate to strong pollution and strong pollution. By calculating from Contamination Degree method, we get that the integrated area isn't polluted. The pollution state of heavy contaninated points by As, Hg, Cd and Pb obtained from these two methods approximately same. For the area whose heavy metal's background value is low in soil, even if it had heavy metal pollution problem, we should still regard it as"nonpollution"when we evaluate it according to critical value in soil environmental quality standard. So it has more pertinence to evaluate heavy metal pollution in soil through geochemical baseline than through standard.Then, based on spatial analyse of As, Hg, Cd and Pb pollution assessment results by Arc GIS, studying the 4 elements'toxicity and migration and transformation law, through correlation analysis between As, Hg, Cd, Pb and other metal elements, non-metal elements, oxides, combined with soil physical and chemical properties'effects on As, Hg, Cd and Pb pollution, industrial characteristics, I analyse reasons of the main toxic heavy metal pollution of soil in Daqing in details. The results show that reasons of the main toxic heavy metal pollution of soil in Daqing include natural reasons, traffic pollution, industry pollution and domestic pollution. The natural reasons are that organin matters have strong adsorption ability for As, Hg, Cd, Pb and As, Hg, Cd, Pb enrich relatively in alkaline soil whose pH is from 8.78 to 9.5. Traffic pollution comes from railway and highway transportion that can produce exhaust and dusts from tire friction. Industry pollution comes from oil production and petroleum chemical industry. Domestic pollution comes from domestic coal combustion, municipal solid wastes and wastewater. Sampling points contaminated by As, Hg, Cd and Pb locate along both sides of Rangtong railway, Binzhou railway, the junction of them, both sides of 301 national highway and urban traffic artery, also there are some degree of pollution around bogs, chemistrial industry area, oil production area, business district in the centre of city, residential area and farming area.Finally, confirming the toxic heavy metals in soil of Daqing to be uptaken by oronasals and skin exposure contact, I calcute the chronic taken-ups per day, make prediction and precaution of carcinogenesis risk of As and Cd and non-corcinogenesis risk of Hg an Pb. As pollution of soil in Daqing can result in increase of at least 9 cancer patients per million persons, we should take preventions. Cd has no carcinogenesis risk, so it won't do harms to local people's health. Hg and Pb won't have obvious non-corcinogenesis health effect on local people.Study on geochemical baselines of the main toxic heavy metals of soil in Daqing city, to apply it on pollution assessment, to anslyze pollution reasons synthetically and to carry out health risk assessment, this systematic research process and results provide scientific basis for coordinating the relationship of Daqing city's development and environment protect, also for putting forward countermeasures of soil heavy metal pollution in Daqing.