Downstream changes of total and partitioned metal concentrations in the flood deposits of the river Geul (The Netherlands)

The floodplain soils in the Guel basin have unacceptably high levels of pollution,v brought about by metal mining and related industrial activities in the past. Spoil heaps still exist along the Geul river and these are susceptible to erosion and leaching processes. An additional source of metals is formed by erosion of older, locally highly contaminated streambank deposits. These older sediments are polluted as a result of solid waste disposal containing metalliferous ore and tailings in the sand fraction. At present, these sediments function as a major source of heavy metals during high flow stages when streambanks are undermined and suspended sediments are deposited on the floodplains. The flood deposits have a relatively coarse texture, i.e. 70% dry weight in the fraction > 63 um.In order to obtain an indication about the potential mobility of the heavy metals in these deposits, 16 samples (8 samples < 63 um and 8 samples > 63 um) out of a set of 122 were subjected to a sequential extraction scheme as proposed by Calmano & Förstner (1983). It was found that up to 80% of the metals may be present in the first three leaching stages (exchangeable cations, carbonate fraction and easily reducible fraction) and that hardly any difference exists between the chemical partitioning of metals in the size fractions < 63 um and > 63 um. Moreover, as the total metal concentrations exponentially decrease along the 40 km distance away from the source area, the percentage of metals in these 3 potentially mobile fractions steadily increases. It is concluded that despite the rapid decay of total metal concentrations, Large amounts of potentially mobile metals are probably stored in the floodplain sediments even at a large distance from the source area.     

Distinguishing between natural and anthropogenic sources of metals entering the Irish Sea

International agreements (e.g. OSPAR) on the release of hazardous substances into the marine environment and environmental assessments of shelf seas require that concentrations and bioavailability of metals from anthropogenic sources can be distinguished from those originating as a result of natural geological processes. The development of a methodology for distinguishing between anthropogenic and natural sources of metals entering the Irish Sea through river inputs is described. The geochemistry of stream, river and estuarine sediments has been used to identify background geochemical signatures, related to geology, and modifications to these signatures by anthropogenic activities. The British Geological Survey (BGS) geochemical database, based on stream sediments from 1 to 2 km² catchments, was used to derive the background signatures. Where mining activity was present, the impact on the signature was estimated by comparison with the geochemistry of sediments from a geologically similar, but mining free, area. River sediment samples taken upstream and downstream of major towns were used respectively to test the validity of using stream sediments to estimate the chemistry of the major river sediment and to provide an indication of the anthropogenic impact related to urban and industrial development. The geochemistry of estuarine sediments from surface samples and cores was then compared with river and offshore sediment chemistry to assess the importance of riverine inputs to the Irish Sea. Studies were undertaken in the Solway, Ribble, Wyre and Mersey estuaries. The results verify that catchment averages of stream sediments and major river samples have comparable chemistry where anthropogenic influences are small. Major urban and industrial (including mining) development causes easily recognised departures from the natural multi-element geochemical signature in river sediment samples downstream of the development and enhanced metal levels are observed in sediments from estuaries with industrial catchments. Stream sediment chemistry coupled with limited river and estuarine sampling provides a cost-effective means of identifying anthropogenic metal inputs to the marine environment. Investigations of field and laboratory protocols to characterise biological impact (bioaccumulation) of metals in sediments of the Irish Sea and its estuaries show that useful assessments can be made by a combination of surveys with bioindicator species such as clams Scrobicularia plana, selective sediment measurements that mimic the ‘biologically available’ fractions, and laboratory (mesocosm) studies.     

