长江口海域表层沉积物重金属元素赋存形态特征

通过长江河口地区水下表层沉积物样品多种化学元素的赋存形态分析测试数据,综合分析重金属元素的赋存形态特征。研究结果显示：镉、汞、铅残渣态所占比例均小于50%,锌、砷、铬、铜、镍残渣态占比均大于50%;8个元素的残渣态与全量呈显著正相关关系。沉积环境和沉积物粒径对重金属元素赋存形态具有重要影响。沉积物的物质来源、矿物组成特征、水动力作用与沉积物粒度和物理化学条件等是长江口地区表层沉积物重金属元素赋存形态的主要控制因素。     

临洪河口现代沉积环境及重金属元素的分布特征

对江苏北部临洪河口不同区域的表层与柱状沉积物进行了粒度分析、石英颗粒表面微细结构和沉积物的测年分析以及沉积物中的重金属含量分析．将河口划分为不同的沉积环境区．探讨了不同沉积环境中沉积物的粒度分布、石英颗粒表面微细结构、沉积速率以及重金属元素分布差异的原因。结果显示,临洪河口可以划分为低潮滩上的波浪与潮流强烈混合作用区、高潮滩上的弱潮流作用区、口门附近的潮流与河流强烈混合作用区和河道内河流与潮流弱混合作用区。重金属的含量在柱样的30～40cm深度呈现向表层递增的趋势,Hg的污染比较严重．其他元素基本无污染,整个河口区域的生态危害性严重;沉积物粒度分布不是该区域重金属分布的主要影响因素,城市污水排放量增加、氧化还原层位、沉降方式和不同沉积区的水动力环境是影响本区域重金属元素分布和累积的主要原因。     

厦门西港沉积环境变化及重金属的污染累积

通过测定柱状沉积物中的重金属、有机碳和硫化物含量, 结合沉积物粒度分析及现代沉积速率, 重现了厦门西港近70a的沉积环境变化及重金属的污染历史, 探讨了沉积环境对重金属累积过程的影响.结果表明, 厦门西港污染指示元素为Cu, Zn, Pb, As, 富集程度依次为As > Cu > Zn > Pb, 元素Cr, Cd和Hg在研究海域内没有富集现象.综观70a来, 厦门西港沉积物组成变化较大, 沉积环境变化明显, 重金属含量的垂向变化特征与当时的水动力、沉积环境变化紧密相关.研究表明, 沉积物来源越稳定, 沉积物粒径越小, 分选性越好, 则沉积物中重金属含量越高; 同时, 各层位的绝大部分重金属与有机碳和硫化物呈显著正相关关系.      

太湖MS岩芯重金属元素地球化学形态研究

采用BCR三步提取法对太湖MS岩芯沉积物中Cu、Fe、Mn、Ni、Pb和Zn等6种重金属元素的化学形态进行了研究.结果表明,有效结合态的Cu、Ni和Pb主要以有机物及硫化物结合态、Fe-Mn氧化物结合态存在,Fe和Zn主要以Fe-Mn氧化物结合态存在,Mn主要以可交换态及碳酸盐结合态存在;Fe-Mn氧化物结合态的Ni、Pb和Zn与可还原态的Mn有较好的正相关关系,有机物及硫化物结合态的Cu、Mn、Ni、Pb和Zn与有机碳含量有较好的正相关关系;重金属形态分布体现了重金属元素地球化学性质的差异,以及重金属形态含量与沉积物理化性质的关系.沉积岩芯重金属元素形态垂向变化规律及次生相富集系数表明,Cu、Mn、Ni、Pb和Zn在沉积岩芯13～4 cm有效结合态含量较稳定,为自然沉积;4～0 cm有效结合态含量明显升高,存在一定程度的人为污染.根据137Cs测年结果判断,沉积岩芯Cu、Mn、Ni、Pb和Zn等重金属污染开始于20世纪70年代末期,主要污染元素及污染历史与太湖流域污染工业类型及经济发展阶段相吻合.     

