The composition and distribution of airborne particles in different locations in a salt mine were determined in terms of their origin, the distance from the air inlet, and the adaptation of post-mining chambers and corridors for tourists and general audience. The composition of aerosols in air was also evaluated from the perspective of human health. Air samples were collected on filters by using portable air pumps, in a historical underground salt mine in Bochnia (Poland), which is currently a touristic and recreation attraction and sanatorium. The particulate matter (PM) concentration was determined using the gravimetric method by weighing quartz filters. The content of carbon, water-soluble constituents, trace elements, and minerals was also determined. A genetic classification of the suspended matter was proposed and comprised three groups: geogenic (fragments of rock salt and associated minerals from the deposit), anthropogenic (carbon-bearing particles from tourist traffic and small amounts of fly ash, soot, and rust), and biogenic particles (occasional pollen). The total PM concentration in air varied between 21 and 79 μg/m3 (with PM4 constituting 4–24 μg/m3). The amount of atmospheric dust components coming from the surface was low and decreased with the distance from the intake shaft, thus indicating the self-cleaning process. NaCl dominated the water-soluble constituents, while Fe, Al, Ag, Mn, and Zn dominated the trace elements, with the concentration of majority of them below 30 ng/m3. These metals are released into air from both natural sources and the wear or/and corrosion of mining and tourists facilities in the underground functional space. No potentially toxic elements or constituents were detected. The presence of salt particles and salty spray in the atmosphere of salt mine, which may have anti-inflammatory and antiallergic properties, is beneficial to human health. This study will allow for a broader look at the potential of halotherapy in underground salt mines from a medical and regulatory point of view.
The aim of this study was to investigate the causes of the evolution of atmospheric dust composition in an open-to-public subterranean site (UNESCO-recognized historic mine) at increasing distances from the air intake. The role of the components imported with atmospheric air from the surface was compared with natural and anthropogenic sources of dust from inside the mine. Samples of deposited dust were directly collected from flat surfaces at 11 carefully selected sites. The morphological, mineralogical, and chemical characteristics were obtained using scanning electron microscopy (SEM), X-ray diffraction (XRD), and inductively coupled plasma spectroscopy (ICP). The study showed that the air in the underground salt mine was free of pollutants present in the ambient air on the surface. Most of the components sucked into the mine by the ventilation system from the surface (regular dust, particulate matter, gaseous pollutants, biogenic particles, etc.) underwent quick and instantaneous sedimentation in the close vicinity of the air inlet to the mine. The dust settled in the mine interior primarily consisted of natural geogenic particles, locally derived from the weathering of the host rock (halite, anhydrite, and aluminosilicates). This was confirmed by low values of enrichment factors (EF) calculated for minor and trace elements. Only one site, due to the tourist railroad and the associated local intensive tourist traffic, represented the anthropogenic sources of elevated concentrations of ferruginous particles and accompanied metals (P, Cr, Mn, Co, Ni, Cu, As, Mo, Cd, Sn, Sb, Pb, and W). The gravitational deposition of pollutants from these sources limits the effects of the emissions to the local range. The used methodology and the results are universal and might also apply to other mines, caves, or underground installations used for museums, tourists, or speleotherapeutic purposes.
The small stalactites found on the ceiling at level I near the Sutoris shaft in the thirteenth-century historic salt mine in Bochnia, Poland, are mainly composed of mirabilite (Na2SO4·10H2O) followed by blödite (Na2Mg(SO4)2·4H2O). The unique presence of these two minerals in only one location in this old underground mine is attributed to contemporary precipitation from percolating solutions. This can be caused by a combination of at least two factors: a specific and stable microclimate (characterised by a low temperature, high humidity, and relatively strong air circulation which accelerates the processes of evaporation and crystallisation) and the specific chemical composition of the leaking solution (contains a low carbonate and high sulphate content, and characterised by acidic pH (4.8) and intermediate-mineralisation (174,308 mg/L)). The microclimate specified above can be linked to the long distance from the ventilation shaft that pumps the air from the surface to the mine, while the composition of the leaking solution as well as the hydrochemical modelling results obtained with PHREEQC can be directly related to the top anhydrite layer and the overlying secondary cap consisting mainly of claystone, anhydrite, and gypsum. In this study, the challenges underlying the preservation of mirabilite in the underground environment of the salt mine are discussed, in terms of both nature and mining law. Based on the results of detailed geological, mineralogical, and chemical research, appropriate solutions that can be practically applied for the management, preservation, and protection of the mirabilite efflorescence are proposed. The presence of this intriguing mineral, with appropriate protection, can be another geological attraction for tourists visiting this thirteenth-century UNESCO-recognised salt mine.
