Soil pollution by a pyrite mine spill in Spain: evolution in time

Revealing the release and migration mechanism of heavy metals in typical carbonate tailings, East China

Refining the occurrence characteristics of tailings hazardous materials at source is of great importance for pollution management and ecological reclamation. However, the release and transport of heavy metals (HMs) from tailings under rainfall drenching in simulated real-world environments is less well portrayed, particularly highlighting the inherent neutralisation in tailings wastes under superimposed dynamic conditions. In this study, dynamic leaching columns simulating actual conditions were used to observe the release and transport of HMs from tailings under acid rainfall infiltration at spatial and temporal scales. The release rate of trace elements (e.g., As, Cr, Ni, Pb, Cd) is high. Neutralisation in the presence of carbonate rocks in the gangue reduces HMs release intensity from tailings with high heavy metal content, along with the precipitation of iron oxides and chromium-bearing minerals, etc. In addition, the vertical differentiation of HMs is more relevant to physical processes. In the absence of carbonate rocks in gangue, the lowest pH value is reached within 1.2 h after acid rain infiltrates the tailings. At the same time, Cu, Zn and Cd are released significantly from the minerals at the superficial level. The release of As(III) is mainly concentrated in the early and late stages of water-rock contact.

Contamination and health risks brought by arsenic, lead and cadmium in a water-soil-plant system nearby a non-ferrous metal mining area

Heavy metal(loid)s contamination prevails in the water-soil-plant system around non-ferrous metal mining areas. The present study aimed to evaluate the heavy metal(loid)s contamination in Nandan Pb-Zn mining area (Guangxi, China). A total of 36 river water samples, 75 paired paddy soil and rice samples, and 128 paired upland soil and plant samples were collected from this area. The concentrations of arsenic (As), lead (Pb), and cadmium (Cd) in these samples were measured. Results showed that the average water quality indexes (WQIs) at the 12 sampling sites along the main river ranged from 41 to 5008, indicating the water qualities decreasing from "Excellent" to "Undrinkable". The WQIs nearby tailings or industrial park were significantly higher than those at the other sites. 34.0% and 64.5% of soil samples exceeded the risk screening values for As and Cd. The Pb and Cd concentrations in all rice samples exceeded the Chinese food safety limits by 18.7% and 82.7%, respectively. Leafy vegetables had a higher concentration of As, Pb, and Cd than other vegetables, exceeding the maximum permissible limits by 14.1%, 61.2%, and 40.0%, respectively. The biological accumulation coefficient (BAC) of Cd was the highest in rice and lettuce leaves. The hazard quotients (HQs) of As and Cd, indicating non-carcinogenic risks, were 4.15 and 1.76 in adult males, and 3.40 and 1.45 in adult females, all higher than the permitted level (1.0). The carcinogenic probabilities of As and Cd from rice and leafy vegetables consumption were all higher than 1 × 10-4. We conclude that metal(loid)s contamination of the water-soil-plant system has posed great non-carcinogenic and carcinogenic risks to the local population.

The use of rare earth element profiles as a proxy for a fractionation source and mine-waste provenance

Rare earth elements (REEs) have been determined in acid mine drainage samples from the Wiśniówka area, south-central Poland. Two benchmark acid pit ponds, i.e., Podwiśniówka (PwIIb) and Wiśniówka Duża (WD), have shown diverse contents of sulfates, phosphates, REEs and metal(loid)s. Moreover, these ponds exhibit different NASC-normalized REE concentration patterns: (i) a positive middle REE anomaly in PwIIb and (ii) a positive heavy REE anomaly in WD, regardless of sampling time. This MREE anomaly has also been highlighted in a small tailings pile pool showing high contents of metal(loid)s, including As (3.86 g/L) and REEs (90.1 mg/L). In contrast, the light REE (LaEu)-rich profiles are recorded in all Upper Cambrian rock series of the study area. However, the Pw geologic section is distinctly enriched in pyrite, goethite/hematite and carbonaceous clayey-silty shales compared to its WD counterpart that contains a lesser amount of these components, but many more quartzite/sandstone beds. The Pw mineral-lithologic pattern favors selective partitioning of heavy REEs to abundant Fe- and Al-oxyhydroxides and organic matter. Both very short solute transport from sheer rock faces to pit ponds and a low pH of acid waters (mean of 2.3 to 3.0) indicate that scavenging/adsorption and mineral co-precipitation of REEs in a water column may be negligible. This inference is also backed up by overlapping REE profiles at different depths of acid pit ponds. Taken together, this implies that preferential fractionation of REEs takes place primarily during on-site weathering of pyrite and REE-bearing minerals in different rock media thus leading to changes in the Pw- and WD shale-normalized REE concentration patterns at source. The characteristic Pw roof-shaped (convex-up) profile in water samples has been used as a proxy for tracing the most detrimental Podwiśniówka As-bearing mine-waste that were scattered within the mining area a couple of years ago.

Ecotoxicological risk assessment in soils contaminated by Pb and As 20 years after a mining spill

This study evaluates the potential toxicity of the soils of the Guadiamar Green Corridor (GGC) affected by the Aznalcóllar mine spill (Andalusia, Spain), one of the most important mining accidents in Europe in recent decades. Twenty years after the accident, although the area is considered to be recovered, residual contamination in soils persists, and the bioavailability of some contaminants, such as As, is showing trends of increasing. Therefore, the potential residual toxicity in 84 soil samples was evaluated by bioassays with lettuce (Latuca sativa L.), earthworms (Eisenia andrei) and determining the microbial activity by basal respiration and metabolic quotient. The selected soils sampled along the GGC were divided into 4 types according to their physicochemical properties. In the closest part of the mine two soil types appear (SS1 and SS2), originally decarbonated and loamy, with a reduction in lettuce root elongation of 57% and 34% compared to the control, as well as a the highest metabolic quotient (23.9 and 18.1 ng Cc_O2 μg Cmicrob^-1 h^-1, respectively) with the highest risk of Pb and As toxicity. While, located in the middle and final part of the affected area of the spill (SS3 and SS4), soils presented alkaline pH, finer textures and the lowest metabolic quotient (<9.5 ng Cc_O2 μg Cmicrob^-1 h^-1). In addition, due to Pb and As exceeded the Guideline values established in the studied area, the human toxicity risk was determined according to US-EPA methodology. Although the total contents were higher than the Guidelines established, the obtained hazard quotients for both contaminants were less than one, so the risk for human health was discarded. However, monitoring over time of the toxicity risks of the GGC soils would be advisable, especially due to the existence of areas where residual contamination persist, and soil hazard quotient obtained for As in children was higher and close to unity.

Does environmental risk really change in abandoned mining areas in the medium term when no control measures are taken?

Studies regarding how environmental risk evolves in abandoned mining areas in the medium term have been seldom carried out. The answer to this question is not obvious despite it is essential in order to evaluate the need to take urgent control measures in these areas. Fifty-two samples corresponding to soils (from natural pasture and arable lands) and mine tailings were collected in the surroundings of an old Spanish Pb/Zn mine (San Quintín, Central Spain). Current concentrations of pseudo-total and available metal (loid)s (Pb, Zn, Cd, Cu, As and Ag) were determined and the environmental risk assessment (ERA) was conducted with these data and those corresponding to a sampling previously carried out in 2006. ERA was carried out by calculating the geoaccumulation index (Igeo), the pollution load index (PLI) and the potential ecological risk index (PER). Results demonstrated that Pb and Zn concentrations have increased in the soils of the plots surrounding the mining areas causing a moderate rise in most of the determined pollution indices between 2006 and 2020. It was especially significant in the pastureland areas, with increases up to 17% in the number of soil samples that reached the highest risk classification in 2020 as compared to those taken in 2006. The results obtained here demonstrate that the environmental risk can actually increase in a continuous way in abandoned mining areas despite the closure of the mining operation and the effect of the possible natural attenuation.

