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Background: The pollution of the aquatic environment with heavy metals has become a worldwide problem during recent years, due to their potential toxic effects and ability to bio-accumulate in aquatic ecosystems. Heavy metals are sensitive indicators for monitoring changes in the aquatic environment.
Methods: In this study, total concentrations of Cr, Pb, Cu, Zn, and Fe were measured in water and sediments from nine sites, based on ecological conditions and human activities and the effects of sediment pH and sediment organic matter on bioavailability of selected metals were determined. Modified degree of contamination (mCd) was computed in order to determine anthropogenically derived sediment contamination.
 Results: Mean concentration of metals in water found to be in the following order: Pb > Fe > Zn > Cu > Cr, while in sediment samples it was Fe > Cr > Zn > Pb > Cu. The average content of examined metals in water was higher than the chronic values in marine surface water guideline values. Mean content of Cr, Pb and Fe in sediments were higher than average of the less contaminated sample but Cu and Zn were lower than this guideline value. In the study area, mCd values were less than 1.5 with values ranging from 0.71 to 1.02. Conclusion: The results of this study indicated with a decrease in organic matter and pH in sediments, the concentration of copper and iron increased. Base on modified contamination degree, the sediments of Hara Biosphere Reserve are considered to be in the zero to very low contamination status.

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Background: Iron, manganese, and aluminum are three abundant metals on earth and their concentrations have increased in aquatic environments as a result of natural and industrial activities. This study was undertaken to report the median acute toxicity (LC50) and accumulation of the sub-lethal concentration (10% 96-h LC50) of iron (Fe), manganese (Mn) and aluminum (Al) in kutum (Rutilus kutum) fingerlings.
Methods: For the 96-h LC50, the fish were exposed to concentrations of 105, 111, 117, 123, 129 and 135 mg/l of Fe and 40, 45, 50, 55, 60, and 65 mg/l of Mn and 18, 22, 26, 30, 34 and 38 mg/l of aluminum for 4 days. For sublethal exposure, they were exposed to mediums with concentrations of 12.3, 5.4 and 2.9 for Fe, Mn, and aluminum, respectively. Metal concentrations were determined by atomic absorption spectrophotometry in the gill tissues.
Results: Probit analysis showed the 96-h LC50 values of 122.98, 54.39, and 28.89 mg/l for Fe, Mn, and aluminum, respectively. Sub-lethal tests were conducted with nominal concentrations of 12.3, 5.4, and 2.9 mg/l of Fe, Mn, and aluminum for four days, respectively. Significant accumulations were observed in gills for all tested metals as compared to the control groups in short-term exposure (P<0.05). Conclusion: Obtained results clearly show that aluminum is the most toxic metal among tested ones for kutum fingerlings and it has the highest branchial AF value during sub-lethal exposure.

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Background: Heavy metals have been recognized as harmful environmental pollutant known to produce highly toxic effects on different organs and systems of both humans and animals. The aim of this paper is to evaluate the adsorption potential of chitosan for the removal of Pb(II), Fe(II) and Cu(II) ions from aqueous solutions.
Methods: This study was conducted in laboratory scale. In this paper chitosan has been used as an adsorbent for the removal of Pb(II), Fe(II) and Cu(II) from aqueous solution. In batch tests, the effects of parameters like pH solution (1.0-8.0), initial metal concentrations (100-1000 mgL-1), contact time (5.0-150 min) and adsorbent dose (1.0-7.0 g) on the adsorption process were studied.
Results: The results showed that the adsorption of Pb(II), Fe(II) and Cu(II) ions on chitosan strongly depends on pH. The experimental isothermal data were analyzed using the Langmuir and Freundlich equations and it was found that the removal process followed the Langmuir isotherm and maximum adsorption capacity for the adsorption of Pb(II), Fe(II) and Cu(II) ions by the chitosan were 55.5mg g−1, 71.4 mg g−1 and 59 mg g−1, respectively, under equilibrium conditions at 25±1 ºC. The adsorption process was found to be well described by the pseudo-second-order rate model.
Conclusion: The obtained results showed that chitosan is a readily, available, economic adsorbent and was found suitable for removing Pb(II), Fe(II) and Cu(II) ions from aqueous solution.