Variability of the metal content of flood deposits

Fresh flood deposits were sampled in the flood-plains of two river systems, the River Meuse, with a catchment area of 33,000 km² and the River Geul, with a catchment area of 3,000 km². As a result of industrial and mining activities, both rivers have a history of severe metal pollution, especially with zinc, lead, and cadmium. The flood deposits of both rivers are heterogeneous mixtures of contaminated bottom sediments (with relatively long residence times in the river) and clean sediments derived from soil erosion on agricultural cropland (with very short residence times). An additional source of sediment is formed by erosion of older, locally highly contaminated streambank deposits. These older sediments are polluted as a result of solid waste disposal containing metalliferous ore and tailings in the sand fraction. This is especially the case in the River Geul, which drains an old zinc and lead mining area. The metal content of the Meuse sediments, however, originates largely from liquid industrial wastes and occurs mainly in the clay fraction. For this reason, the positive correlation between textural composition, organic matter content, and heavy metal concentration, which is often reported, was not observed, and normalization of the metal content was not possible. Nevertheless, a clear decrease of contamination was noticed along the River Geul; this trend was absent along the River Meuse. An attempt has been made to model the longitudinal decay pattern for each of the investigated havey metals.     

Environmental effects of river sand mining: a case from the river catchments of Vembanad lake,Southwest coast of India

Rivers in the southwest coast of India are under immense pressure due to various kinds of human activities among which indiscriminate extraction of construction grade sand is the most disastrous one. The situation is rather alarming in the rivers draining the Vembanad lake catchments as the area hosts one of the fast developing urban-cum-industrial centre, the Kochi city, otherwise called the Queen of Arabian Sea. The Vembanad lake catchments are drained by seven rivers whose length varies between 78 and 244 km and catchment area between 847 and 5,398 km². On an average, 11.73 million ty⁻¹ of sand and gravel are being extracted from the active channels and 0.414 million ty⁻¹ of sand from the river floodplains. The quantity of instream mining is about 40 times the higher than the sand input estimated in the gauging stations. As a result of indiscriminate sand mining, the riverbed in the storage zone is getting lowered at a rate of 7–15 cm y⁻¹ over the past two decades. This, in turn, imposes severe damages to the physical and biological environments of these river systems. The present paper deals with the environmental effects of indiscriminate sand mining from the small catchment rivers in the southwest coast of India, taking the case of the rivers draining the Vembanad lake catchments as an example.     

Current impact of mining alkaline rocks on Save River water quality in Zimbabwe

Alkaline rocks (phosphate deposits in particular) of igneous origin are currently being mined in Zimbabwe. Exploitation of these deposits, which are associated with metals and non-metals, provides a potential for changing the river water quality in the surrounding areas by increasing metal and phosphates levels in the water, thereby endangering the beneficial use of the river. The aim and objectives of this paper are to enumerate the current impacts associated with mining alkaline rocks on Save River water quality in Zimbabwe using the Dorowa mine as a case study. Though there are several impacts associated with the mining of alkaline rocks, this paper deals only with impacts on water quality.A preliminary assessment of the water quality in the Save River downstream of the Dorowa phosphate mine showed an increase in conductivity, iron content, manganese content, nitrates and hardness when compared to those taken before mining activity began. However, there was no notable increase in phosphate and metals except for Fe and Mn. A plausible explanation for the low phosphate values in the water is that the phosphates are precipitating and settling as sediments. Phosphate is known to effectively remove metals from the surface water through the formation of metal–phosphate minerals. Thus, various pollutants may be adsorbed into sediments accumulated on the bottom of the river. These sediments may accumulate pollutants over long periods and act as new pollutant sources to the overlying water when phosphate desorbs from sediments due to changes in water conditions. Therefore, the sediments can act as a source of water pollution in the future.     

陕西潼关金矿区太峪河底泥重金属元素的含量及污染评价

通过对潼关金矿区太峪河和太峪水库底泥中重金属元素总量的调查,探讨了金矿开发活动中重金属元素对河流底泥的污染程度。研究结果表明,除As外,河流底泥中重金属元素的含量与尾矿渣中重金属元素的含量变化一致,表明其主要来源于尾矿渣,但又明显高于尾矿渣。在同一地点河流底泥中重金属元素的含量平均高出河水中的1048.61～666030.08倍,呈显著富集。以邻近地区不受工矿活动影响的河流底泥重金属元素的含量均值作为评价参比值,太峪河底泥受到了Hg、Pb、Cd、Cu、Zn元素的极度污染,单项污染超标倍数及综合污染指数法评价结果表明,Hg、Pb、Cd平均污染超标倍数达366.90、217.42和149.97,是底泥中最主要的污染元素。河流底泥重金属元素的综合污染指数高达278.97,表明河流的复合污染亦呈极度状态。太峪河底泥受重金属元素极度污染的现实提示,矿区的环境防治工作已刻不容缓。     

