铅、锌、镉同位素示踪技术在沉积物重金属污染源解析中的应用：综述与展望.pdf

Received date：2023-09-19；Revised date：2023-10-19Fund projects：This study is supported by the Science and Technology Plan Project of Qinghai Province（2022-ZJ-732），“Kunlun Talents High-end Innovative and Entrepreneurial Talents”Plan Project（Grant to Chunliang Gao），and the Second Tibetan Plateau Scientific Expedition andResearch Program（2019QZKK0805）First author：GAO Chunliang（1983-），Male，PhD，Associate professor，mainly engaged in the study of Lake Sediment Records and EnvironmentalEvolution.E-mail：Corresponding author：WEI Haicheng（1983-），Male，PhD，Professor，mainly engaged in the study of Palynology and Environmental Evolution.E-mail：高春亮，文进心，成艾颖，等.铅、锌、镉同位素示踪技术在沉积物重金属污染源解析中的应用：综述与展望 J.盐湖研究，2024，32（1）：128-138.Gao C L，Wen J X，Cheng AY，et al.Pb，Zn and Cd isotopes as the tracers of heavy metal pollution sources in the sediments：a review and prospect J.Journal of Salt Lake Research，2024，32（1）：128-138.DOI：10.12119/j.yhyj.202401014Pb，Zn and Cd Isotopes as the Tracers of Heavy Metal Pollution Sources in theSediments：A Review and ProspectGAO Chunliang1，2，WEN Jinxin1，2，3，CHENG Aiying1，2，MIN Xiuyun1，WEI Haicheng1，2*（1.CAS Key Laboratory of Comprehensive and Highly Efficient Utilization of Salt Lake Resources，QinghaiInstitute of Salt Lakes，Chinese Academy of Sciences，Xining，810008，China；2.Qinghai Provincial KeyLaboratory of Geology and Environment of Salt Lakes，Xining，810008，China；3.University of ChineseAcademy of Sciences，Beijing，100049，China）Abstract：Effective prevention and control of heavy metal pollution in sediments necessitates the preciseidentification of their pollution sources.Among the available methods，the application of lead（Pb），zinc（Zn），and cadmium（Cd）isotope tracers stands out as a highly reliable means of analyzing pollutionsources.While the Pb isotope tracer technique has been widespread used，the application of Zn and Cd isotopes，as emerging tracers，can substantially enhance the study of heavy metal pollution source analysis.This study offers a systematic exploration of the isotope tracer mechanisms，compositional characteristics，and their application in tracing heavy metal pollution sources in sediments.We propose that future researchshould focus on employing multi-isotope tracer techniques and integrating the isotopic compositions withsediment morphology to further enhance the precision of pollution source tracing.Key words：Pb-Zn-Cd isotopes；Sediment；Heavy metal pollution；Source apportionment；Tracer techniqueCLC number：X142Document code：AArticle ID：1008-858X（2024）01-0128-111IntroductionThe ecosystems that thrive within mountainouslandscapes，encompassing mountains，rivers，forests，fields，lakes，grasslands and sandy terrains，play apivotal role in metamorphosing matters concerningecological and environmental preservation into an intricate fusion with open aquatic systems，which includecatchment areas，wetlands and confluence rivers1-3.Especially in the ecological environment，sediment isa huge storage reservoir that records rich informationon natural environmental changes and the influence ofhuman activities on the ecosystem4-9.Human activities，such as mining operations，waste incineration，fossil fuel combustion and agricultural activities，giverise to substantial discharges of heavy metals intoaquatic environments4，8-9.Once introduced into thewater，the majority of heavy metals ultimately sediment within the substrate，posing a challenge for biodegradation by organisms，and upon reaching a certainconcentration threshold，they can induce toxic effects，第 32 卷第 1 期2 0 2 4年 2 月JOURNAL OF SALT LAKE RESEARCH盐湖研究Vol.32 No.1Feb.2024高春亮，等：铅、锌、镉同位素示踪技术在沉积物重金属污染源解析中的应用：综述与展望第1期thereby posing a peril to the ecological environment 10-15.Therefore，the study of heavy metal pollution in sediments had been attracted much attention.However，prior studies have predominantly focused on assessingthe extent of heavy metal contamination in sediments，with minimal emphasis on the tracing of pollutionsources and sinks16-19.The identification of pollution sources is the prerequisite for the correct evaluation of environmentalpollution degree and the effective treatment of pollution sources.In particular，the compositions of heavymetal in sediments is complex and diverse，renderingthe attainment of precision and scientific rigor throughthe application of a singular methodology challenging.Moreover，the coexistence of multiple sources ofheavy metals within environmental matrices is a commonplace phenomenon，further amplifying the complexitiesassociatedwithsourceapportionment8-10，18-21.Theisotopetracingtechnique，awell-established method in the field of geochemistry，hasemerged as a classic tool for traceability research.Withthe advancements of high-precision detection technology of heavy metal isotopes，the heavy metal stableisotopes（e.g.Pb，Zn，Cd，Hg，Sr and Cu）has alsobeen widely used in the study on pollution source apportionment22-26.While previous source apportionment studies primarily focused on atmospheric particle，and have been