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Background: The presence of lead in natural waters has become an important issue around the world. Lead has been identified as a highly toxic metal that can cause severe environmental and public health problems and its decontamination is of utmost importance. The aim of this work was to evaluate the adsorption of lead (Pb(II)) on waste tea leaves as a cheap purification method.
Methods: In this experimental study, prepared waste tea leaves were used as adsorbent for the removal of Pb(II) from aqueous solutions. Adsorption experiments were carried out as batch studies at different contact time, pH, amount of adsorbent, initial metal concentration and temperature.
Results: The results showed that maximum removal efficiency was observed at pH 6. Also the adsorption of Pb(II) ions increased with decreasing initial metal concentration. The Langmuir isotherm model fits well with the equilibrium adsorption isotherm data and its calculated maximum monolayer adsorption capacity was 166.6 mg g-1 at a temperature of 25±0.1˚C. The kinetic data obtained have been analyzed using pseudo-first-order and pseudo-second-order models. The best fitted kinetic model was found to be pseudo-second-order.
Conclusion: The results suggest that tea wastes could be employed as cheap material for the removal of lead from aqueous solutions.

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Background: This study aimed to evaluate the pollution levels of surface water with heavy metals including Pb, Cd and Cr in Gheshlagh River, western Iran.
Methods: Water and sediment were sampled in five monitoring stations with three replicates in time along the river. The concentration of Cr, Pb and Cd in both water and sediment samples were measured with graphite furnace atomic absorption spectrometer (Australia, Varian 220). The Geoaccumulation Index and Pollution Load Index were employed to assess the pollution level of sediments with heavy metals.
Results: The mean value of Cd, Cr, Pb in sediment samples were 0.69, 17.19 and 10.69 µgg-1 per dry weight, respectively. Water samples contained Cd, Cr and Pb concentration of 1.99, 1.45 and 12.92 µgL-1, respectively. The Geoaccumulation Index and Pollution Load Index indicates that the sediments were not polluted with Pb and Cr, and unpolluted to moderately contaminated with Cd in Gheshlagh River.
Conclusion: This study concludes that the Gheshlagh River is threatened by heavy metals particularly Cd and Pb.

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Background: Since heavy metals can accumulate in the tissues of aquatic organisms, they can cause a range of hazardous effects which can become harmful to humans. The aim of this study was to investigate the acute effects of some heavy metals as potential dangerous substances by assessing the mortality effects of Mercuric Chloride (HgCl2), Lead Chloride (PbCl2) and Zinc Sulfate (ZnSO4) pollutants on a freshwater fish, silver dollar (Metynnis fasciatus).
Methods: Fish samples were exposed to different concentrations of mercuric chloride (HgCl2), lead chloride (Pbcl2) and zinc sulfate (ZnSO4) for 96h and their cumulative mortality was calculated in 24h intervals.Results were analyzed by SPSS 16 to obtain number of cumulative mortality and lethal concentrations (LC10-99).
Results: LC50-96h was 0.94±0.41ppm, 86.84±1.04ppm and 32.24±1.41ppm for mercuric chloride, lead chloride and zinc sulfate, respectively. So, mercury had the highest toxicity to silver dollar fish.
Conclusion: Mercuric chloride and lead chloride has the lowest and highest rate of mortality among these tree metals on silver dollar fish however, the mortality rate was increased with increasing concentrations of toxins with time.

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Background: Anthropogenic activities release high concentrations of heavy metals into the aquatic ecosystems, which can be absorbed by the aquatic organisms. In this study, the accu-mulation of cadmium (Cd) and arsenic (As) was compared in liver, gill and muscle tissues of toothed carp (Aphanius sophiae) in fresh and salt water.
Methods: A total of 175 fish samples were collected from the Shoor River, Iran during the spring and summer of 2011. Samples were divided into two groups for salt and freshwater ex-periments. The individuals of each group were also divided into seven groups, a control group and the other six exposed to the concentrations of 5, 10 and 20 mg/L of arsenic and 5, 10 and 20 mg/L of cadmium. The liver, gills and muscle tissues of the specimens were dissected. The tissues were wet digested in acid and the concentrations of metals were measured using an ICP-OES instrument.
Results: The concentrations of both metals were significantly different in various organs in both fresh and salt water and it were in order of liver > gill > muscle (P <0.001). Based on t-test results, no significant difference was observed between the concentrations of As in related tis-sues of fish cultivated in fresh and salt water. However, Cd accumulation was significantly higher in the tissues of fish specimens cultivated in freshwater (P <0.001).
Conclusion: The bioaccumulation of Cd and As depends on organs, metals, and water condi-tion.