鸭绿江河口及近岸地区沉积物的稀土元素对物质运移的指示意义

稀土元素(REE)的稳定性使其在物源示踪中得到广泛应用,而针对沉积物REE在运移过程中的微弱变化却往往被忽略。本文以鸭绿江河口地区沉积物为研究对象,探讨该区沉积物Ce、Eu的分异特征及其对物质运移格局变化的指示作用。鸭绿江河口地区沉积物的REE含量与平均粒径呈显著正相关关系,而与δEu呈较好的负相关关系,即随着REE的富集,Eu的亏损程度加剧。Eu的异常发生于岩浆结晶过程,长石类矿物的Ca~(2+)与Eu~(2+)发生置换,造成富集REE矿物的Eu亏损。河流来源的溶解态Ce的氧化沉淀作用,造成河口地区沉积物的Ce呈正异常。此外,柱样历史时期与表层样的δCe差异及河口地区不同亚环境间的δCe差异,有效指示了河口地区物质的运移及沉积环境的变迁。辽东半岛南侧沉积物中砂组分(大于63μm)的δEu指示,水深超过50 m后,Eu呈显著正异常,该处可能为鸭绿江砂组分的运移极限。     

厦门湾现代沉积环境特征研究

应用系统聚类和因子分析的方法分别对厦门湾112个表层沉积物样品的粒度组成和其中35个样品的矿物组成进行分析。结果表明:厦门湾可以划分为三种与沉积动力特征相对应的主要沉积环境区;表层沉积物中共发现碎屑矿物50种,其中重矿物38种,优势重矿物为磁铁矿、钛铁矿、褐铁矿、赤铁矿、绿帘石、角闪石、锆石等;表层沉积物主要由九龙江等入海泥沙和厦门湾周缘基岩风化侵蚀产物组成,部分为来自台湾海峡的物质。物质来源是影响研究区表层沉积物中重矿物分布的主要因素。     

渤海西部河口潮间带区海水及沉积物中重金属研究

通过对渤海湾西部永定新河河口潮间带区海水及沉积物中重金属含量及污染状况的研究,认为海水中重金属含量平均值的大小顺序为Zn＞Cu＞Pb＞Hg＞Cd;因海水中重金属输入径的不同,不同潮期海水中重金属含量存在差异:大潮期海水中重金属Cu,Pb和Hg的含量大于小潮期海水中的含量,而重金属Zn和Cd的含量则小于小潮期海水中的含量;因受海水中悬浮物含量、种类及河口区成淡水混合发生絮凝作用等的影响,海水中重金属含量在垂向上也存在差异.无论是大潮期还是小潮期,海水中重金属舍量总是表层略大于底层;按一类水质标准对海水中重金属污染状况的分析,认为研究区海水已局部受到重金属污染,污染最严重的是重金属Zn,其次为重金属Pb,Hg和Cu,不存在重金属Cd污染;沉积物中重金属舍量平均值的大小顺序与海水中的相同,说明海水与沉积物中重金属循环处于相对平衡状态.沉积物中重金属含量平均值均在渤海湾环境背景值范围内,且是渤海海域含量最低的区域.经过对沉积物重金属污染状况的分析,研究区沉积物重金属污染轻微.     

天津市潮间带表层沉积物的类型及其分布

根据在天津市潮间带地区采集的108个底质样品的粒度分析结果,划分了潮间带表层沉积物的类型,并探讨了潮间带的粒度分布特征和沉积作用。结果表明,天津潮间带可分为3个岩性区,分别以海河口、独流减河口为界,海河口以北至涧河口为片状粘土质粉砂分布区,海河口以南至独流减河口为多岩性、条带状的砂-粉砂分布区,独流减河口至歧口为片状粘土质粉砂分布区。海河口以北的潮间带是以低能潮汐作用为主的泥质粉砂潮滩沉积环境,海河口以南的潮间带是以河口沉积为主体,后经潮汐改造的潮滩环境,驴驹河-独流减河河口岸段潮间带早期水动力较强,后受到潮滩环境的改造,歧口岸段潮间带以潮滩沉积环境为主。     