Transportation and evolution of trace element bearing phases in stream sediments in a mining – Influenced basin (Upper Isle River,France)

Arsenic-bearing stream sediments enter the Upper Isle River, an Au mining-influenced basin (France), by the discharge of mining sites, tailings runoff and weathering of mineralized veins in granites and gneiss. Some fresh ochreous As-rich deposits on the river banks and in floodplains are identified as additional As-rich point sources (As between 0.07 and 6.5 wt.%). The <63 μm fraction of stream sediments contains elevated As bulk concentrations, ranging from 160 to 890 mg/kg, compared to the geochemical background (70 mg/kg on average). It is also enriched in Cd, Hg and W. Spatial variations of these trace elements show 3 significant increases corresponding to the 3 drained mining districts. They decrease down river but are still enriched 30 km downstream of the mining districts due to downstream transportation. Three types of trace element-bearing phases have been identified as: (i) detrital primary sulfides, with high in situ As percentages (up to 43.7 wt.%). They also carry significant amounts of W according to the differences in chemical compositions of the total and light <63 μm fractions. These sulfide particles do not show any sign of alteration in the oxygenated stream sediments; (ii) Secondary Fe–Mn oxyhydroxides,some with very high in situ As₂O₅ concentrations (up to 59.8 wt.%) and with about 40% of the total Cd composition. They occur as fresh precipitates in the river banks and floodplains and as discrete particles in stream sediments and (iii) Al–Si fine-grained phases. Their major element composition is highly variable with in situ As₂O₅ concentrations ranging between 430 and 5020 mg/kg. This type of solid phase is also the major carrier of Hg.     

Geochemistry and provenance of bed sediments of the large rivers in the Tibetan Plateau and Himalayan region

We investigated the geochemical characteristics of major, trace and rare earth elements and Sr–Nd isotope patterns of bed sediments from the headwaters and upper reaches of the six large rivers draining the Tibetan Plateau (the Jinsha River—Yangtze, Lancang River—Mekong, Nujiang River—Salween, Huang He—Yellow, Indus, and Yarlung Tsangpo—Brahmaputra). By using Ca/Al versus Mg/Al, La/Sc versus Co/Th, and ⁸⁷Sr/⁸⁶Sr versus ε_Nd (0) binary differentiation diagrams of provenance, some typical contributors to the different catchment sediments can be identified. In the Three-River (the Jinsha, Lancang, and Nujiang Rivers) tectonomagmatic belt, acidic–intermediate-acidic volcanic rocks are very important provenance of sediments. Carbonate rocks and Permian Emeishan basalts are dominant in the Jinsha River. The Yellow River sediments have similar geochemical characteristics with loess in catchments. The Indus and Yarlung Tsangpo Rivers sediments are mainly from ultra-K volcanic rocks and Cenozoic granitoids widely distributed in the Indus–Yarlung suture. The intensity of chemical weathering in these river catchments is evaluated by calculating the chemical indices of alteration (CIA) of sediments and comparing them with bedrocks. The CIA values of the six river sediments are from 46.5 to 69.6, closing to those of bedrocks in the corresponding catchment, which indicates relatively weak chemical weathering intensity. Lithology, climate, and topography affect the chemical weathering intensity in these river catchments.     

Holocene alluviation and land-use change on Callaly Moor,Northumberland, England

Archaeological survey and palaeoenvironmental investigations in Coe Burn, Callaly Moor, Northumberland, have examined the chronology and nature of prehistoric and historic land-use change in a small upland river catchment. These studies have revealed an intensively used landscape with evidence of late Neolithic to Bronze Age, medieval and post-medieval land use and settlement. Two episodes of valley floor alluviation are identified and dated to the middle-late Bronze Age and post-medieval periods. Magnetic mineral and geochemical analyses of fine sediments from the older alluvial fill show it to contain a high proportion of topsoil, which is believed to have been produced by soil erosion resulting from Bronze Age tree clearance and cultivation. Deposition of the younger alluvial fill (post AD 1500) was associated with the inwash of relatively unweathered bedrock generated by coal mining in the catchment. It is demonstrated that by integrating archaeological field survey with off-site palaeoenvironmental investigations a much fuller picture of human activity and land-use change has emerged than otherwise would have been the case. Studies of this type may be particularly useful in other upland river catchments where archaeological survival is limited or poor.     