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Background: The increasing use of nanomaterials and nanoproducts has increased the possibility of contamination of the environment, which may have adverse effects on different organisms. The aim of this study was to evaluate the effects of silver nanoparticles on histopathology and gill ultrastructure of zebrafish (Danio rerio) under laboratory conditions.

Methods: Zebrafish were exposed to four concentrations of silver nanoparticles (0.0015, 0.00375, 0.0075, and 0.015 mg/l) for a period of 4 days. Gill ultrastructure and histopathological changes were studied using scanning electron microscope and haematoxylin - eosin staining.

Results: Exposure to silver nanoparticles significantly (P < 0.001) increased the diameter of gill filaments and secondary lamellae, while silver nanoparticles significantly reduced the length of the secondary gills in zebrafish. Moreover, other changes such as vacuolization, dilated and clubbed tips, hyperplasia, edema, fusion, swelling of mucocytes, hypertrophy, and necrosis were observed. The effects of silver nanoparticles in zebrafish gills were dose dependent.

Conclusion: Based on the adverse effects of AgNPs on zebrafish gills, silver nanoparticle solutions can be hazardous pollutants for the environment.

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Background: Phenol and nitrophenol are common compounds found in different types of industrial wastewater known as serious threats to human health and natural environment. In this study, Daphnia magna was used to evaluate the effectiveness of "baffle fixes film up flow sludge blanket filtration" (BFUSBF) system in elimination of phenolic compounds from water.

Methods: D. magna cultures were used as toxicity index of phenol and 2,4-DNP mixtures after treatment by a pilot BFUSBF system which consisted of baffle in anoxic section and biofilm in aerobic sections. Initial concentrations were 312 mg/L phenol and 288 mg/L 2,4-dinitrophenol (2,4-DNP).

Results: Bioassay tests showed that D. magna was influenced by the toxicity of phenol and 2,4 DNP mixtures. The comparison between the toxicity of initial phenol and 2,4-DNP mixtures and the output toxic unit (TU) derived from BFUSBF treatment system showed that the TU of the effluent from BFUSBF reactor was much lower than that of the solution that entered the reactor.

Conclusion: Based on the acute toxicity test, BFUSBF process could reduce phenol and 2,4-DNP in aqueous solutions. Therefore, it is possible to use BFUSBF process as an appropriate treatment option for wastewaters containing phenolic compounds.

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Background: Among different pollutants released into the environment, dyes are considered as one of the most dangerous contaminants. In recent years, magnetic nanomaterials have attracted much attention for their dye removal capacity. The aim of this study was to explore the adsorption kinetics of an anionic dye (Reactive Orange 13 (RO)) by NiFe₂O₄ nanoparticles (NiFe₂O₄ NPs) under various conditions.

Methods: NiFe₂O₄ nanoparticles (NiFe₂O₄ NPs) were prepared and characterized by X-ray diffraction (XRD), transmission electronic microscopy (TEM), pH_pzc and BET methods. The adsorption characteristics of the NiFe₂O₄ NPs adsorbent were examined using Reactive Orange 13 as an adsorbate. The influences of parameters including pH, dose of adsorbent and contact time were investigated to find the optimum adsorption conditions.

Results: Decreasing solution pH and increasing contact time were favorable for improving adsorption efficiency. The kinetic and isotherm data of RO adsorption on NiFe₂O₄ NPs were well fitted by pseudo-second-order and Langmuir models, respectively.

Conclusion: The maximal adsorption capacity of RO was 243.9 mg g^-1 at 25^◦C and pH 3.0 and the adsorption of RO on the NiFe₂O₄ NPs follows a monolayer coverage model. NiFe₂O₄ NPs might be an effective and potential adsorbent for removing anionic dyes from aqueous solutions.

