论文部分内容阅读
Abstract Cadmium （Cd） is a strong carcinogenic heavy metal element. Because of its physical， chemical and toxicological characteristics， Cd environmental geochemical research has been concerned， and Cd detection technology is becoming more and more perfect. Cd isotope is one of the hotspots of non-traditional isotope research in recent years. One-way fractionation takes place in its evolution process， which makes the region or process significantly different and contains the information of its evolution environment and process， and Cd isotope tracer technique has been successfully applied to the study of the genesis of lead-zinc deposits， lunar soil and meteorites， marine environment and heavy metal pollution， and has become an important means to the analysis of the sources of Cd pollution. The determination technology of Cd and Cd isotope and its application were reviewed， and the future research points of Cd isotope technology were prospected.
Key words Cadmium； Isotope； Tracer； Application
Cadmium （Cd） is a typical toxic microelement nonessential for human， which is a precedent-controlled cancerogen and food contaminant， as well as one of the global contaminant. Due to its physical chemistry and toxicology specificity， the geochemical research of Cd always attracts much attention. One-way fractionation happens during its evolution process， which makes the region or process significantly different and carry the its evolution or process information， which could be used for tracing the sources of Cd-containing substances. With the development of isotopic analysis technique， especially the wide application of multiple collector inductively coupled plasma source mass spectrometer （MC-ICP-MS）， the determination and research of many non-traditional isotopes has become a hotspot. Cd isotope is one of the research hotspots on non-traditional isotopes rising in recent years， and Cd isotope research has been successfully applied to the fields including genesis of lead-zinc deposits， lunar soil and meteorites， marine environment and heavy metal pollution， and has become an important means for the analysis of the sources of Cd pollution. In this paper， The determination technology of Cd and Cd isotope and its application progress were reviewed， and future research points of Cd isotope were prospected.
Determination technology of Cd
Atomic absorption spectrometry
Atomic absorption spectrometry has the advantages of high analysis speed， good selectivity， high sensitivity， strong resistant to interference， high precision and simple operation. This method is widely applied to various fields， and its results are accurate and reliable. Flame atomic absorption spectrometry
The detection results of conventional atomic absorption spectrometry are closely related to factors including atomization and gas， so trace sample could not be detected. The gradual development combined this technique with other techniques， to improve the sensitivity of this technique， and atomic trapping technique rises in response to the proper time and conditions. Wei et al.[1]determined Cd element by microwave digestion-flame atomic absorption spectrometry， and the results showed that this method has the advantages of complete digestion， low pollution， high efficiency and high accuracy in the analysis of heavy metal elements in soil sample. Wen et al.[2]constructed a new method for the determination of trace Cd in rice sample by cloud point extraction-flame atomic absorption spectrometry. Under optimal conditions， the method had detection limit lower than 1 ng/ml， relative standard deviation of 4.2% and recovery over 91.0%. Zhao et al.[3]tested Cd content in coal， and the results showed that the recoveries of Cd were in the range of 95%-104%. Liu et al.[4]trapped Cd with double-slit quartz tube in their study on surface water， in which the test sensitivity of trace Cd was improved by two grades compared with conventional test， and the detection limit of Cd was also reduced to 2.23×10-5 μg/ml.
Graphite furnace atomic absorption spectrometry
Graphite furnace atomic absorption spectrometry is most widely applied in the determination of Cd content as it has high sensitivity for the determination of elements. Wang et al.[5]determined heavy metal Cd by microwave digestion-graphite furnace atomic absorption spectrometry. The test results showed that the recovery of microwave digestion method was in the range of 90%-108%， the relative standard deviation was lower than 5% for the samples in the same batch， and the determination results satisfied test requirements. Song et al.[6]determined Cd content in wheat flour by graphite furnace atomic absorption spectrometry， and the results showed that the Cd content in wheat flour was 0.44 mg/kg. Zhu et al.[7]determined Cd content in soil by rapid digestion-graphite furnace atomic absorption spectrometry， and the results showed that the lowest detected limit of Cd in soil was 2.0 μg /kg. Zhu et al.[8]performed cloud point extraction to Cd with surfactant Triton X-100 and complexing agent 1-（2-pyridylazo）-2-naphthol （PAN） under pH of 8.5. Under the optimal condition， Cd in micelle phase was determined by graphite furnace atomic absorption spectrometry， and the determination results showed that Cd was enriched by 50 times， the extraction rate reached the maximum value of 98%， the detection limit was 5.9 ng/L， and the relative standard deviation was 2.1%. He et al.[9]improved the determination condition of graphite furnace atomic absorption spectrometry， and constructed a rapid effective method for the detection of Cd in rapeseed and seed cake. The study showed that the detection limit of Cd was 0.243 μg/L， and the determination recovery of sample was over 80%. Atomic fluorescence spectrometry
Atomic fluorescence spectrometry has the characteristics of low detection limit， low interference， high sensitivity， simple spectral line， wide linear range of standard curve， simple instrument structure and simultaneous determination of multiple elements. The method could be combined with other methods for the determination of Cd isotope.
Microwave digestion-atomic fluorescence spectrometry
Microwave digestion-atomic fluorescence spectrometry has the advantages of simple operation， high sensitivity and good reproducibility， and could satisfy the determination requirements for Cd. Zhang et al.[10]determined Cd in marine products by microwave digestion-atomic fluorescence spectrometry. In the three samples， the black carp， freshwater shrimp and river crab samples， 0.15， 0.30 and 0.45 μg of Cd were added， respectively， and the results showed that the average recoveries of the three samples were 84.4%， 90.0% and 88.9%， respectively， and the lowest detection limit of the method was 88 ng/L. Yang et al.[11]constructed a method for the determination of trace Cd in traditional Chinese medicinal materials by microwave digestion-atomic fluorescence spectrometry， and the results showed that the lowest detection concentration of the method was 0.010 4 g/ml， and the recoveries were all over 80%. Gao et al.[12]determined Cd in milk and dairy products by microwave digestion-atomic fluorescence spectrometry， and the results showed that the detection limit of the method was 0.20 μg/L， and the recovery was in the range of 90.0%-93.6%.
Hydride generation-atomic fluorescence spectrometry
Hydride generation-atomic fluorescence spectrometry has the characteristics of simple instrument structure， high sensitivity and low interference. Ai et al.[13]determined Cd in vegetables by hydride generation-atomic fluorescence spectrometry， and the results showed that the detection limit of Cd in vegetables was 0.03 μg/L， and the recovery was in the range of 92%-105%. Chen et al.[14]determined Cd in soil by hydride generation-atomic fluorescence spectrometry， and the results showed that the detection limit of Cd in soil was 0.20 μg/L， and the recovery was over 85%. Jiang et al.[15]determined Cd in tobacco by hydride generation-atomic fluorescence spectrometry， and the results showed that the detection limit of Cd was 0.003 1 μg/L， and the adding standard recovery was 88.7%-99.5%.