Application of Biochar for the Restoration of Metal(loid)s Contaminated Soils

Biochar has recently aroused great interest for the restoration of contaminated soils since it improves soil properties and induces the immobilization of pollutants. This study evaluates the use of biochar from plant pruning, applied as an amendment, for immobilizing metal(loid)s in a highly contaminated soil as well as for reducing the phytotoxicity of these pollutants by promoting natural revegetation. For this purpose, a bioassay with Trifolium pratense L. was used to test the effectiveness of the soil amendment in greenhouse conditions. Three treatments were carried out including soil contaminated with metal(loid)s (RA), and this soil was amended with biochar at different dosage: 4% (RA4B) and 8% (RA8B). A non-contaminated soil (NC) from a nearby area not affected by contamination was used as a control. The results show that biochar increased soil pH by several units depending on the dose used, 8% being the most effective one. Biochar treatments also reduced soluble and bioavailable forms of Zn and Cu. Likewise, phytotoxicity was significantly reduced, promoting seed germination and biomass with plant growth values similar to the non-polluted soil. In light of the results obtained, the evaluation of the bioremediation potential of biochar under field conditions can be considered.

Eurasian otter (Lutra lutra) as sentinel species for the long-term biomonitoring of the Guadiamar River after the Aznalcóllar mine spill

Accidents at mines involving stored tailings have produced catastrophic environmental damage. In April 1998 the dam of the Aznalcóllar mine tailings pond in the surroundings of the Doñana National Park (southwestern Spain) broke, discharging into the Guadiamar River more than 6 million m³ of toxic mud and acidic water with high concentrations of heavy metals and arsenic. We used the Eurasian otter (Lutra lutra) as sentinel species to assess the potential impact of the toxic spill on the river ecosystems and their recovery with time by studying the spatial and temporal variation (1999-2003, 2006) of selected trace element (Cu, Zn, Cd, Pb and As) concentrations in feces. Throughout the sampling period, the highest heavy metal and As levels were found in the most spill-affected reaches of the Guadiamar River (i.e., the Middle and, to a lesser extent, the Lower reaches), pointing out the mining accident as the main origin of the contamination. Overall, levels of trace elements decreased with the time elapsed since the toxic spill, except for Cd (F_1,352 = 0.29, P = 0.59). However, rebounds for some elements (Pb, As, and Cu) were also observed, especially in the Middle and Lower reaches of the river, which might be attributed to the residual contamination in abiotic compartments and/or new inputs from industrial and agricultural activities in the nearby areas. Concentrations were relatively high when compared to those reported for both our reference area (Guadalete River) and other metal-polluted zones. We found that the estimated amounts of Pb and As ingested during the first years after the spill in the Guadiamar Middle reach would be high enough to cause reproductive issues. This could affect the local population recovery, although evidence on distribution range and numbers suggests otherwise, with thriving populations at regional scale. Our results support the role of otters as sentinel species for biomonitoring contaminants and thus to evaluate fluvial ecosystem health.

Assessment of biopiles treatment on polluted soils by the use of Eisenia andrei bioassay

A long-term case of residual pollution is studied after 20 years since the largest mining accident in Spain (the Aznalcóllar spill) happened. This pollution is manifested through a surface zoning consisting of bare soils (B0), sparsely vegetated soils (B1), and densely vegetated and recovered soils (B2). A biopiles treatment with a mixture of contaminated soils (B0 and B1) with recovered soils (B2) at 50% (w/w), and vermicompost addition (50 tons ha-1) was evaluated. To assess the effectiveness of treatments, total, water-soluble, and bioavailable fractions of the most polluting elements in the zone (Cu, Zn, As, Pb, Cd, and Sb) was analyzed. To evaluate the potential risk of contamination for the ecosystem, a bioassay with earthworm Eisenia andrei was carried out. Twenty years after the accident, there are still soils where total As and Pb exceed the regulatory levels and water-soluble Zn and As exceed the toxicity guidelines. According to toxicity bioassay, weight variation and juvenile production of earthworms showed an improvement after biopiles treatment, with values that trend to be similar to those of recovered soils. The only bioaccumulated element in earthworms was Cd (BAF>1), both in polluted as in treated soils, which indicates the possible existence of exclusion mechanisms of the other pollutants by earthworms. The comparison between biopiles and polluted soils showed no significant differences for the bioaccumulation factor of trace elements, with the exception of Zn and Cu, which slightly increased after treatment. According to our results, biopiles treatment combined with vermicompost addition is a good technique for the recovery of residual contaminated areas, by the improvement of soil properties and the reduction of the potential toxicity; anyway, monitoring of soils and organisms is needed to prevent the increase of bioavailability of some potentially pollutant elements over time.

Rehabilitation of waste rock piles: Impact of acid drainage on potential toxicity by trace elements in plants and soil

The restoration of mining areas, in particular if they are located near towns or villages, is essential to reduce their potential risks for human health and to minimize their visual impacts. In this study, we assess the rehabilitation of a waste rock pile adjacent to the town of Tharsis (SW Spain). We measured vegetation cover and its diversity, and chemical composition of plants and soil, twelve years after remediation by lime amendments, added topsoil and planted vegetation. In general, the applied measures were successful covering with woody vegetation the upper part of the waste rock pile, and providing a greening visual landscape for the town nearby. The most abundant species were the gum rockrose (Cistus ladanifer) and the legume shrub Retama sphaerocarpa, this latter species most probably introduced in the seedbank of the added topsoil. Also in the soil seedbank, probably arrived the invasive Acacia saligna, of fast growth. In contrast, the lower part of the slopes was almost devoid of vegetation. We interpret that partial failure in the rehabilitation process as due to the acid mine drainage, which caused downslope a decrease of soil pH and increased availability of trace elements, thus impeding growth and establishment of plants. In addition, some plants, like C. ladanifer, growing at the base of the rock pile, had concentrations of Cd above the maximum tolerable level for animals, therefore representing a toxicity risk. Finally, we propose here an alternative technique to restore waste rock piles, by sorting and selectively handling the extractive wastes, thus reducing infiltration rates, seepages and the negative effect of the acid mine drainage. Those modified waste rock piles will be rehabilitated by the addition of topsoil and planted vegetation, as successfully worked out in the upper slopes of the study site.

Evolution of the Residual Pollution in Soils after Bioremediation Treatments

This study is focused on one of the most important spills that ever happened in Europe, the Aznalcóllar’s mine spill. The extensive application of phytostabilization in the area led to the implementation of the Guadiamar Green Corridor (GGC). Soil physicochemical properties were analyzed and the total concentration of Pb, As, Zn and Cu was measured by X-ray fluorescence (XRF); bioassay using Lactuca sativa L. was applied to assess potential toxicity. Two decades after the accident, some soils affected by residual contamination continue to appear in the area. According to regulatory levels, Pb and As concentrations are exceeded in around 13%and 70%, respectively, in the uppermost part of the soils (first 10 cm). The change in soil properties after bioremediation treatment positively promoted the reduction in the potential mobility of pollutants by the increase in pH, CaCO3 content and organic carbon. Anyway, the bioassay with Lactuca sativa, indicated that around 25% of the soils showed toxicity by the reduction of the root elongation in relation to the control samples. Our results indicate that monitoring of the GGC is still needed, together with the application of soil recovery measures to reduce the potential toxicity in some sectors of the affected area.

