Trace metals in suspended particulate matter and in sediment trap material from a permanently anoxic fjord — Framvaren, South Norway

Geochemical studies of the trace metal concentrations in suspended particulate matter (SPM) and sediment trap material from a permanently anoxic fjord, Framvaren, South Norway in 1989 and 1993 indicate that extremely high concentrations of zinc (max = 183920 mg/kg), copper (max = 4130 mg/kg), lead (max = 2752 mg/kg), and cadmium (max= 8.1 mg/kg) sometimes (1993) occur in the SPM collected in the anoxic water layer. The highest concentrations of Zn occur just below the redoxcline at 22 m water depth (in 1993), and copper, lead and cadmium have maximum concentrations between 30 and 80 m depth, where the amount of total SPM is at a minimum (about 0.3 mg/L). On a mass per volume (g/L) basis, the maximum concentrations of Cd, Cu and Fe occur at the interface (21m) and those of Zn occur just below the redoxcline (22 m depth). The SPM and sediment trap data suggest that the metals are precipitated as sulfide minerals in the anoxic water. The presence of particulate sulfides was confirmed by SEM studies that show the occurrence of discrete metal (Cu, Fe, Pb, and Zn) sulfide particles in size from 10–20 m as well as framboidal pyrites (1–5 m in size). Higher levels of metal sulfides at intermediate depths rather than in the deep water of Framvaren (> 100 m), may be due to input of trace metals by water exchange over the sill in the upper part of the water column. In the deep water, less metal sulfide precipitation takes place due to depletion of trace metals, and the dilution of particulate metal concentrations by organic matter and by the chemogenic formation of calcite.     

A study on the physico-chemical speciation of heavy metals in waters of rivers, and lakes in the Changjiang River Valley, China

In the aquatic system, heavy metals always exist in a number of physico-chemical forms: particulate (Cp), soluble which consists of labile (MALI) and bound (inorganic MAb and organic MLb). The environmental behaviors of a metal are critically dependent on these forms. In this paper, the forms of heavy metals in waters from the Changjiang River source to mainstream and lakes were determined by ASV method. The main results are as follows: 1. The total contents (Ct) of Zn, Pb, Cu and Cd in the source were 4.0, 1.88, 1.28 and 0.07 (g/L) respectively, while Ct (g/L) in the mainstem were in the order of Zn (20.1) > Cu (14.9) > Pb (6.73) > Cd (0.15). Ct (g/L) in Dianchi Lake were Zn (7.2) > Pb (0.72) > Cu (0.53) > Cd (0.05), and in Poyang Lake were Zn (12.5) > Pb (4.2) > Cu (3.4) > Cd (0.05), and in Poyang Lake were Zn (12.5) > Pb (4.2) > Cu (3.4) > Cd (0.05). However, most of them were presented as Cp. Their dissolved contents (Cs, /L) were lower. 2. The distribution of soluble forms was related to the type of metal and to environmental variables. In general, Zn and Cd have a tendency to be present in MALi, Pb in MAb and Cu in MLb.     

Heavy metal contamination in overbank sediments of the Geul river (East Belgium): Its relation to former Pb-Zn mining activities

Overbank sediments of the Geul River (East Belgium) are highly contaminated by the heavy metals Pb, Zn, and Cd due to former Pb-Zn mining activities in the drainage basin. Geochemical variations in vertical overbank sediment profiles sampled 1 km north of the mine tailings of Plombiéres allow metal fluxes back to the 17th century to be reconstructed. The vertical profiles are subdivided into three major units corresponding to different industrial periods based on sedimentological criteria as well as on the distribution of contaminants. Alluvial sediments with the highest heavy metal concentrations correspond to the major period of mining activity of the 19th century. The fact that Zn mining at the La Calamine open mine started before large-scale mining of the PbS-ZnS subsurface exploitations is reflected in the vertical profiles by an increase in Zn content before a marked increase in Pb and Cu. The regional extent of contamination in the alluvial deposits was evaluated on the basis of the geochemical analysis of sediments at depths of the 0–20 cm and 80–100 cm. Most of the upper samples are extremely contaminated. Significant local variations in heavy metal concentration in the lower samples are interpreted in terms of which overbank sediment horizon has been sampled at a depth of 80–100 cm. This indicates that blind sampling of overbank sediments to characterize the degree of contamination in shallow boreholes can give very erratic results.     