长江河口盐沼湿地酸挥发性硫化物的时空分布特征及影响因素

以长江河口典型潮间带(崇明东滩湿地)不同地貌单元植被根际柱样沉积物(0~33 cm)为研究对象,探讨了长江河口潮间带表层沉积环境中酸挥发性硫化物(AVS)的时空间变化特征及其与环境因子的关系.结果表明,不同植被根际沉积物中 AVS 含量存在显著季节变化,表现为:互花米草大于海三棱藨草和芦苇.各采样点根际沉积物中 AVS 含量垂向变化为:高潮滩芦苇,随深度的增加而降低;中潮滩互花米草与海三棱藨草,随深度的增加先增大后减小,且在地面下约20 cm 处显著增大. Pearson 相关分析表明,沉积物中 AVS含量与<16μm 的颗粒物、有机碳含量及含水率之间不存在简单的正相关关系.根际沉积物中 AVS 含量的时空变化可能受潮汐、植被生长等因素的综合影响,其时空变化特征反映了长江河口潮滩复杂多变的氧化还原条件.与芦苇和海三棱藨草相比,入侵物种互花米草对沉积物中硫酸盐异化还原有显著影响,其可能改变了潮滩湿地生态系统原有的氧化-还原生物地球化学循环过程     

成都市中心城区地表沉积物中重金属分布及矿物学特征

城市地表沉积物已成为城市环境污染的重要组成部分,是城市环境中各种污染物的"源"和"汇",通过研究城市地表沉积物的物化及矿物学特征对城市环境质量的监测具有良好的指示作用。本文在成都市中心城区不同区域采集40件地表沉积物样品,利用激光粒度分析仪、扫描电镜能谱和X射线衍射等技术分析研究了地表沉积物的粒径分布特征、重金属分布特征、矿物组成特征及微区形貌特征。结果表明:地表沉积物粒径的质量和体积分布特征具有较高一致性,均以中细颗粒物为主,其中小于0. 3mm的地表沉积物占总质量或体积的70%以上,小于0. 125mm的地表沉积物占总质量或体积的40%左右; Cu、Pb、Zn、As、Hg、Cr、Cd、Ni等重金属随着沉积物粒径的减小而呈明显增加的趋势,主要存在于小于0. 125mm粒径的沉积物中,同时在成都市中心城区各方位区域和各环路区域的分布上存在一定的差异; Si、Ca、K、Na等造岩元素在不同粒径级别沉积物中都大量存在;地表沉积物矿物组成主要是石英、长石类、方解石等,且各类矿物在不同粒径级别沉积物中所占含量大致相当,但细粒径矿物表现出胶体行为,极易吸附各种微量重金属。研究认为,城市地表沉积物的粒径分布特征和矿物组成特征是影响重金属在沉积物中分布的内在因素,而人类活动是决定地表沉积物重金属污染程度的关键因素。     

Heavy metal pollution and assessment of the tidal flat sediments near the coastal sewage outfalls of shanghai,China

Zn, Cu, Cr and Pb concentrations of the sediment collected from three tidal flat sites of Yangtze estuary were investigated in October 2003. Results showed that the average concentrations of heavy metals in the sediments were two to three times to the environment background values of Yangtze estuary tidal flat sediment. The heavy metal concentrations in the sediments near the Bailonggang (BLG) and Laogang (LG) sewage outfalls were obviously higher than those of Chaoyang (CY) tidal flat where there are no sewage outfalls near the coast. And the concentrations of heavy metals in the surface sediments of LG tidal flat decreased with the increasing of the distance to the sewage outfalls. The heavy metal concentration profile in the sediment core changed with the depth, and generally reached maximum values at the depth of plant roots. The assessment results showed that the sediments of LG, BLG and CY tidal flat had been polluted by heavy metals in different level. The pollution degree of heavy metals in the sediments was as follows: Zn > Cu > Pb > Cr. The potential ecological risks of the four heavy metals in three tidal flat sites sediment were all at a middle level, and Cu and Pb made the main contributions. The adverse ecological effects caused by the four heavy metals did not occur frequently.     

Accumulation discrepancy of heavy metal and organic pollutants in three near-shore depositional environments, southeastern China

Heavy metal and organic pollutants in sediments along the coastal zone of southeastern China have been investigated. Sediment samples are retrieved from three depositional environments: coast, estuary, and tide-affected river mouth. The relative abundance of heavy metal and organic pollutants is related to their geochemical properties as well as depositional environments and anthropogenic discharge. Based on a sequential extraction method, it is revealed that anthropogenic Pb, Cr, Cu, and Cd are mainly bound to Fe–Mn oxides, suggesting that adsorption and co-precipitation of Fe–Mn oxides are in the control of their transfer processes from water column to sediment. Heavy metal bound to carbonates is also an important pool especially for Cd, Mn, and Pb. The main organic pollutants found in the study area include petroleum-related alkanes, phthalic acid ester, organic silicon, chlorophenol, phenyl ether, and amine. The accumulation of heavy metals and organics in surficial sediments has a decrease tendency from estuarine environment to coastal environment and to tide-affected river mouth.     