The role of organic amendment in soils affected by residual pollution of potentially harmful elements

The addition of organic amendment in soils affected by residual pollution of potentially harmful elements (PHEs) is evaluated. The area was polluted twenty years ago and remediation actions were intensively applied, but evidence of pollution are still detected in some sectors. The amendment application produces significant changes in the main soil properties and modifies the mobility and availability of the pollutants. In general, Cu, Zn, Cd and Pb, showed a significant reduction in soluble and exchangeable forms after the vermicompost addition (percentage of reduction ranging from 59% for soluble Pb to 95% for exchangeable Zn), both in highly (UVS) as in moderately (VS1) polluted soils. This reduction is strongly related to the rise in OC content and pH. Arsenic presented no significant reduction or even an increase in soluble forms in moderately polluted soils (VS1), where the competing effects of OC and phosphorous could be responsible for this increase. Pb also showed an increase in availability after vermicompost application, probably related to the competing effect of Mg²⁺ coming from the organic amendment. The less mobile forms (those extracted with oxalic-oxalate, pyrophosphate and EDTA), indicate that vermicompost application reduce medium-long term mobility to similar values of those found in less polluted soils (VS2); anyway, an increase in available forms of Pb and As was detected in some cases, indicating a potential risk of toxicity that should be monitored over time.

Extreme enrichment of arsenic and rare earth elements in acid mine drainage: Case study of Wiśniówka mining area (south-central Poland)

The Wiśniówka rock strip mining area (south-central Poland) with quartzite quarries, acid water bodies and tailings piles is one of the most unique acid mine drainage (AMD) sites throughout the world. This is due to the occurrence of enormous amounts of pyrite unknown in sedimentary formations worldwide. Of the two mineralization zones, one that is the most abundant in arsenical pyrite occurs in the lowermost Upper Cambrian formation of the Podwiśniówka quarry. The As-rich pyritiferous clastic rocks are exposed as a result of deep quartzite extraction during 2013-2014. In addition, the clayey-silty shale interbeds are enriched in rare earth element (REE) minerals. The mining operation left an acidic lake with a pH of about 2.4-2.6 and increased contents of sulfates, metal(loid)s and REE. The Podwiśniówka pyrite-rich waste material was stacked up in many places of the mining area giving rise to strongly acidic spills that jeopardized the neighboring environment. One of these unexplored tailings piles was a source of extremely sulfate- and metal(loid)-rich pools with unusual enrichments in As (up to 1548 mg L^-1) and REE (up to 24.84 mg L^-1). These distinctly exceeded those previously reported in the Wiśniówka area. A broad scope of geochemical, mineralogical and petrographic methods was used to document these specific textural and mineralogical properties of pyrite facilitating its rapid oxidation. The pyrite oxidation products reacted with REE-bearing minerals releasing these elements into acid water bodies. Statistical methods were employed to connect the obtained tailings pool hydrogeochemical data with those derived from this and the previous studies of the Podwiśniówka and Wiśniówka Duża acid pit lakes. In contrast to metal(loid) profiles, the characteristic shale-normalized REE concentration patterns turned out to be more suitable for solving different AMD issues including provenance of mine waste material in the tailings pile examined.

Soil-plant relationships and contamination by trace elements: A review of twenty years of experimentation and monitoring after the Aznalcóllar (SW Spain) mine accident

Soil contamination by trace elements (TE) is a major environmental problem and much research is done into its effects on ecosystems and human health, as well as into remediation techniques. The Aznalcóllar mine accident (April 1998) was a large-scale ecological and socio-economic catastrophe in the South of Spain. We present here a literature review that synthesizes the main results found during the research conducted at the affected area over the past 20years since the mine accident, focused on the soil-plant system. We review, in depth, information about the characterization of the mine slurry and contaminated soils, and of the TE monitoring, performed until the present time. The reclamation techniques included the removal of sludge and soil surface layer and use of soil amendments; we review the effects of different types of amendments at different spatial scales and their effectiveness with time. Monitoring of TE in soil and their transfer to plants (crops, herbs, shrubs, and trees) were evaluated to assess potential toxicity effects in the food web. The utility of some plants (accumulators) with regard to the biomonitoring of TE in the environment was also evaluated. On the other hand, retention of TE by plant roots and their associated microorganisms was used as a low-cost technique for TE stabilization and soil remediation. We also evaluate the experience acquired in making the Guadiamar Green Corridor a large-scale soil reclamation and phytoremediation case study.

Effect of soil organic matter on antimony bioavailability after the remediation process

We evaluated the long-term (18 year) and short-term (4 weeks) changes of Sb in contaminated soil with SOM increase under remediation process. In the Aznalcóllar mine accident (1998) contaminated area, the remediation measurement implemented the Guadiamar Green Corridor, where residual pollution is still detected. Soils of the re-vegetated area (O2) with high pH and high SOM content, moderately re-vegetated area (O1) and unvegetated area (C) were sampled. Soil pH, CEC, SOM amount and soil Sb forms were evaluated. Soil Sb was measured as total, soluble, exchangeable, EDTA extractable, acid oxalate extractable, and pyro-phosphate extractable fractions. Further, the short-term effect of artificial organic matter addition was also evaluated with incubation study by adding compost to the sampled soil from C, O1 and O2 areas. After 4 weeks of incubation, soil chemical properties and Sb forms were evaluated. In re-vegetated area (O2), soil total Sb was two times lower than in unvegetated area (C); however, soluble, exchangeable, and EDTA extractable Sb were 2-8 times higher. The mobile/bioavailable Sb increase was also observed after 4 weeks of incubation with the addition of compost. Soluble, exchangeable, and EDTA extractable Sb was increased 2-4 times by compost addition. By the linear regression analysis, the significantly related factors for soluble, exchangeable, and EDTA extractable Sb values were pH, CEC, and SOM, respectively. Soluble Sb increase was mainly related to pH rise. Exchangeable Sb should be bound by SOM-metal complex and increased with CEC. EDTA extractable fraction should be increased with increase of SOM as SOM-Fe associated Sb complex. From these results, it was shown that increase of SOM under natural conditions or application of organic amendment under remediation process should increase availability of Sb to plants.

Potential of Eucalyptus camaldulensis for phytostabilization and biomonitoring of trace-element contaminated soils

Soil pollution by trace elements (TEs) from mining and industrial activity is widespread and presents a risk to humans and ecosystems. The use of trees to immobilize TEs (phytostabilization) is a low-cost and effective method of soil remediation. We aimed to determine the chemical composition of leaves and flower buds of Eucalyptus camaldulensis in seven sites along the Guadiamar River valley (SW Spain), an area contaminated by a mine-spill in 1998. E. camaldulensis trees in the spill-affected area and adjacent non affected areas were growing on a variety of soils with pH from 5.6 to 8.1 with low concentration of plant nutrients. The spill affected soils contained up to 1069 mg kg^-1 of As and 4086 mg kg^-1 of Pb. E. camaldulensis tolerated elevated TE concentrations in soil and, compared to other species growing in the same environment, had low TE concentrations in the aerial portions. Besides tolerance to soil contamination, E. camaldulensis had low bioaccumulation coefficients for soil contaminants. TE concentrations in the aboveground portions were below levels reported to be toxic to plants or ecosystems. Flower buds had even lower TE concentrations than leaves. Despite the relatively low concentration of TEs in leaves they were significantly correlated with the soil extractable (0.01 M CaCl₂) Cd, Mn and Zn (but not Cu and Pb). The general features of this tree species: tolerance to impoverished and contaminated soils, fast growth and deep root system, and low transfer of TEs from soil to aboveground organs makes it suitable for phytostabilization of soils contaminated by TEs. In addition, eucalyptus leaves could be used for biomonitoring the soil extractability of Cd, Mn and Zn but not Cu or Pb.