Relationships Between Geochemical Parameters (pH, DOC, SPM, EDTA Concentrations) and Trace Metal (Cd, Co, Cu, Fe, Mn, Ni, Pb, Zn) Concentrations in River Waters of Texas (USA)

Water samples from eight major Texas rivers were collected at different times during 1997–1998 to determine the dissolved and particulate trace metal concentrations, expected to show differences in climate patterns, river discharge and other hydrochemical conditions, and human activities along the different rivers. Specifically, two eastern Texas rivers (Sabine, Neches) lie in a region with high vegetation, flat topography, and high rainfall rates, while four Central Texas rivers (Trinity, Brazos, Colorado, and San Antonio) flow through large population centers. Relatively high dissolved organic carbon (DOC) concentrations in the eastern Texas rivers and lower pH led to higher Fe and Mn concentrations in river waters. The rivers that flow through large population centers showed elevated trace metal (e.g., Cd, Pb, Zn) concentrations partly due to anthropogenically produced organic ligands such as ethylenediaminetetraacetic acid (EDTA) present in these rivers. Trace metal levels were reduced below dams/reservoirs along several Texas rivers. Statistical analysis revealed four major factors (suspended particulate matter [SPM], EDTA, pH, and DOC) that can explain most of the observed variability of trace metal concentrations in these rivers. SPM concentrations directly controlled particulate metal contents. Variation in pH correlated with changes of dissolved Co, Fe, Mn, and Ni, and particulate Mn concentrations, while DOC concentrations were significantly related to dissolved Fe concentrations. Most importantly, it was found that, more than pH, EDTA concentrations exerted a major control on dissolved concentrations of Cd and Zn, and, to a lesser extent, Cu, Ni, and Pb.     

Heavy metal contamination in water and sediment of the Port Klang coastal area, Selangor, Malaysia

This investigation presents the temporal and spatial distribution of heavy metals (As, Cd, Cr, Cu, Ni, Pb, Hg, and Zn), in water and in sediments of Port Klang, Malaysia. Water and sediment samples were collected from 21 stations at 3-month intervals, and contamination factor $ (C_{\text{f}} ) $ and contamination degree $ (C_{\text{d}} ) $ were calculated to estimate the contamination status at the sampling stations. Cluster analysis was used to classify the stations based on the contamination sources. Results show that concentrations of As, Cd, Hg, and Pb in sediment and As, Cd, Hg, Pb, Cr, and Zn in water were significantly higher than the background values at which these metals are considered hazardous. The main sources of heavy metal contamination in Port Klang were industrial wastewater and port activities.     

The transfer and fate of Cd, Cu, Pb and Zn from two historic metalliferous mine sites in the U.K.

Monitoring of heavy metal transfers, aerial deposition and fluvial transport to soil, stream sediment and vegetation compartments surrounding two former PbZn mines are reported. Results show that 80–100 a after the closure of the mines relatively large amounts of Cd, Pb, Zn and, in once case, Cu are entering the soil and fluvial systems.Aerial deposition of heavy metals within a 300 m radius of the centre of the tailings heaps is shown to be contributing up to 3.3 kg Cd, 71 kg Cu, 373 kg Pb and 1041 kg Zn annually to the surrounding soil and vegetation compartments. It is shown that more than 4.2 kg Cd/a and 1387 kg Zn/a are being transferred from the tailings heaps via the streams in the form of dissolved load. However, the greatest quantities of Cu (38 kg/a) and Pb (74 kg/a) are transported from the heaps as wash load. Transfers calculated as percentages of the total metal quantities in the tailings heaps highlight the greater relative mobility within the fluvial system of Cd and Zn compared to Cu and Pb. Outside of the tailings heaps, the greatest accumulation of metals is in the surrounding soil, while the smallest was observed to occur in the surrounding mixed grassland vegetation.The most important implications of these findings are in the long-term release and partitioning of pollutant metal species from historic metalliferous mine tailings within the terrestrial and fluvial environments. This information is of major ecotoxicological and agronomic importance and is necessary for the effective reclamation and remediation of such contaminated sites.     

