The aim of this study was to investigate the effect of pH 4 and 7 on the cellular toxicity impact of silver nanoparticles (AgNPs) on the green alga Chlamydomonas acidophila. Changes in chlorophyll content, cellular viability, and reactive oxygen species (ROS) formation were determined permitting the characterization of the toxicity of AgNPs. Chemical characterization of AgNPs in suspension showed that nanoparticle size distribution was dependent to the pH of the culture medium, and a higher solubility was observed at pH 4 compared to that at pH 7. After 24 h of exposure, results indicated that the chlorophyll content and cellular viability decreased significantly, while the intracellular ROS production increased significantly, in relation to the increasing concentration of AgNPs (0.1–100 mg/L). Therefore, our results demonstrated that AgNP-induced toxicity was pH dependent as indicated by the cytotoxicity mediated through the induction of oxidative stress. In conclusion, the characterization of the physicochemical properties of AgNPs in aqueous solution having different pH is essential for the understanding of their toxicity impact on algal cells.

Citrus peels were utilized for dynamic biosorption of Pb, Cd, and Zn from mono- and bi-component solutions in fixed-bed columns at feed concentrations of 0.1 meq/L. Uptake at breakthrough and saturation followed the order Zn < Cd < Pb in single-metal biosorption. An overshoot of the Zn or Cd effluent concentration was observed in Pb-Zn and Pb-Cd bimetal systems, where Pb displaced initially bound Zn and Cd. The desorption efficiency of the saturated column using 0.1 N nitric acid was 74 to 100 %, achieving a concentration factor (CF) of 34 to 129, based on the average desorbed metal concentration. The common practice of defining the concentration factor based on the peak concentration overestimates the CF value. Increasing Ca concentrations in Pb-Ca and Cd-Ca systems reduced target metal uptake, especially for Cd which had a lower affinity than Pb. Actual mining effluent was treated successfully. A sigmoid function was applied to describe experimental breakthrough data. A novel simple two-parameter model was introduced to simulate overshoot and desorption curves.

In this study, Scenedesmus quadricauda ABU12 was immobilized with sodium alginate to determine its potential for decolorizing indigo blue dye under different incubation conditions. The microalga was incubated at different pH (6.5–9.5), biomass concentrations (0.1–1.0 g l⁻¹), dye concentrations (12–75 mg l⁻¹) and temperatures (25–40°C). The concentration of biomass used significantly determined the rate of dye decolorization, as the lowest biomass concentration (0.10 g) was able to completely decolorize the dye by day 3, while the highest biomass concentration (1.00 g l⁻¹) attained 100 % decolorization on day 4. Neutral pHs supported the highest dye decolorization rates compared alkaline pHs. The rate of dye decolorization had a linear relationship with the concentration of the dye in solution as increasing dye concentration in the medium significantly reduced the rate of decolorization (p < 0.05). At 25°C, the rate of dye decolorization was consistently higher from day 2 to the end of the experiment. Infra-red analyses of the algal biomass and the dye solution was done in Kbr by pressing between flat aperture plates of sodium chloride and scanning from 4,000 to 625 cm⁻¹. This revealed the presence of functional groups associated with the biomass and dye that provided possible explanations for the decolorization of the dye under the different incubation conditions. These results showed that immobilized S. quadricauda is capable of decolorizing indigo blue dye at low biomass when immobilized with sodium alginate. However, this was dependent on the incubation temperature and dye concentration.

The objective of this study was to compare the relative impact of humic and non-humic natural organic matter (NOM) on the aggregation behaviors of engineered TiO₂nanoparticles (nano-TiO₂). After exposure of nano-TiO₂to varying concentrations of Suwannee River fulvic acid (SRFA) and Bacillus subtilis exudate in high and low ionic strength (IS) solutions at pH 3 to pH 7.5, aggregation behaviors were evaluated via dynamic light scattering (DLS) measurements and sedimentation studies. Although pH, IS, and NOM concentration exerted strong controls on nano-TiO₂aggregation behaviors, suspensions exposed to either SRFA or bacterial exudate at normalized dissolved organic carbon (DOC) concentrations exhibited remarkably similar behaviors. In high IS systems, nano-TiO₂exposed to either SRFA or bacterial exudate sedimented rapidly, except in the presence of high NOM concentrations at pH 6 and 7.5. Low IS treatments exhibited a larger range of effects. In fact, relative to NOM-free controls, nano-TiO₂aggregates in SRFA and bacterial exudate exposures sedimented up to 14 times faster at pH 3 and up to 13 times slower at pH 7.5. Adsorption of organic molecules onto nano-TiO₂can enhance aggregation via colloidal bridging and/or charge neutralization, or with more complete surface coverage, can diminish aggregation via electrostatic repulsion and/or steric hindrance. Collectively, these data suggest that solution pH, IS, and NOM concentration, and to a lesser extent NOM origin, can control the fate and mobility of nano-TiO₂in geologic systems.

