Ecotoxicidade de nanocatalisadores de óxidos de ferro, produzidos a partir da drenagem ácida de mina, quando submetidos à ação de ozônio em meio aquoso / Ecotoxicity of iron oxide nanocatalysts, produced from acid mine drainage, when submitted to the action of ozone in aqueous medium

RESUMO Óxidos de ferro recuperados da drenagem ácida de minas representam uma matéria-prima potencial para a produção de baixo custo de nanogoetita ou nanohematita, com grau de pureza adequado para o seu uso como catalisador em processos de tratamento de efluentes líquidos com ozônio. Assim, a toxicidade das nanopartículas de ferro precisa ser determinada para prever seu impacto no meio ambiente, antes e depois de terem sido utilizadas nesses processos. Nesse contexto, o objetivo deste estudo foi avaliar a toxicidade de nanogoetita e nanohematita produzidas a partir da drenagem ácida de minas bem como comparar os resultados com hematita sintética de alta pureza. A nanogoetita foi obtida da drenagem ácida de minas e, após seu tratamento térmico a 450°C, produziu nanopartículas de hematita. Os materiais foram caracterizados por difração de raios X, microscopia eletrônica de transmissão e determinação da área superficial específica e porosidade com base nas isotermas de adsorção/dessorção de N2. Foram realizados os ensaios de ecotoxicidade usando os protocolos padronizados para bioluminescência com Vibrio fischeri, letalidade da Artemia sp., germinação de sementes de Lactuca sativa L. (alface) e crescimento das raízes de Allium cepa L. (cebola). Os resultados de toxicidade indicaram estabilidade das nanopartículas, que não são alteradas significativamente pela ação do ozônio em meio aquoso. Para todas as amostras, os valores indicaram baixa ou nenhuma toxicidade nas condições dos experimentos, para os bioindicadores utilizados. Esses resultados fornecem indicação de que as nanopartículas de ferro recuperadas da indústria de resíduos podem ser usadas como catalisadores sem efeitos adversos ao meio ambiente.

ABSTRACT Iron oxides recovered from acid mine drainage represent a potential raw material for the low-cost production of nanogoethite or nanohematite, with a degree of purity suitable for its use as a catalyst in processes for treating liquid effluents with ozone. Thus, the toxicity of iron nanoparticles needs to be determined to predict their impact on the environment, before and after they have been used in these processes. In this context, the objective of this study was to evaluate the toxicity of nanogoethite and nanohematite produced from acid mine drainage as well as to compare the results with high-purity synthetic hematite. Nanogoethite was obtained from acid mine drainage and, after its heat treatment at 450°C, produced nanoparticles of hematite. The materials were characterized by X-ray diffraction, transmission electron microscopy, and determination of the specific surface area and porosity based on N2 adsorption/desorption isotherms. Ecotoxicity tests were carried out using standardized protocols for bioluminescence with Vibrio fischeri, lethality of Artemia sp, germination of Lactuca sativa L (lettuce) seeds, and growth of Allium cepa L (onion) roots. The toxicity results indicated stability of the nanoparticles, which are not significantly altered by the action of ozone in aqueous medium. For all samples, the values indicated low or no toxicity under the conditions of the experiments. These results provide an indication that the iron nanoparticles recovered from the waste industry can be used as catalysts without adverse effects on the environment.

Estudo do potencial de adsorção de íons de ferro de água contaminada com drenagem ácida de mina utilizando geopolímero à base de cinza da casca de arroz e resíduo cerâmico / Removal of iron ions from water contaminated with acid mine drainage by geopolymer derived from rice husk ash and ceramic residue