<p>Underground salt mines represent the most extreme environments which combine low nutrient availability, darkness, and hypersaline conditions. Halophilic (&#8220;salt-loving&#8221;) microorganisms are known to constitute the natural microbial communities of hypersaline ecosystems around the world (salt rocks, underground brines, saline lakes, etc.). For the first time halophilic microorganisms were detected in the air of the Bochnia Salt Mine, Poland.&#160;</p> <p>The purpose of this study was to determine the impact of various abiotic factors of the atmosphere on the presence and abundance of halophilic microbial communities present in mine air. Samples of aerosol components were collected at four different locations: one on the surface (at the air intake) and three underground at increasing distances from the intake. The inorganic aerosol was collected by dry (filter-based) and wet (scrubber-based) sampling method using portable air pumps. Besides microclimatic conditions, the content of water-soluble constituents, trace elements, carbon, and minerals were determined in aerosols. Simultaneously, the airborne cultivable microorganisms were collected by MAS-100 sampler. Mesophilic microorganisms were cultivated as a control, on general tryptic-soya (TSA) media, at 37&#176;C and 28&#176;C for up to one month. Halophilic ones were grown on a specific HBM medium containing 20% and 25% of NaCl concentration, at 37&#176;C and 28&#176;C for up to three months.</p> <p>The primary component of aerosol was NaCl (1000-3000 &#181;g&#183;m<sup>-3</sup>). It enters the air mainly in the form of a solution droplets due to the deliquescence of rock salt in humid air (up to 80% of relative humidity). The wet aerosol in salt mine is also composed of SO<sub>4</sub><sup>2-</sup> (110-300 &#181;g&#183;m<sup>-3</sup>), Ca<sup>2+ </sup>(90-280 &#181;g&#183;m<sup>-3</sup>), K<sup>+</sup> (50-190 &#181;g&#183;m<sup>-3</sup>), Mg<sup>2+</sup> (15-40 &#181;g&#183;m<sup>-3</sup>), and Fe<sup>3+</sup> (10-50 &#181;g&#183;m<sup>-3</sup>). The dry fraction of aerosol does not exceed 200 &#181;g m<sup>-3</sup> and is composed of fragments of natural rock salt (halite), anhydrite, gypsum, and clay minerals. The maximum indoor concentrations of airborne halophilic microorganisms cultivated at 37&#176;C or 28&#176;C reached 1910 CFU (colony-forming units) &#183;m<sup>-3</sup> and 1210 CFU&#183;m<sup>-3</sup>, respectively. Moreover, the content of halophilic microorganisms increased with the increase of the water-soluble constituents and NaCl concentrations. Our results suggest that airborne salt-saturated droplets may be a major factor influencing the abundance of live halophilic microorganisms in the atmosphere while the presence of mesophilic microorganism (which are associated with the outdoor environment) and the presence of humans seem to have no effect on the presence of halophilic microbial community.</p> <p>Our research indicates that halophilic microorganisms can survive in the air of the underground Bochnia Salt Mine. Abiotic factors, like high moisture content in the air and saline aerosol in liquid form may play an important role in their survival in the air. This way some extremophile microorganisms, given favorable environmental conditions, can survive even in such a hostile environment as the atmosphere in the underground mine. This could be important for astrobiology research, since various extremophiles, including halophiles, are considered excellent candidates for life beyond our planet.</p> <p>The study was supported by the Polish National Science Center (NCN) grant No. 2021/41/N/ST10/02751.</p> <p>&#160;</p>
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