Sediment generation on a volcanic island with arid tropical climate: A perspective based on geochemical maps of topsoils and stream sediments from Santiago Island,Cape Verde

The present research tests the application of geochemical atlas of soils and stream sediments in the investigation of weathering and erosion processes on volcanic islands. The composition of surface soils collected in six catchments from Santiago Island (Cape Verde) are compared with bedload stream deposits sourced by these catchment areas in order to evaluate the spatial variability of these exogenous processes. The geochemistry of bedload stream deposits is between that of the fresh rocks and the topsoils of their source areas. Relative to average soil composition, bedload deposits are depleted in most of less-mobile elements (e.g., Al, Fe, La, Sc) and strongly enriched in Na and, usually, Ca. When the topsoil weathering intensity in the catchment areas is highly variable and the composition of bedload deposits is substantially different from the average soil composition, bedload deposits should incorporate significant amounts of poorly-weathered rocks and sectors from erosion occur within the drainage basin. Ratios of non-mobile elements allow the identification of highly vulnerable and erosion-protected sectors within the catchments. It is proposed that the catchments of the rivers in the SW flanking side of Santiago Island include sectors where lava shields formed during the post-erosional eruptive phases are capable of an effective protection to erosion. Conversely, the NE-facing part of the island is highly dissected and any younger post-erosional cover was either completely eroded away, or never existed in the first place. Simple compositional parameters derived from the databases of geochemical maps of soil and stream sediments provide important information for the analyses of weathering, erosion and denudation processes at the catchment scale.     

Environmental impact of the former Pb–Zn mining and smelting in East Belgium

In the mining district of Plombières-La Calamine (East Belgium), extensive Pb–Zn mining activities resulted in an important contamination of overbank sediments along the Geul river. Moreover, a huge amount of heavy metals is stored in a dredged mine pond tailing, which is located along the river. In the dredged mine pond tailing sediments, Pb–Zn minerals control the solubility of Zn, Pb and Cd. Although Pb, Zn and Cd display a lower solubility in overbank sediments compared to the mine tailing pond sediments, elevated concentrations of Pb, Zn and Cd are still found in the porewater of the overbank sediments. The considerable ‘actual’ and ‘potential’ mobility of Zn, Pb and Cd indicates that the mine pond tailing sediments and the overbank sediments downstream from the mine pond tailing represent a considerable threat for the environment. Besides the chemical remobilisation of metals from the sediments, the erosion of overbank sediments and the reworking of riverbed sediments act as a secondary source of pollution.     

Nonpoint pollution load in river catchments with different anthropic impacts: a case study in Southern Brazil

Diffuse or nonpoint source (NPS) pollution results in different pollutant concentrations, which depend on river catchments, land use and precipitation events and may vary along a single event. This study aimed to assess NPS pollution loads of organic matter, nutrients, bacteria and heavy metals in four river catchments associated with different types of land use in Southern Brazil. Cluster analysis was used to identify similarities between basins and main component analysis (PCA) to identify the main variables that characterize diffuse pollution in each basin. The use and occupation of the soil were determinant in the formation of the clusters. The basins with rural characteristics formed one group, whereas the basin with urban characteristic generated another group. PCA suggests that changes in the water quality of the catchments in this study can be explained by organic pollutants and farming activities. The Rancho do Amaral catchment, with 55.8% of native forest, displayed the lowest NPS pollution load for all tested parameters. The Alto da Colina catchment, with the largest urban area and largest agricultural land use (50%), showed the highest NPS for all variables in the study, even though it has the smallest area. The differences in pollutant loads can be attributed to the intense degradation processes associated with anthropic activities, such as urbanization, agricultural activity and the discharge of effluents, which are different for each catchment.     

