| The rapid economic development,population growth,urban expansion and the change of social form have greatly changed the natural environment of our survival,and increased the pollution to the ecological environment.Among them,heavy metal pollution has been widely concerned because of its latent,persistent,irreversible and difficult to repair and so on.Human factors have been considered to be the main source of heavy metal pollution in soil and dust,but the specific impact mechanism of human activities on soil and dust and other environmental factors of heavy metal pollution remains to be studied.To understand the mechanism of the influence of human activities in soil and dust accumulation of heavy metals,this paper takes the urban area of Hangzhou,the peri-urban area of Hangzhou and the densely populated rural area of Hangzhou Bay as an example,to study the characteristics of soil heavy metal pollution in urban,peri-urban and densely populated rural areas respectively;The temporal variation characteristics of soil heavy metals in the process of land use were discussed;The pollution characteristics of heavy metals in the urban dust and the relationship with the pollution characteristics of heavy metals in the urban soil in the area were analyzed.At the same time,the effect mechanism of agricultural activity on soil heavy metal environmental pollution behavior was analyzed with the application of P fertilizer as an example;And through the analysis of pollution sources,pollution characteristics and pollution intensity of the three regions,the effects of different intensity of human activities on soil heavy metal pollution were discussed.In this paper,the mechanism of heavy metal accumulation in soil and dust has been deeply analyzed,which has theoretical and practical significance to guide the control of regional environmental pollution.The main conclusions of the study are as follows:1.The characteristics and ecological risk of heavy metal pollution in soils of the urban,peri-urban and the densely populated rural area.In the urban area of Hangzhou,the peri-urban area of Hangzhou and the densely populated rural area of Hangzhou Bay,50,87,66 soil samples were collected through scientific sampling points,respectively.The basic physical and chemical properties of soil and the total amount of heavy metals(Pb,Cd,Cu,Zn,Cr)were analyzed.Under the influence of human activities,Pb,Cd,Zn and Cu in urban,peri-urban and rural areas have different levels of enrichment and human disturbance,but the Cr concentration and human disturbance is not obvious.Although the degree of heavy metal accumulation in different regions is different,but the risk of environmental safety and human health is in a relatively safe area.Need to pay special attention to the the Cd,Pb pollution near the industrial base and Cu,Zn pollution on economic crop planting base.Although the concentration of heavy metals in urban soils is high,it has not yet produced a carcinogenic risk to humans(CR=8.59E-07).Soil Cd,Cu,Zn does not produce non-carcinogenic risk,soil Pb and Cr of some areas have produced non-carcinogenic risk on human body.2.The impacts of different human intensity on soil heavy metal pollutionThe characteristics of heavy metal accumulation in the urban,peri-urban and rural area were analyzed and compared with the methods of classical statistics,geostatistics,GIS and so on.The results show that,from the urban,peri-urban,to the densely populated rural areas,the concentration of heavy metals in soil and the degree of variation in soil are decreasing with the decreasing intensity of human being.The soil Pb,Cd was significantly affected by human strength;the Cu and Zn was significantly affected by human strength to a certain extent,but more affected by agricultural production;the concentration of Cr is not affected by the intensity of human,but there is a certain relationship with industrial production.The concentration of heavy metals in urban soils is mainly influenced by land use types,administrative divisions and other factors.The concentration of heavy metals in peri-urban agricultural soils is affected by the distance from the urban areas,the location of pollution sources,and other factors.The atmospheric deposition,sewage irrigation,natural sources,agricultural materials are main sources.The concentration of heavy metals in rural soil is related to land use time,regional economic development level and so on.3.Changes of soil heavy metal concentration in the process of land useThe temporal variation of soil heavy metal accumulation in 1000 years was explored by the method of space instead of time,and the cause of soil pollution in this area was analyzed.The annual accumulation rate of heavy metals in soil has been accelerated with the development of regional urbanization and social economy,with obvious turning at 1952 and 1995.The added value concentration of heavy metals in soil in the last 50 years is more than or equal to the sum of the value added in 1000 before 1952.After 1995,soil heavy metal accumulation rate has reached the highest level in history.4.Impacts of excessive application of phosphate fertilizer on soil heavy metals.The effect of excessive application of P fertilizer on the mobility of heavy metals in soil was evaluated under the experimental conditions.By observing the changes of pH,EC,DOC and other parameters,the main mechanism of phosphorus application on soil heavy metal mobility was explored.Excess phosphorus can increase the vertical migration of Cu,Cd,Zn and other heavy metal elements in soil,and the key role of DOC in Cu,Cd and Zn migration was confirmed.With the increase of Cu,Cd and Zn concentrations in the soil leachate,the formation of the Metal-DOM complex was closely related with the high level of phosphorus treatment.The decrease of Pb concentration in soil leaching solution may be caused by the formation of insoluble lead phosphate.5.Characteristics of heavy metal pollution in urban dustFive sampling points are collected as outdoor dust samples in the industrial area,commercial service area,residential area,scenic spots and peri-urban agricultural settlements,respectively.Indoor dust samples were collected from the main living areas in the residential buildings near each outdoor dust samples.Indoor and outdoor dust Pb,Cd,Cu,Zn are more obvious enriched and human disturbed,Cr enrichment and disturbance is not obvious.The Cu in indoor dust are mainly from the metal products,Cd are from coal,heating and so on.The Pb in outdoor dust is mainly influenced by the industry and traffic emission.Pb accumulation in urban environment is not mainly from the legacy of history,but still continue to produce new Pb emissions.The carcinogenic risk of heavy metals in indoor dust are 2.69E-06,and the outdoor dust are 6.91 E-07.The ratio of Pb,Cu,Cd and Zn in the sediment phase was 99.07%,95.65%,98.26,98.89%,respectively.When the heavy metal in dust formed along with the rainfall runoff migration,mostly accumulated after short distance around the city water sediments,only a small part can be dissolved or suspended with a long-distance migration.But when the dust is inhaled by the body,there is a high proportion(>12%)of heavy metals can be dissolved in hydrochloric acid environment,resulting in harm to human health.In the same region environment and human impact intensity,urban dust and urban soil pollution elements are basically the same,all with Pb,Cd,Cu,Zn pollution,Cr pollution is not obvious.The distribution of Cu,Cd,Zn and Pb in soil and dust is generally expressed as follows:Industrial Zone,commercial service area,scenic area,residential area,peri-urban.Cr concentration is the highest in the industrial area.The concentrations of Cu,Cd and Zn are:indoor dust>outdoor dust>soil.Cr concentration are:soil>outdoor dust>indoor dust.Pb concentration are:outdoor dust>soil>indoor dust.The content of heavy metals in urban dust was higher than that in soil,and the ecological risk and health risk were higher than that of soil.The enrichment coefficient and vailability of heavy metals in urban soil and urban surface dust increased gradually with the decrease of particle size. |
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