Inductively coupled plasma mass spectrometry （ICP-MS） ICP-MS has very high sensitivity and very good precision， and could perform rapid isotope ratio analysis. Therefore， trace elements in various samples could be rapidly accurately determined by isotope dilution method. Chen et al.[16]determined Cd in vegetable soil by ICP-MS and isotope dilution method， and the results showed that the Cd content in standard soil was in the range of 0.091 6-0.098 2 μg/g. Yin[17]determined Cd in food samples by ICP-MS， and the determination results showed that the Cd contents in wheat flour， rice and tea were 0.13， 0.083 and 0.061 mg/kg， respectively.
Determination Technology of Cd Isotope
There are eight Cd isotopes in nature， i.e.， 106Cd， 108Cd， 110Cd， 111Cd， 112Cd， 113Cd， 114Cd and 116Cd， the abundance values of which are 1.25%， 0.89%， 12.8%， 12.8%， 24.1%， 12.2%， 28.7% and 7.49%， respectively. One-way fractionation happens during the evolution process， which makes the region or process significantly different and carries the its evolution or process information， which could characterize specific environment and process "fingerprint". At present， Cd isotope research has been successfully applied to the genesis of leaf and zinc deposits， lunar soil and meteorites， marine environment and heavy metal contamination. The determination of Cd isotope in early period generally adopts TIMS[18-19]， and the tested objects are mainly extraterrestrial samples. However， the separation effect caused by ionization process of the samples often results in distortion of the analysis results， the requirement for sample purity is higher， and the working efficiency is lower[20]. Furthermore， the analysis precision is worse， and the requirement for test precision of Cd isotope in geochemical samples is hard to be satisfied. Generally， Cd isotope composition is mostly determined by multi-collector inductively coupled plasma mass spectrometry （MC-ICPMS）， which is related to very high ionization rate of Cd by plasma （Cd has higher the first ionization energy）[21]. At present， MC-ICPMS is generally applied， mass fractionation correlation is performed on instrument by andard-Sample Bracketing method， and consequently， the analysis precision is significantly improved[22]. However， Cd isotope analysis is susceptible to nuclear isobar， and ionic groups and molecules with the same weight. The interference of nuclear isobar is mainly from Pd （106， 108 and 110）， In （113） and Sn （112， 114 and 116）， while the ionic groups formed from the combination of other elements and 40Ar or 16O also would cause the interference by ionic groups and molecules with the same weight （for instance， 66Zn40Ar interferes 106Cd， 68Zn40Ar interferes 108Cd， 70Zn40Ar and 94Mo16O interfere 110Cd， 96Mo16O interferes 112Cd， and 74Ge40Ar and 98Mo16O interfere 114Cd）. Therefore， before instrumental analysis， samples must be separated and purified， to remove substrate and interference elements to the highest degree， and the sample concentration is controlled in a proper range， to ensure that the instrument collects the optimal signal value[23-24]. Gao et al.[25]constructed the experiment method for analyzing the isotope composition of Cd standard solution by MC-ICPMS， and the results showed that the values of δ114/110CdJMC， δ114/110CdSPEX-1， δ114/110CdBAM 1012 and δ114/110CdMǜnster were 0.55‰， 0.56‰， -0.65‰ and 5.14‰， respectively. Application of Cd Isotope Tracer Technique
Application of Cd isotope tracer technique in the research about the genesis of lead-zinc deposits
Lead-zinc deposits are a kind of important Cd reservoirs on earth， which has very high Cd content[26]， and the Cd content in blende could reach 3% （such as Fule lead-zinc deposit in Yunnan）[27]. Therefore， Cd is an ore-forming element in some lead-zinc deposits， and its isotope may provide the evolution information of ore-forming elements in the formation process of lead-zinc deposits for the research on lead-zinc deposits， and important direct information for the research on the genesis of lead-zinc deposits. Schmitt et al.[28]determined the composition of Cd isotope in sulfide from submarine chimney， the sulfide and solid silicate of Bio9 chimney have similar Cd isotope composition， and it was deemed that the metallogenic material of Bio9 chimney came from the lixiviation of basalt oceanic crust， and Cd isotope fractionation did not exist in this process. Zhou et al.[29]found through the study on Zn isotope in blende of Banbanqiao and Tianqiao lead-zinc deposits in northwest Guizhou that the blende was enriched with light isotope of Zn in early period and with heavy isotope in late period of Zn， and it was deemed that that the fractionation of Zn isotope followed rayleigh fractional model. Zhu et al.[30]studied Cd isotope in Yunnan Fule lead-zinc deposit， and found that from bottom to top of the deposit， the δ114/110Cd value in blende increased regularly， and the fractional model could be explained by rayleigh fractional model， with a fractionation coefficient α equal to 0.999 65. Above studies show that Cd and Zn iostopes might have the same fractionation mechanism in lead-zinc deposits， and suggest that Cd isotope has a great application potential in lead-zinc deposits. Scholars at home and abroad could judge the genesis of lead-zinc deposits applying Cd isotope tracer technique， which has unparalleled superiority in the research about the genesis of lead-zinc deposits.
Application of Cd isotope tracer technique in research about lunar soil and meteorites
Research on chondrite and lunar soil shows that greater Cd isotope fractionation exists， and the fractionation value ranges from -21εCd/amu-1 and +63εCd/amu-1[31-33]. The fractionation of Cd isotope in chondrite might be caused by rayleigh fractionation， original heterogeneity or differentiation of nebula[34]. Schediwy et al.[35]analyzed 9 soil samples from the moon， and found that the mechanism affecting Cd isotope fractionation in soil of the moon might be the collision between ions and particles on the surface of the moon. Wombacher et al.[36]found that during vacuum evaporation of liquid Cd， greater Cd isotope fractionation would happen， and it was deemed that the non-dynamic mass balance in the experiment was not caused by the self-diffusion or mixing of Cd molecules， but more likely to be caused by Cd evaporation into vapor or condensation during melting process； and the determination of mass balance relation could provide effective information for the fractional mechanism of Cd isotope， and this method is more suitable for the research about massive isotope fractionation， such as evaporation， diffusion and bio-utilization. Wombacher et al.[37]reckoned that Cd could produce larger isotope fractionation during evaporation and condensation， which could be used for studying evolution of solar system. Scholars could deduce the variation conditions of lunar soil and meteorites in spatial scale through the fractional mechanism of Cd isotope. Application of Cd isotope tracer technique in research about marine environment
In recent years， the research about Cd isotope in marine environment advanced obviously whether in spatial and time scale or application of marine organism. Emilie et al.[38]marked seawater and food eaten by pacific oyster by stable isotopes 110Cd and 112Cd， respectively， and discussed Cd isotope pathway， and the current method is also suitable for seawater with lower concentration. Shiel et al.[39]studied the distribution in different tissues of the organism （digestive glands， cheek and other parts） in Western Canada and Hawaii， and the results showed that various Cd isotopes could be used to successfully trace the migration of Cd in oyster； and the concentrations and isotope composition of Cd， Zn and Pb in mussels sea clams from the eastern coast of America were determined， and the results showed that Cd isotope and Zn isotope could effectively trace the artificial sources and natural sources of these metals， and could be effectively combined with Pb "fingerprint" technique. Lambelet et al.[40]determined Cd concentration and isotope composition in the water sample from Siberian coast， and the results showed that erosion effect had little effect on Cd isotope fractionation， indicating that the analysis of stable isotope is important to the research about trace elements in biogeochemistry environment， and especially in the research about Cd circulation in environment， Cd isotope could provide important information. Scholars could carry out tracing of biogenic migration way and research about trace elements in biogeochemistry environment using Cd isotope.