Changing hillslope and fluvial Holocene sediment dynamics in a Belgian loess catchment

Floodplain deposition is an essential part of the Holocene sediment dynamics of many catchments and a thorough dating control of these floodplain deposits is therefore essential to understand the driving forces of these sediment dynamics. In this paper we date floodplain and colluvial deposition in the Belgian Dijle catchment using accelerator mass spectrometric radiocarbon and optical stimulated luminescence dating. Relative mass accumulation curves for the Holocene were constructed for three colluvial sites and 12 alluvial sites. A database was constructed of all available radiocarbon ages of the catchment and this database was analysed using relative sediment mass accumulation rates and cumulative probability functions of ages and site‐specific sedimentation curves. Cumulative probability functions of ages were split into different depositional environments representing stable phases and phases of accelerated clastic deposition. The results indicate that there is an important variation between the different dated sites. After an initial stable early and middle Holocene phase with mainly peat growth in the floodplains, clastic sedimentation rates increased from 4000 BC on. This first phase was more pronounced and started somewhat earlier for colluvial deposits then for alluvial deposits. The main part of the Holocene deposits, both in colluvial and alluvial valleys, was deposited during the last 1 ka. The sedimentation pattern of the individual dated sites and the catchment‐wide pattern indicate that land use changes are responsible for the main variations in the Holocene sediment dynamics of this catchment, while the field data do not provide indications for a climatological influence on the sediment dynamics. Copyright © 2011 John Wiley & Sons, Ltd.     

Chemical and mineralogical composition of fluvial sediments (Bistrita River,Romania): Geogenic vs. anthropogenic input into rivers on its way through mining areas

The upper reaches of the Bistrita drainage system were selected as a natural test site to determine the geogenic and anthropogenic input into fluvio-lacustrine systems in humid mid-latitude morphoclimatic zones. The reason for this selection lies in the complex geology and its metallogenic evolution leading to a great variety of Fe, Mn, U, and polymetallic sulfides ore deposits. It sparked an intense mining activity during the past centuries with a strong impact on the drainage system similar to many mineralized sites in the world which are still under exploitation. Sediment samples from Bistrita River were analyzed by means of X-ray fluorescence spectrometry (XRF), X-ray diffraction (XRD), near-infrared (NIR) and micro-Raman spectroscopy (μ-Raman).Our results revealed that the chemical and mineralogical built-up of the stream sediments is mainly geogenic, with most of the trace elements accumulated in the river sediments derived from the source rocks exposed in catchment area of the River Bistrita. A strong input by man has been detected in the drainage system near abandoned mining sites. The trace elements are mainly accommodated in the structure of detrital minerals representative of the clastic aureole around the source rocks, and to a lesser extent adsorbed onto the surface of clay minerals. The REE incorporated into muscovite furnish evidence of having derived from the source rocks, prevalently mica schists exposed by supergene processes in the provenance area and rule out a neoformation of clay minerals on transport and deposition.     

白音诺尔铅锌矿区河流沉积物重金属的形态分布特征

为了研究内蒙古赤峰市巴林左旗白音诺尔铅锌矿区采矿对哈力黑河生态环境造成的影响,从上游向下游采集了6个河流沉积物样品,测定其pH、LOI、粒度以及As、Cu、Pb、Zn、Cd等5种重金属的总量和赋存形态,并对测试结果进行分析。研究结果表明:（1）1#尾矿库是造成沉积物中Pb、Zn和Cd等重金属显著升高的主要原因。（2）沉积物重金属与粗粉砂（16~63 μm）的相关系数为0.79~0.95,表明重金属易富集于粗粉砂上,而沉积物的pH和有机质对重金属总量的变化影响不显著。（3）沉积物中As和Pb以残渣态和铁锰结合态为主,分别占总量的78.82%~89.87%和36.96%~78.20%。Cu和Zn以残渣态、强有机结合态和铁锰结合态为主,分别占总量的76.38%~85.96%和74.94%~90.34%。Cd则以离子交换态、碳酸盐结合态和强有机结合态为主,占总量的51.15%~79.53%,而离子交换态Cd占了总量的5.72%~49.63%。因此,Cd对河流生态环境的潜在威胁最大。（4）离子交换态Cd与沉积物pH相关系数为-0.813,两者呈极强负相关性。当沉积物pH由弱酸性转化为弱碱性时,离子交换态Cd含量从33.44%降低至5.72%,显著减小。     