Scenario of particulate trace metal and metalloid transport during a major flood event inferred from transient geochemical signals

High-resolution sampling (every 3 h) of SPM was performed during a major flood event in a heterogeneous, medium scale watershed of the Garonne-Gironde fluvial-estuarine system (the Lot River; A = 10,700 km²; Q = 151 m³/s). Particulate metal and metalloid (Cd, Zn, Pb, Co, Cr, Ni, Mo, V, U, As, Sb, Th) concentrations were compared with monthly data of the same site (Temple site) obtained during 1999–2002. During the flood event, suspended particulate matter (SPM) concentrations closely followed river discharge with a maximum value (1530 mg/L) coinciding with the discharge peak (2970 m³/s). Trace metal/metalloid concentrations showed significant temporal variations and very contrasted responses. Particulate concentrations were similar to baseline values at the beginning of the flood and mostly increased during the event, showing anticlockwise and complex shape hystereses. Comparison of SPM yield (440,000 t) and particulate metal/metalloid fluxes during the flood with annual fluxes (1999–2002) highlights the great importance of major flood events in fluvial transport. Adequate sampling frequency during floods is necessary for reliable annual flux estimates and provides geochemical signals that may greatly improve our understanding of fluvial transport processes. The scenario of SPM and metal and metalloid transport during the flood are reconstructed by combining variations of Zn, Cd and Sb concentrations, concentration ratios (e.g. Zn/Cd, As/Th, Cd/Th) and hysteresis loops. Changes in SPM and metal/metalloid transport during distinct key stages of the flood were attributed to successive dominance of different water masses transporting material from different sources (e.g. industrial point source, bed sediment from reservoirs, plain erosion). Flood management (dam flushing) clearly enhanced the remobilization of up to 30-a old polluted sediment from reservoir lakes. Sediment remobilization accounted for ∼185,000 t of SPM (i.e. 42% of the total SPM fluxes during the flood) and strongly contributed to particulate metal/metalloid transport for Cd (90%), Zn (83%) and Pb (61%). Therefore, flood management needs to be taken into consideration in future models for erosion and pollutant transport.     

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。     

Heavy metals in the Derwent Estuary

Analyses of the concentrations of Cd, Cr, Co, Cu, Fe, Pb, Mn, Hg, Ni, and Zn in filtered waters, suspended particulates, sediments, shellfish, fish, airborne particulates, and sewage have confirmed work of other investigators showing that the Derwent Estuary is heavily contaminated, particularly withmercury, cadmium, lead, andzinc, and have added further information regarding the distribution of each metal. Apparently most of the contamination originated from the earlier operation of a zinc refining plant. A study of shellfish growing in variously contaminated regions found that more than 20 species could be listed in order of their respective abilities to accumulate each heavy metal. For example, the mussel (Mytilus edulis) was found to be a good indicator of cadmium and mercury contamination, but less valuable as an indicator of zinc. The surf barnacle, (Catophragmus polymerus) was found to be one of the most sensitive biological indicators of cadmium contamination. An indication of the steps by which a waste metal is eventually accumulated at high and even toxic concentrations in seafoods, may be seen from a comparison of the relative concentrations of cadmium, lead, mercury, and zinc found in mussels, sediments, suspended particulates, and filtered waters. The high concentrations recorded for metals include: 1,100 μg/g Hg, 10,000 μg/g Zn, and 862 μg/g Cd in dried sediments; 1,500 μg/g Cd in airborne dust fallout; 200 μg/g Cd and 100,000 μg/g Zn in dried oysters; and 16 μg/l Hg, 15 μg/l Cd and 1,500 μg/l Zn in filtered waters.     

Lead, zinc, and antimony contamination of the Rio Chilco-Rio Tupiza drainage system, Southern Bolivia