Evaluation of remediation techniques in soils affected by residual contamination with heavy metals and arsenic

Residual soil pollution from the Aznalcóllar mine spill is still a problem in some parts of the affected area, today converted in the Guadiamar Green Corridor. Dispersed spots of polluted soils, identified by the absence of vegetation, are characterized by soil acid pH and high concentrations of As, Pb, Cu and Zn. Ex situ remediation techniques were performed with unrecovered soil samples. Landfarming, Composting and Biopiles techniques were tested in order to immobilize pollutants, to improve soil properties and to promote vegetation recovery. The effectiveness of these techniques was assessed by toxicity bioassays: Lactuca sativa L. root elongation test, Vibrio fischeri bioluminescence reduction test, soil induced respiration test, and Eisenia andrei survival and metal bioaccumulation tests. Landfarming and Composting were not effective techniques, mainly due to the poor improvement of soil properties which maintained high soluble concentrations of Zn and Cu after treatments. Biopile technique, using adjacent recovered soils in the area, was the most effective action in the reduction of soil toxicity; the improvement of soil properties and the reduction in pollutants solubility were key to improve the response of the tested organisms. Therefore, the mixture of recovered soils with polluted soils in the areas affected by residual contamination is considered a more suitable technique to reduce the residual pollution and to promote the complete soil recovery in the Guadiamar Green Corridor.

Rare earth and trace element signatures for assessing an impact of rock mining and processing on the environment: Wiśniówka case study, south-central Poland

A detailed hydrogeochemical study was performed in the Wiśniówka mining area (south-central Poland). This covered three acid pit bodies, historic tailings acid ponds, acid pools, and additionally two neighboring rivers. All these acid mine drainage (AMD) waters are characterized by the pH in the range of 1.7 (pools) to 3.5 (tailings ponds). The most interesting is the Podwiśniówka acid pit lake that shows a very low pH (2.2-2.5) and very high concentrations of SO42- (2720-5460 mg/L), Fe (545-1140 mg/L), Al (86.2 mg/L), As (9603-24,883 μg/L), Co (1317-3458 μg/L), Cr (753-2047 μg/L), Cu (6307-18,879 μg/L), Ni (1168-3127 μg/L), and rare earth element (REE) (589-1341 μg/L). In addition, seeps that drain the Podwiśniówka mine tailings and partly aggregate piles form strong acid pools in the mining area. Along with these pools, in which As and REE contents reach 369,726 and 6288 μg/L, respectively, these waters are among the most distinctive As- and REE-rich AMD surface waters across the world. It is noteworthy that the Podwiśniówka acid pit lake and Wiśniówka Duża acid pit sump exhibit different element signatures and REE concentration patterns normalized to North American Composite Shale (NASC): the Podwiśniówka acid pit lake always shows a characteristic roof-shaped medium REE (MREE) profile with distinct enrichments in Gd, Eu, and Tb whereas the other one displays a step-shaped heavy REE (HREE) profile with positive Tb and Gd anomalies. The REE undergo fractionation during weathering and the subsequent leaching of dissolved and suspended fractions from rocks to acid water bodies where these and other elements are further fractionated by geochemical processes. This study shows that the individual REE have greater affinities for Mn, HREE for Fe and SO42-, and only La and Ce for Al. This specific water geochemistry has enabled us to (i) pinpoint the location of AMD "hot spots" originated from quartzite mining and processing operations conducted by current and previous mining companies, (ii) predict the directions and effects of future strip mining for quartzites in the Wiśniówka Duża and Podwiśniówka open pits, and (iii) evaluate the potential impact of mining and processing effluents on the quality of rivers.

Anomalous abundance and redistribution patterns of rare earth elements in soils of a mining area in Inner Mongolia, China

The Bayan Obo Mine, the largest rare earth element (REE) deposit ever found in the world, has been mined for nearly 60 years for iron and rare earth elements. To assess the influences of mining activities on geochemical behavior of REEs in soils, 27 surface soil samples and three soil profile samples were collected from different directions in the vicinity of the mine area. The total concentrations of REEs in surface soils varied from 149.75 to 18,891.81 mg kg(-1) with an average value of 1906.12 mg kg(-1), which was apparently higher than the average values in China (181 mg kg(-1)). The order of the average concentrations of individual REEs in surface soils was similar to that in Bayan Obo ores, which confirmed that the concentration and distribution of REEs in the soils was influenced by the mining activities. The concentrations of single REE in the soil profiles showed a similar trend with depth with an increase at 0-25 cm section, then decreased and remained relatively stable in the deep part. The normalized curves inclined to the right side, showing the conspicuous fractionation between the light and heavy REEs, which supported by the North American Shale Composite (NASC) and Post-Archean Australian Shale (PAAS) normalized concentration ratios calculated for selected elements (La N /Yb N , La N /Sm N , Gd N /Yb N ). Slight positive Ce anomaly and negative Eu anomaly were also observed.

Risk assessment of atmospheric heavy metals exposure in Baotou, a typical industrial city in northern China

Industrial activities have led to serious air pollution and the potentially toxic elements in atmospheric particles can cause various health problems to humans. In this study, inhalable particulate matter (PM10) and fine particles (PM2.5) were collected from four typical sites in Baotou, an industrial city in northern China. We investigated both the mass concentrations of particulate matter and the concentrations of heavy metals (Cr, Ni, Pb, Cd, Cu, Mn, Co, and Zn) in the collected samples. We assessed the public health risks associated with atmospheric heavy metal exposure. The results showed that the mass concentrations of PM2.5 and PM10 as well as these heavy metal concentrations varied notably influenced by the prevailing wind directions. Among the studied metals, Zn, Mn, Pb, and Cr were the main metal pollutants in both PM10 and PM2.5. The results of the health assessment showed that the eight heavy metals studied pose significant non-carcinogenic risks and Cr, Cd, and Co pose lifetime lung cancer risks to local residents, especially to children.

Arsenopyrite weathering under conditions of simulated calcareous soil

Mining activities release arsenopyrite into calcareous soils where it undergoes weathering generating toxic compounds. The research evaluates the environmental impacts of these processes under semi-alkaline carbonated conditions. Electrochemical (cyclic voltammetry, chronoamperometry, EIS), spectroscopic (Raman, XPS), and microscopic (SEM, AFM, TEM) techniques are combined along with chemical analyses of leachates collected from simulated arsenopyrite weathering to comprehensively examine the interfacial mechanisms. Early oxidation stages enhance mineral reactivity through the formation of surface sulfur phases (e.g., S n (2-)/S(0)) with semiconductor properties, leading to oscillatory mineral reactivity. Subsequent steps entail the generation of intermediate siderite (FeCO3)-like, followed by the formation of low-compact mass sub-micro ferric oxyhydroxides (α, γ-FeOOH) with adsorbed arsenic (mainly As(III), and lower amounts of As(V)). In addition, weathering reactions can be influenced by accessible arsenic resulting in the formation of a symplesite (Fe3(AsO4)3)-like compound which is dependent on the amount of accessible arsenic in the system. It is proposed that arsenic release occurs via diffusion across secondary α, γ-FeOOH structures during arsenopyrite weathering. We suggest weathering mechanisms of arsenopyrite in calcareous soil and environmental implications based on experimental data.

