RESUMEN
The soil pollution status, levels of exposure, and potential ecological and health risks to workers and residents by potentially harmful elements (PHEs) in the Angouran mining area (Iran), the biggest Zn-Pb mine in the Middle East, were studied. To this aim, topsoil (0-5 cm) samples (n = 63) from different land-uses were analyzed for their total PHEs concentrations. Mine worker's blood analysis and in vitro digestion extractions were applied in conjunction with human health risk assessment (HHRA) to assess the potential health impacts by exposure to PHEs. The maximum PHEs total concentrations were found in the soils near the waste rock dumps. HHRA indicated that ingestion of soils may induce a non-carcinogenic risk due to As and Pb (for both age groups of children and adults), while dermal contact for children may induce the same type of risk due to Cd, and Pb. The carcinogenic risks (CRs) of As, Cd, Cr, and Ni through ingestion route were above the acceptable value of 1 × 10-4, and children may face greater health risks. The average blood Zn, Pb, and Cd levels in the mine workers largely exceeded the safe concentration for adults, while 30% of the workers were tested positive for As in blood. In vitro digestion extractions indicated that the highest bioaccessible contents of As, Cd, Pb, Ni and Zn were found for the industrial-residential and mine soils in the area, while those of Cr and Cu were observed in the agricultural use soils. This study illustrates that a combination of techniques, including geochemical analysis, in vitro bioaccessibility extractions, HHRA, and blood analysis, is a workable integrated approach for evaluating pollution and health risks in mining districts.
Asunto(s)
Metales Pesados , Contaminantes del Suelo , Adulto , Niño , Humanos , Suelo/química , Monitoreo del Ambiente/métodos , Metales Pesados/análisis , Plomo , Irán , Cadmio , Contaminantes del Suelo/análisis , Medición de Riesgo , Zinc/análisis , ChinaRESUMEN
The geochemical stability, in terms of potential mobility and derived ecological and human health risks of potentially toxic elements (PTEs), of diverse fresh and old porphyry Cu-mine tailings from Chile was assessed through an integrated methodology comprising four interrelated investigation levels: (1) chemical composition and contamination degree of tailings by PTEs, (2) mineralogical characterization by X-ray diffraction and quantitative automated mineralogy analysis by scanning electron microscopy (QEMSCAN®), (3) partitioning and potential mobility of PTEs within the tailings by a sequential extraction procedure (SEP) and leaching tests, and (4) ecological risk assessment (ERA) and human health risk assessment (HHRA). According to pollution indices, Cu, As, Pb, and Mo are most concerning PTEs present in the tailings. SEP shows that major portion of the PTEs are strongly fixed as residual fraction, and thus are poorly mobilizable and bioavailable. Among the PTEs, Cu, As, and Mo were identified as the PTEs most prone to mobilization. Leaching tests show that a low fraction of PTEs is water-leachable. Seawater enhances Mn and As leaching, while process water increases the leaching of Cu, Mn, and Mo. Phosphate particularly promotes leaching of As and Cu, whereas it does not mobilize or even immobilize Pb in the tailings. ERA suggests that mainly old tailings pose a very high potential risk for ecological receptors (PERI = 663-3356), mostly due to Cu and As. HHRA indicates that the old tailings pose higher potential non-carcinogenic and carcinogenic health risks, while the risk decreases in the order ingestion > dermal > inhalation for both children and adults. Non carcinogenic and carcinogenic HHRA points to As as the main PTE of concern via ingestion pathway in the tailings. Overall, the results revealed that particularly old tailings, containing mixed slag-tailings, pose considerable risks to the environment and human health due to potential PTEs mobilization and this aspect requires scrutiny for proper tailings management, including storage, sealing, and eventual tailings reprocessing and/or site rehabilitation after closure.