Mussel (Mytilus galloprovincialis (Lamarck, 1819)) is directly exposed to sea water contamination that elicits significant physiological and cellular response, although its extent mounted in aquaculture-reared in comparison to wild bivalve populations is scarcely known. Therefore, we have compared contamination biomarkers in mussels from reared (Marina farm) and wild, anthropogenically affected site (Vranjic Bay). While predictably, the levels of metals (Cu, Cd, Pb, Zn, Fe, and Hg) in whole bivalve tissues determined by atomic absorption spectrophotometry resulted in significantly higher concentrations in wild mussels, accompanied by elevated number of apoptotic cells in gills, the activity of multixenobiotic resistance defense mechanism (MXR), measured as the accumulation rate of model substrate rhodamine B (RB) gave contrasting results. The functional RB assay evidenced a lower MXR efflux activity in the gill tissue of wild mussels, indicating two possible scenarios that will need further focus: (1) persisting sea water pollution increased cell damage of bivalve gill cells and consequently led to leakage of the RB into cytoplasm and dysfunctional MXR efflux in wild mussels; or/and (2) a mixture of different toxic compounds present in Vranjic Bay sea water induced oversaturation of MXR efflux, inducing elevated accumulation of the dye. Consequently, it seems that an efficient physiological functioning of MXR in wild mussels is strongly hampered by existence of an unknown quantity of sea water pollutants that may endanger intrinsic organismal defense system and lead toward the enhancement of toxicity.

Natural and anthropogenic aerosols over coal mines regions in India play a significant role in influencing the regional radiation budget, causing climate implications to the overall hydrological cycle of India. In the reference of regional climate change and air quality, we discuss aerosol optical depth (AOD) variability and long-term trends (from Mar 2000–Dec 2012) over eastern, southeast, and south coalfield regions in India. The present work analyses the variations and trends in aerosol loading using Terra-MODIS (Moderate-Resolution Imaging Spectroradiometer) AOD₅₅₀data in the period 2000–2012. Overall, an increasing trend in AOD₅₅₀has been observed over all regions namely Raniganj (7.31 %) in eastern and Korba (5.0 %) in southeast, and Godavari Valley (32 %) in the south coalfield region in India. This increasing trend predominantly owes to a constant increase in the seasonal/monthly averaged AOD during the winter (Dec–Feb) and post-monsoon (Oct–Nov) seasons dominated by anthropogenic emissions. In contrast, a decreasing trend is observed during pre-monsoon (Mar–May) season over eastern coalfield region (−13 %), while at south coalfield region (44 %) and southeastern coalfield region (0.8 %), increasing trends are observed. Similarly, increasing trends is observed over all regions in monsoon (Jun–Sep) months. Furthermore, the values of Hurst exponent, fractal dimension, and predictability index for AODs are 0.5, 1.5, and 0, respectively suggesting that the AODs in all sites follow the Brownian time series motion (true random walk). High AOD values (0.59 ± 0.21) are observed over eastern region Raniganj.

Cyanobacterial toxins have caused worldwide concern because of their lethal effects, which has led to intensive search of cost-effective removal techniques. With the application of a Box–Behnken experimental design combined with response surface methodology, the adsorption process of the potent and commonly occurring microcystin-LR (MC-LR) onto nano-sized montmorillonite (NMMT) K10 was investigated through the HPLC-UV system. The quadratic statistical model was established to predict the interactive effects of pH (1–12), NMMT K10 dose (1–10 mg mL⁻¹), and MC-LR initial concentration (100–1,000 μg L⁻¹) on MC-LR adsorption and to optimize the controlling parameters. The MC-LR adsorption by NMMT K10 was pH dependent and was found to reach a maximum at pH 2.96 with a removal peak of 186.37 μg g⁻¹. The range of optimal pH for MC-LR adsorption was 2.96–3.48, and higher adsorption capacities were achieved with increasing adsorbent dose and MC-LR initial concentration. Sorption kinetics revealed that the sorption process of MC-LR on NMMT K10 was rapid (short equilibrium time) and involved several kinetic stages. The Langmuir isotherm model predicted that the theoretical maximum adsorption capacity at pH 3 was 285.20 μg g⁻¹. Alkali eluting media (0.1 M NaOH) showed the highest desorption percentage (75.3 %) during regeneration studies. The high Brunauer–Emmett–Teller (BET) specific surface area (204.65 m² g⁻¹) of NMMT K10 was also characterized. NMMT K10 was determined to be an effective and economic adsorbent for MC-LR removal on a large scale.