Long-term toxicity assessment of soils in a recovered area affected by a mining spill

Residual pollution in the Guadiamar Green Corridor still remains after Aználcollar mine spill in 1998. The polluted areas are identified by the absence of vegetation, soil acidic pH and high concentrations of As, Pb, Zn and Cu. Soil toxicity was assessed by lettuce root elongation and induced soil respiration bioassays. In bare soils, total As and Pb concentrations and water-extractable levels for As, Zn and Cu exceeded the toxicity guidelines. Pollutants responsible for toxicity were different depending on the tested organism, with arsenic being most toxic for lettuce and the metal mixture to soil respiration. Soil properties, such as pH or organic carbon content, are key factors to control metal availability and toxicity in the area. According to our results, there is a risk of pollution to living organisms and the soil quality criteria established in the area should be revised to reduce the risk of toxicity.

Long-term contamination in a recovered area affected by a mining spill

Soil pollution from the spill of Aznalcóllar mine (S Spain) was monitored by analysing polluted soils in 1998, 1999, and 2004. Following the methodology used in previous studies, in 2013 we conducted a new sampling and analysis of the soils affected by the spill and the data were compared with those of 2004. The results confirm that the pH tended to rise and concentration of pollutants tended to diminish over time. In 2013, the total concentration of pollutants was within the normal range for uncontaminated soils and close to the background concentration of the soils prior to the spill; while the soluble concentration of pollutants was clearly below the toxic level. These results indicate that remediation measures implemented have been effective. However, the removal of tailings (first remediation measure applied) was deficient and in many places the tailings were mixed with the soil. The high concentration of sulphides and metal(loid)s in the tailings gave rise to spots with very acidic and highly polluted soils devoid of vegetation. In 2013, fifteen years after the spill, these spots of bare soils remain a major source of pollution from which pollutants are scattered through the solid and liquid phases of runoff water, requiring action to immobilize pollutants and encourage the restoration of vegetation on these soils. In this type of pollution in a Mediterranean environment, the complete removal of tailings is more important than the speed at which they are removed.

The importance of evaluating the physicochemical and toxicological properties of a contaminant for remediating environments affected by chemical incidents

In the event of a major chemical incident or accident, appropriate tools and technical guidance need to be available to ensure that a robust approach can be adopted for developing a remediation strategy. Remediation and restoration strategies implemented in the aftermath of a chemical incident are a particular concern for public health. As a result an innovative methodology has been developed to help design an effective recovery strategy in the aftermath of a chemical incident that has been developed; the UK Recovery Handbook for Chemical Incidents (UKRHCI). The handbook consists of a six-step decision framework and the use of decision trees specifically designed for three different environments: food production systems, inhabited areas and water environments. It also provides a compendium of evidence-based recovery options (techniques or methods for remediation) that should be selected in relation to their efficacy for removing contaminants from the environment. Selection of effective recovery options in this decision framework involves evaluating the physicochemical and toxicological properties of the chemical(s) involved. Thus, the chemical handbook includes a series of tables with relevant physicochemical and toxicological properties that should be assessed in function of the environment affected. It is essential that the physicochemical properties of a chemical are evaluated and interpreted correctly during the development of a remedial plan in the aftermath of a chemical incident to ensure an effective remedial response. This paper presents a general overview of the key physicochemical and toxicological properties of chemicals that should be evaluated when developing a recovery strategy. Information on how physicochemical properties have impacted on previous remedial responses reported in the literature is also discussed and a number of challenges for remediation are highlighted to include the need to develop novel approaches to remediate sites contaminated by mixtures of chemicals as well as methods for interpreting chemical reactions in different environmental matrices to include how climate change may affect the speciation and mobility of chemicals in the environment.

Factors influencing recovery and restoration following a chemical incident

Chemicals are an important part of our society. A wide range of chemicals are discharged into the environment every day from residential, commercial and industrial sources. Many of these discharges do not pose a threat to public health or the environment. However, global events have shown that chemical incidents or accidents can have severe consequences on human health, the environment and society. It is important that appropriate tools and technical guidance are available to ensure that a robust and efficient approach to developing a remediation strategy is adopted. The purpose of remediation is to protect human health from future exposure and to return the affected area back to normal as soon as possible. There are a range of recovery options (techniques or methods for remediation) that are applicable to a broad range of chemicals and incidents. Recovery options should be evaluated according to their appropriateness and efficacy for removing contaminants from the environment; however economic drivers and social and political considerations often influence decision makers on which remedial actions are implemented during the recovery phase of a chemical incident. To date, there is limited information in the literature on remediation strategies and recovery options that have been implemented following a chemical incident, or how successful they have been. Additional factors that can affect the approach taken for recovery are not well assessed or understood by decision makers involved in the remediation and restoration of the environment following a chemical incident. The identification of this gap has led to the development of the UK Recovery Handbook for Chemical Incidents to provide a framework for choosing an effective recovery strategy. A compendium of practical evidence-based recovery options (techniques or methods for remediation) for inhabited areas, food production systems and water environments has also been developed and is included in the chemical handbook. This paper presents the key factors that should be considered when developing a recovery strategy with respect to how these may impact on its effectiveness. The paper also highlights the importance of these factors through an evaluation of recovery strategies implemented following real chemical incidents that have been reported in the literature.

State of rare earth elements in different environmental components in mining areas of China

China has relatively abundant rare earth elements (REEs) reserves and will continue to be one of the major producers of REEs for the world market in the foreseeable future. However, due to the large scale of mining and refining activities, large amounts of REEs have been released to the surrounding environment and caused harmful effects on local residents. This paper summarizes the data about the contents and translocation of REEs in soils, waters, atmosphere, and plants in REE mining areas of China and discusses the characteristics of their forms, distribution, fractionation, and influencing factors. Obviously high concentrations of REEs with active and bioavailable forms are observed in all environmental media. The mobility and bioavailability of REEs are enhanced. The distribution patterns of REEs in soils and water bodies are all in line with their parent rocks. Significant fractionation phenomenon among individual members of REEs was found in soil-plant systems. However, limited knowledge was available for REEs in atmosphere. More studies focusing on the behavior of REEs in ambient air of REE mining areas in China are highly suggested. In addition, systematic study on the translocation and circulation of REEs in various media in REEs mining areas and their health risk assessment should be carried out. Standard analytical methods of REEs in environments need to be established, and more specific guideline values of REEs in foods should also be developed.

Germination and early growth of Brassica juncea in copper mine tailings amended with technosol and compost

Mine tailings represent a serious threat to the environment and human health; thus their restoration has become a major concern. In this study, the interactions between Brassica juncea and different mine soil treatments were evaluated in order to understand their effect on germination and early growth. Three soil treatments containing 25% and 50% of technosol and 30% of compost were prepared. Germination and early growth were assessed in soil and pore water extracts from the treatments. Unlike the untreated mine soil, the three treatments allowed germination and growth, achieving levels comparable to those of seedlings from the same species developed in normal conditions. The seedlings grown in 50% of technosol and 30% of compost exhibited greater germination percentages, higher growth, and more efficient mechanisms against oxidative stress, ascribed to the organic matter and nutrients content of these treatments. Considering the unequivocal ability of B. juncea for phytoremediation, the results suggest that technosol and compost may be an auspicious solution to allow the germination and early growth of this species in mine tailings.

Application of Using Sphingomonas-Paucimobilis of Sodium Alginate Fossilization Bacillus Subtilis Pellet to Heavy Metal of Mine Wastewater

This study use purely bacteria on suitable condition, eliminate other bacteria come in life-form bacteria. Through the orthogonal experiment obtains the optimum condition of sodium alginate fossilization bacillus subtilus pellet to chrome adsorption, and discusses the influence of single factor to the sodium alginate fossilization bacillus subtilus pellet to chrome adsorption, including the time, the temperature,pH, the initial adsorbent density, the speed of the shaker, the absorbent which the different periods of growth bacterium does, coexistent ion, desorption. From the research, we know the maximum adsorption rate to chrome is about 80%. Dynamics research indicated that in the several methods of the Sphingomonas-paucimobilis of chrome , the methods of embedded micro-organisms embodies much advantages ,as operating easily, effecting clearly, less pollution, costing low, etc.

