جستجوی مقالات مرتبط با کلیدواژه « heavy metal » در نشریات گروه « محیط زیست »

Soil pollution by heavy metals, especially in industrial regions is one of the main environmental problems. Cadmium (Cd) is a heavy metal that causes oxidative stress in plants and has many destructive effects on product quality. Nowadays, various methods are used to reduce the negative effects of high concentrations of heavy metals in the soil. In this regard, using biochar is a cost-effective and environmentally-friendly method and its influence on the reduction of heavy metals bioavailability of soil is an important advantage. Biochar is a carbon-rich material obtained by pyrolysis of biomass, such as agricultural residues and manures in conditions without oxygen or with limited oxygen content.

In this study, a factorial experiment was conducted in a completely randomized blocks design with three replications on Marigold (Calendula officinalis L.) medicinal plant with six levels of Cd (0, 1, 3, 5, 7, and 10 mg/l) and three levels of biochar (0, 1.5, and 3 w/w). The effect of experimental treatments was investigated separately and combined on the morphological (wet and dry weights of aerial parts and roots), physiological (the amount of chlorophyll a, chlorophyll b, total chlorophyll, and carotenoid), and biochemical (soluble sugar, catalase, peroxidase, and proline) characteristics of this medicinal plant. Means comparisons were done by Duncan's multiple range test at a probability level of 5%.

The results showed that different concentrations of Cd decreased the wet and dry weights of roots and aerial parts of the plant. The most reduction effect was related to the concentration of 10 mg/l of Cd. The interaction effect of biochar and Cd was significant only on the dry weight of aerial parts. The effect of stress caused by increasing the concentration of Cd on the plant's physiological processes was different. Considering that the first effect of Cd on the plant is the reduction of photosynthesis and chlorosis of the leaves, at the highest level of Cd, the amount of total chlorophyll decreased by 40% compared to the control sample, but the amount of carotenoid increased by 50% (p<0.05). The reduction of chlorophyll content under Cd stress can be due to oxidative damage and inhibition of different stages of chlorophyll synthesis. However, the increase in carotenoids in response to heavy metal stress occurs because these molecules, as part of the non-enzymatic antioxidant defense system, play a protective role against oxidative stress. In contrast, the use of biochar treatment caused a significant increase in the wet weight of aerial parts, the amount of chlorophyll a and carotenoid. Also, the interaction effect of the treatments indicated that at different levels of Cd, the characteristics of the dry weight of aerial parts, the amount of chlorophyll b, and the total chlorophyll increased with the increase in the biochar level. Among the investigated biochemical traits, the interaction effect of the treatments was significant only on the amount of soluble sugar (p<0.05) and catalase (p<0.01). This means that the absorption of Cd by biochar and the reduction of its toxicity effect on seedlings provided the conditions for more production of soluble sugar and catalase. In fact, biochar had high adsorption of Cd due to its high cation exchange capacity, high specific surface, and presence of functional groups.

In total, the results showed the biochar capacity to stabilize and inactivity Cd absorption. Therefore, the incorporation of biochar to soil can improve Cd bioavailability by plants in the phytoremediation, although the effect of type and plant variety on the amount of decreasing Cd stress should not be ignored.

The chemical precipitation using lime, caustic soda and soda ash was investigated for the simultaneous removal of Cu and Zn from copper mine industrial wastewater by conducting jar tests in the present study. Jar experiments were performed with a set of polyethylene beakers (500 ml) in order to investigate the effect of two reaction parameters (precipitant doses and initial pH) on the removal of heavy metals. X-ray Diffraction (XRD) and Scanning Electron Microscope (SEM) equipped with X-Ray Energy Diffraction Spectroscopy (EDX) were used to identify the important chemical compounds and to study the surface morphology, chemical composition and particle size of the sludge samples. An increase in the removal of Cu and Zn was observed by increasing the precipitant dose (10-400 mg/L) for each reagent used. Removal efficiency of 90% were obtained for both heavy metal ions. The chemical precipitation efficiency was affected by pH. At high final pH levels (8<pH<10), Cu had higher removal efficiency than Zn by all precipitating agents. In the sludge produced, Zn and Cu were precipitated as amorphous hydroxides including Zn(OH)2 and Cu(OH)2. SEM images showed that the produced sludges have small size and compact structure. EDX analysis determined that in all sludge samples, the content of Cu was higher than Zn. Effluent treatment with soda ash resulted in the sludge production with lower volume and larger particle size. As a result, the use of this precipitating agent can be less expensive for sludge drying steps.

The use of nanoparticles in various industries has led to the release of very large amounts of these materials in the environment, and therefore, its spread in nature has increased the likelihood of their impact on organisms. In this study, the simultaneous and separate effects of mercury ions with/without silver nitrate and silver nanoparticles on Artemia salina were investigated. For this purpose, A. salina was grown in vitro and A. salina nauplius was exposed to different concentrations of silver nanoparticles and mercury ions and its mortality rate was evaluated after 24 and 48 hours. The effects of these contaminants on the fatty acid profile of A. salina were also evaluated. A. salina losses were reduced by simultaneous exposure of mercury and silver nitrate and simultaneous exposure of mercury and silver nanoparticles due to the mercury uptake by silver nitrate and silver nanoparticles, and the effect of mercury toxicity was reduced and mercury caused fewer losses in simultaneous exposure. Also, in the study of A. salina fatty acid profile in comparison with separate mercury treatment, a decrease in SFA fatty acids in the simultaneous exposure of mercury and silver nitrate to the amount of this type of fatty acids in the control was observed. In addition, the amount of MUFA fatty acids in the simultaneous exposure of mercury and silver nitrate was significantly higher than the control (P˂0.05). In conclusion, toxicity effects of mercury on the artemia was reduced in simultaneous exposure to silver ions and nanoparticles compared with the separate exposure, indicating the necessity of paying more attention to the contaminants interactions in aquatic ecosystems and the effects of this interaction on the contaminants bioavailability and toxicity.

