Mercury availability by operationally defined fractionation in granulometric distributions of soils and mine wastes from an abandoned cinnabar mine

Mercury contamination from historic cinnabar mines represents a potential risk to the environment. Asturias, in Northern Spain, was one of the largest metallurgic and mining producer areas of Hg in Europe during the 20th century until the end of activities in 1974. Mining operations have caused Hg release and dispersion throughout the area. In this study, soils collected from calcine piles and surrounding soils at an abandoned Hg mine and metallurgical plant in Mieres (Asturias, Spain) were distributed in different particle-size subsamples. Fractionation of Hg was performed by means of a Hg-specific sequential extraction procedure complemented with the selective determination of organic Hg fraction by a specific extraction method. Extremely high concentrations of total Hg were found in calcine piles. Concentrations and mobility of Hg decreased markedly with the distance in soils located 25 m both above and below the chimney of the metallurgical plant. The sequential extraction results indicated that Hg is primarily found as elemental Hg followed by sulfide Hg in the finest subsamples. However, this distribution is inverted in the coarser grain fractions where sulfide Hg prevails. Calcine piles exhibited exceptionally high values of mobile Hg (up to 5350 μg g(-1) in the finest subsample). Accumulation of Hg in the elemental Hg fraction was observed at decreasing grain size which is indicative of deposition of Hg vapors from the metallurgical plant. Enrichment of sulfide Hg was found in the finest subsamples of soils sampled below the chimney (up to 99 μg g(-1)). Significant organic Hg contents were observed in the soil samples (up to 2.8 μg g(-1)), higher than those found in other abandoned Hg mining sites. A strong correlation was observed between organic Hg and Hg humic and fulvic complexes, as well as with the elemental Hg fraction. This indicates that both humic and fulvic material and elemental Hg must be the primary variables controlling Hg methylation in these soils.

Arsenic input into the catchment of the River Caudal (Northwestern Spain) from abandoned Hg mining works: effect on water quality

In Asturias (NW Spain) there are many abandoned mines, of which Hg mines are of particular significance from an environmental point of view, due to the presence of Hg and particularly As, which is found either in the form of specific (orpiment and realgar) or non-specific minerals (As-rich pyrite). The instability of these minerals leads to the presence of As-rich mine drainage and spoils heap leachates that enter surface waters or groundwaters. A study including the three most important Hg mines in the region (La Soterraña, Los Rueldos and El Terronal) has been conducted. Watercourses flowing through these mining areas are tributaries of the River Caudal, one of the most important rivers in the area. High concentrations of As were found in some of these waters, which were monitored over a period of three hydrological years and classified according to a water quality index. Those waters sampled close to the mines are generally of poor-to-bad quality, with low alkalinity and in some cases high metal content, but the quality of these waters improves with distance from the mines. The average mass load of As entering the River Caudal has been evaluated as: 200, 12 and 9,800 kg year(-1) from La Soterraña, Los Rueldos and El Terronal mine sites, respectively. Despite the constant input of about 10 tonnes of As per year, the total As concentration remains below analytical detection thresholds on account of the river's high water flow. Nevertheless, an important part of this As load is presumably retained in the river sediments, representing a potential risk of pollution of the aquatic ecosystems.

Asturian mercury mining district (Spain) and the environment: a review

Mercury is of particular concern amongst global environmental pollutants, with abundant contaminated sites worldwide, many of which are associated with mining activities. Asturias (Northwest of Spain) can be considered an Hg metallogenic province with abundant epithermal-type deposits, whose paragenetic sequences include also As-rich minerals. These mines were abandoned long before the introduction of any environmental regulations to control metal release from these sources. Consequently, the environment is globally affected, as high metal concentrations have been found in soils, waters, sediments, plants, and air. In this paper, a characterization of the environmental affection caused by Hg mining in nine Asturian mine sites is presented, with particular emphasis in Hg and As contents. Hg concentrations found in the studied milieu are similar and even higher than those reported in previous studies for other mercury mining districts (mainly Almadén and Idrija). Furthermore, the potential adverse health effects of exposure to these elements in the considered sites in this district have been assessed.