widely used in many environmental media such as soil and sediment27-32.In light of this，this study has selected multi-isotopes，including those of Pb，Zn and Cd isotope，as its subjects of investigation，with a dedicated focuson the tracer mechanism，compositional attribute andresearch progress.Our primary objective is to interpretthe isotopic composition of specific pollution sources，thus providing crucial evidence for the arbitration ofenvironmental pollution events.2Pb isotope tracer technique2.1Isotope tracer mechanismPb stable isotopes encompass204Pb，206Pb，207Pband208Pb，among which204Pb is a non-radiogenic isotope and the abundance is generally considered to remain constant over time33.However，206Pb，207Pb and208Pb are radiogenic isotopes generated through the decay of238U，235U and232Th with increasing abundance，respectively.Pb isotopic compositions mainly dependon the initial Pb，uranium（U）and thorium（Th）contents in the source region，as well as the time of radioactive U/Th decay reaction.Importantly，these compositions remain relatively impervious to alterations inthe geochemical environment following their formation23，34.Therefore，distinct ratios of Pb isotopesserve as reliable geochemical fingerprint，facilitatingeffective identification of diverse pollutant sources.Inthe context of studying the tracing of heavy metal pollution in soils and sediments，Pb isotope ratios，suchas206Pb/204Pb，207Pb/204Pb，208Pb/204Pb and206Pb/207Pb，are serve as primary parameters for comprehensiveanalysis23，34-44.The measured data on Pb isotope ratios is graphically represented and analyzed to effectively identify the sources and migration pathways ofheavy metal pollution.The proportion of anthropogenic heavy metals within sediment can be estimatedthrough the utilization of Pb isotope ratios，revealing adynamic equilibrium between anthropogenic and natural sources of lead within sediment，as expressed inthe following equation：Pbm（207Pb/206Pb）m=Pbgeo（207Pb/206Pb）geo+Pbanth（207Pb/206Pb）anth（1）where Pbm，Pbgeoand Pbanthrepresent mixed lead（i.e.Pb in sediment samples），geological source lead andanthropogenic source lead，respectively.The application of this formula allows for the calculation of theproportion of anthropogenic lead（Pbanth）within thesediments.2.2Natural isotope composition characteristicsThe diverse origins and formation within differentenvironmental media lead to distinct characteristics inPb isotope compositions，rendering Pb isotopes asvaluable geochemical fingerprints23，35-44（Fig.1）.However，its important to recognize that the variousenvironmental media are interconnected，and Pb isotope compositions result from the amalgamation ofvarious substances.The significant increase in Pb con129盐湖研究第 32卷centration is primarily attributed to human activities，such as mining and smelting，coal combustion，transportation emissions and industrial production，whichserve as the primary sources of lead in environmentalmedia（i.e.soil，atmosphereandsediment）25，28，30，34-44.Therefore，a paramount objective is to establish a comprehensive reference library of isotopiccomposition characteristics，which aims to facilitate athorough and accurate analysis of Pb pollution sourcesand associated heavy metals within the environment.2.3Tracing of heavy metal pollution sources insedimentsIn previous studies，only the206Pb/207Pb ratio wasutilized，limiting the accurate analysis of Pb sourcesfrom automobile exhaust and industrial emissions45-52.To address this limitation，a comprehensive approachencompassing206Pb/204Pb，207Pb/204Pb，208Pb/204Pb，and206Pb/207Pb ratios was adopted for discussion53-54.For example，sedimentary record ofheavy metal pollution in the West Taihu Lake showedthat the sediments were mainly affected by gasolineand vehicular emissions，coal combustion，industrialwastewater and domestic sewage，the local soil and atmospheric dustfall had become the main materialsources of the sediments in recent years20.The sediment records of trace metals from alpine lakes ofsouthwest China showed that the historical trends of206Pb/207Pb ratio reflected an important source of anthropogenic Pb associated with preindustrial mining andsmelting，suggesting a substantial impact of legacycontamination from ancient mines21.In addition，Pb isotopic composition of bulk sediments and 1 M HCl leachates/residues of samples fromthe Four Riversinlets to Dongting Lake was determined to identify and differentiate the source of Pb inputs（Fig.2）.Results highlighted that Xiangjiang river（XY-QS）sediments were highly enriched in Pb withless radiogenic Pb isotopes（e.g.，206Pb/207Pb ratios of1.183 0 0.003），indicating the predominance of anthropogenic Pb inputs.In contrast，sediments of the Zijiang，Yuanjiang and Lishui rivers（ZD-LH）weremoderately enriched in Pb and exhibited more radiogenic Pb（e.g.