潮滩沉积物重金属累积特征研究进展

在分析总结国内外潮滩重金属研究现状和成果的基础上，指出潮滩重金属来源的定量分析尚很不完整；沉积物的物质组成、粒径、水动力作用、潮滩生物、河流输入量、人类活动等都对重金属在潮滩的分布有着重要影响。在垂岸方向，重金属从高潮滩到低潮滩含量逐渐降低，反应了水动力以及粒径对潮滩重金属的分布的控制；沿岸方向，淤涨岸段，重金属含量低，排污口严重影响着重金属的沿程分布，重金属含量随离排污口的距离增大而呈指数减少；垂向方向，在许多地方重金属分布与人类活动、经济发展状况相吻合。生物活动使潮滩重金属的累计特征变得复杂，改变了潮滩局部的微环境。与国内外河口重金属研究相比，潮滩重金属的研究远远不足。沉积物中重金属常用研究方法，如Tes sier地球化学相连续提取法、Meso cosm模型，以及数值和现场模拟的方法的应用，对潮滩重金属的研究将有很大帮助。在潮滩重金属的污染评价中，生物标准较其它标准更为适合。     

Changing depositional environment and factors controlling the growth of mudflat in a tropical estuary,west coast of India

Mudflats and associated mangroves are most important ecosystems of tropical coastal regions. Mangroves play a very important role in maintaining the environmental balance; thus in addition to mangrove reforestation and restoration, afforestation has also been practiced. We studied distribution of sediment components (sand, silt, clay) organic carbon (OC), heavy metals (Fe, Mn, Cu, Zn, Cr and Co) and pH in six cores collected from one of the largest mudflats of Mandovi estuary, west coast of India. The temporal distribution patterns of these proxies suggested that past changes in tidal energy conditions, fresh water inflow and anthropogenic activities over the last few decades, together helped in development of a middle tidal flat in this estuary. In cores collected from the mangroves, trapping and deposition of finer particles and organic matter were enhanced by a complex aerial mangrove root system in recent years. Mangroves were, therefore, suggested to enhance the buildup of mudflats in Mandovi estuary. Cores collected from mudflats also exhibited higher deposition of finer particles and organic matter (except MF2) in recent years, suggesting maturity and greater stability of the entire mudflat in recent years. Middle tidal flats (mudflats) of Mandovi estuary may, therefore, prove to be suitable substrates for mangrove proliferation in the near future. Finer sediments deposited mainly from mining activities in recent years exhibited lower pH and higher metal content. Organisms dwelling in these recently deposited sediments are, therefore, at higher risk of bioaccumulation and metal toxicity.     

Heavy metal distribution in surface sediments of the Tirumalairajan river estuary and the surrounding coastal area, east coast of India

Surface sediments collected at the Tirumalairajan river estuary and their surrounding coastal areas were analyzed for the bulk metal concentration. The sediments were collected from post- and premonsoon seasons. Dominances of heavy metals are in the following order: Fe > Mn > Zn > Pb > Cu in both seasons from estuary and coastal area. The results reveal that Fe, Mn, Cu, Pb, and Zn demonstrated an increased pattern from the estuary when compared to the coastal area. The heavy metal pattern of the sediments of the Tirumalairajan river estuary and its surrounding coastal area offered strong evidence that the coastal area was a major source of heavy metals to the estuarine region. For various metals, the contamination factor and geoaccumulation index (I _geo) have been calculated to assess the degree of pollution in sediments. The contamination factor and geoaccumulation index show that Zn, Pb, and Cu unpolluted to moderately pollute the sediments in estuarine part. This study shows the major sources of metal contamination in catchment and anthropogenic ones, such as agriculture runoff, discharge of industrial wastewater, and municipal sewage through the estuary and adjoining coastal area.     

Heavy metals in sediments of the rhine and elbe estuaries: Mobilization or mixing effect?