The fate of colored natural organic matter (CNOM) was investigated for a period of 16 months at a municipal wastewater treatment plant of a mid-sized city in Northern Ontario, Canada, using fluorescence spectroscopy. Our objectives were to assess the changes of CNOM at the inlet and outlet of the plant and to determine if these changes were correlated with parameters routinely measured at the plant. The fluorescence signals were spectrally resolved into humic-like, fulvic-like, and protein-like components using a parallel factor analysis (PARAFAC) routine. We found that the signals of the CNOM components in the raw sewage had protein-like characteristics, followed by fulvic-like and humic-like characteristics. Conversely, after treatment, the CNOM signals were dominated by fulvic-like components, followed by approximately equal signals of humic-like and protein-like components. The fluorescence signals were, on average, ∼60 % lower in the effluent for the protein-like components and ∼28 % lower for the humic-like components, suggesting a decomposition of these CNOM materials. The fluorescence signals showed a small apparent increase of fulvic-like components, by ∼4 %, suggesting that the material showing this signal is recalcitrant to decomposition, or it could be potentially produced in the process. We found weak but statistically significant correlations (R ² > 0.3) between the total fluorescence signals and total carbon (TC), the flow rate through the plant, and rainfall in the raw sewage. Similarly, correlations were found between protein-like fluorescence of the protein-like components and total Kjeldahl nitrogen (TKN) and ammonium at the effluent (R ² > 0.3).

Samples of soil and food plants were collected from wastewater-irrigated and control fields in the vicinity of Gaziantep, in southeast Turkey. The samples were analyzed for concentrations of several macro and trace elements to evaluate spatial differences and bioaccumulation. Emphasis was placed on redoximorphic metal (Mn/Fe) interactions. The plants and tissues that studied were corn (Zea mays) seeds, mint (Mentha) leaves, the vegetables eggplant (Solanum melongena L.) and pepper (Capsicum annuum L.), and tomato (Solanum lycopersicum L.) fruits. Concentrations of Mn and Fe in corn were generally lower than in the other food plants, while concentrations of Mn, Fe, and several elements in mint were higher in other plants. Except for mint, the Mn deficiencies in the various plant samples can be attributed to low Mn soil concentrations and the chemical and physical characteristics of the soil. Mn concentrations in both wastewater-irrigated soils and control soils were lower than what has been reported as an average for the Earth’s crust (crustal average). There was considerable variability in the concentrations of Fe, with mint having the highest concentration (650 mg/kg) and corn the lowest (20 mg/kg). Significant positive relationships (coefficient of determination (R²) >0.50) were calculated between Mn and Fe in corn (R² = 0.83). The R²for tomato was 0.43, but all other relationships were much poorer for all other species. Several elements (trace and macro) demonstrated positive relationships with Mn or Fe, although there was little across-species consistency. For example, the R²values for both Mn and Fe correlated with Zn, P, and Mg were all >0.80 for Z. mays, but were all <0.10 for Mentha. The response of the members of the Solanaceae family (eggplant, pepper, and tomato) to the presence of Mn, Fe, and other soil constituents was similar in many respects, showing differences from Z. mays and, in particular, Mentha. Similarities among related plants are not surprising and would be expected given similar physiologies and metabolic pathways. Higher uptake of certain metals may be associated with the dominant form of the element in the soil matrix. The uptake of chemicals to plant tissues is influenced by the chemical and physical characteristics of the soil and species-specific factors.

The widespread use of alkylphenols in European industry has led to their presence in the environment and the living organisms of the Baltic Sea. The present study (2011–2012) was designed to determine the concentrations of alkylphenols, 4-nonylphenol (NP) and 4-tert-octylphenol (OP), in surface sediments of the Gulf of Gdansk, a section of the Baltic that lies in close proximity to industrial and agricultural areas and borders with an agglomeration of nearly one million inhabitants. It is also where the Vistula, the largest Polish river, ends its course. In spring, large concentrations of 4-nonylphenol and 4-tert-octylphenol were washed off into the coastal zone with meltwater. In summertime, sediments near the beach had the highest alkylphenol concentrations (NP—2.31 ng g⁻¹dw, OP—13.09 ng g⁻¹dw), which was related to tourism and recreational activity. In silt sediments located off the coast, the highest NP (1.46 ng g⁻¹dw) and OP (6.56 ng g⁻¹dw) amounts were observed in autumn. The origin of OP and NP at those test stations was linked to atmospheric transport of black carbon along with adsorbed alkylphenols.