Wetland-based passive treatment systems for gold ore processing effluents containing residual cyanide, metals and nitrogen species

Gold extraction operations generate a variety of wastes requiring responsible disposal in compliance with current environmental regulations. During recent decades, increased emphasis has been placed on effluent control and treatment, in order to avoid the threat to the environment posed by toxic constituents. In many modern gold mining and ore processing operations, cyanide species are of most immediate concern. Given that natural degradation processes are known to reduce the toxicity of cyanide over time, trials have been made at laboratory and field scales into the feasibility of using wetland-based passive systems as low-cost and environmentally friendly methods for long-term treatment of leachates from closed gold mine tailing disposal facilities. Laboratory experiments on discrete aerobic and anaerobic treatment units supported the development of design parameters for the construction of a field-scale passive system at a gold mine site in northern Spain. An in situ pilot-scale wetland treatment system was designed, constructed and monitored over a nine-month period. Overall, the results suggest that compost-based constructed wetlands are capable of detoxifying cyanidation effluents, removing about 21.6% of dissolved cyanide and 98% of Cu, as well as nitrite and nitrate. Wetland-based passive systems can therefore be considered as a viable technology for removal of residual concentrations of cyanide from leachates emanating from closed gold mine tailing disposal facilities.

Release of toxic metals and metalloids from Los Rueldos mercury mine (Asturias, Spain)

The abandoned mercury mining works of "Los Rueldos" are located 20 km from Oviedo, along the northwestern border of the Asturian Central Coal Basin, in an area with intense tectonization. Hg mainly appears as cinnabar, but occasionally metacinnabar and native Hg are present; associated with Hg ore appear As-rich minerals (arsenopyrite, As-rich pyrite, realgar and scorodite). In the spoil heap, Hg content ranges from 14 to 2224 mg kg(-1), and As from 4746 to 62,196 mg kg(-1). Mine drainage and spoil heap leachates show acidic conditions (pH: 2.43-2.50), 2900-4600 mg l(-1) sulphate, 1.4-9.2 mg l(-1) As, 0.03-0.48 mg l(-1) Pb, and 3.6-14 microg l(-1) Hg. According to the analytical data and characteristics of the site, the application of corrective measurements to avoid the dispersion of contaminants in the environment must be considered.

Influence of industry on the geochemical urban environment of Mieres (Spain) and associated health risk

This study is concerned with the elemental composition of soils and street dust collected in an historical industrial city of approximately 27,000 inhabitants, where old Hg mining and metallurgical activities strongly affected the load of heavy metals in the urban environment. For the purpose of the study, representative samples of soils and street dust were collected at different locations in the whole urban area (3 km2). Elevated mean concentrations of As in soils and street dust (69 and 135 micrograms g-1, respectively), and Hg (3.07 and 4.24 micrograms g-1, respectively), compared to background levels and to those found in other cities, reflect the anomalous geochemical nature of these materials and the strong influence exerted by the old mining sites.

Distribution of heavy metals in the street dusts and soils of an industrial city in northern Spain

This study characterizes the elemental composition of street dust and soils in Avilés (N. Spain), a medium-size city of approximately eighty thousand inhabitants, where industrial activities and traffic strongly affect heavy metal distribution. A total of 112 samples of street dust were collected within a 7-km(2) area, encompassing residential and industrial sites (ferrous and non-ferrous plants). Elevated geometric mean concentrations of zinc (4,892 microg x g(-1)), cadmium (22.3 microg x g(-1)), and mercury (2.56 microg x g(-1)) in street dust were found in samples located near industrial areas. Two types of anthropic influence were distinguishable: the first and most important one is that related to metallurgical activity and transportation of raw materials for local industries. Secondly, exhaust emissions from traffic are an important source of lead concentration in areas with high vehicular density (geometric mean: 514 microg x g(-1)). The zinc content in the dust samples decreased with the distance from a zinc smelter located in the northern part of the city. The same trend was found for other elements in association with zinc in the raw materials used by the smelter, such as cadmium and mercury. A simultaneous research campaign of urban soils, that involved the collection of 40 samples from a 10-km(2) area, revealed geometric mean concentrations of 376 microg x g(-1) Zn, 2.16 microg x g(-1) Cd, 0.57 microg x g(-1) Hg, and 149 microg x g(-1) Pb, and distribution patterns almost identical to those found for street dust.