On their way from the Rhine estuary into the North Sea and Dutch Wadden Sea, Rhine sediments “lose” large portions of their original heavy metal concentrations. Until now these losses were explained by a mobilization process, solubilization — the decomposition products of organic matter form soluble organometallic complexes with the metals of the sediment. Our investigations of the sediments of the Elbe clearly indicate that a mixing process, whereby highly polluted Elbe sediments mix with relatively non-polluted North Sea sediments, rather than solubilization, is the cause of the dilution of heavy metals in the sediments of the Elbe estuary. Because of the similarity of the Elbe data with those from the Rhine River, we propose that a mixing process is also effective in the Rhine estuary and adjacent North Sea areas. The mechanism by which heavy metals are “diluted” is important to the marine ecosystem. In the mixing process proposed in this paper, the heavy metals fixed to the suspected material are trapped in bottom sediments of the marine environment, whereas solubilization would increase the concentration of heavy metals in the sea water and thus they would be more available for uptake by aquatic organisms.     

Heavy metal distribution and accumulation in two Spartina sp.-dominated macrotidal salt marshes from the Seine estuary (France) and the Medway estuary (UK)

The upper intertidal zone, and salt marshes in particular, have been shown by numerous authors to be effective medium to long-term storage areas for a range of contaminants discharged or transported into the estuarine environment. A detailed understanding of the specific controls on the trapping and storage of contaminants, however, is absent for many estuarine systems. This paper examines heavy metal distribution and accumulation in two contrasting Spartina sp.-dominated macrotidal salt marsh systems – a rapidly prograding, relatively young marsh system at the Vasiere Nord, near the mouth of the Seine estuary, France, and a more mature, less extensive marsh system in the Medway estuary, UK. The spatial distribution of the heavy metals Zn, Cu, Pb, Ni and Co is assessed and compared in both systems via detailed surface sampling and analysis, while the longer-term accumulation of these metals and its temporal variability is compared via analysis of dated sediment cores. Of the two sites studied, the more extensive marsh system at the Vasiere Nord in the Seine estuary shows a clear differentiation of heavy metals across the marsh and fronting mudflat, with highest metal concentrations found in surface sediments from the more elevated, interior marsh areas. At Horrid Hill in the Medway estuary, the spatial distribution of heavy metals in surface sediments is more irregular, and there is no clear relationship between heavy metal concentration and site elevation, with average concentrations similar in the marsh and fronting mudflats. Sediment core data indicate that the more recent near-surface sediments at Horrid Hill are clearly more contaminated than those at greater depth, with most heavy metal contamination confined to the upper 20 cm of the sediment column (with peak metal input in the late 1960s/early 1970s). In contrast, due to extremely rapid sediment accretion at the mouth of the Seine, heavy metal distribution with depth at the Vasiere Nord site is relatively erratic, with metal concentrations showing a general increase with depth. These sediments provide little information on temporal trends in heavy metal loading to the Seine estuary. Overall, heavy metal concentrations at both sites are within typical ranges reported for other industrialised estuaries in NW Europe.     

Heavy metal anomalies in the Tinto and Odiel River and estuary system,Spain

The Tinto and Odiel rivers drain 100 km from the Rio Tinto sulphide mining district, and join at a 20-km long estuary entering the Atlantic Ocean. A reconnaissance study of heavy metal anomalies in channel sand and overbank mud of the river and estuary by semi-quantitative emission dc-arc spectrographic analysis shows the following upstream to downstream ranges in ppm (μg g^?1): As 3,000 to <200, Cd 30 to <0.1, Cu 1,500 to 10, Pb 2,000 to <10, Sb 3000 to <150, and Zn 3,000 to <200. Organic-rich (1.3–2.6% total organic carbon, TOC), sandysilty overbank clay has been analyzed to represent suspended load materials. The high content of heavy metals in the overbank clay throughout the river and estuary systems indicates the importance of suspended sediment transport for dispersing heavy metals from natural erosion and anthropogenic mining activities of the sulfide deposit. The organic-poor (0.21–0.37% TOC) river bed sand has been analyzed to represent bedload transport of naturally-occurring sulfide minerals. The sand has high concentrations of metals upstream but these decrease an order of magnitude in the lower estuary. Although heavy metal contamination of estuary mouth beach sand has been diluted to background levels estuary mud exhibits increased contamination apparently related to finer grain size, higher organic carbon content, precipitation of river-borne dissolved solids, and input of anthropogenic heavy metals from industrial sources. The contaminated estuary mud disperses to the inner shelf mud belt and offshore suspended sediment, which exhibit metal anomalies from natural erosion and mining of upstream Rio Tinto sulphide lode sources (Pb, Cu, Zn) and industrial activities within the estuary (Fe, Cr, Ti). Because heavy metal contamination of Tinto-Odiel river sediment reaches or exceeds the highest levels encountered in other river sediments of Spain and Europe, a detailed analysis of metals in water and suspended sediment throughout the system, and epidemiological analysis of heavy metal effects in humans is appropriate.     