An intense, but localized rainfall event in February 2003, led to the severe erosion and failure of a tailings disposal impoundment at the Abarόa Antimony Mine in southern Bolivia. The failure released approximately 5,500 m³ of contaminated tailings into the Rio Chilco-Rio Tupiza drainage system. The impacts of the event on sediment quality are examined and compared to contamination resulting from historic mining operations in the headwaters of the basin. Of primary concern are contaminated floodplain soils located along downstream reaches of the Rio Tupiza which were found to contain lead (Pb), zinc (Zn), and antimony (Sb) concentrations that locally exceed Canadian, German, and Dutch guidelines for agricultural use. Spatial patterns in sediment-borne trace metal concentrations, combined with Pb isotopic data, indicate that Pb, Zn, and Sb are derived from three tributary basins draining the Abarόa, Chilcobija, and Tatasi-Portugalete mining districts. Downstream of each tributary, geographical patterns in trace metal concentrations reflect local geomorphic changes throughout the drainage system. Trace metal concentrations within the Rio Chilco decrease rapidly downstream as a result of dilution by uncontaminated sediments and storage of metal enriched particles (e.g., sulfide minerals) in the channel bed as a result of ongoing aggradation. Storage in the floodplains is limited. These processes significantly reduced the dispersal and, thus, the relative environmental affects of tailings eroded from the Abarόa Mine during the 2003 flood. In contrast, storage of Pb, Zn, and Sb in floodplains along the Rio Tupiza is significant, the majority of which is derived from historic mining operations, particularly mining within the Tatasi-Portugalete district.     

Anthropogenic components of heavy metal (Cd,Zn, Cu,Pb) budgets in the Lot-Garonne fluvial system (France)

Heavy metal (Zn, Cd, Cu and Pb) mass balances in the Lot-Garonne fluvial system have been established for 1999 and 2000. The mean annual discharges of these years are close to the mean discharge of the previous decade. The estimated annual dissolved and particulate fluxes in this model watershed integrate daily input from diffuse and point sources, diffusive fluxes at the water/sediment interface, changes in the dissolved-particulate partition and changes in sediment stock. Cadmium, Zn, Cu and Pb entering the Gironde estuary via the Garonne River (11–14 t a⁻¹ of Cd; 1330–1450 t a⁻¹ of Zn; 126–214 t a⁻¹ of Cu and 127–155 t a⁻¹ of Pb) are mainly transported in the particulate phase and the major part (i.e. ∼74 to 96% for Cd, ∼60% for Zn, ∼50 to 60% for Cu and ∼80% for Pb) is transported by the Lot River. The main anthropogenic heavy metal point source is located in a small upstream watershed (Riou-Mort River) accounting for at least 47% (Cd), ∼20% (Zn), ∼4% (Cu) and ∼7 to 9% (Pb) of the total heavy metal inputs into the Garonne River, although it contributes only 1% of the discharge. Mass balances for 1999 suggest that under mean annual hydrologic conditions on the basin scale, the heavy metal budget of the Lot-Garonne fluvial system is balanced and that the stocks of Cd [200 t; Environ. Tech. 16 (1995) 1145] and Zn in the Lot River sediment are constant under mean discharge conditions. Heavy metal input by molecular diffusion at the sediment surface represents an important component of dissolved metal inputs into the system (e.g. 30% for Cu). Except for Cu, these dissolved inputs are totally removed from solution by SPM. Based on the generally constant Zn/Cd (∼50) concentration ratio in sediment cores from the polluted Lot River reaches and the sediment stock of Cd [200 t; Environ. Tech. 16 (1995) 1145], the present day Zn stock in the Lot River sediments has been estimated at about 10,000 t. In addition to the mobilization of river-bed sediment and associated heavy metals by intense floods, local human activities, including river-bed dredging, may strongly modify the heavy metal budget of the river system. In 2000, the dredging-related remobilization of polluted Lot River sediment released 2–6 t Cd. This additional Cd point source was estimated to account for 15–43% of the gross inputs into the Gironde Estuary.     

Heavy metal contamination of soils and waters in and around the Imcheon Au–Ag mine,Korea