In this paper, the preparation of nano zeolite was carried out at different grinding times using a dry planetary ball mill. Sodium Hexa Meta Phosphate (SHMP) was introduced as the dispersant in the milling of natural zeolite adsorbent. In the next step, to remove and adsorb heavy metal ions such as nickel, copper, and cadmium, the application of nano zeolite was studied in batch mode.

In this paper, zeolite nanoparticles were produced using planetary and ball mills. Adsorption experiments were conducted to investigate the adsorption of nickel, copper, and cadmium using new nano zeolite adsorbent. 

The effect of Sodium Hexa Meta Phosphate (SHMP) on grinding and adsorption of ion metals by nano zeolite was investigated and results showed that the application of SHMP led to lower energy consumption in grinding and had a positive effect on nickel and cadmium removal from aqueous solution by nano zeolite particles.

The effect of sodium hexametaphosphate on the absorption of nickel, cadmium, and copper metals showed that this reagent had a positive effect on the absorption of nickel and cadmium ions on nanozeolite particles, but it did not affect the absorption of copper ions. Nano-zeolites have a larger external surface area and a shorter diffusion path length due to having nano-sized particles, so their absorption capacity is very high.

Industrial plating wastewater contains various types of detrimental heavy metals in high concentrations. One of this toxic metal is Nickel that its discharge into the surface waters and soil is considered as an environmental problem. Hence removing of this metal from wastewaters is crucial and vital for protecting the environment and human health. Applying of nanotechnology in elimination of environmental contaminants is one of the methods which attracted a great deal of attention in recent years. In present research, nanographite was utilized as efficient adsorbent in order to remove Ni ions.

In order to investigate the adsorption process, nanographite with a purity of 99.9% and a specific surface area of ​​18-24 m2/g and a plate morphology was prepared from Pishgaman Iranian Nanomaterials Company and used as an adsorbent. Also, the wastewater used in the experiments was prepared from one of the plating workshops in Tehran, which contained 765 mg/L of nickel and a pH of about 1. The parameters of pH, time and amount of adsorbent were evaluated. In each experiment, one of the parameters was considered variable and the other two parameters were considered constant. The amount of nickel was determined before and after each test.

In this study, the parameters including pH, adsorption time and adsorbent dosage were investigated as effective factors on Ni adsorption process. In order to analyze the adsorption mechanism, the obtained results were examined by the Langmuir and Fruendlich isotherm models. In addition, pseudo-first-order and pseudo-second-order models were studied to investigate adsorption kinetics. According to the results, the Ni uptake by nanographite was enhanced significantly with increasing of the pH value from 5 to 7. Thus the pH of 7 was determined as optimum pH for Ni removal. Investigations also showed that increasing the time up to the first 80 minutes had a relatively good effect on nickel adsorption by the nanoparticle, and after that the adsorption almost reached equilibrium. Finally, it was observed that in a constant time, increasing the amount of adsorbent led to an increase in adsorption, and to achieve the maximum adsorption of nickel, the amount of 2g was chosen for the adsorbent. Based on the obtained results, 97.52% primary nickel was adsorbed by nanographite. Results also revealed that the data were best fitted to the Fruendlich models. After determining the amount of nickel adsorption at different times, the resulting data were analyzed by the kinetic model.Kinetic studies also indicated that the adsorption data were described well by pseudo-second-order model.

Examining the results showed that pH plays an important role in the adsorption process and the adsorption rate increases with increasing time until the equilibrium time is reached. One of the effective factors is the amount of adsorbent, which has a direct effect on adsorption. Following the Freundlich isotherm in this research indicates that the adsorption sites in the adsorbent have different energies. Also, the pseudo-second-order model in adsorption kinetics refers to the process of chemical adsorption in addition to physical adsorption.

Heavy metal pollutants in water source sediments are a serious environmental concern in aquatic ecosystems. Sediments collect different amounts of metals and are both a source and a reservoir of heavy metals in aquatic ecosystems. In this study, four heavy metals, including nickel, lead, mercury, and cadmium, were collected and examined from the surface sediments of Bandar Imam (Ghanam Estuary, Zangi Estuary, Petrochemical Estuary, and Ahmadi Estuary). Increased industrial and petrochemical activities in Mahshahr and Imam Khomeini ports have led to an increase in pollutants, most of which enter the waters of the Persian Gulf. The amount of sediment contamination to metals was compared with international standards. Then, the amount of sediment contamination was compared between different estuaries in the region. Surface sediment sampling was performed using the Vane Veen grab method. All four heavy metals were identified in all sampling sites with concentrations higher than the standard value based on correlation analysis and principal component analysis. The results show that the concentration of some metals in sediments is higher than the limits set by the standards. Their mean concentrations decreased by Ni>Pb>Cb>Hg. Contamination in Khor Petrochemicals seems to be more serious, probably due to the contamination source's proximity to a point where there is a very high ecological risk and must be carefully surveyed and corrected. The data analysis showed that lead and cadmium originate mainly from human activities (industrial effluents). Due to their location, the waters of the Mahshahr and Khor Musa regions, which are the location of many petrochemical plants, are directly and indirectly exposed to organic and mineral pollutants. Organic matter and particle size are the main factors influencing the distribution of heavy metals in the sediment. More organic matter and smaller particle sizes result in settlement of heavy metals in the sediment.