沉积物微量金属元素在重建水体环境变化中的意义

沉积物所记录的微量金属含量与形态的变化是指示人类活动影响下水体环境变化的有效指标,主要用于指示沉积物重金属污染、水体初级生产力变化和氧化还原条件等方面的水体环境状况。总体而言,沉积物中微量金属含量在近一个世纪以来显著上升,反映了采矿、冶金、污水排放、化肥使用、煤炭和石油燃烧等各种人类活动造成水体和沉积物重金属污染的记录作为浮游植物微量营养元素,Cu、Zn、Ni、Ba、Cd等在沉积物中的记录可以指示水体初级生产力水平。U、Mo、V、Cu、Cd、Mn等氧化还原敏感元素在沉积物中的富集或贫化,及其比值(如Re/Mo、Cd/U、Th/U和V/Sc)的变化,是指示水体和沉积物氧化还原环境的有效指标。但需要指出的是,在受人类活动影响的水体中,这些生产力和氧化还原指标很少能指示水体生产力或氧化还原状况,可能主要与人类活动同时造成这些金属元素大量污染输入而掩盖了其自生来源和内在变化的沉积记录有关。所以,对沉积物中微量金属元素来源的判别(陆源碎屑输入、人为输入和水体自生来源)是重建水体环境变化的重要前提。本文总结了多种化学和统计学方法(包括同位素示踪法、化学提取法、富集因子法和主成分分析法等)在沉积物金属来源判别中的应用另外,成岩作用等多种因素会干扰沉积物金属记录对环境变化的指示作用,所以构建多元素指标来综合判断沉积物记录所反映的环境信息是今后的研究所必须关注的     

Reconstructing historical trends in metal input in heavily-disturbed,contaminated estuaries: studies from Bilbao,Southampton Water and Sicily

Estuaries may be important reservoirs for contaminants as they tend to act as sinks for fine, contaminant-reactive sediments, and, historically, they have acted as centres for industrial and urban development. Analysis of dated sediment cores from these areas may allow historical trends in heavy metal input to be reconstructed, and recent and historical inputs of metal contaminants to be compared. Undisturbed saltmarsh settings have been used widely in the reconstruction of historical trends in metal input as saltmarshes provide a stable, vegetated substrate of dominantly fine sediments, and are less prone to erosion and reworking than adjacent mudflat areas. In comparison, much less research on historical pollution trends has been undertaken at estuarine sites which are prone to severe local disturbance, such as intertidal areas which are routinely dredged or where sedimentary processes have been modified by human activities such as shipping, salt working, port activities, land claim etc. This paper assesses the usefulness of ²¹⁰Pb and ¹³⁷Cs dating, combined with geochemical studies, in reconstructing historical trends in heavy metal input and sediment accretion in 3 heavily-modified, industrialised estuarine areas in Europe: the Bilbao estuary (Spain), Southampton Water (UK), and the Mulinello estuary (Sicily). Of these sites, only a salt marsh core from the Mulinello estuary provides a high-resolution record of recent heavy metal inputs. In Southampton Water only a partial record of changing metal inputs over time is retained due to land-claim and possible early-diagenetic remobilisation, while at Bilbao the vertical distribution of heavy metals in intertidal flats is mainly controlled by input on reworked sediment particles and variations in sediment composition. Where ¹³⁷Cs and ²¹⁰Pb distributions with depth allow a chronology of sediment deposition to be established, and early-diagenetic remobilisation has been minimal, mudflat and saltmarsh cores from even the most heavily-disturbed estuarine sites can provide useful information on variations in historical contaminant input. When the sediments have been vigorously mixed or reworked, large-scale compositional variations are present, or significant early-diagenetic remobilisation has occurred, however, only general information on the scale of contamination can be obtained.