Resumo A drenagem ácida de mina da mineração de carvão é um dos mais graves problemas ambientais que existem atualmente e é caracterizada, principalmente, por apresentar elevada acidez, baixo pH e expressiva concentração de metais tóxicos, como ferro, Mn e muitos outros, afetando diretamente mananciais e rios. Em busca de uma alternativa que pudesse melhorar, de forma eficiente e econômica, os níveis de acidez e ferro da água impactada pela drenagem ácida de mina, foi desenvolvido um adsorvente geopolimérico à base de materiais residuais da indústria cerâmica e do beneficiamento de arroz (cinzas da casca de arroz). O objetivo desta pesquisa foi avaliar a eficiência do geopolímero na remoção de íons ferro em água contaminada com drenagem ácida de mina. Foram avaliados aspectos de dosagem do adsorvente, efeito da temperatura, concentrações iniciais de ferro, cinética e parâmetros termodinâmicos do processo de adsorção. O percentual de ferro removido foi de 92,76%, à temperatura de 25 °C, em um período de 20 min, com uma concentração de adsorvente de 4 g L-1. A capacidade máxima de adsorção de ferro pelo geopolímero foi de 7,18 mg.g-1. O principal mecanismo de adsorção ocorreu em razão da quimissorção, que segue o modelo cinético de pseudossegunda ordem. O geopolímero se mostrou como uma alternativa eficiente ao tratamento de água contaminada com drenagem ácida de mina.

Abstract Acid mine drainage is a worldwide problem and is characterized by high acidity, low pH and expressive concentration of heavy metals, such as iron, Mn and many others, directly affecting water sources and rivers. In search of an alternative that could efficiently and economically improve the levels of acidity and water iron impacted by acid mine drainage, a geopolymeric adsorbent based on residual materials was developed: from the ceramic industry and rice processing (rice husk ash). In this work, it was evaluated the efficiency of the geopolymer in removing iron ions in water contaminated with acid mine drainage. Aspects of adsorbent dosage, temperature effect, initial iron concentrations, kinetics and thermodynamic parameters of the adsorption process were evaluated. The percentage of iron removed was 92.76%, at a temperature of 25 °C, for 20 min, with an adsorbent concentration of 4 g L-1, with the maximum capacity for adsorption of iron by the geopolymer being 7.18 mg.g-1. The main mechanism of adsorption occurred due to chemisorption, which follows the kinetic model of pseudo-second order. Geopolymer appears potentially useful an efficient alternative in the treatment of water contaminated with acid mine drainage.

Evaluation of toxic and genotoxic potential of a wet gas scrubber effluent obtained from wooden-based biomass furnaces: A case study in the red ceramic industry in southern Brazil.

Red ceramic industry in southern Brazil commonly uses wood biomass as furnace fuel generating great amounts of gas emissions and ash. To avoid their impact on atmospheric environment, wet scrubbing is currently being applied in several plants. However, the water leachate formed could be potentially toxic and not managed as a common water-based effluent, since the resulting wastewater could carry many toxic compounds derived from wood pyrolysis. There is a lack of studies regarding this kind of effluent obtained specifically and strictly from wooden-based biomass furnaces. Therefore, we conducted an evaluation of toxic and genotoxic potentials of this particular type of wet gas scrubber effluent. Physical-chemical analysis showed high contents of several contaminants, including phenols, sulphates and ammoniacal nitrogen, as well as the total and suspended solids. The effluent cause significant toxicity towards microcrustacean Artemia sp. (LC50 = 34.4%) and Daphnia magna (Toxicity Factor = 6 on average) and to higher plants (Lactuca sativa L. and Allium cepa L.) with acute and sub-acute effects in several parameters. Besides, using plasmid DNA, significant damage was observed in concentrations 12.5% and higher. In cellular DNA, concentrations starting from 12.5% and 6.25% showed significant increase in Damage Index (DI) and Damage Frequency (DF), respectively. The results altogether suggest that the effluent components, such phenols, produced by wood combustion can be volatilized, water scrubbed, resulting in a toxic and genotoxic effluent which could contaminate the environment.

Pyrite-enhanced methylene blue degradation in non-thermal plasma water treatment reactor.

In this study, methylene blue (MB) removal from an aqueous phase by electrical discharge non-thermal plasma (NTP) over water was investigated using three different feed gases: N(2), Ar, and O(2). The results showed that the dye removal rate was not strongly dependent on the feed gas when the electrical current was kept the same for all gases. The hydrogen peroxide generation in the water varied according to the feed gas (N(2)

Efficacy assessment of acid mine drainage treatment with coal mining waste using Allium cepa L. as a bioindicator.