Application of Cd isotope tracer technique in research about heavy meal pollution sources
Heavy metal pollution sources of soil
Because Cd isotope does not produce isotope fractionation or very little isotope fractionation， Cd isotope has very good indication function on Cd pollution sources in soil. Cloquet et al.[41]conducted a study of pollution source tracing on soil around an abandoned Pb-Zn smelting plant in northern France， and found that the δ114/110Cd of smelting slag was +0.36， the δ114/110Cd of chimney dust was -0.64%， and the δ114/110Cd of polluted soil was between them but more close to that of chimney dust. It indicated that in the polluted region， there were mainly three kinds of pollution sources （chimney dust， smelting slag and other pollution sources related to agriculture）， and the main pollution source was chimney dust. Wen et al.[42]studied the Cd isotope in the soil of Yunnan Jinding Pb-Zn mine， and found that the δ114/110Cd value of polluted soil was -0.31%-（1+0.15%）， and compared with background soil （with δ114/110Cd of +0.40%）， the soil contained remarkably-enriched light isotope， which was mainly from dust produced during artificial mining process. Zhang[43]attempted to trace soil heavy metal Cd pollution co-caused by different pollution sources around Jinding Town in the ultra-large lead and zinc ore area in Lanping County of Yunnan Province using Cd isotope， and conducted a pilot study on Cd pollution in this area， and rational results were obtained. Scholars could trace heavy metal pollution sources of soil using Cd isotope tracer technique， so as to guide soil management and remediation. Heavy metal pollution sources of sediment
Cd isotope fractionation caused by industrial activity could be detected in environmental pollution， which enables the application of Cd isotope tracer technique in the research about heavy metal pollution sources of sediment[44]. Gao et al.[45]studied Cd isotope in the surface sediment of the Bei River in Zhuhai of China， and the results showed that Cd isotope in sediment close to smelting plants and e-waste dismantling areas suffered from obvious fractionation， and heavy metal pollution sources in river sediment could be well traced using Cd isotope. Shiel et al.[46]determined the isotope composition of Zn， Cd and Pb in the products of various stages of the smelting process in some Zn-Pb smelting plant in Canada， and found that Cd isotope fractionation was mainly from the concentrated smelting process of zinc ore， and the isotope composition in exhaust gas （with δ114/110Cd of -0.52% per thousand） and wastewater （with δ114/110Cd in the range of 0.31%-0.46% per thousand） effectively verified the fractionation of Cd isotope. The research results revealed that Zn and Cd isotope technique could be applied to trace environmental Zn and Cd pollution. It could thus been that Cd isotope could effectively trace the sources of Cd isotope in soil， sediment and smelting process.
Prospect
（1） Most studies on Cd isotope at home and abroad focus on celestial body and marine research fields， while few studies have been done in environmental field. Furthermore， most existing tracer studies are concentrated on metal smelting pollution， and tracer application on other important sources （such as agricultural activity） remains to be supplemented. Foundation database of Cd isotope composition remains to be enriched and broadened. With the deepening of research， Cd isotope composition becomes a new kind of geochemical means， and its application in environmental field also will become more extensive， deeper and more important.
（2） Multivaricate isotope tracer research could make up for the shortcomings of the application of single isotope， such as narrow application range and rough analysis results， so as to make the analysis of pollution sources more accurate and objective. How to better judge special pollution source and its migration and transformation mechanism according to the characteristics of metal elements in environment is one of the direction for multivaricate isotope tracer research in future. References
[1] WEI XL， LEI YD， MA XN， et al. Determination of chromium plumbum cadmium in soil by microwave digestion-AAS method[J]. Journal of Anhui Agricultural Sciences， 2014， 42（11）： 3243-3244， 3247.
[2] WEN SP， XIANG GQ， WANG RL， et al. Determination of trace cadmium in rice samples by cloud point extraction and flame atomic absorption spectrometry[J]. Journal of Henan University of Technology： Natural Science Edition， 2010， 31（2）： 66-70.
[3] ZHAO ZB， ZHAO WX， ZHANG L. Determination of trace cadmium in fly-ash by derivative atomic absorption spectrometry using atom trapping technique[J]. Contributions To Geology and Mineral Resources Research， 2004， 19（B12）： 187-190.
[4] LIU ZM， ZHAO AH. Study on the detection of trace elements Pb and Cd by collection and release atom absorption spectrographic method[J]. Chemical Analysis and Meterage 2001， 10（2）： 16-17.
[5] WANG M， ZHAO CH， ZHANG Q， et al. Determination of heavy metals in soil by microwave digestion-atomic absorption spectrometry[J]. Journal of Anhui Agricultural Sciences， 2013， 41（16） ：7128-7129， 7176.
[6] SONG MY， GUO QL， SUN Y， et al. Evaluation of measurement uncertainty of cadmium in wheat flour by microwave digestion graphite furnace atomic absorption spectrometry[J]. Sichuan Food and Fermentation.， 2016， 52（01）： 96-100.
[7] ZHU WQ， ZHANG XY， WANG H. Determination of cadmium in soil by microwave dissolving-graphite furnace atomic absorption method[J]. Chinese Journal of Health Laboratory Technology， 2017， 27（6）： 789-794.
[8] ZHU XS， ZHU XH， FENG K， et al. Study of trace cadmium in environmental samples by graphite furnace atomic absorption spectrometry after cloud point extraction[J]. Chinese Journal of Analytical Chemistry， 2006， 34（7）： 951-954.
[9] HE XM， WANG M， WANG XD， et al. Determination of lead and cadmium in rapeseed and rapeseed meal with microwave digestion by graphite furnace atomic absorption spectrometry[J]. Spectroscopy and Spectral Analysis， 2007， 27（11）： 2353-2356.
[10] ZHANG MQ， CHEN HP， ZHU YZ， et al. Determination on Cd in aguatic products by microwave digestion-atomic fluorescence spectroscopy[J]. Jiangsu Journal of Agricultural Sciences， 2004， 20（2）： 116-119.
[11] YANG DC， NING DQ， LI WL， et al. Determination of micro cadmium in Chinese herbal medicine material with the microwave digestion and VG-AFS[J]. Chinese Journal of Pharmaceutical Analysis， 2006， 26（01）： 30-34.
[12] GAO W， QI Q， WU NE， et al. Determining cadmium in dairy products by microwave digestion-atomic fluorescence spectrographic methods[J]. China Dairy Industry， 2010， 38（02）： 55-57. [13] AI LH， WANG MH， ZHU XP， et al. Determination of cadmium in vegetables by hydride generation-atomic fluorescence spectrometry[J]. Chinese Journal of Analysis Laboratory， 2007，26（05）： 119-121.