Bioremediation of diesel-contaminated soils: evaluation of potential in situ techniques by study of bacterial degradation

The development of a simple laboratory methodology allows the implementation of in situ bioremediation of polluted soils with diesel fuel. In this investigation microbiological and chemical analyses and a suitable bioreactor design, were very useful for suggesting the best ways to improve biodegradation extents in a diesel-enriched soil. Biostimulation with inorganic nitrogen and phosphorus produced the best results in a simple bioreactor, with biodegradation extents higher than 90% after 45 days. Also, the addition of activated sludge from a domestic wastewater plant increased the degradation rate to a great extent. In both cases, microbiological studies showed the presence of Acinetobacter sp. degrading most of the hydrocarbons. Simultaneously, a diesel fuel release (approximately 400,000 l) was studied. Samples taken in polluted soil and water revealed that bacteria from the genus Acinetobacter were predominant. In plate studies, Acinetobacter colonies produced a whitish substance with the characteristics of a biosurfactant. Remarkably, the presence of this product was evident at the field site, both in the riverbanks and in the physical recovery plant. The study of the similarities between laboratory results and the diesel spill site strongly suggested that natural conditions at the field site allowed the implementation of in situ bioremediation after physical removal of LNAPL (light nonaqueous-phase liquids).

Exposure of the hydrophobic components of porcine lung surfactant to oxidant stress alters surface tension properties

We have tested the hypothesis that oxidation of lung surfactant results in loss of surface tension lowering function. Porcine lung surfactant was exposed to conditions known to cause lipid peroxidation (0.2 mM FeCl2 + 0.1 mM H2O2 or 5 microM CuCl2). Lipid peroxidation was verified by detection of conjugated dienes, thiobarbituric acid reactive substances, fluorescent products, hydroxy alkenals, and loss of unsaturated fatty acids. Exposed samples had significantly diminished surface tension lowering ability in vitro as measured in a bubble surfactometer. Samples exposed to FeCl2 + H2O2 had significantly diminished surface tension lowering ability in vivo as indicated by their reduced ability to improve lung compliance of surfactant-deficient fetal rabbits. Oxidation of phospholipid mixtures with surface tension lowering activity and containing unsaturated acyl groups resulted in partial loss of activity as determined in vitro. These results suggest that the effect of oxidants on lung surfactant function is due, in part, to effects on the phospholipid components and that acute pulmonary inflammation accompanied by oxygen radical production may result in surfactant lipid peroxidation and loss of surface tension lowering function.

Taxonomical, clinical and pathological findings in moradilla (Lobelia-like) poisoning in sheep

Each year during late winter and spring, grazing sheep and cattle in the State of Tamaulipas in northeastern Mexico develop toxicoses which have been empirically associated to consumption of a toxic plant locally known as moradilla. This investigation was undertaken to determine whether moradilla was a toxic plant not yet reported in Tamaulipas or was an unrecognized species of the Lobelaceae or Campanulaceae family. Taxonomic determination of moradilla plants collected from February to April showed that it was a species of Lobelia. Five alkaloids were identified by thin-layer chromatography in the mature stages of moradilla, while only 1 and 3 alkaloids were found in the growing and flowering stages of this plant, respectively. The alkaloids were not affected by making silage, drying in hay or freezing. Experimental intoxication of sheep with moradilla caused clinical signs and pathologic changes identical to those previously described for lobelia toxicosis. It was concluded that Lobelia berlandieri was the cause of moradilla toxicosis in grazing cattle and sheep of northeastern Mexico.