The aim of this study was to evaluate the efficacy of the treatment of acid mine drainage (AMD) with calcinated coal mining waste using Allium cepa L. as a bioindicator. The pH values and the concentrations of aluminum, iron, manganese, zinc, copper, lead and sulfate were determined before and after the treatment of the AMD with calcinated coal mining waste. Allium cepa L. was exposed to untreated and treated AMD, as well as to mineral water as a negative control (NC). At the end of the exposure period, the inhibition of root growth was measured and the mean effective concentration (EC(50)) was determined. Oxidative stress biomarkers such as lipid peroxidation (TBARS), protein carbonyls (PC), catalase activity (CAT) and reduced glutathione levels (GSH) in the fleshy leaves of the bulb, as well as the DNA damage index (ID) in meristematic cells, were evaluated. The results indicated that the AMD treatment with calcinated coal mining waste resulted in an increase in the pH and an expressive removal of aluminum, iron, manganese and zinc. A high sub-chronic toxicity was observed when Allium cepa L. was exposed to the untreated AMD. However, after the treatment no toxicity was detected. Levels of TBARS and PC, CAT activity and the DNA damage index were significantly increased (P<0.05) in Allium cepa L. exposed to untreated AMD when compared to treated AMD and also to negative controls. No significant alteration in the GSH content was observed. In conclusion, the use of calcinated coal mining waste associated with toxicological tests on Allium cepa L. represents an alternative system for the treatment and biomonitoring of these types of environmental contaminants.

Textile effluents induce biomarkers of acute toxicity, oxidative stress, and genotoxicity.

The present work consists of a comparative evaluation of the toxicity of a nonremediated textile effluent (NRTE) with an effluent remediated by a pulverized chitosan system (RCTS) or by a conventional effluent process (remediated biologic and physico-chemical effluent [RBPC]). Acute toxicity assays, oxidative stress biomarkers, physico-chemical parameters, and genotoxicity indices were analyzed to achieve the toxicity of all effluents. After RCTS treatment, approximately 80% of dyes were removed, together with a significant decreased of the metal content, compared with a relatively increase in metal content after RBPC treatment. RBPC and RCTS treatments did not cause acute toxicity to Vibrio fischeri and Artemia sp., whereas RBPC caused acute toxicity to Daphnia magna but RCTS did not. Compared with NRTE, chitosan remediation decreased oxidative stress biomarkers, such as the contents of lipoperoxidation (measured as thiobarbituric acid-reactive substances [TBARS], 29.9%) and the reduced form of glutathione (GSH; 73.5%) levels in D. rerio, whereas animals exposed to RBPC showed enhanced TBARS (57.2%) and decreased GSH concentrations (56.4%). RCTS and RBPC remediation elicited catalase activity induction (161.8% and 127.3%, respectively) compared with NRTE. Accordingly, DNA fragmentation and micronucleus frequency in D. rerio decreased after remediation with RBPC or RCTS compared with NRTE, but RCTS treatment was more effective than RBPC in decreasing genotoxicity (90.5% and 73.8% decrease in DNA fragmentation and 67.8% and 50.4% decrease in micronucleus frequency, respectively). The results indicate that chitosan adsorption system is a useful tool for textile effluent remediation compared with the conventional remediation by biologic and physico-chemical processes.

Antihyperlipidemic effect of Casearia sylvestris methanolic extract.

Casearia sylvestris methanolic extract (MCE) was screened at doses of 125-500 mg/kg for its antihyperlipidemic activity. The antihyperlipidemic effect was evaluated in olive oil-loaded mice. Acute treatment caused inhibition in the triglyceride (TG) and serum lipase elevation-induced by 5 ml/kg of olive oil.

Reduction of acidity and removal of metal ions from coal mining effluents using chitosan microspheres.

Effluents from coal mining operations are not only highly acid but also depict elevated concentrations of metals which may contaminate the environment. Due to the polybasic characteristic of chitosan, this biopolymer is capable of both neutralizing and removing iron, aluminum and copper ions from such effluents. The present study aimed at evaluating the use of chitosan microspheres for their importance in continuous systems. The microspheres were prepared by the phase inversion method. Their average diameter and morphology were determined. Water samples from decantation pool (DP) and acidic mine drainage (AMD) effluents were treated using different amounts of microspheres. The pH and concentration of Fe, Al and Cu ions were evaluated both before and after treatment of effluent samples. The results revealed that the microspheres were capable of increasing the pH of DP and AMD samples from 2.34 and 2.58, respectively, to 6.20, i.e., close to neutrality. The treatment also resulted in full removal of the metals investigated.