Pb isotope evidence for contaminant-metal dispersal in an international river system: The lower Danube catchment,Eastern Europe

Lead isotope signatures (²⁰⁷Pb/²⁰⁶Pb, ²⁰⁸Pb/²⁰⁶Pb, ²⁰⁸Pb/²⁰⁴Pb, ²⁰⁶Pb/²⁰⁴Pb), determined by magnetic sector ICP-MS in river channel sediment, metal ores and mine waste, have been used as geochemical tracers to quantify the delivery and dispersal of sediment-associated metals in the lower Danube River catchment. Due to a diverse geology and range of ore-body ages, Pb isotope signatures in ore-bodies within the lower Danube River catchment show considerable variation, even within individual metallogenic zones. It is also possible to discriminate between the Pb isotopic signatures in mine waste and river sediment within river systems draining individual ore bodies. Lead isotopic data, along with multi-element data; were used to establish the provenance of river sediments and quantify sedimentary contributions to mining-affected tributaries and to the Danube River. Data indicate that mining-affected tributaries in Serbia and Bulgaria contribute up to 30% of the river channel sediment load of the lower Danube River. Quantifying relative sediment contributions from mining-affected tributaries enables spatial patterns in sediment-associated metal and As concentrations to be interpreted in terms of key contaminant sources. Combining geochemical survey data with that regarding the provenance of contaminated sediments can therefore be used to identify foci for remediation and environmental management strategies.     

金矿区河水和底泥中重金属含量分布与耦合关系

河流中河水与底泥中重金属含量之间的关系对于河流污染防治意义重大。对某金矿区3种典型河流的河水与底泥中的重金属含量进行分析,发现4条河流均有超过国家标准限值的情况,河水中7种重金属元素均出现超标,Cr、As元素超标不严重;底泥中Hg、Pb、Cr、Cu、Zn超标,其中Hg超标最严重,河水和底泥中Hg最大超标倍数分别达到3099倍和244倍。河流中重金属主要赋存形态为沉积态,底泥的吸附解吸作用是河流底泥和河水中重金属沿程变化的主控因素;金矿区区域上河水和底泥中重金属很好地服从Langmuir等温吸附模式。矿业活动、地层岩性均会影响底泥对重金属的平均最大吸附容量,流径黄土区的双桥河平均最大吸附容量最大。研究结果为矿山河流污染防治与预警提供了参考依据。     

Using total suspended solids (TSS) and turbidity as proxies for evaluation of metal transport in river water

The present study was carried out in Haraz basin (Iran) that is located in south of the Caspian Sea. The goal of this study was to establish correlations amongst total suspended solids concentration (TSS) and turbidity with total pollutant concentrations to evaluate the dissolved and particle-bound concentrations of major toxic metals. It also aimed to validate TSS and/or turbidity measurements as proxies to monitor pollutant fluxes. Eight metals, namely nickel, lead, cadmium, copper, zinc, cobalt, arsenic and strontium were analyzed for dissolved and total concentrations in water at ten locations within the catchment. TSS and turbidity were also measured. Sampling campaigns were designed to cover both the rainy (December) and the dry (May) season within the basin. The robust relationship between TSS (202–1212 mg/l) and turbidity (63–501 NTUs) in both seasons warranted their interchangeable potential as proxies within the observed ranges. Total element concentrations were plotted in separate attempts versus TSS and turbidity for all locations and both events. Very good linear correlations were attained where the slopes represent the metals concentration on suspended solids and the intercept the dissolved concentration in water. The results achieved by these linear regressions were in very good agreement with independently measured values for dissolved concentration and concentrations on river bed sediments taken at the same locations. This demonstrates that turbidity and/or TSS measurements may be used for monitoring of metal loads if once calibrated against total concentration of metals. The results also revealed that in the lower Haraz catchment metal concentrations on suspended and river bed sediment were homogeneously distributed along the investigated river stretch. This is assumed to be due to intensive gravel and sand mining activities in the upper and middle part of the catchment.     