Asunto(s)
Metales Pesados , Contaminantes del Suelo , Adulto , Niño , Chile , Cobre , Monitoreo del Ambiente , Humanos , Metales Pesados/análisis , Medición de Riesgo , Contaminantes del Suelo/análisisRESUMEN
The sorption of AsV on red mud (bauxite residue), produced in the ALCOA-San Cibrao factory (Spain), was assessed in view of its potential use as sorptive liner of landfills for the attenuation of As-rich leachates. The operating parameters evaluated, using batch-type procedures, comprised the effects of time, solution pH, AsV concentration (sorption isotherm) and presence of phosphate on the AsV sorption. The results showed that the red mud efficiently sorbed AsV. The sorption was fast, with a major fraction of initial AsV being removed in a few minutes or hours of contact, depending on AsV concentration. The kinetic process was well described by the pseudo-second order equation, which points to chemisorption is involved, whereas surface (film) diffusion chiefly governs the rate of AsV sorption for the red mud system. Sorption of AsV was strongly pH-dependent. Maximum removal (>98%) was observed at slightly acidic pH (pHmax = 5.5-6), while AsV sorption considerably decreased at both highly acidic and alkaline pH. The percentages of sorbed AsV decreased with the increasing solution AsV concentration, and the AsV sorption capacity (up to 43.5 mmol/kg) of the red mud was higher (â¼4 -fold) at pH â¼6 than at pH â¼9.2 (natural pH of the red mud). The presence of P at equimolar or 1:10 As/P molar ratios reduced AsV sorption by â¼20% and 30%, respectively. Simulations of AsV migration taking into account the effects of dispersion and diffusion through an hypothetical red mud liner, using the sorption parameters and the geotechnical-hydraulic conductivity characteristics of the RM, predicted a deeper migration of AsV in the liner at pHâ¼9.2 than at pHâ¼6 and a minimum thickness of â¼90 cm and â¼20 cm, respectively, for a RM liner to decrease the solution AsV concentration from highly toxic 1 mM to a safe <0.133 µM (<10 µg/L) level, after a 35-years period.
Asunto(s)
Arsénico , Adsorción , Óxido de Aluminio , Concentración de Iones de Hidrógeno , España , Instalaciones de Eliminación de ResiduosRESUMEN
The ability of red mud (RM) (bauxite residue) to remove HgII from landfill leachate (LL) was assessed. The studied aspects comprised the effects of time, pH, HgII concentration and the sorption isotherm, besides the influence of chloride and representative organic ligands. HgII removal by RM exhibited a complex kinetics where initial rapid sorption was followed by desorption at longer times. The sorption of HgII on RM was strongly pH-dependent. Outstanding maximum sorption was observed at pHâ¼4-5 (≥99.6%), while it abruptly dropped at higher pH values down to a minimum â¼28% at pHâ¼10.5. Chloride decreased HgII sorption at acid pH and shifted the pHmax towards higher pHâ¼9.4, which opposes to sorption in LL and suggests Cl- did not primarily control the process in LL. Amongst the organic ligands, acetate and salicylate slightly affected HgII sorption. Conversely, glycine affected sorption in a pH-dependent manner resembling that in LL, which suggests the relevant role of the organic nitrogenated compounds of LL. EDTA suppressed HgII sorption at any pH. HgII speciation modelling and dissolved organic matter (DOM) sorption support complexation of HgII by DOM as the primary factor governing the removal of HgII in LL. The sorption isotherm was better described by the Freundlich equation, which agrees with the heterogeneous composition of RM. The results indicate that HgII sorption on RM is favorable, but reveal differences in sorption and reduced efficiency, in LL media. Notwithstanding, RM possesses a notable capacity to remove HgII, even under the unhelpful complexing and competing conditions of LL.