Phytostabilisation with Mediterranean shrubs and liming improved soil quality in a pot experiment with a pyrite mine soil

Phytoremediation can be a suitable option to manage derelict mine soils. A pot experiment was carried out under semi-controlled conditions with a mine-impacted soil. A further contamination event was mimicked by applying 5% of pyritic sludge. Four species were planted in pots (Myrtus communis, Retama sphaerocarpa, Rosmarinus officinalis and Tamarix gallica), and some pots remained unplanted as a control. The substrates were moderately to highly contaminated, mainly with arsenic and zinc. The strong acidification induced by the pyritic sludge was buffered with lime and plants survived in all the pots. Liming provoked an effective immobilisation of metals and arsenic. Plant establishment decreased labile As in the substrate by 50%, mainly M. communis, although the levels of extractable metals were not affected by the plants. R. sphaerocarpa and M. communis increased the levels of C and N in the soil by 23% and 34% respectively, and also enhanced enzymatic activities and microbial respiration to the double in some cases. The low transfer of trace elements to shoots limited the phytoextraction rate. Our results support the use of phytostabilisation in Mediterranean mine soils and show how plants of R. sphaerocarpa and M. communis may increase soil health and quality during revegetation.

Changes in the sorption, desorption, distribution, and availability of copper, induced by application of sewage sludge on Chilean soils contaminated by mine tailings

The effect of mine tailings and sewage sludge was evaluated on sorption, desorption, availability and distribution of copper in two soils, one high (sandy soil) and one low in copper (clay soil). In both soils contaminated by mine tailings the copper sorption capacity and the affinity of the substrate for the metal decreased substantially compared to the uncontaminated soils, however, the sorption remained always high in the clay soil substrates. In the substrates with sandy soil, the high Cu content and lower clay content were determining factors in the lower magnitude of the sorption. Similarly, metal desorption was closely related to these two parameters, and it was higher in clay soil with lower pH. In general, the application of sewage sludge favored the sorption of Cu in soils contaminated and uncontaminated with mine tailings, and in all cases desorption decreased, an effect that remained for at least 30 days. Simple extraction of Cu with CaCl2 and diethylenetriaminepentaacetic acid gave contradictory results, so a careful choice of the procedure is required, depending on the level of metal in the soil and on the acting principle of the extracting agent. In that relation, more complete information on the changes in the metal forms was obtained by application of the sequential extraction procedure proposed by the European Community Bureau of Reference.

Using Mediterranean shrubs for the phytoremediation of a soil impacted by pyritic wastes in Southern Spain: a field experiment

Re-vegetation is the main aim of ecological restoration projects, and in Mediterranean environments native plants are desirable to achieve successful restoration. In 1998, the burst of a tailings dam flooded the Guadiamar river valley downstream from Aznalcóllar (Southern Spain) with sludges that contained elevated concentrations of metals and metalloids, polluting soils and waters. A phytoremediation experiment to assess the potential use of native shrub species for the restoration of soils affected by the spillage was performed from 2005 to 2007, with soils divided into two groups: pH < 5 and pH > 5. Four native shrubs (Myrtus communis, Retama sphaerocarpa, Rosmarinus officinalis and Tamarix gallica) were planted and left to grow without intervention. Trace element concentrations in soils and plants, their extractability in soils, transfer factors and plant survival were used to identify the most-interesting species for phytoremediation. Total As was higher in soils with pH < 5. Ammonium sulphate-extractable zinc, copper, cadmium and aluminium concentrations were higher in very-acid soils, but arsenic was extracted more efficiently when soil pH was >5. Unlike As, which was either fixed by Fe oxides or retained as sulphide, the extractable metals showed significant relationships with the corresponding total soil metal concentration and inverse relationships with soil pH. T. gallica, R. officinalis and R. sphaerocarpa survived better in soils with pH > 5, while M. communis had better survival at pH < 5. R. sphaerocarpa showed the highest survival (30%) in all soils. Trace element transfer from soil to harvestable parts was low for all species and elements, and some species may have been able to decrease trace element availability in the soil. Our results suggest that R. sphaerocarpa is an adequate plant species for phytostabilising these soils, although more research is needed to address the self-sustainability of this remediation technique and the associated environmental changes.

Bioavailability and accumulation of trace elements in soils and plants of a highly contaminated estuary (Domingo Rubio tidal channel, SW Spain)

The Domingo Rubio tidal channel (Palos de la Frontera, Huelva, Spain) is an estuary located in the mouth of the Tinto River. The estuary is affected by different sources of pollution (waters of the Tinto River, contaminated with trace elements from the Iberian Pyrite belt, and effluent from the Huelva chemical industrial area). Soil and the most frequent plant species were collected in 2004 and 2006 at six different locations on the estuary. In general, N-Kjedahl, Total Organic Carbon values, salinity and contamination (total trace elements up to 1,000 mg kg(-1) As, 6 mg kg(-1) Cd, 2,500 mg kg(-1) Cu, 1,900 mg kg(-1) Pb and 1,300 mg kg(-1) Zn) tended to increase downstream of the tidal channel. Soil biochemical properties were not negatively affected either by the high salinity or by trace element contamination. Despite the high values of the trace elements, analysed plant samples showed that Cu was the only metal that could be a serious risk for the food chain.

Phytostabilization of amended soils polluted with trace elements using the Mediterranean shrub: Rosmarinus officinalis

We evaluate the mid-term effects of two amendments and the establishment of R. officinalis on chemical and biochemical properties in a trace element contaminated soil by a mine spill and the possible use of this plant for stabilization purposes. The experiment was carried out using containers filled with trace element polluted soil, where four treatments were established: organic treatment (biosolid compost, OAR), inorganic treatment (sugar beet lime, IAR), control with plant (NAR) and control without plant (NA). Amendment addition and plant establishment contributed to restore soil chemical (pH, total organic carbon, and water soluble carbon) and biochemical properties (microbial biomass carbon and the enzymatic activities: aryl-sulphatase and protease). The presence of rosemary did not affect soluble (0.01 M CaCl2) Cd and Zn and decreased trace element EDTA extractability in amended soils. There were no negative effects found on plant growth and nutrient content on polluted soils (NAR, OAR, and IAR). Trace element contents were within normal levels in plants. Therefore, rosemary might be a reliable option for successful phytostablization of moderate trace element contaminated soils.

Trace elements, pH and organic matter evolution in contaminated soils under assisted natural remediation: a 4-year field study

A 4-year study was undertaken on the effect of three amendments (biosolid compost (BC), sugar beet lime (SL), and combination of leonardite plus sugar beet lime (LESL)) on reclamation of a moderately trace element-contaminated soil under field conditions. Results showed that organic C increased in BC and LESL treatments. BC and SL treatments increased soil pH and reduced CaCl(2)-extractable metal concentrations more efficiently. At the end of the experiment, CaCl(2)-extractable metal concentrations decreased and were similar in all treatments pointing out the importance of the natural remediation processes in contaminated soils. Addition of amendments showed no clear reduction in EDTA-extractable trace element concentrations, even, BC and LESL subplots showed some little increase of these elements with time. Amendments did not cause any change in total trace element concentration in soil. Addition of amendments could be a successful and reliable long term technique for stabilization of trace elements in contaminated soils at a field scale with minimum maintenance.