[14] CHEN XJ， HT， SHEN FX. Determination of cadmium in soil by hydride generation-atomic fluorescence spectrometry[J]. Analytical Instrumentation， 2005， （03）： 37-39.
[15] JIANG Q， WANG RH， SUN XL， et al. Study on the determination of cadmium in tobacco by hydride generation-atomic fluorescence spectrometry[J]. Chinese Agricultural Science Bulletin， 2010， 26（13）： 118-121.
[16] CHEN T， HUANG ZY， CHEN L， et al. ICP-MS-isotope dilution method for determination of trace amounts of cadmium in soil of vegetable farm[J]. Physical Testing and Chemical Analysis （chemistry）， 2009， 45 （7）： 761-764.
[17] YIN Z. ICP-MS determination of cadmium in food with microwave assisted sample digestion[J]. Physical Testing and Chemical Analysis Part B： Chemical Analysis， 2013， 49（05）： 597-599.
[18] ROSMAN KJR， DE LAETER JR. The isotopic composition of cadmium in terrestrial minerals[J]. International Journal of Mass Spectrometry and Ion Physics， 1975， 16（4）： 385-394.
[19] SCHEDIWY S， ROSMAN KJR， DE LAETER JR. Isotope fractionation of cadium in lunar material[J]. Earth and Planetary Science Letters， 2006， 243（3）： 326-335.
[20] GAO B. Heavy metals pollution in typical environment samples and preliminary study on Cd and Pb isotopic tracing[D]. Guangzhou： Guangzhou Institute of Geochemistry， Chinese Academy of Sciences， 2008.
[21] REHKMPER M， WOMBACHER F， HORNER TJ， et al. Natureal and anthropogenic Cd isotope variations[M]. Hand Book of Enviromental Isotope Geochemistry. Berlin， Heidelberg： Springer， 2012： 125-154.
[22] CLOQUET C， ROUXEL O， CARIGNAN J， et al. Natural cadmium isotopic variations in eight geological reference materials and anthropogenic samples， measured by MC-ICP-MS [J]. Geostandards and Geoanalytical Research， 2005， 29（1）： 95-106.
[23] LI SZ， ZHU XK， TANG SH， et al. The application of MC-ICP-MS to high-precision measurement of Zn isotope ratios[J]. Acta Petrologica et Mineralogica， 2008， 27（4）： 273-278.
[24] LI J， ZHU XK， TANG SH. The application of double spike in non-traditional stable isotopes-a case study on Mo isotopes[J]. Rock and Mineral Analysis， 2011， 30（2）： 138-143.
[25] GAO H， LIANG XR， LIU Y， et al. Measurement of cadmium isotopic composition of standard solutions by multi-collector inductively coupled plasma mass spectrometry[J]. Rock and Mineral Analysis， 2008， 27（5）： 321-324. [26] SCHWARTZ MO. Cadmiuminzinc deposits： Economic geology of a polluting element [J]. International Geology Review， 2000， 4（5）： 445-469.
[27] SI RJ. Ore deposit geochemistry of the Fule dispersed element-polymetallic deposit， Yunnan Province[D]. Guiyang： Institute of Geochemistry， Chinese Academy of Sciences， 2005.
[28] SCHMITT AD， GALER SJG， ABOUCHAMI W. Mass-dependent cadmium isotopic variations in nature with emphasis on the marine environment[J]. Earth and Planetary Science Letters， 2009， 2007（1）： 262-272.
[29] ZHOU JX， HUANG ZL， ZHOU MF， et al. Zinc， sulfur and lead isotopic variations in carbonate-hosted Pb-Znsulfide deposits， Southwest China [J]. Ore Geology Reviews， 2014， 58： 41-54.
[30] ZHU CW. Isotope geochemistry of dispersed elements Cd and Ge in lead and zinc deposits in Guizhou， Yunnan and Sichuan area and its application[D]. Guiyang： Institute of Geochemistry， Chinese Academy of Sciences， 2014.
[31] ROSMAN KJR， DE LAETER JR. Cadmium mass fractionation in unequilibrated ordinary chondrites[J]. Earth and Planetary Science Letters， 1988， 89： 163-169.
[32] ROSMAN KJR， DE LAETER JR， GORTON MP. Cadmium isotope fractionation in fractions of two H3 chondrites[J]. Earth and Planetary Science Letters， 1980， 48： 166-170.
[33] SANDS DG， ROSMAN KJR， DE LATER JR. A preliminary study of cadmium mass fractionation in lunar soil[J]. Earth and Plnetary Science Letters， 2001， 186： 103-111.
[34] WOMBACHER F， REHKAMPER M， MEZGER K. Determination of the mass-dependence of cadmium isotope fractionation during evaporation[J]. Geochimica et Cosmochimica Acta， 2003， 68：2349-2357.
[35] SCHEDIWY S， ROSMAN KJR， DE LAETER JR. Isotope fractionation of cadmium in lunar material[J]. Earth and Planetary Science Letters， 2006. 243： 326-335.
[36] WOMBACHER F， REHKAMPER M， MEZGER K， et al. Stable isotope compositions of cadmium in geological materials and meteorites determined by multiple-collector ICP MS[J]. Geochimica et Cosmochimica Acta， 2003， 67： 4639-4654.
[37] WOMBACHER F， REHKAMPER M， MEZGER K， et al. Cadmium stable isotope cosmochemistry[J]. Geochimica et Cosmochimica Acta， 2008， 72： 646-667.
[38] EMILIE S， SCHAFER J， BAUDRIMONT M， et al. Tracing cadmium contamination kinetics and pathways in oysters （Crassostrea-gigas） by multiple stable Cd isotope spike experiments[J]. Ecotoxicology and Environmental Safety， 2011， 74： 600-606.
[39] SHIEL AE， WEIS D， ORIANS KJ. Tracing cadmium， zinc and lead sources in bivalves from the coasts of western Canada and the USA using isotopes[J]. Geochimica et Cosmochimica Acta， 2012， 76： 175-190. [40] LAMBELET M， AMPER MR. Isotopic analysis of Cd in the mixing zone of Siberian rivers with the Arctic Ocean-New constraints on marine Cd cycling and the isotope composition of riverine Cd[J]. Earth and Planetary Science Letters， 2013， 361： 64-73.
[41] CLOQUET C， CARIBNAN， LIBOUREL G， et al. Tracing source pollution in soils using cadmium and lead isotopes[J]. Eenviromental Science &Technology， 2006， 40（8）： 2525-2530.
[42] WEN HJ， ZHANG YX， CLOQUET C， et al. Tracing sources of pollution in soils from the Jinding Pb-Zn mining district in China using cadmium and lead isotopes[J]. Applied Ueochemistry， 2015， 52： 147-154.
[43] ZHANG YX. Analytical test method of non-traditional stable isotopes of Mo and Cd and its geological application[D]. Beijing： Graduate University of Chinese Academy of Science， 2010.
[44] YU WH， YU RL， HU GR. Application progress of Pb， Zn and Cd isotopes in research about sources of heavy metal pollution in soil and sediment[J]. Nonferrous Metals， 2012 （4）： 57-62.