，206Pb/207Pb ratios of 1.188 0 0.008）54.Residual Pb isotope ratios suggested that Pb isotopic composition of lithologically inherited Pb in inletsediments was similar，which was attributed to mixing，hydrological sorting，and averaging of differentPb sources from diverse geological settings.Pb isotopic tracing showed that Pb in XY-QS sediments resulted from the mixing of two end member sources，ananthropogenic source（less radiogenic Pb）from downstream ore smelting and upstream ore mining activities（53%）and a lithological source（37%）from granitethrough weathering.In contrast，Pb in ZD-LH sediments resulted from the mixing of multiple sources including Pb from upstream mining activities（20%），coal combustion（20%）and lithologically inherited Pb（60%）while surface sediments from the Yuanjiangriver contained Pb from diesel oil usage（50%）54.The Pb isotope ratios of measured sediment sampleswere depicted and analyzed graphically.Combiningmultiple statistical analysis methods，the source apportionment of heavy metal pollution in the offshore sediments from Xiamen Western Bay was conducted using208Pb/（206Pb+207Pb）and206Pb/207Pb plots55.The findings revealed that the heavy metals in drill core sediments mainly originated from three major sources：transportationandindustrialactivities，naturalsources，industrial and domestic sewage discharge，with contribution rates of 72.8%，12.2%and 10.9%，respectively55.Fig.1The diagram（206Pb/207Pb vs.208Pb/206Pb）showingthe isotopic composition of different Pb sources，and the data from references23，35-44130高春亮，等：铅、锌、镉同位素示踪技术在沉积物重金属污染源解析中的应用：综述与展望第1期3Zn isotope tracer technique3.1Isotope tracer mechanismZinc（Zn）stable isotopes encompass five isotopes，each with its own relative abundance，including 64Zn（48.63%），66Zn（27.90%），67Zn（4.10%），68Zn（18.75%）and 70Zn（0.62%）56.Due to the highest64Zn abundance in nature，the ratio of three other isotopes（e.g.，66Zn，67Zn and 68Zn）to64Zn is usuallyused in the stable isotopic analysis.In Zn stable isotope composition analysis，66Zn/64Zn，67Zn/64Zn and68Zn/64Zn are usually adopted，so the value of 66Znwas calculated as follows57：66Zn=（Rsample：Rstandard-1）100 0（）（2）where Rsampleis the66Zn/64Zn ratio of sample，and Rstandardis the66Zn/64Zn ratio of the bracketing IMP Zn standard.Various anthropogenic activities such as the production emissions of lead and zinc smelters，batterymanufacturers，power plants are all great contributors28-29，58.In addition，other anthropogenic sources suchas pesticides and fertilizers，automobile exhaust gas，tire wear，as well as sewage and wastewater have intensified the exogenous input of Zn29，59-61.High-precision Zn isotope test results had been reportedfirstly since 1999，marking the onset of rapid development in environmental Zn tracing research22，28-29，60-62.Especially，heavy metal pollution in sediments is affected by multiple pollution sources，Pb isotope traceris relatively well-developed.Therefore，Zn isotope asan valuable complement，enhancing the accuracy andreliability of tracing results.3.2Natural isotope composition characteristicsIn addition to the weathering input from zinc-bearing rocks28，anthropogenic sources，includingautomobile exhaust emissions and tire wear29，60，sewage sludge61，disposal of pig manure62，rainwaterrunoff61and industrial discharge63，can significantly contribute to the elevated zinc concentration insediments.Its important to note that in nature，zincisotopic compositions exhibit significant variationsamong different geological samples（Fig.3）.Fig.2The diagram of206Pb/207Pb ratios from Dongting Lake，including lithologically inherited Pb andanthropogenic source Pb，and the data from references46-52，54131盐湖研究第 32卷3.3Tracing of heavy metal pollution sources insedimentsAs depicted in Fig.4，the Zn isotope compositionwas determined in settling particles collected monthlyover a year in the hypolimnion of the eutrophic LakeGreifen in Switzerland75，when the Zn in the settlingparticles was predominantly associated with organicmaterial，Zn concentrations in the epilimnion werelowest.However，in other months，the sediment trapsrevealed higher 66Zn values，reflecting an increasingcontributions of anthropogenic or lithogenic components75.Furthermore，the applicaiton of Zn stableisotope as tracers for anthropogenic metal contributions were demonstrated in a sediment core from LakeBiwa76.The study indicated that higher contributionfrom mafic and intermediate igneous rocks，driven byhuman-induced processes，could account for the elevated Zn and Cu accumulation rates from the late1910s until approximately 1940；additionally，the elevated Zn accumulation and slightly declining 66Znvalues from the late 1950s indicated urban and industrial anthropogenic Zn contributions76.In addition，sediment core 66Zn values in downstream Cajarc hydroelectric reservoir are consistentlyheavier（+0.75 to+1.35）than the regional geochemical background，both top-core Zn concentrationsand isotopic signatures can be explained by the contribution of 9%of present-day Riou Mort sediments；66Zn variations in the137Cs dated downcore sedimentsare suggested to reflect historical changes in metallurgical processes of the Viviez facility，such as improved Zn extraction efficiency and the related evolution of tailing