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Background: In the current study,the hazard quotient, the hazard index (HI) and spatial variations of Fe,Mn,Cu and Cr in drinking water sources of Andimesk-Shush, Khuzestan Province, Southern Iranaquifer were assessed.

Methods: We compared theconcentrations of aforementioned heavy metals in wells and springs inAndimeshk and Shush regions. The non-carcinogenic risk assessment of heavy metals was implemented usingUnited States Environmental Protection Agency (USEPA) index.The spatial maps in the area were developed by geostatistical methods.

Results: Mean concentrations of heavy metals in groundwater sources of the study area in decreasing order was as follows: Cu >Mn> Fe> Cr. Except for iron,mean heavy metal concentrations were higher than the standard levels. Manganese concentration in 41.5% of the samples exceeded the permissible limits. Copper was higher than the safety limit in 74% of the samples, and chromium in 54% of the cases. The spatial pattern of heavy metals concentrations indicated higher concentrations in the southern parts of the region. The mean hazard quotients of most samples for the four heavy metals were lower than one, indicating that there was no immediate threat due to the exposure to these heavy metals.  The calculated accumulated hazards of these heavy metals produced different results, with hazard indices of higher than one.

Conclusion: The accumulated hazard indicesfor the evaluated metals were higher than one, indicating that chronic ingestion of these waters threatens the health of local consumers on the long run.

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Background: Synthetic dyes are serious pollutants and wide ranges of methods have been employed for their removal from aquatic systems. We studied the adsorption of "Nile blue A" (NBA), an anionic dye, from aqueous solution by oxidized multi-walled carbon nanotubes (MWCNTs).

Methods: Scanning electron microscope and Fourier transform infrared spectroscopy were used to characterize function groups produced at MWCNTs surface. Kinetics and adsorption isotherms of NBA, the effect of temperature, pH, contact time and initial dosage of nanotubes on the adsorption capacity were also assessed. The experimental data were analyzed by Langmuir and Freundlich models.

Results: Most of the dye was removed in the first 5 min and best adsorption percentage was at pH 7.0. The equilibrium reached at 45 min. The experimental data were analyzed by Langmuir and Freundlich models and the results fitted well with the Freundlich model. The adsorption kinetic data were analyzed using first-order and the pseudo-second order model and the adsorption kinetic data of NBA dye onto MWCNTs fitted the pseudo-second order model. The maximum adsorption capacity was obtained as 169.49 mg g-1.

Conclusion: Freundlich model suggested that the adsorption process followed heterogeneous distribution onto MWCNTs and pseudo-second model of adsorption implied that chemical processes controlled the rate-controlling step. Oxidized MWCNTs could be used as an effective adsorbent for the removal of "Nile Blue A" dye. Oxidization of MWCNTs by nitric acid, improves the efficiency of NBA removal due to increases in functional groups and total number of adsorption sites.

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Background: In recent years, various toxic chemicals/compounds have been widely detected at dangerous levels in drinking water in many parts of the world posing a variety of serious health risks to human beings. One of these toxic chemicals is lead, so this paper aimed to evaluate of efficiency coconut husk as cheap adsorbent for removal lead under different conditions.

Methods: In the spring of 2015, batch studies were performed in laboratory (Branch of Hamadan, Islamic Azad University,) to evaluate the influences of various experimental parameters like pH, initial concentration, adsorbent dosage, contact time and the effect of temperature on the adsorption capacity of coconut husk for removal lead from aqueous solution.

Results: Optimum conditions for Pb (II) removal were pH 6, adsorbent dosage 1g/100ml of solution and equilibrium time 120 min. The adsorption isotherm was also affected by temperature since the adsorption capacity was increased by raising the temperature from 25 to 45 °C. The equilibrium adsorption isotherm was better described by Freuindlich adsorption isotherm model.

Conclusion: It is evident from the literature survey that coconut-based biosorbents have shown good potential for the removal of various aquatic pollutants.  Coconut husk-based activated carbon can be a promising adsorbent for removal of Pb from aqueous solutions.