[45] GAO B， LIU Y， SUN K， et al. Precise determination of cadmium and lead isotopic compositions in river sediments compositions in river sediments[J]. Analytica Chimica Acta， 2008， 612： 114-120.
[46] SHIEL AE， WEIS D， ORIANS KJ. Evaluation of zinc， cadmium and lead isotopic fractionation during smelting and refining[J]. Science of the Total Environment， 2010， 408： 2357-2368.
Key words Cadmium； Isotope； Tracer； Application
Cadmium （Cd） is a typical toxic microelement nonessential for human， which is a precedent-controlled cancerogen and food contaminant， as well as one of the global contaminant. Due to its physical chemistry and toxicology specificity， the geochemical research of Cd always attracts much attention. One-way fractionation happens during its evolution process， which makes the region or process significantly different and carry the its evolution or process information， which could be used for tracing the sources of Cd-containing substances. With the development of isotopic analysis technique， especially the wide application of multiple collector inductively coupled plasma source mass spectrometer （MC-ICP-MS）， the determination and research of many non-traditional isotopes has become a hotspot. Cd isotope is one of the research hotspots on non-traditional isotopes rising in recent years， and Cd isotope research has been successfully applied to the fields including genesis of lead-zinc deposits， lunar soil and meteorites， marine environment and heavy metal pollution， and has become an important means for the analysis of the sources of Cd pollution. In this paper， The determination technology of Cd and Cd isotope and its application progress were reviewed， and future research points of Cd isotope were prospected.
Determination technology of Cd
Atomic absorption spectrometry
Atomic absorption spectrometry has the advantages of high analysis speed， good selectivity， high sensitivity， strong resistant to interference， high precision and simple operation. This method is widely applied to various fields， and its results are accurate and reliable. Flame atomic absorption spectrometry
The detection results of conventional atomic absorption spectrometry are closely related to factors including atomization and gas， so trace sample could not be detected. The gradual development combined this technique with other techniques， to improve the sensitivity of this technique， and atomic trapping technique rises in response to the proper time and conditions. Wei et al.[1]determined Cd element by microwave digestion-flame atomic absorption spectrometry， and the results showed that this method has the advantages of complete digestion， low pollution， high efficiency and high accuracy in the analysis of heavy metal elements in soil sample. Wen et al.[2]constructed a new method for the determination of trace Cd in rice sample by cloud point extraction-flame atomic absorption spectrometry. Under optimal conditions， the method had detection limit lower than 1 ng/ml， relative standard deviation of 4.2% and recovery over 91.0%. Zhao et al.[3]tested Cd content in coal， and the results showed that the recoveries of Cd were in the range of 95%-104%. Liu et al.[4]trapped Cd with double-slit quartz tube in their study on surface water， in which the test sensitivity of trace Cd was improved by two grades compared with conventional test， and the detection limit of Cd was also reduced to 2.23×10-5 μg/ml.
Graphite furnace atomic absorption spectrometry
Graphite furnace atomic absorption spectrometry is most widely applied in the determination of Cd content as it has high sensitivity for the determination of elements. Wang et al.[5]determined heavy metal Cd by microwave digestion-graphite furnace atomic absorption spectrometry. The test results showed that the recovery of microwave digestion method was in the range of 90%-108%， the relative standard deviation was lower than 5% for the samples in the same batch， and the determination results satisfied test requirements. Song et al.[6]determined Cd content in wheat flour by graphite furnace atomic absorption spectrometry， and the results showed that the Cd content in wheat flour was 0.44 mg/kg. Zhu et al.[7]determined Cd content in soil by rapid digestion-graphite furnace atomic absorption spectrometry， and the results showed that the lowest detected limit of Cd in soil was 2.0 μg /kg. Zhu et al.[8]performed cloud point extraction to Cd with surfactant Triton X-100 and complexing agent 1-（2-pyridylazo）-2-naphthol （PAN） under pH of 8.5. Under the optimal condition， Cd in micelle phase was determined by graphite furnace atomic absorption spectrometry， and the determination results showed that Cd was enriched by 50 times， the extraction rate reached the maximum value of 98%， the detection limit was 5.9 ng/L， and the relative standard deviation was 2.1%. He et al.[9]improved the determination condition of graphite furnace atomic absorption spectrometry， and constructed a rapid effective method for the detection of Cd in rapeseed and seed cake. The study showed that the detection limit of Cd was 0.243 μg/L， and the determination recovery of sample was over 80%. Atomic fluorescence spectrometry
Atomic fluorescence spectrometry has the characteristics of low detection limit， low interference， high sensitivity， simple spectral line， wide linear range of standard curve， simple instrument structure and simultaneous determination of multiple elements. The method could be combined with other methods for the determination of Cd isotope.
Microwave digestion-atomic fluorescence spectrometry
Microwave digestion-atomic fluorescence spectrometry has the advantages of simple operation， high sensitivity and good reproducibility， and could satisfy the determination requirements for Cd. Zhang et al.[10]determined Cd in marine products by microwave digestion-atomic fluorescence spectrometry. In the three samples， the black carp， freshwater shrimp and river crab samples， 0.15， 0.30 and 0.45 μg of Cd were added， respectively， and the results showed that the average recoveries of the three samples were 84.4%， 90.0% and 88.9%， respectively， and the lowest detection limit of the method was 88 ng/L. Yang et al.[11]constructed a method for the determination of trace Cd in traditional Chinese medicinal materials by microwave digestion-atomic fluorescence spectrometry， and the results showed that the lowest detection concentration of the method was 0.010 4 g/ml， and the recoveries were all over 80%. Gao et al.[12]determined Cd in milk and dairy products by microwave digestion-atomic fluorescence spectrometry， and the results showed that the detection limit of the method was 0.20 μg/L， and the recovery was in the range of 90.0%-93.6%.
Hydride generation-atomic fluorescence spectrometry
Hydride generation-atomic fluorescence spectrometry has the characteristics of simple instrument structure， high sensitivity and low interference. Ai et al.[13]determined Cd in vegetables by hydride generation-atomic fluorescence spectrometry， and the results showed that the detection limit of Cd in vegetables was 0.03 μg/L， and the recovery was in the range of 92%-105%. Chen et al.[14]determined Cd in soil by hydride generation-atomic fluorescence spectrometry， and the results showed that the detection limit of Cd in soil was 0.20 μg/L， and the recovery was over 85%. Jiang et al.[15]determined Cd in tobacco by hydride generation-atomic fluorescence spectrometry， and the results showed that the detection limit of Cd was 0.003 1 μg/L， and the adding standard recovery was 88.7%-99.5%.
Inductively coupled plasma mass spectrometry （ICP-MS） ICP-MS has very high sensitivity and very good precision， and could perform rapid isotope ratio analysis. Therefore， trace elements in various samples could be rapidly accurately determined by isotope dilution method. Chen et al.[16]determined Cd in vegetable soil by ICP-MS and isotope dilution method， and the results showed that the Cd content in standard soil was in the range of 0.091 6-0.098 2 μg/g. Yin[17]determined Cd in food samples by ICP-MS， and the determination results showed that the Cd contents in wheat flour， rice and tea were 0.13， 0.083 and 0.061 mg/kg， respectively.
