Assessment of the environmental impact of an abandoned mine using an integrative approach: A case-study of the "Las Musas" mine (Extremadura, Spain)

Ecotoxicological Assessment of Polluted Soils One Year after the Application of Different Soil Remediation Techniques

The present work evaluated the influence of eight different soil remediation techniques, based on the use of residual materials (gypsum, marble, vermicompost) on the reduction in metal(loid)s toxicity (Cu, Zn, As, Pb and Cd) in a polluted natural area. Selected remediation treatments were applied in a field exposed to real conditions and they were evaluated one year after the application. More specifically, five ecotoxicological tests were carried out using different organisms on either the solid or the aqueous (leachate) fraction of the amended soils. Likewise, the main soil properties and the total, water-soluble and bioavailable metal fractions were determined to evaluate their influence on soil toxicity. According to the toxicity bioassays performed, the response of organisms to the treatments differed depending on whether the solid or the aqueous fraction was used. Our results highlighted that the use of a single bioassay may not be sufficient as an indicator of toxicity pathways to select soil remediation methods, so that the joint determination of metal availability and ecotoxicological response will be determinant for the correct establishment of any remediation technique carried out under natural conditions. Our results indicated that, of the different treatments used, the best technique for the remediation of metal(loid)s toxicity was the addition of marble sludge with vermicompost.

Status of Ecosystem Services in Abandoned Mining Areas in the Iberian Peninsula: Management Proposal

An abandoned sphalerite mining area in the southwest (SW) of the Iberian Peninsula was studied to evaluate the impact that the presence of metal(loid)s has on soil and ecosystem health. Five zones were delimited: sludge, dump, scrubland, riparian zone, and dehesa. Critical total levels of lead (Pb), zinc (Zn), thallium (Tl), and chromium (Cr), well above the limit indicative of toxicity problems, were found in the areas close to the sources of contamination. Pb-Zn concentrations were very high in the riparian zone, reaching values of 5875 mg/kg Pb and 4570 mg/kg Zn. The whole area is classifiable as extremely contaminated with Tl, with concentrations above 370 mg/kg in the scrubland. Cr accumulation mainly occurred in areas away from the dump, with levels up to 240 mg/kg in the dehesa. In the study area, several plants were found growing luxuriantly despite the contamination. The measured metal(loid)s content is the cause of a significant decrease in ecosystem services, resulting in unsafe soils for food and water production, so the implementation of a decontamination program is advisable. The plant species Retama sphaerocarpa, present in the sludge, scrubland, riparian zone, and dehesa, is postulated as suitable for use in phytoremediation.

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.

Threats of metal mining on ecosystem services. Conservation proposals

We have studied, in a protected area with intense hunting activity, the consequences of the abandonment of facilities and tailings of a metal mine. The area studied has the peculiarity of having a steep slope and containing a water reservoir for irrigation and human consumption. Soil, sludge, vegetation, and water samples were analyzed, in which many metal(loid)s exceeded the generic reference levels (NGR) established for the health of the ecosystem. The concentration of Tl in the soils ranged between 300 and 700 mg kg^-1, because of continuous diffuse pollution, produced both by the alteration of sphalerite and the combustion products of a coal-fired power plant near the study area. Soil concentrations of Pb (250-1500 mg kg^-1) and Zn (350-700 mg kg^-1) from the tailings indicate extreme contamination in the areas adjacent to them and in the reservoir. The contamination affects the water quality of the stream running through the study area, with 64 μg L^-1 of Tl and 9.1 μg L^-1 of Zn having been detected in the reservoir water. To ensure protection of human and ecosystem health, the following is proposed: (i) soil stabilization for erosion control and reduction of diffuse pollution, (ii) monitoring of soils for agricultural use and water quality, and (iii) study the impact of contamination on wildlife, both hunting and non-game species. Given their capacity to accumulate heavy metals it is proposed to use Cistus ladanifer, Lavandula stoechas and Retama sphaerocarpa as phytoremedial species. The novelty of this research lies in two considerations. First, a proposal for the analysis of environmental compartments as an interconnected and interdependent network in terms of impacts and their repercussions on the ES. Secondly, the application of the model DPSIR, which assumes that anthropogenic activities have an impact on the environment.

