【作者】 喻超；

【导师】 凌其聪；

【作者基本信息】 中国地质大学 ， 地球化学， 2010， 硕士

【摘要】 本研究以典型旅游城市杭州市为例,研究城市环境中Cd元素的环境地球化学特征,选择城市环境中的城市绿地土、街道尘埃和水-底泥样品为研究对象,为城市环境进行一次全面“体检”,分析了城市多介质中Cd的空间分布特征,探讨了介质中Cd背景情况,利用多元统计分析的因子分析法获知介质中元素组合特征和物源性,分析了土尘介质中Cd的化学形态特征,并以苔藓作为环境指示剂研究了地表大气环境中Cd的生物可利用性。最后以杭州市的农业活动为研究对象,研究蔬菜根系土和蔬菜的Cd含量特征和联系。通过如上分析,得出以下几点认识：1.城市各环境介质中Cd的含量特征和背景值研究等表明,杭州市不同区域均出现一定程度的Cd污染超标。城市表层绿地土(0-20cm)Cd的含量：江南城区(0.11mg/kg)<主城区(0.18 mg/kg)<半山区(0.21mg/kg),其中位于主城区的西湖风景区为：0.12mg/kg;街道尘埃：主城区(1.53mg/kg)<江南城区(2.00mg/kg)<半山区(2.11mg/kg),西湖风景区为1.11mg/kg;水样：江南城区(0.0002mg/L)<主城区(0.0003 mg/L)<半山区(0.0020 mg/L),底泥：江南城区(0.37 mg/kg)<主城区(0.65 mg/kg)<半山区(1.15 mg/kg)。城市蔬菜根系土耕作层(0-20cm)：Cd含量的均值表现为江南城区(0.13mg/kg)、主城区(0.19mg/kg)、半山区(0.29mg/kg)依次上升。三个区多种介质Cd含量均大致表现为：江南城区<主城区<半山区。根据国家土壤环境质量二级标准(0.3mg/kg)和地表水环境质量Ⅰ级标准(0.001mg/L)来衡量介质的污染超标情况,江南城区：绿地土和水样介质超标率为0%,底泥超标34.7%。主城区：绿地土浅层和深层超标率12.31%和9.24%,水样超标率1.8%,底泥超标率47.2%。半山区：绿地土浅层和深层超标率13.95%和9.3%,水样超标73%(其中9.5%超Ⅳ类水标准,包括7.1%的超V类水标准,此两类超过了农田灌溉水质标准限值0.005mg/L),底泥超标率50%。街道尘埃的Cd含量全部超过土壤环境质量标准,但Cd含量在江南城区、主城区和半山区依次上升。相比而言,街道尘埃、底泥和半山区的水样污染情况较严重。对于蔬菜根系土,依照国家土壤质量标准值0.30mg/kg为参照依据,江南城区表层和深层土壤超标率均为0%；主城区表层超标率为0%,深层超标率为6.7%；半山区表层超标22.2%,深层超标率为5.6%,且均低于三类土壤标准(1.0mg/kg).研究得出杭州市绿地土Cd元素自然背景值为0.10mg/kg,底泥自然背景为0.14mg/kg,街道尘埃背景值为1.39mg/kg。西湖风景区绿地土Cd含量(0.12mg/kg)与杭州市沉积母质Cd含量(0.12mg/kg)、城市绿地土自然背景值(0.10mg/kg)较为相近,且西湖区街尘Cd含量(1.11mg/kg)与所得街尘背景值(1.39mg/kg)亦接近。这说明绿地土和底泥母质与沉积母质来源一致,西湖风景区可能与原始特征接近,受到人为污染相对最少。街道尘埃中的Cd含量具备高含量可能是一个普遍现象,与世界多个城市的对比发现,杭州市的街尘Cd污染相对尚轻,Cd含量特征可能与城市的发展背景有关。2.由所得自然背景值和沉积母质Cd含量可知,第一环境所产生的Cd元素未超过国家土壤质量标准,不会造成自然污染,因而杭州市的Cd污染主要是由第二环境人为产物释放叠加致超标所致。绿地土和底泥中外来Cd的多少主要直接与所处环境有关,在半山区受人为影响最大,主城区次之,江南城区相对最低。对于街尘而言,由于其超细的粒径特征(<0.75μm),较易通过交通、风力等作用在空气中再悬浮而出现二次迁移,在动力环境相对较低的环境下沉降,形成Cd含量再分配的现象,结果导致街尘Cd含量大致表现为：厂区>居民区≈公园>交通区≈商业区>风景区。因子分析和背景值计算结果表明,杭州市街尘和底泥中Cd元素受到人为干扰较大,绿地土次之,而介质中外来Cd的来源可能与工厂作业和交通相关的活动等有关。3.由街道尘埃、底泥和蔬菜根系土中Cd的化学形态可知,街道尘埃中可活动态(非残渣态(Cd约占88%,底泥中约85%,蔬菜根系土则约为87.5%。这其中弱酸可提取态Cd在底泥中的百分含量最高,占全量约53%,蔬菜根系土为42%,街道尘埃为38%。这表明城市环境介质中Cd的化学活性较强,向食物链转移的潜在危害较大。在半山区的水体-底泥Cd含量关系中也说明半山区的底泥Cd有极高的化学活性。4.苔藓和蔬菜中的Cd含量分析结果表明,环境中Cd已经产生了现实危害性,全区苔藓和蔬菜中均出现不同程度的Cd负荷。苔藓中Cd含量：主城区(1.02mg/kg)>江南城区(0.90mg/kg)>半山区(0.77mg/kg)。其含量与环境特征关系较大：公园社区>交通区≈商业区>居民区>厂区>风景区,反映了近地表空间的大气环境质量,与街尘Cd的分布较为一致,均与周围动力环境等因素有关。相关性分析也表明,厂区苔藓Cd含量较低与厂区街尘弱酸提取态Cd含量较低有关。在不同种蔬菜中叶菜类(0.22mg/kg)>根茎类(0.18mg/kg)>瓜果类(0.17mg/kg),其可能表明瓜果类、根茎类和叶菜类蔬菜吸收土壤Cd的能力依次增强。叶菜类蔬菜Cd含量表现为：江南城区(0.29mg/kg)>半山区(0.22 mg/kg)>主城区(0.17 mg/kg),根据国家食品卫生标准Cd的限值规定,江南城区叶菜类超标77.8%,平均超标1.7倍,最高超标3.5倍。主城区叶菜类超标25%,平均超标1.23倍,最高超标1.3倍。半山区叶菜类超标35.3%,平均超标2.5倍,最高超标4.1倍；根茎类超标55.6%,平均超标2.8倍,最高超标5.5倍；瓜果类超标54.5%,平均超标5.7倍,最高超标12.8倍。这表明杭州市蔬菜均存在一定程度的Cd污染,情况较严峻。对比分析蔬菜中Cd含量与根系土中Cd含量以及根系土中Cd的化学形态分量的相关性均不明显,这说明除了根系土中Cd的化学活性外,植物对土壤中Cd的吸收可能还与植物的基因等因素有关。更多还原