Determination Technology of Cd Isotope
There are eight Cd isotopes in nature， i.e.， 106Cd， 108Cd， 110Cd， 111Cd， 112Cd， 113Cd， 114Cd and 116Cd， the abundance values of which are 1.25%， 0.89%， 12.8%， 12.8%， 24.1%， 12.2%， 28.7% and 7.49%， respectively. One-way fractionation happens during the evolution process， which makes the region or process significantly different and carries the its evolution or process information， which could characterize specific environment and process "fingerprint". At present， Cd isotope research has been successfully applied to the genesis of leaf and zinc deposits， lunar soil and meteorites， marine environment and heavy metal contamination. The determination of Cd isotope in early period generally adopts TIMS[18-19]， and the tested objects are mainly extraterrestrial samples. However， the separation effect caused by ionization process of the samples often results in distortion of the analysis results， the requirement for sample purity is higher， and the working efficiency is lower[20]. Furthermore， the analysis precision is worse， and the requirement for test precision of Cd isotope in geochemical samples is hard to be satisfied. Generally， Cd isotope composition is mostly determined by multi-collector inductively coupled plasma mass spectrometry （MC-ICPMS）， which is related to very high ionization rate of Cd by plasma （Cd has higher the first ionization energy）[21]. At present， MC-ICPMS is generally applied， mass fractionation correlation is performed on instrument by andard-Sample Bracketing method， and consequently， the analysis precision is significantly improved[22]. However， Cd isotope analysis is susceptible to nuclear isobar， and ionic groups and molecules with the same weight. The interference of nuclear isobar is mainly from Pd （106， 108 and 110）， In （113） and Sn （112， 114 and 116）， while the ionic groups formed from the combination of other elements and 40Ar or 16O also would cause the interference by ionic groups and molecules with the same weight （for instance， 66Zn40Ar interferes 106Cd， 68Zn40Ar interferes 108Cd， 70Zn40Ar and 94Mo16O interfere 110Cd， 96Mo16O interferes 112Cd， and 74Ge40Ar and 98Mo16O interfere 114Cd）. Therefore， before instrumental analysis， samples must be separated and purified， to remove substrate and interference elements to the highest degree， and the sample concentration is controlled in a proper range， to ensure that the instrument collects the optimal signal value[23-24]. Gao et al.[25]constructed the experiment method for analyzing the isotope composition of Cd standard solution by MC-ICPMS， and the results showed that the values of δ114/110CdJMC， δ114/110CdSPEX-1， δ114/110CdBAM 1012 and δ114/110CdMǜnster were 0.55‰， 0.56‰， -0.65‰ and 5.14‰， respectively. Application of Cd Isotope Tracer Technique
Application of Cd isotope tracer technique in the research about the genesis of lead-zinc deposits
Lead-zinc deposits are a kind of important Cd reservoirs on earth， which has very high Cd content[26]， and the Cd content in blende could reach 3% （such as Fule lead-zinc deposit in Yunnan）[27]. Therefore， Cd is an ore-forming element in some lead-zinc deposits， and its isotope may provide the evolution information of ore-forming elements in the formation process of lead-zinc deposits for the research on lead-zinc deposits， and important direct information for the research on the genesis of lead-zinc deposits. Schmitt et al.[28]determined the composition of Cd isotope in sulfide from submarine chimney， the sulfide and solid silicate of Bio9 chimney have similar Cd isotope composition， and it was deemed that the metallogenic material of Bio9 chimney came from the lixiviation of basalt oceanic crust， and Cd isotope fractionation did not exist in this process. Zhou et al.[29]found through the study on Zn isotope in blende of Banbanqiao and Tianqiao lead-zinc deposits in northwest Guizhou that the blende was enriched with light isotope of Zn in early period and with heavy isotope in late period of Zn， and it was deemed that that the fractionation of Zn isotope followed rayleigh fractional model. Zhu et al.[30]studied Cd isotope in Yunnan Fule lead-zinc deposit， and found that from bottom to top of the deposit， the δ114/110Cd value in blende increased regularly， and the fractional model could be explained by rayleigh fractional model， with a fractionation coefficient α equal to 0.999 65. Above studies show that Cd and Zn iostopes might have the same fractionation mechanism in lead-zinc deposits， and suggest that Cd isotope has a great application potential in lead-zinc deposits. Scholars at home and abroad could judge the genesis of lead-zinc deposits applying Cd isotope tracer technique， which has unparalleled superiority in the research about the genesis of lead-zinc deposits.
Application of Cd isotope tracer technique in research about lunar soil and meteorites
Research on chondrite and lunar soil shows that greater Cd isotope fractionation exists， and the fractionation value ranges from -21εCd/amu-1 and +63εCd/amu-1[31-33]. The fractionation of Cd isotope in chondrite might be caused by rayleigh fractionation， original heterogeneity or differentiation of nebula[34]. Schediwy et al.[35]analyzed 9 soil samples from the moon， and found that the mechanism affecting Cd isotope fractionation in soil of the moon might be the collision between ions and particles on the surface of the moon. Wombacher et al.[36]found that during vacuum evaporation of liquid Cd， greater Cd isotope fractionation would happen， and it was deemed that the non-dynamic mass balance in the experiment was not caused by the self-diffusion or mixing of Cd molecules， but more likely to be caused by Cd evaporation into vapor or condensation during melting process； and the determination of mass balance relation could provide effective information for the fractional mechanism of Cd isotope， and this method is more suitable for the research about massive isotope fractionation， such as evaporation， diffusion and bio-utilization. Wombacher et al.[37]reckoned that Cd could produce larger isotope fractionation during evaporation and condensation， which could be used for studying evolution of solar system. Scholars could deduce the variation conditions of lunar soil and meteorites in spatial scale through the fractional mechanism of Cd isotope. Application of Cd isotope tracer technique in research about marine environment
In recent years， the research about Cd isotope in marine environment advanced obviously whether in spatial and time scale or application of marine organism. Emilie et al.[38]marked seawater and food eaten by pacific oyster by stable isotopes 110Cd and 112Cd， respectively， and discussed Cd isotope pathway， and the current method is also suitable for seawater with lower concentration. Shiel et al.[39]studied the distribution in different tissues of the organism （digestive glands， cheek and other parts） in Western Canada and Hawaii， and the results showed that various Cd isotopes could be used to successfully trace the migration of Cd in oyster； and the concentrations and isotope composition of Cd， Zn and Pb in mussels sea clams from the eastern coast of America were determined， and the results showed that Cd isotope and Zn isotope could effectively trace the artificial sources and natural sources of these metals， and could be effectively combined with Pb "fingerprint" technique. Lambelet et al.[40]determined Cd concentration and isotope composition in the water sample from Siberian coast， and the results showed that erosion effect had little effect on Cd isotope fractionation， indicating that the analysis of stable isotope is important to the research about trace elements in biogeochemistry environment， and especially in the research about Cd circulation in environment， Cd isotope could provide important information. Scholars could carry out tracing of biogenic migration way and research about trace elements in biogeochemistry environment using Cd isotope.