Heavy metals generate reactive oxygen species in terrestrial and aquatic ciliated protozoa

Reactive oxygen species (ROS) induction by exposure to heavy metals (Cd, Cu or Zn) in diverse free-living ciliated protozoa (Tetrahymena sp. and three strains of Colpoda steinii, isolated from freshwater and soils with different level of metal pollution) has been evaluated. Using specific fluorophores, such as 2',7'-dichlorofluorescein diacetate, hydroethidine and dihydrorhodamine 123, and a fluorescence microscope with the program MetaMorph Imaging System 4.0, we have analyzed both the average fluorescence emission and the heterogeneous distribution of fluorescence in control and treated cells. This is the first time that these fluorophores are used to detect ROS production in ciliated protozoa. All metals generate ROS, mainly superoxide and peroxides, showing a remarkable inter- and intra-specific variations. Likewise, resistance against each metal was also very diverse. Cu and specially Cd, the most toxic heavy metal for these ciliates, are the best oxidative stress inducers. However, a correlation between fluorescence emission intensity and cellular metal sensitivity for each strain cannot be established. Results are discussed and compared with similar findings previously published in other unicellular and pluricellular organisms.

Trace element mobility in soils seven years after the Aznalcóllar mine spill

The long-term influence of the Aznalcóllar mine spill on soils was studied seven years after the accident in the area of Vado del Quema. Soils where the pyritic sludge was not removed after the cleaning operations and soils where this process was accomplished successfully were sampled and studied in detail. Sludge and soil horizons were characterised, determining their physico-chemical parameters, mineralogy and the total concentrations of major and trace elements. Moreover, leaching studies were performed using batch tests. The main mineralogical changes detected in the soil beneath the weathered sludge are the neo-formation of jarosite, gypsum and sainfeldite, together with the almost total depletion of calcite. An important acidification of soil has been also produced, especially in the uppermost soil layers. These two factors show to be the main responsible for the vertical distribution and leachability displayed by trace elements. Critical total concentrations were found for most trace elements in the soil still affected by the sludge weathering. Furthermore, the Cd and Zn leachable contents showed to be extremely high. Therefore, in those areas affected by the mine spill where the removal of sludge was not accomplished properly, special care should be paid to trace elements highly mobile in acidic conditions. Additional restoration measures should be undertaken to avoid further pollutant dispersion.

Bioavailability of metals and As from acidified multicontaminated soils: use of white lupin to validate several extraction methods

White lupin is an annual crop that has been used for phytostabilization of acidified multicontaminated (heavy metals and As) soils from the Aznalcóllar spill-affected area, Southern Spain. One of the most important factors for successful phytostabilization is monitoring the pollutant bioavailability in the soil. The aim of this work was to determine the best-suited method for assessing the bioavailability of heavy metals together with As in the Aznalcóllar spill-affected area, by means of a systematic comparison between different extraction methods (Ammonium bicarbonate-diethylenetriamine pentaacetic acid (AB-DTPA), CaCl2, NaNO3, BCR, (NH4)2SO4 and rhizo). Both AB-DTPA and the first step of the BCR method were found to be unsuitable for assessing the bioavailability of heavy metals and As to plants growing in acidic soils. However, CaCl2-extractable As, Cu, and Zn and NaNO3-extractable As and Zn were well correlated with their concentrations in plant organs. Rhizo and (NH4)2SO4, with the highest determination coefficients, were the most recommended simple extraction methods to assess the bioavailability of As, Cu, Fe, Mn, and Zn in acidified multicontaminated soils using white lupin as an excluder model plant.

Zn mobility and geochemistry in surface sulfide mining soils from SE Spain

The extraction of metallic minerals and the mineral dressing operations in concentrators produced a high impact in soils and sediments. Heavy metals in soils constitute a high risk of pollution, not only for mining areas, but also for agriculture and villages placed in subsidiary areas. This research has been focused on the assessment of the real environmental and health hazards of Zn in relation to geochemistry and metal mobility in surface soils from a mining area in SE Spain, under semiarid weather conditions. Mineralogy of the studied soils revealed major presence of quartz, but also of other silicates, sulfates, carbonates, and sulfides. Regarding Zn minerals, the presence of sphalerite as the main Zn sulfide, and of goslarite as Zn sulfate, and of smithsonite as Zn carbonate should be highlighted. Soil pH ranged between 4.4 and 4.9 and the electrical conductivity between 55 and 85 microS/cm. By using the sequential extraction procedure, the achieved results show that zinc is not only mainly associated to primary but also to secondary sulfides. Total concentration of the non-available fractions rises up to 98.45% of total Zn in the studied soils. On the other hand, available Zn fraction did not exceed more than 1.55% in percentage and less than 2000 ppm in absolute terms, and when referred to more easily available fraction (water-soluble and exchangeable fractions), these values are not more than 0.44% and then 800 ppm. Therefore, although there is a significant pollution level in this area, immediate hazard for the environment can be assessed as moderate. Finally it should be highlighted that these surface soils have undergone concentration processes of sphalerite, whose mechanisms should be related to the ascending flow of capillary water and the dragging of sphalerite crystals and Zn salts by electrokinetic and colloidal processes These processes seem to occur based on environmental pollution by wind and water erosion, and therefore directly associated to environmental pollution and risks by free metals.

Contribution of heavy metals and As-loaded lupin root mineralization to the availability of the pollutants in multi-contaminated soils

White lupin (Lupinus albus L.) is an annual crop that has been used for phytostabilization of acidified multi-contaminated soils. Once the culture cycle is over, after shoot harvesting, a progressive transference of contaminants from roots to soil may take place as decomposition of roots occurs. An incubation experiment with Cu, Zn, Cd, and As-loaded roots of white lupin and soils with different pH values and concentrations of these contaminants from the area affected by a mine spill at Aznalcóllar (near Seville, Spain) was performed in order to assess the effect of the decomposition of the roots to the pH and (NH4)2SO4-extractable levels of these pollutants in the soils. Pollutants loaded-roots were mineralized (56 d) at a ratio similar to animal manures (15.8-19.4% of total organic carbon) in soil. The estimated root inputs of contaminants in comparison to their extractable concentrations in soil were high, especially in the control, non-contaminated and neutral contaminated soils. However, the extractable concentrations of the toxic elements in the soil were mainly governed by soil pH. Hence, the correction and maintenance of the soil pH within the range 5-6 after lupin culture is essential for long-time phytostabilization of acidified multi-contaminated soils.

Warming and drought change trace element bioaccumulation patterns in a Mediterranean shrubland

A field experiment consisting of drought and warming manipulation was conducted in a Mediterranean shrubland dominated by the shrubs Erica multiflora and Globularia alypum. The aim was to investigate the effects of the climatic changes predicted by IPCC models for the coming decades on trace element concentration and accumulation in aboveground biomass, plant litter, and soil. Warming increased concentrations and aboveground accumulation of some trace elements related to plant root uptake, such as Al, As, Cr, Cu, and partially Pb. This effect was more general in E. multiflora than in G. alypum. The stronger effects were increases in Al leaf concentrations (42%) and aboveground accumulation (500gha(-1)) in E. multiflora, in As stem biomass accumulation (0.2gha(-1)) in E. multiflora, and in Cr leaf concentrations (51%) in G. alypum and stem aboveground accumulation in E. multiflora (1.1gha(-1)). These species-specific increases were related to greater retranslocation, photosynthetic capacity and growth in E. multiflora than in G. alypum. Warming decreased the concentrations of some trace elements in leaf litter, implying the existence of an increased leaf retranslocation. Drought increased As (40%) and Cd (55%) in E. multiflora stems, whereas it decreased Cu (50%) in leaves, Ni (28%) in stems and Pb (32%) in leaf litter of G. alypum. The increasing concentrations of some trace elements in E. multiflora and not in G. alypum were related to a greater growth reduction in E. multiflora than in G. alypum. Warming increased As soil solubility (67%) and decreased total soil As (21%). Those changes were related to a greater Fe mobilization in warming plot and to a greater plant capture. Drought increased Hg (350%) concentrations in soils but had no significant effects on trace element accumulation in aboveground biomass. The different response to warming and drought in the two dominant species implies uneven changes in the quality of the plant tissues that may have implications for herbivores. This may be specially important for the performance of the studied Mediterranean ecosystems under the warmer and drier conditions predicted by the next decades by the GCM and ecophysiological models.