Asunto(s)
Óxido de Aluminio/química , Mercurio/química , Contaminantes Químicos del Agua/química , Adsorción , Cloruros/química , Ácido Edético/química , Concentración de Iones de Hidrógeno , Cinética , Compuestos Orgánicos/química , Purificación del Agua/métodosRESUMEN
The effectiveness of the oxide-rich residue from bauxite refining (red mud) to remove inorganic Hg(II) from aqueous solutions was assessed. The aspects studied comprised the kinetics of the process (t = 1 min-24 h), the effect of pH (3.5-11.5), the interacting effect between salt concentration (0.01-1 M NaNO3) and pH and the Hg(II) sorption isotherm. Hg leaching from spent red mud was evaluated using the toxicity characteristics leaching procedure (TCLP) method. The sorption of Hg(II) onto red mud was very fast, with most of Hg(II) (97.0-99.7%) being removed from 0.5-50 µM Hg solutions in few minutes. The kinetic process was best described by Ho's pseudo-second order equation, pointing to chemisorption as the rate controlling step. Hg(II) sorption efficiency was very high (% removal between 93.9 and 99.8%) within all the studied pH range (3.5-11.5) and added Hg concentrations (5 and 50 µM), being optimal at pH 5-8 and decreasing slightly at both lowest and highest pH. The effect of background electrolyte concentration suggests specific sorption as the main interaction mechanism between Hg(II) and red mud, but the increasing non-sorbed Hg concentrations at low and high pH for higher electrolyte concentrations also revealed the contribution of an electrostatic component to the process. The sorption isotherm showed the characteristic shape of high affinity sorbents, and it was better described by the Redlich-Peterson and Freundlich equations, which are models that assume sorbent heterogeneity and involvement of more than one mechanism. The estimated Hg(II) sorption capacity from the Langmuir equation (q m ~9 mmol/kg) was comparable to those of some inorganic commercial sorbents but lower than most bio- or specifically designed sorbents. The leachability of retained Hg(II) from spent red mud (0.02, 0.25 and 2.42 mmol Hg/kg sorbed concentration) was low (0.28, 1.15 and 2.23 µmol/kg, respectively) and accounted for 1.2, 0.5 and 0.1% of previously sorbed Hg, indicating that Hg(II) is tightly bound by red mud once sorbed.
Asunto(s)
Óxido de Aluminio/química , Residuos Industriales , Mercurio/aislamiento & purificación , Contaminantes Químicos del Agua/aislamiento & purificación , Adsorción , Concentración de Iones de Hidrógeno , Residuos Industriales/análisis , Cinética , Mercurio/química , Tamaño de la Partícula , Soluciones , Contaminantes Químicos del Agua/químicaRESUMEN
In this study, we investigated the effect of some potential alleviative compounds against the acute toxicity of arsenic (As(V), As(III) and DMA(V)) on Aliivibrio fischeri (formerly Vibrio fischeri), a bioluminescent model bacterium, through the Microtox bioassay. The compounds studied differed in their mechanism of action, and they included the following: phosphate and glycerol, as chemical analogues (and potential competitors) of As(V) or As(III), respectively; citrate, a weak natural organic ligand; and the antioxidant ascorbic acid. Special attention was paid to phosphate effects, a widespread pollutant in natural environments. As(V) was found to be more acutely toxic than As(III) to A. fischeri, in accordance with its higher interaction with the bacteria. Both As(V) and As(III) were found to be much more acutely toxic than DMA(V), which was essentially non-acutely toxic even at very high concentrations. Phosphate presence (at equimolar P/As ratios or higher) resulted in the almost total suppression of bioluminescence inhibition, suggesting it exerts an alleviative effect against As(V) acute toxicity on A. fischeri. Interestingly, the uptake and the percentage of extracellular As(V) were not affected by the addition of phosphate, suggesting that such protective effect does not result from the competition for their common transporters. In contrast, the acute toxicity of As(III) was essentially unaffected by phosphate. Glycerol did not decrease the acute toxicity or the uptake of As(III) by A. fischeri, denoting the likely occurrence of an additional mechanism for As(III) uptake in such bacteria. Similarly, citrate and ascorbic acid essentially did not caused alleviation of As(V) or As(III) acute toxicity. As for environmental and operational implications, P could beneficially protect aquatic microorganisms against acute detrimental effects of As(V), whilst its presence could mask the toxicity due to As(V) when assessed using the Microtox bioassay, thus leading to seriously underestimate the actual ecological and health risks.
