Environmental Geochemistry Of Cadmium In Typical Tourist City

In this study, Hangzhou city was took as a case study of typical tourist city for understand the environment geochemistry of Cd. Environmental materials of urban green land soil, street dust, water and bottom mud samples were collected for a comprehensive environmental health check of Cd in the city. Cd spatial distribution and background of materials were analyzed to check the current status of contamination, factor analysis method were applied to understand the association of elements as well as its sources, chemical partitioning analysis of Cd in soil, dust and mud was conducted to investigate its chemical activity and potential harm, in the meanwhile, bioindicator moss was chose to study the bioavailability of Cd in airborne particulate. And then, vegetable cultivation in Hangzhou was studied including Cd concentration in root soil and vegetables, chemical partitioning of Cd in root soil and its connection with Cd in vegetables. The above analysis comes to following understanding:1.The concentration of Cd and its background in various environmental materials indicates that some parts of Hangzhou loaded with Cd exceeded the environmental quality standard value, which suggests the Cd contamination in environment. The Cd content trend in urban surface layer (0～20cm) of green land soil samples:Jiangnan City (suburb area) (0.11mg/kg)residential area≈park> traffic area≈commercial area> scenic area. The factor analysis and calculation of background value reveals that urban green land soil, street dust, and bottom mud samples were loaded with anthropogenic Cd, and the sources may be attributed to factory, traffic and its relevant activities.3.The chemical partitioning analysis reveals a high chemical mobility of Cd in street dust, bottom mud and vegetable root soil samples.88% street dust total Cd content were bound in non-residue phases, while 85% for bottom mud and 87.5% for vegetable root soil, in which highest mobile phase Cd (acetic acid extractable phase) percentage were highest, and bottom mud, root soil and street dust accounts for 53%,42% and 38% respectively. It reveals that high mobility of Cd in environment of Hangzhou, and might pose a high risk potential to human. The relationship of Cd content between water and bottom mud samples also shows that Cd of water and bottom mud in Banshan have a high chemical mobile characteristic.4. The Cd concentration of moss and vegetables reveals that the pollution has resulted in real bioavailability, the samples in Banshan, Downtown and Jiangnan area were loaded Cd. For moss samples, Downtown (1.02mg/kg)> Jiangnan (0.90mg/kg)> Banshan (0.77mg/kg). The content level is related to environment characteristic:park>traffic area≈commercial area> residential area> factory area> scenic area, reflecting the near-surface atmospheric environmental quality, and this distribution pattern is consistent with street dust samples. The correlation analysis also explained that one of the reasons that the lower Cd content of moss in factory area may be attributed to the lower accounts of acetic acid extractable Cd of street dust in factory area.In different types of vegetables, Cd content trend as:Leaf vegetables (0.22mg/kg)> Rootstalk vegetables (0.18mg/kg)> Fruit vegetables (0.17mg/kg). It might indicated that the absorptive capacity of Cd of vegetables follows the same trend. The Cd content trend of leaf vegetables, Jiangnan (0.29mg/kg)> Banshan (0.22mg/kg)> Downtown (0.17mg/kg). According to national food hygiene limits for Cd,77.8% leaf vegetable samples in Jiangnan exceed the limit (average 1.7 times of the limit, and the maximum to 3.5 times of the limit). The leaf vegetable in Downtown accounts for 25%(average 1.23 times, and maximum to 1.3 times). In Banshan area, the leaf vegetable accounts for 35.3%(average 2.5 times, and maximum to 5.5 times), the rootstalk vegetables accounts for 55.6%(average 2.8 times, and maximum to 5.5 times), and the fruit vegetables accounts for 54.4%(average 5.7 times, and maximum to 12.8 times). These suggest that vegetables in Hangzhou are serious polluted with Cd element. The correlation analysis among Cd content of leaf vegetables, total Cd content of root soil and Cd chemical partitioning content of root soil were not significantly correlated, indicating that except for Cd chemical mobility in soil, the gene of plant could also be one of the reasons to affect the intake of Cd in plant-soil system.