The heavy metal contamination of soils and waters by metalliferous mining activities in an area of Korea was studied. In the study area of the Imcheon Au–Ag mine, soils and waters were sampled and analyzed using AAS for Cd, Cu, Pb and Zn. Analysis of HCO₃⁻, F⁻, NO₃⁻ and SO₄²⁻ in water samples was also undertaken by ion chromatography. Elevated concentrations of the metals were found in tailings. The maximum contents in the tailings were 9.4, 229, 6160 and 1640 mg/kg extracted by aqua regia and 1.35, 26.4, 70.3 and 410 mg/kg extracted by 0.1 N HCl solution for Cd, Cu, Pb and Zn, respectively. These metals are continuously dispersed downstream and downslope from the tailings by clastic movement through wind and water. Because of the existence of sulfides in the tailings, a water sample taken on the tailings site was very acidic with a pH of 2.2, with high total dissolved solids (TDS) of 1845 mg/l and electric conductivity (EC) of 3820 μS/cm. This sample also contained up to 0.27, 1.90, 2.80, 53.4, 4,700 mg/l of Cd, Cu, Pb, Zn and SO₄²⁻, respectively. TDS, EC and concentrations of metals in waters decreased with distance from the tailings. The total amount of pulverized limestone needed for neutralizing the acid tailings was estimated to be 46 metric tons, assuming its volume of 45,000 m³ and its bulk density of 1855 kg/m³.     

Heavy metal contamination in the vicinity of the Daduk Au–Ag–Pb–Zn mine in Korea

The heavy metal contamination and seasonal variation of the metals in soils, plants and waters in the vicinity of an abandoned metalliferous mine in Korea were studied. Elevated levels of Cd, Cu, Pb and Zn were found in tailings with averages of 8.57, 481, 4,450 and 753 mg/kg, respectively. These metals are continuously dispersed downstream and downslope from the tailings by clastic movement through wind and water. Thus, significant levels of the elements in waters and sediments were found up to 3.3 km downstream from the mining site, especially for Cd and Zn. Enriched concentrations of heavy metals were also found in various plants grown in the vicinity of the mining area, and the metal concentrations in plants increased with those in soils. In a study of seasonal variation on the heavy metals in paddy fields, relatively high concentrations of heavy metals were found in rice leaves and stalks grown under oxidizing conditions rather than a reducing environment (P<0.05).     

Phosphate amendment of metalliferous tailings, Cannington Ag–Pb–Zn mine, Australia: implications for the capping of tailings storage facilities

This study appraised the use of phosphate fertilisers in immobilising metals in mine tailings to prevent their uptake into Curly Mitchell grass (Astrebla lappacea), when grown on capped, phosphate-amended tailings. Leaching experiments showed that Pb mobility was reduced by both bone meal and superphosphate amendment. Bone meal amendment also reduced Cd mobility. By contrast, Cd, Mn and Zn mobility increased in superphosphate-amended tailings due to increased acid production and, Cu was mobilised in bone meal-amended tailings possibly through the formation of soluble metal-complexing organic compounds. Arsenic and Sb were mobilised in both treatments due to phosphate ligand exchange. Greenhouse trials used Curly Mitchell grass grown on 1-m-high columns stacked with waste materials and different amendments overlain by clean topsoil. Curly Mitchell grass showed substantial uptake of Cd, Mn, Pb and Zn from unamended tailings and waste rock, where these were penetrated by the plant’s root system. Addition of phosphate fertilisers to the surface of tailings did not result in reduced metal uptake by Curly Mitchell grass. In tailings capped with limestone, the limestone layer formed an effective physical barrier preventing root penetration into the tailings and led to substantially reduced metal uptake in grass. The study demonstrates that thorough mixing of waste materials and fertilisers as well as irrigation may be required for successful phosphate immobilisation of metals in base metal tailings. Alternatively, the placement of a thin layer of crushed limestone on top of the tailings pile prior to capping may lead to the formation of a chemical and physical barrier and prevent the transfer of environmentally significant elements into the above-ground biomass of Mitchell grasses.     

Heavy metal contamination in surface sediments of Gökçekaya Dam Lake,Eskişehir,Turkey