【Abstract】 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)<Downtown (0.18 mg/kg)<Banshan (industrial area) (0.21mg/kg), and the West Lake Scenic area is 0.12mg/kg, which is at the southwest of downtown of Hangzhou. In street dust samples:Downtown (1.53mg/kg)<Jiangnan (2.00mg/kg)<Banshan (2.11mg/kg), West Lake Scenic area is 1.11mg/kg. In water samples:Jiangnan (0.0002mg/L)< Downtown (0.0003 mg/L)<Banshan (0.0020 mg/L). In bottom mud:Jiangnan (0.37 mg/kg)<Downtown (0.65 mg/kg)<Banshan (1.15 mg/kg). In surface layer of vegetable root soil:Jiangnan (0.13mg/kg)< Downtown (0.19mg/kg)< Banshan (0.29mg/kg). The Cd concentration trend in various materials of three areas were generally as: Jiangnan<Downtown<Banshan.According to the national soil environmental quality 2nd level standard value 0.3mg/kg, about 0% urban green land soil samples in Jiangnan city exceed the limit, while Downtown accounts for 12.31% in topsoil (0～5cm) and 9.24% in subsurface soil (15～20) samples, as well as Banshan for 13.95% in topsoil and 9.3% in subsurface soil samples. In the meantime, bottom mud samples in Jiangnan, Downtown and Banshan accounts for 34.7%,47.2% and 50% exceed the limit, respectively. All of the street dust samples exceed the limit. In comparison with environmental quality standards for surface water (1st type limit 0.001mg/L), about 0% water samples in Jiangnan, 1.8% in Downtown, and 73% (including 9.5% exceed typeⅣlimit, in which 7.1% exceed typeⅤlimit. This two type of water exceed the national irrigation water limit value of Cd) in Banshan exceed typeⅠlimit. The data indicates that street dust, bottom mud, and the water in Banshan were serious polluted. Still, according to soil standard value 0.3mg/kg, about 0% surface (0～20cm) and deep (20～40cm) layer of vegetable root soil of Jiangnan exceed the limit, while accounts for 0% surface and 6.7% deep layer in Downtown, and accounts for 22% surface and 22.2% deep layer in Banshan exceed the limit, furthermore, all of the root soil below theⅢlimit (1.0mg/kg).Results suggest that the natural background value of Cd of urban green land soil surface layer (0～20cm) is 0.10mg/kg, the bottom mud is 0.14mg/kg, and the street dust is 1.39mg/kg. The mean Cd concentration of urban green soil surface layer in West Lake Scenic is 0.12mg/kg, which is close to sedimentary parent material (0.12mg/kg) and the suggested background value of urban green land soil surface layer. Moreover, the mean Cd content of street dust (1.11mg/kg) in West Lake Scenic is close to the suggested background value of street dust. These may explain that the parent material of urban green land soil and bottom mud is consistent with sedimentary parent material, and the West Lake Scenic is more likely close to original status, relatively less polluted by human. The elevated Cd content of street dust might be a common phenomenon, however, the Cd content of street dust in Hangzhou is much less than other developed cities, and the Cd content level might related to development background of the city.2.By the suggested natural background value of Cd and the geochemistry background value of Cd of sedimentary parent material, the Cd released by the first environment of Hangzhou city does not exceed the national soil quality 2nd level standard value 0.3mg/kg, which means the first environment couldn’t cause natural pollution, and the Cd pollution of Hangzhou city comes mainly from the superposition of Cd released by the second environment caused by anthropogenic sources tills to exceed the quality standards. The superposition of Cd to urban green land soil and bottom mud is directly related to anthropogenic sources, which led to Banshan industrial area been affected most seriously, and follows with Downtown of Hangzhou, the Jiangnan city is affetcted relatively lowest. As for street dust samples, due to its fine particle size (<0.75μm), it could be re-suspended by dynamic like wind and vehicles, and be transported again, then deposit in peaceful environment. These process led to Cd.content trend in street dust samples as:factory area>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.更多还原