Drought changes the dynamics of trace element accumulation in a Mediterranean Quercus ilex forest

We conducted a field drought manipulation experiment in an evergreen oak Mediterranean forest from 1999 to 2005 to investigate the effects of the increased drought predicted for the next decades on the accumulation of trace elements that can be toxic for animals, in stand biomass, litter and soil. Drought increased concentrations of As, Cd, Ni, Pb and Cr in roots of the dominant tree species, Quercus ilex, and leaf Cd concentrations in Arbutus unedo and of Phillyrea latifolia codominant shrubs. The increased concentration of As and Cd can aggravate the toxic capacity of those two elements, which are already next or within the levels that have been shown to be toxic for herbivores. The study also showed a great reduction in Pb biomass content (100-135 gha(-1)) during the studied period (1999-2005) showing the effectiveness of the law that prohibited leaded fuel after 2001. The results also indicate that drought increases the exportation of some trace elements to continental waters.

Heavy metal concentrations in the general population of Andalusia, South of Spain: a comparison with the population within the area of influence of Aznalcóllar mine spill (SW Spain)

Levels of metalloids (As - urine) and heavy metals (Hg - urine, Cd - whole blood and Zn - serum) were determined by atomic absorption spectrometry in 601 subjects living in the area affected by the Aznalcóllar mine spill (SW, Spain) and compared with those of a representative sample (960 subjects) selected from the Andalusian community (non-affected area), southern Spain. The characteristic parameters of the analytical method including uncertainty were determined for each metal. Potential associations of metal concentration with age, sex and body mass index as well as life-style habits (smoking, alcohol consumption and food habits) were explored. Concentrations of all the metals studied were statistically higher in the population of the affected area with respect to that of the non-affected area in Andalusia, although levels were always lower or similar to the values reported for the general population and below occupational reference limits. In conclusion, there is a lack of evidence that the spill had any incidence on human health in the population living in the affected area. There are few references in scientific literature reporting values from large series of samples, and hence our data could be useful for further studies.

Long-term effects of the Aznalcóllar mine spill-heavy metal content and mobility in soils and sediments of the Guadiamar river valley (SW Spain)

In 1998, a toxic spill from a pyrite mine (Aznalcóllar, SW Spain) contaminated some 40 km2 of the Agrio and Guadiamar river valley with heavy metal-enriched tailings sludge and acidic mine water. The aim of this study is to describe the long-term effects of heavy metal migration particularly with respect to the extent of vertical redistribution of As, Cd, Cu, Fe, Pb, S, Sb and Zn in soils and sediments of the river Guadiamar 4 years after the accident. For an assessment of the mobility behaviour, chemical associations of Cu, Pb, Sb and Zn in depth profiles polluted by tailings were determined by using sequential extraction procedures. In 2002, residues of toxic tailings were found in several places along the river Guadiamar. Heavy weathering has accelerated heavy metal displacement and contamination of the surrounding soil. Two element groups of contrary mobility can be distinguished: Cd and Zn are highly mobile and show strong displacements in acidic surroundings. Accumulation zones for Cd and Zn develop in less acidic soil layers due to the occurrence of Fe oxides, which constitute retaining fractions for these elements. The immobile elements Pb and Sb represent the second group. Highest concentrations of Pb and Sb are found in the tailings sludge. Cu and As show a variable distribution pattern. As a consequence of the heavy metal migration, an accumulation zone has formed up to 30 cm into the underlying soil at the time of investigation. In the future, there may be further penetration of heavy metals to greater depths.

Evaluation of heavy metal acute toxicity and bioaccumulation in soil ciliated protozoa

Laboratory toxicity tests, using ciliated protozoa, are scarce and they have been carried out usually with freshwater species. In this study, we have analysed the acute cytotoxicity of Cd, Zn and Cu in five different strains of very common soil ciliate species (Colpoda steinii, Colpoda inflata and Cyrtolophosis elongata), which were isolated from very different soil samples (polluted or not with heavy metals). Soil ciliates are quite resistant to heavy metals pollution with regard to ciliates from other habitats. The toxicity sequence was Cd>Cu>>Zn. Results from Cd+Zn mixtures indicated that Cd cytotoxicity decreases in the presence of low or moderate Zn concentrations. A broad heavy metal resistance level diversity exists among isolates of colpodid ciliates and it is seen to be a genetic feature rather than a habitat dependence. Bioaccumulation is seen to be the main mechanism involved in the metal resistance, except for Cu. For the first time in ciliates, a fluorescent method has been applied to detect Zn intracellular deposits. This methodology might be an useful tool for monitoring heavy metal pollution in soils.

Soil amendments reduce trace element solubility in a contaminated soil and allow regrowth of natural vegetation

We tested the effects of three amendments (a biosolid compost, a sugar beet lime, and a combination of leonardite plus sugar beet lime) on trace element stabilisation and spontaneous revegetation of a trace element contaminated soil. Soil properties were analysed before and after amendment application. Spontaneous vegetation growing on the experimental plot was studied by three surveys in terms of number of taxa colonising, percentage vegetation cover and plant biomass. Macronutrients and trace element concentrations of the five most frequent species were analysed. The results showed a positive effect of the amendments both on soil chemical properties and vegetation. All amendments increased soil pH and TOC content and reduced CaCl(2)-soluble-trace element concentrations. Colonisation by wild plants was enhanced in all amended treatments. The nutritional status of the five species studied was improved in some cases, while a general reduction in trace element concentrations of the aboveground parts was observed in all treated plots. The results obtained show that natural assisted remediation has potential for success on a field scale reducing trace element entry in the food chain.

Study of fractionation and potential mobility of metal from the Guadalquivir estuary: changes in mobility with time and influence of the aznalcollar mining spill

This study analyzed the evolution of metal levels in surface sediments from the Guadalquivir estuary between 1997 and 2002 and assessed the impact of the April 1998 Aznalcollar tailings dam failure and subsequent cleanup on metal concentrations in surface sediments. We also analyzed metal distribution with time in five chemical fractions of the surface sediments: exchangable, carbonate, reducible, oxidizable, and residual. This work showed that the April 1998 Aznalcollar tailings dam failure caused a considerable increase in the concentrations of Cd, Zn, Cu, and Pb in the surface sediments of the Guadalquivir estuary. It was also found there was a change in the distribution of Cd, Zn, Cu, and Pb between the chemical fractions of the sediment after the failure of the dam. There were increases in the percentages of Cd in the carbonate fraction, of Zn and Pb in the reducible fraction, and of Cu in the oxidizable fraction, whereas the percentages of these elements associated with the residual fraction decreased. In 1999, there was a decrease in the metal concentrations in the surface sediments from the Guadalquivir estuary, and by 2000 the chemical distribution and metal levels had returned to levels similar those before the dam failure.