Multi-elemental composition of the Sava River sediments (Slovenia,EU)

The Sava River is the longest river in Slovenia and has been subjected to pollution in the past. Fine-grained channel sediments, which were deposited during the high-water event in July 2009, along the river course in Slovenia were sampled at 12 locations in order to determine the content of a large set of chemical elements and assess possible levels of pollution. Sediment samples were air-dried. Two grain size fractions (<0.063 and <0.125 mm) were prepared for chemical analyses by dry sieving. Elemental levels of each sample were determined after aqua regia extraction (1 h, 95 °C) by inductively coupled plasma mass spectrometry. Elemental levels did not exceed the legislation action limit values, indicating that the Sava River recently deposited alluvial sediments are not contaminated with potentially toxic metals. The results show that the chemical composition of the Sava River sediments is comparable to the average composition of stream sediments within Europe. Some light impacts of anthropogenic activities and lithological-driven influential factors to the elemental composition of sediments were observed. Slight As enrichment is possibly a consequence of eroding of slag dumps and As-contaminated soil on Sava River banks and emissions from treated sewage waters. Lead (Pb) is increased in the Litija area as a consequence of historic mining and increased zinc (Zn) and cadmium (Cd) concentrations after the Savinja River confluence because of historic smelting industry in its catchment area. Phosphorous levels in sediments are very likely driven by the emissions from farming and urbanisation. Increased Ba and Pb levels (but still being below the action value) are detected in sample downstream Kr?ko.     

Heavy metal mobility assessment in sediments from the Odiel River (Iberian Pyritic Belt) using sequential extraction

The Tessier sequential extraction scheme (SES) was applied to sediments from the Odiel river catchment (Iberian Pyritic Belt, SW of Spain), one of the most acid rivers on Earth, to assess the chemical association (exchangeable, carbonatic, bound to manganese and iron oxides, bound to organic matter and residual mineral) of heavy metals (Zn, Cd, Pb, Cu, Cr, Mn, Ni, Fe, and Hg). Sediments are very heterogeneous in their textural characteristics, showing different grain size. Twenty-seven samples were studied from from areas along the Odiel River, from the source to the mouth, with special interest in the Odiel Marshes Natural Park due to its ecological significance. Samples were classified as sandy (especially at the river mouth with low iron oxide and organic matter content) and clay-silty (in the middle of the river catchment with high iron oxide content). The numerous sandy samples with low pH values explain the low levels of metals upstream, although potential metals contributions arise from mining and ore. However, the presence of sulfate in the mining area and carbonate at the mouth may explain the high presence of lead and iron in these sandy zones. Some percentage of mobile Ni, Cu, and Zn were detected in the mining area, but the elevated relative percentage of exchangeable Cd in the estuary is even more remarkable. The percentage of Zn bound to carbonate is considerable in the catchment but especially in the estuary. However, Cu is only detected in the carbonate phase downstream, in spite of the low concentration of carbonate, which represents a drawback in the application of the Tessier SES to these types of samples. Finally, relatively high percentages of residual, non-mobile, Hg and Pb were observed, in the estuarine and mining areas, respectively. Sand, lime, and clay fractions of representative samples from Areas I, II, and III were used in a metal speciation study. Mainly, the elements analyzed had accumulated in the non-residual fractions. In the mining area of the Pyrite Belt, the elements analyzed are mainly bound to Fe–Mn oxides (Fe + Mn + Cu + Cr + Pb + Mn ± Zn) and the organic matter/sulfide fraction (Ni + Zn + Hg ± Cd), independent of sediment grain size. In conclusion, we show that the results of the study of chemical speciation in sediments from acid rivers are independent of the sediment grain size considered.