The present study to find seasonal (September 2010–June 2011) heavy metal (Cd, Pb, Cr, Co, Ni, Zn, Cu, Fe, As) contamination and the origins thereof in surface sediments of Gökçekaya Dam Lake, as constructed on Sakarya River, the third-longest river in Turkey and the largest river of the Northwestern Anatolia. Upon analyses for the purpose thereof, heavy metal contamination in annual average concentrations in the lake sediment varied, respectively, as Fe > Zn > Cr > Ni > Cu > Pb > Co > As > Cd. Statistical assessments performed in order to see whether the average values of the heavy metal contamination as measured at stations placed in the lake changed by seasonal periods. There found statistically significant differences especially in Cd, Zn, and Pb between seasonal periods. In accordance with the Sediment Quality Index, Gökçekaya Dam Lake sediment was classified as “highly polluted” in terms of the amount of anthropogenic contaminants of As, Cr, Cu, Ni, Pb, and Zn. Enrichment factor and geoaccumulation index values (I _geo) were calculated in order to geochemically interpret the source of contamination due to heavy metal concentration in the lake sediment and the level of pollution. The As, Co, Cr, Cu, Ni Pb, and Zn values demonstrated that the sediment was rich for anthropogenic contaminants. The lake was found especially rich for arsenic (14.97–34.70 mg/kg) and lead (68.75–98.65 mg/kg) in accordance with annual average values. In general the lake was geochemically characterized as “moderately contaminated” in terms of As, Co, Cr, Cu, Ni, Pb, and Zn content.     

Geochemical Control of Heavy Metal Concentrations and Distribution Within Bahia Blanca Estuary (Argentina)

Chromium and lead concentrations and distribution have been fully studied within Bahía Blanca estuary inner area, which is strongly influenced by urban and industrial stress. Not only metals dissolved in estuarine water but also those included in sediments and suspended particulate matters (SPM) were measured. In all cases, internationally standardized protocols were applied to metal measurements, including analytical quality check test through analysis of certified reference materials. Total metal contents from surface sediments and SPM were compared with those from a historical database of the area, as well as with values representing the natural geochemical baseline within the system. Results showed that heavy metal pollution is mainly localized in the areas close to both industrial effluents discharge system and urban sewage outfall discharge. Data from sequential extractions indicate that metals from anthropogenic sources (i.e., Pb) are potentially more mobile than those inherited from geological parent material (i.e., Cr). The influences of other potential sources of metals (i.e., streams, runoff) were also considered. SPM was clearly identified as the main carrier of the studied heavy metals within the system, and its significance to metals input into sediments and/or biota was verified. Finally, the normalization of measured metal concentrations against background reference elements (i.e., Al or Fe) has allowed to identify that most of the measured Cr was lithogenic, while a significant percentage of Pb was from anthropogenic origin within Bahía Blanca estuary.     

The chemistry of suspended particulate material in a highly contaminated embayment of Port Jackson (Australia) under quiescent,high-wind and heavy-rainfall conditions

This study investigated physico-chemical characteristics of the water column and chemistry of suspended particulate material (SPM) under quiescent, high-wind and high-wind/heavy-rainfall conditions in Homebush Bay, a highly contaminated embayment of Port Jackson (Australia) to distinguish source and possible adverse effects to benthic and pelagic animals. Mean concentrations in surficial sediment were <1, 14, 181, 141, 37, 290 and 685 μg g⁻¹ for Cd, Co, Cr, Cu, Ni, Pb and Zn, respectively. Sediment chemistry indicated these metals had multiple sources, i.e. the estuary, stormwater and industry. Mean total suspended solids (TSS) were 7, 17 and 20 mg L⁻¹ during quiescent, high-rainfall and heavy rainfall/high wind conditions, respectively, whereas SPM Cd, Co, Cr, Cu, Ni, Pb and Zn concentrations varied between 13–25, 166–259, 127–198, 38–82, 236–305 and 605–865 μg g⁻¹, respectively under these conditions. TSS and total water metal concentrations were lowest during quiescent conditions. High TSS and metal loads in surface water characterised high-rainfall events. Wind-induced resuspension contributed the greatest mass of SPM and metals to the water column. Benthic animals may be adversely affected by Pb and Zn in sediment. Total water Cu and Zn concentrations may pose a risk to filter-feeding animals in the water column due to resuspension of contaminated sediment.     

Changes in lead and zinc lability during weathering-induced acidification of desert mine tailings: Coupling chemical and micro-scale analyses