Application of an Ecotoxicological Battery Test to the Paddy Field Soils of the Albufera Natural Park

Albufera Natural Park (ANP) (Valencia, Spain) is one of the most important wetland areas of the Mediterranean coast subject to high anthropogenic pressure, on whose soils a battery of bioassays has never been applied to evaluate the ecotoxicological risk. The present study determined available and water-soluble heavy metal content in four paddy soils used in the ANP, and the ecotoxicological effect on these soils was evaluated by performing the bioassays regulated in Spanish Royal Decree 9/2005. Soil properties and extractable Co, Cr, Cu, Ni, Pb and Zn (EDTA pH = 7) were analyzed in soils. These elements and macro- and micronutrients were also assessed in soil leachate. A test battery covering the following was needed: acute toxicity test in Eisenia foetida (OECD TG 207); mineralization tests of nitrogen (OECD TG 2016) and carbon (OECD TG 217); growth inhibition test in Raphidocelis subcapitata (OECD TG 201); mobility inhibition test in Daphnia magna (OECD TG 202). The soils found in the most anthropized areas to the north of the ANP (Massanassa and Alfafar) demonstrated a higher concentration of available heavy metals than in the southern ones (Sueca and Sollana). The aqueous leachate of the studied soils contained very low concentrations, which would be related to soil properties. Despite the high concentration of available potentially toxic elements (PTEs) in the Massanassa and Alfafar soils, the studied soils showed no toxicity during the performed battery bioassays. Therefore, soils can be considered non-toxic despite the obtained PTEs available concentration.

Soil and Freshwater Bioassays to Assess Ecotoxicological Impact on Soils Affected by Mining Activities in the Iberian Pyrite Belt

This study aims to use geochemical, mineralogical, ecotoxicological and biological indicators for a comprehensive assessment of the ecological risks related to the mobility, ecotoxicity and bioavailability of potentially harmful elements in the Lousal mining district. Particularly, toxicity was evaluated using four assays: algae, cytotoxicity assays with HaCaT cell line (dermal), earthworms and Daphnia magna. The geochemical and mineralogical characterization of the studied area shows that the mine wastes underwent intense weathering processes, producing important contamination of the adjacent soils, which also led to the release and mobilization of PHEs into nearby water courses. Total PTE results indicate that the soils affected by mining activities were highly contaminated with As and Cu, while Zn and Pb content ranged from low to very high, depending on the analyzed samples. Cadmium levels were found to be very low in most of the soil samples. The test using Daphnia magna was the most sensitive bioassay, while the Eisenia foetida test was the least sensitive. Except for the LOS07 soil sample, the rest of the soils were classified as “High acute toxicity” and “Very high acute toxicity” for aquatic systems. The results in HACaT cells showed results similar to the ecotoxicological bioassays. The application of biotests, together with geochemical and mineralogical characterization, is a very useful tool to establish the degree of contamination and the environmental risk of potentially harmful elements.

Increase in fluoride concentration in mine water in Shendong mining area, Northwest China: Insights from isotopic and geochemical signatures

Mine water poses severe threats to the quality of the water supply and ecological environment of the Shendong mining areas owing to its excessive fluoride (F^-) content. However, the geochemical behaviours and enrichment mechanisms responsible for F⁻ enrichment during mining activities are not fully understood. In total, 18 Yanan groundwater and 45 mine water samples were collected to analyse the spatial distribution, hydrogeochemical behaviours, and formation mechanisms related to elevated F^- levels by analysing the stable isotopes and water-rock interactions. In this study, F^- concentrations in mine water samples varied from 0.16 to 12.75 mg/L, with a mean value of 6.10 mg/L, and 77.78% of the mine water samples had a concentration that exceeded China's national standards (1.00 mg/L) for drinking water. The F^- concentration was markedly high in the mine water samples, with the mean F^- concentration being 1.58 times of that in the Yanan groundwater samples. The results of stable isotopes (¹⁸O_H2O, D, ³⁴S_SO4, and ¹⁸O_SO4) and water-rock interaction analyses suggested that cation exchange and competitive effects were the dominant factors responsible for elevated F^- concentration in mine water during mining activities. Thus, the weathering of F-bearing minerals, agriculture, and domestic activities do not play a significant role in the secondary enrichment of F^- concentration.

Assessment of legacy mine metal contamination using ants as indicators of contamination

Most legacy mines contributed to contamination of the environment before and after cessation of mining. Contamination from waste rock, slag and tailings can introduce large concentrations of metals and metalloids to the surface soil and downstream sediments. Since ants are able to accumulate metals in their bodies, we investigated the possibility of using the elemental compositions of ants as indicators of metals at legacy mines developed on ores rich in copper (Cu), zinc (Zn), arsenic (As), silver (Ag) and lead (Pb). Our results showed the concentrations of manganese (Mn) and Cu in ants were not significantly different between mine and reference samples and only Zn was significantly different between contaminated and reference areas. Crematogaster spp. and Notoncus spp. from reference areas accumulated larger concentrations of metals in their bodies compared to ants from the mine. Ants accumulated metals in different parts of their bodies. The abdomen was the main site for accumulation of Mn, iron (Fe) and Zn. Mandibles were only associated with accumulation of Zn. Copper and Pb showed no area of preferential accumulation and traces were detected in the whole body of the ants. Ants from five genera had similar regions for metal accumulation. The exoskeleton did not contribute to accumulation of metals; instead all metals were stored in internal organs. Not all genera were suitable for use as indicators; only Iridomyrmex spp. and Ochetellus spp. accumulated larger amount of metals in mine samples compared to reference samples.