Application of Cd isotope tracer technique in research about heavy meal pollution sources
Heavy metal pollution sources of soil
Because Cd isotope does not produce isotope fractionation or very little isotope fractionation， Cd isotope has very good indication function on Cd pollution sources in soil. Cloquet et al.[41]conducted a study of pollution source tracing on soil around an abandoned Pb-Zn smelting plant in northern France， and found that the δ114/110Cd of smelting slag was +0.36， the δ114/110Cd of chimney dust was -0.64%， and the δ114/110Cd of polluted soil was between them but more close to that of chimney dust. It indicated that in the polluted region， there were mainly three kinds of pollution sources （chimney dust， smelting slag and other pollution sources related to agriculture）， and the main pollution source was chimney dust. Wen et al.[42]studied the Cd isotope in the soil of Yunnan Jinding Pb-Zn mine， and found that the δ114/110Cd value of polluted soil was -0.31%-（1+0.15%）， and compared with background soil （with δ114/110Cd of +0.40%）， the soil contained remarkably-enriched light isotope， which was mainly from dust produced during artificial mining process. Zhang[43]attempted to trace soil heavy metal Cd pollution co-caused by different pollution sources around Jinding Town in the ultra-large lead and zinc ore area in Lanping County of Yunnan Province using Cd isotope， and conducted a pilot study on Cd pollution in this area， and rational results were obtained. Scholars could trace heavy metal pollution sources of soil using Cd isotope tracer technique， so as to guide soil management and remediation. Heavy metal pollution sources of sediment
Cd isotope fractionation caused by industrial activity could be detected in environmental pollution， which enables the application of Cd isotope tracer technique in the research about heavy metal pollution sources of sediment[44]. Gao et al.[45]studied Cd isotope in the surface sediment of the Bei River in Zhuhai of China， and the results showed that Cd isotope in sediment close to smelting plants and e-waste dismantling areas suffered from obvious fractionation， and heavy metal pollution sources in river sediment could be well traced using Cd isotope. Shiel et al.[46]determined the isotope composition of Zn， Cd and Pb in the products of various stages of the smelting process in some Zn-Pb smelting plant in Canada， and found that Cd isotope fractionation was mainly from the concentrated smelting process of zinc ore， and the isotope composition in exhaust gas （with δ114/110Cd of -0.52% per thousand） and wastewater （with δ114/110Cd in the range of 0.31%-0.46% per thousand） effectively verified the fractionation of Cd isotope. The research results revealed that Zn and Cd isotope technique could be applied to trace environmental Zn and Cd pollution. It could thus been that Cd isotope could effectively trace the sources of Cd isotope in soil， sediment and smelting process.
Prospect
（1） Most studies on Cd isotope at home and abroad focus on celestial body and marine research fields， while few studies have been done in environmental field. Furthermore， most existing tracer studies are concentrated on metal smelting pollution， and tracer application on other important sources （such as agricultural activity） remains to be supplemented. Foundation database of Cd isotope composition remains to be enriched and broadened. With the deepening of research， Cd isotope composition becomes a new kind of geochemical means， and its application in environmental field also will become more extensive， deeper and more important.
（2） Multivaricate isotope tracer research could make up for the shortcomings of the application of single isotope， such as narrow application range and rough analysis results， so as to make the analysis of pollution sources more accurate and objective. How to better judge special pollution source and its migration and transformation mechanism according to the characteristics of metal elements in environment is one of the direction for multivaricate isotope tracer research in future. References
[1] WEI XL， LEI YD， MA XN， et al. Determination of chromium plumbum cadmium in soil by microwave digestion-AAS method[J]. Journal of Anhui Agricultural Sciences， 2014， 42（11）： 3243-3244， 3247.
[2] WEN SP， XIANG GQ， WANG RL， et al. Determination of trace cadmium in rice samples by cloud point extraction and flame atomic absorption spectrometry[J]. Journal of Henan University of Technology： Natural Science Edition， 2010， 31（2）： 66-70.
[3] ZHAO ZB， ZHAO WX， ZHANG L. Determination of trace cadmium in fly-ash by derivative atomic absorption spectrometry using atom trapping technique[J]. Contributions To Geology and Mineral Resources Research， 2004， 19（B12）： 187-190.
[4] LIU ZM， ZHAO AH. Study on the detection of trace elements Pb and Cd by collection and release atom absorption spectrographic method[J]. Chemical Analysis and Meterage 2001， 10（2）： 16-17.
[5] WANG M， ZHAO CH， ZHANG Q， et al. Determination of heavy metals in soil by microwave digestion-atomic absorption spectrometry[J]. Journal of Anhui Agricultural Sciences， 2013， 41（16） ：7128-7129， 7176.
[6] SONG MY， GUO QL， SUN Y， et al. Evaluation of measurement uncertainty of cadmium in wheat flour by microwave digestion graphite furnace atomic absorption spectrometry[J]. Sichuan Food and Fermentation.， 2016， 52（01）： 96-100.
[7] ZHU WQ， ZHANG XY， WANG H. Determination of cadmium in soil by microwave dissolving-graphite furnace atomic absorption method[J]. Chinese Journal of Health Laboratory Technology， 2017， 27（6）： 789-794.
[8] ZHU XS， ZHU XH， FENG K， et al. Study of trace cadmium in environmental samples by graphite furnace atomic absorption spectrometry after cloud point extraction[J]. Chinese Journal of Analytical Chemistry， 2006， 34（7）： 951-954.
[9] HE XM， WANG M， WANG XD， et al. Determination of lead and cadmium in rapeseed and rapeseed meal with microwave digestion by graphite furnace atomic absorption spectrometry[J]. Spectroscopy and Spectral Analysis， 2007， 27（11）： 2353-2356.
[10] ZHANG MQ， CHEN HP， ZHU YZ， et al. Determination on Cd in aguatic products by microwave digestion-atomic fluorescence spectroscopy[J]. Jiangsu Journal of Agricultural Sciences， 2004， 20（2）： 116-119.
[11] YANG DC， NING DQ， LI WL， et al. Determination of micro cadmium in Chinese herbal medicine material with the microwave digestion and VG-AFS[J]. Chinese Journal of Pharmaceutical Analysis， 2006， 26（01）： 30-34.
[12] GAO W， QI Q， WU NE， et al. Determining cadmium in dairy products by microwave digestion-atomic fluorescence spectrographic methods[J]. China Dairy Industry， 2010， 38（02）： 55-57. [13] AI LH， WANG MH， ZHU XP， et al. Determination of cadmium in vegetables by hydride generation-atomic fluorescence spectrometry[J]. Chinese Journal of Analysis Laboratory， 2007，26（05）： 119-121.
[14] CHEN XJ， HT， SHEN FX. Determination of cadmium in soil by hydride generation-atomic fluorescence spectrometry[J]. Analytical Instrumentation， 2005， （03）： 37-39.
[15] JIANG Q， WANG RH， SUN XL， et al. Study on the determination of cadmium in tobacco by hydride generation-atomic fluorescence spectrometry[J]. Chinese Agricultural Science Bulletin， 2010， 26（13）： 118-121.