Desert mine tailings may accumulate toxic metals in the near surface centimeters because of low water through-flux rates. Along with other constraints, metal toxicity precludes natural plant colonization even over decadal time scales. Since unconsolidated particles can be subjected to transport by wind and water erosion, potentially resulting in direct human and ecosystem exposure, there is a need to know how the lability and form of metals change in the tailings weathering environment. A combination of chemical extractions, X-ray diffraction, micro-X-ray fluorescence spectroscopy, and micro-Raman spectroscopy were employed to study Pb and Zn contamination in surficial arid mine tailings from the Arizona Klondyke State Superfund Site. Initial site characterization indicated a wide range in pH (2.5–8.0) in the surficial tailings pile. Ligand-promoted (DTPA) extractions, used to assess plant-available metal pools, showed decreasing available Zn and Mn with progressive tailings acidification. Aluminum shows the inverse trend, and Pb and Fe show more complex pH dependence. Since the tailings derive from a common source and parent mineralogy, it is presumed that variations in pH and “bio-available” metal concentrations result from associated variation in particle–scale geochemistry. Four sub-samples, ranging in pH from 2.6 to 5.4, were subjected to further characterization to elucidate micro-scale controls on metal mobility. With acidification, total Pb (ranging from 5 to 13 g kg⁻¹) was increasingly associated with Fe and S in plumbojarosite aggregates. For Zn, both total (0.4–6 g kg⁻¹) and labile fractions decreased with decreasing pH. Zinc was found to be primarily associated with the secondary Mn phases manjiroite and chalcophanite. The results suggest that progressive tailings acidification diminishes the overall lability of the total Pb and Zn pools.     

Spatial distribution of trace elements in floodplain alluvium of the upper Blackfoot River,Montana

The Mike Horse Mine tailings dam in western Montana was partially breached in 1975 due to heavy rainfall and a failed drainage bypass. Approximately 90,000 tons of metal and arsenic-enriched tailings flowed into Beartrap Creek and the Blackfoot River. The spatial distribution of trace elements As, Cd, Cu, Mn, Pb, and Zn in floodplain alluvium of the upper Blackfoot River were examined along 20 transects in the upper 105 river kilometers downstream from the tailings dam. Trace element concentrations decrease with distance from the failed dam, with As reaching background concentrations 15 km from the Mike Horse dam, Cd and Pb at 21 km, Cu at 31 km, and Mn and Zn at 37 km. Distance from the Mike Horse tailings dam and mine area is the dominating factor in explaining trace element levels, with R ² values ranging from 0.67 to 0.89. Maximum floodplain trace element concentrations in the upper basin exceed US. EPA ecological screening levels for plants, birds and other mammals, and reflect adverse hazard quotients for exposure to As and Mn for ATV/motorcycle use. Trace element concentrations in channel bank and bed alluvium are similar to concentrations in floodplain alluvium, indicating active transport of trace elements through the river and deposition on the floodplain. The fine fraction (<2 mm) of floodplain alluvium is dominated by sand-sized particles (2.0–0.05 mm), with Cu and Mn significantly correlated with silt-sized (0.05–0.002 mm) alluvium. Ongoing remediation in the headwaters area will not address metal contamination stored downstream in the channel banks and on the floodplain. Additionally, some trace elements (Cu, Mn and Zn) were conveyed farther downstream than were others (As, Cd, Pb).     

Metal extractability in acidic and neutral mine tailings from the Cartagena-La Unión Mining District (SE Spain)

Mine tailings are ubiquitous in the landscapes of mined areas. Metal solubilities were compared in two chemically distinct mine tailings from the old Mining District of Cartagena-La Unión (SE Spain). One of the tailings was acidic (pH 3.0) with 5400 mg/kg Zn, 1900 mg/kg As and 7000 mg/kg Pb. The other was neutral (pH 7.4) with 9100 mg/kg Zn, 5200 mg/kg Pb and 350 mg/kg As. In samples from the acidic tailings, more than 15% of the Zn and 55% of the Cd were extractable with 0.1 M NaNO₃, and distilled water. In the neutral tailings, using the same reagents, less than 1% of the metals were extractable. A sequential extraction procedure revealed that the sum of the residual and the Fe oxide fractions of Cu, Zn and Pb comprised 80–95% in the acidic tailings and 70–90% in the neutral tailings. The acidic mine tailings had a higher metal solubility, resulting in more metal leaching in the short-term, but also a higher fraction of inert metal. In contrast, in the neutral tailings, the metals were evenly distributed between, oxides and the residual fraction. This implies lower metal mobility in the short-term, but that metal mobility may increase in the long-term. When applied to mine tailings, sequential extractions may provide misleading results because the strong cation exchange capacity of some extractants may induce pH changes and thereby significantly change metal solubility.