Environmental impact of mining-associated carbon emissions and analysis of cleaner production strategies in China

In recent years, concern has been increasing regarding the carbon emissions generated by mining activities. China is an extremely large coal producer (3695 Mt/2015) and consumer (3698 Mt/2015), and Shanxi Province (i.e., a major coal-producing province in China) is a crucial element in China's energy conservation and emission reduction goals. In this study, the Pingshuo mining area (PMA) in Shanxi Province was chosen as a case to analyze the dynamic changes in carbon emissions based on the Intergovernmental Panel on Climate Change (IPCC) method, and the factors influencing carbon emissions were analyzed via the IPAT equation. Carbon emission sources in opencast mines mainly included fuel and explosive use, coal mine methane escape, coal and gangue spontaneous combustion, and electricity consumption. The carbon emission of the PMA increased from 4 × 10⁴ Mg in 1986 to 1.05 × 10⁶ Mg in 2015, with an average annual increase of 11.64%. In the PMA, 4.71 × 10⁶ Mg of carbon emissions from fuel consumption accounted for 41.79% of carbon emissions, and 5.26 × 10⁶ Mg of carbon emissions from methane emissions accounted for 46.66%. Carbon emissions from explosives and electricity use were 4.1 × 10⁵ Mg and 8.8 × 10⁵ Mg, respectively. In this mining area, the factors influencing carbon emissions included population, GDP, and coal output. The results of this study not only provide a reference for cleaner production in mining areas but also lay a foundation for the study of global opencast coal mining carbon emissions.

History of environmental contamination at Sunny Corner Ag-Pb-Zn mine, eastern Australia: A meta-analysis approach

Environmental impacts associated with mining can be important even after cessation of ore extraction, particularly where sites are abandoned and unremediated. Acid Mine Drainage (AMD) is a common concern in such legacy mines where sulfide ores were extracted. AMD can introduce large concentrations of heavy metals to aquatic systems and contaminate the environment for many kilometres downstream of old mines. Understanding the pattern and history of contamination from legacy mines can help environmental managers make better management decisions. Meta-analysis is a statistical tool that can help determine the significance of changes in metal contamination over the years since cessation of mining. Here we use meta-analysis to examine metal contamination at and downstream of Sunny Corner silver (Ag)-lead (Pb)-zinc (Zn) mine in eastern Australia. Copper (Cu), Zn and Pb concentrations in water increased from 1978 to 2018 within 2 km downstream of the main mine adit, whereas for stream sediment, only Zn concentrations increased significantly over the same period. In contrast, Pb concentrations in surface soil decreased over the years from 2000 to 2018.

Land-Cover Patterns and Hydrogeomorphology of Tributaries: Are These Important Stressors for the Water Quality of Reservoirs in the Mediterranean Region?

Four streams in the Guadiana watershed were followed up to assess hydrogeomorphological and physicochemical characteristics, and to analyze its correlation with land use/land cover (LULC), analyzing their possible influence in reservoir water quality and possible influence in the reservoir water quality. The highest amounts of organic descriptors and nutrients were quantified in streams with the major percentage of olive groves and vineyards and urban land cover classes. Streams more influenced by agro-silvo-pastoral class presented better water quality, as this type of LULC acts as a buffer of the contamination runoff. The results highlighted that the hydrogeomorphology of the streams may influence the transfer of pollutants loads to reservoirs. Hence, in intermittent streams characterized by coarse particles in the sediment, high amounts of pollutants are accumulated when the flow ceases, and are further transported to the reservoirs when the flow retakes. On the contrary, streams with sediments characterized by a great percentage of fine particles and organic matter do not induce so much stress in reservoirs, since these allow the adsorption of nutrients and trace elements, without their transfer to reservoirs.

Lead content in soils and native plants near an abandoned mine in a protected area of south-western Spain: an approach to determining the environmental risk to wildlife and livestock

A study of the impact of an abandoned lead (Pb) mine ("Las Musas"), located in SW Spain, on the contamination of the surface soil and pastures in its vicinity revealed the presence of widely distributed, high levels of Pb contamination. The total Pb concentrations in soils sampled at distances from 3 to 998 m from the mine ranged between 129 and 1053 mg/kg, when it has been reported that non-polluted soils have concentrations of 29-40 mg/kg. These exceed the maximum tolerable levels in agricultural soils for the protection of environmental and human health as established in international and regional regulations. While the concentrations of potentially bioavailable Pb in the soils also surpassed the regulatory levels, the effective bioavailable fractions were low. The Pb concentrations measured in native plants ranged from 1.70 to 129 mg/kg dry weight, with Cynosurus echinatus, Philadelphus coronarius, and Fraxinus angustifolia being the species that bioaccumulated the greatest concentrations of this metal. Estimation of the environmental risk to wildlife and livestock grazing in the studied area showed no potential toxicity for these animals.