Asunto(s)
Aliivibrio fischeri/efectos de los fármacos , Arsénico/toxicidad , Compuestos Orgánicos/química , Arsénico/química , Ácido Ascórbico/química , Bioensayo/métodos , Ácido Cítrico/química , Interacciones Farmacológicas , Glicerol/química , Fosfatos/química , Sustancias Protectoras , Pruebas de Toxicidad AgudaRESUMEN
Red mud (RM) is a strongly alkaline residue generated in enormous amounts worldwide from bauxite refining using the Bayer chemical process. RM is composed mainly of Fe, Ti and Al oxides and hydroxides, but it also contains an array of trace metals and metalloids at different concentrations. The purpose of this paper is to assess the potential mobility of metals in RM, with special emphasis on pH effect. The 'operational' distribution and leachability of metals within/from RM was studied by applying a sequential extraction procedure (SEP) and several leaching tests (rapid titration, equilibration acidification, batch leaching with acetic acid and also the toxicity characteristics leaching procedure (TCLP) and the DIN 38414-S4 procedures, used as reference methods) carried out at different pH, solid/liquid ratio, extraction period and type of acid (HCl or acetic acid). Chemical analysis showed that, in addition to the major metals Fe, Al and Ti, RM contains several trace metals, some of them (Cr, Cu and Ni) in concentrations exceeding the regulatory limits. SEP showed that a majority of the metals in the RM (between the 32.2±8.5 for Cd and 95.3±0.4% for Ni) were found in the residual fraction, suggesting that they are not readily mobile under normal environmental conditions. Leaching tests performed at different pH showed that a significant fraction of the metals is mobilised from RM only under very strong acid conditions (pH<2), whereas Al is released in considerable amounts at pH<5.3. Among the trace metals, Cr requires special attention because of its relative high concentration in RM and the higher concentrations of this metal mobilised at low pH. The leaching tests using acetic acid showed that the standard TCLP largely underestimates the release of trace metals from RM, and therefore it is not advisable to evaluate the actual potential leaching of trace metals from this residue.
Asunto(s)
Óxido de Aluminio/química , Fraccionamiento Químico/métodos , Metalurgia/métodos , Metales/química , Contaminación Ambiental/prevención & control , Metales/análisis , Modelos Químicos , Administración de Residuos/métodosRESUMEN
The utilization of biosurfactants for the bioremediation of contaminated soil is not yet well established, because of the high production cost of biosurfactants. Consequently, it is interesting to look for new biosurfactants that can be produced at a large scale, and it can be employed for the bioremediation of contaminated sites. In this work, biosurfactants from Lactobacillus pentosus growing in hemicellulosic sugars solutions, with a similar composition of sugars found in trimming vine shoot hydrolysates, were employed in the bioremediation of soil contaminated with octane. It was observed that the presence of biosurfactant from L. pentosus accelerated the biodegradation of octane in soil. After 15 days of treatment, biosurfactants from L. pentosus reduced the concentration of octane in the soil to 58.6 and 62.8%, for soil charged with 700 and 70,000 mg/kg of hydrocarbon, respectively, whereas after 30 days of treatment, 76% of octane in soil was biodegraded in both cases. In the absence of biosurfactant and after 15 days of incubation, only 1.2 and 24% of octane was biodegraded in soil charged with 700 and 70,000 mg/kg of octane, respectively. Thus, the use of biosurfactants from L. pentosus, as part of a well-designed bioremediation process, can provide mechanisms to mobilize the target contaminants from the soil surface to make them more available to the microbial population.