[16] CHEN T， HUANG ZY， CHEN L， et al. ICP-MS-isotope dilution method for determination of trace amounts of cadmium in soil of vegetable farm[J]. Physical Testing and Chemical Analysis （chemistry）， 2009， 45 （7）： 761-764.
[17] YIN Z. ICP-MS determination of cadmium in food with microwave assisted sample digestion[J]. Physical Testing and Chemical Analysis Part B： Chemical Analysis， 2013， 49（05）： 597-599.
[18] ROSMAN KJR， DE LAETER JR. The isotopic composition of cadmium in terrestrial minerals[J]. International Journal of Mass Spectrometry and Ion Physics， 1975， 16（4）： 385-394.
[19] SCHEDIWY S， ROSMAN KJR， DE LAETER JR. Isotope fractionation of cadium in lunar material[J]. Earth and Planetary Science Letters， 2006， 243（3）： 326-335.
[20] GAO B. Heavy metals pollution in typical environment samples and preliminary study on Cd and Pb isotopic tracing[D]. Guangzhou： Guangzhou Institute of Geochemistry， Chinese Academy of Sciences， 2008.
[21] REHKMPER M， WOMBACHER F， HORNER TJ， et al. Natureal and anthropogenic Cd isotope variations[M]. Hand Book of Enviromental Isotope Geochemistry. Berlin， Heidelberg： Springer， 2012： 125-154.
[22] CLOQUET C， ROUXEL O， CARIGNAN J， et al. Natural cadmium isotopic variations in eight geological reference materials and anthropogenic samples， measured by MC-ICP-MS [J]. Geostandards and Geoanalytical Research， 2005， 29（1）： 95-106.
[23] LI SZ， ZHU XK， TANG SH， et al. The application of MC-ICP-MS to high-precision measurement of Zn isotope ratios[J]. Acta Petrologica et Mineralogica， 2008， 27（4）： 273-278.
[24] LI J， ZHU XK， TANG SH. The application of double spike in non-traditional stable isotopes-a case study on Mo isotopes[J]. Rock and Mineral Analysis， 2011， 30（2）： 138-143.
[25] GAO H， LIANG XR， LIU Y， et al. Measurement of cadmium isotopic composition of standard solutions by multi-collector inductively coupled plasma mass spectrometry[J]. Rock and Mineral Analysis， 2008， 27（5）： 321-324. [26] SCHWARTZ MO. Cadmiuminzinc deposits： Economic geology of a polluting element [J]. International Geology Review， 2000， 4（5）： 445-469.
[27] SI RJ. Ore deposit geochemistry of the Fule dispersed element-polymetallic deposit， Yunnan Province[D]. Guiyang： Institute of Geochemistry， Chinese Academy of Sciences， 2005.
[28] SCHMITT AD， GALER SJG， ABOUCHAMI W. Mass-dependent cadmium isotopic variations in nature with emphasis on the marine environment[J]. Earth and Planetary Science Letters， 2009， 2007（1）： 262-272.
[29] ZHOU JX， HUANG ZL， ZHOU MF， et al. Zinc， sulfur and lead isotopic variations in carbonate-hosted Pb-Znsulfide deposits， Southwest China [J]. Ore Geology Reviews， 2014， 58： 41-54.
[30] ZHU CW. Isotope geochemistry of dispersed elements Cd and Ge in lead and zinc deposits in Guizhou， Yunnan and Sichuan area and its application[D]. Guiyang： Institute of Geochemistry， Chinese Academy of Sciences， 2014.
[31] ROSMAN KJR， DE LAETER JR. Cadmium mass fractionation in unequilibrated ordinary chondrites[J]. Earth and Planetary Science Letters， 1988， 89： 163-169.
[32] ROSMAN KJR， DE LAETER JR， GORTON MP. Cadmium isotope fractionation in fractions of two H3 chondrites[J]. Earth and Planetary Science Letters， 1980， 48： 166-170.
[33] SANDS DG， ROSMAN KJR， DE LATER JR. A preliminary study of cadmium mass fractionation in lunar soil[J]. Earth and Plnetary Science Letters， 2001， 186： 103-111.
[34] WOMBACHER F， REHKAMPER M， MEZGER K. Determination of the mass-dependence of cadmium isotope fractionation during evaporation[J]. Geochimica et Cosmochimica Acta， 2003， 68：2349-2357.
[35] SCHEDIWY S， ROSMAN KJR， DE LAETER JR. Isotope fractionation of cadmium in lunar material[J]. Earth and Planetary Science Letters， 2006. 243： 326-335.
[36] WOMBACHER F， REHKAMPER M， MEZGER K， et al. Stable isotope compositions of cadmium in geological materials and meteorites determined by multiple-collector ICP MS[J]. Geochimica et Cosmochimica Acta， 2003， 67： 4639-4654.
[37] WOMBACHER F， REHKAMPER M， MEZGER K， et al. Cadmium stable isotope cosmochemistry[J]. Geochimica et Cosmochimica Acta， 2008， 72： 646-667.
[38] EMILIE S， SCHAFER J， BAUDRIMONT M， et al. Tracing cadmium contamination kinetics and pathways in oysters （Crassostrea-gigas） by multiple stable Cd isotope spike experiments[J]. Ecotoxicology and Environmental Safety， 2011， 74： 600-606.
[39] SHIEL AE， WEIS D， ORIANS KJ. Tracing cadmium， zinc and lead sources in bivalves from the coasts of western Canada and the USA using isotopes[J]. Geochimica et Cosmochimica Acta， 2012， 76： 175-190. [40] LAMBELET M， AMPER MR. Isotopic analysis of Cd in the mixing zone of Siberian rivers with the Arctic Ocean-New constraints on marine Cd cycling and the isotope composition of riverine Cd[J]. Earth and Planetary Science Letters， 2013， 361： 64-73.
[41] CLOQUET C， CARIBNAN， LIBOUREL G， et al. Tracing source pollution in soils using cadmium and lead isotopes[J]. Eenviromental Science &Technology， 2006， 40（8）： 2525-2530.
[42] WEN HJ， ZHANG YX， CLOQUET C， et al. Tracing sources of pollution in soils from the Jinding Pb-Zn mining district in China using cadmium and lead isotopes[J]. Applied Ueochemistry， 2015， 52： 147-154.
[43] ZHANG YX. Analytical test method of non-traditional stable isotopes of Mo and Cd and its geological application[D]. Beijing： Graduate University of Chinese Academy of Science， 2010.
[44] YU WH， YU RL， HU GR. Application progress of Pb， Zn and Cd isotopes in research about sources of heavy metal pollution in soil and sediment[J]. Nonferrous Metals， 2012 （4）： 57-62.
[45] GAO B， LIU Y， SUN K， et al. Precise determination of cadmium and lead isotopic compositions in river sediments compositions in river sediments[J]. Analytica Chimica Acta， 2008， 612： 114-120.
[46] SHIEL AE， WEIS D， ORIANS KJ. Evaluation of zinc， cadmium and lead isotopic fractionation during smelting and refining[J]. Science of the Total Environment， 2010， 408： 2357-2368.