Colistin is a peptide antibiotic widely used as a food additive in animal farming, specially swine and poultry, and also has recently been applied in human medicine to treat infections caused by multiresistant gram-negative bacteria strains. When orally administered, colistin is eliminated in feces virtually unaltered; thus, it may reach water bodies and wastewater treatment facilities in its active form. Apart from the risks associated with development of antimicrobial resistance and environmental toxicity issues, the presence of antimicrobials in wastewater can, additionally, interfere in biological processes commonly used to treat them. Nitrifying bacteria are among the most sensitive microorganisms to inhibitory compounds, including pharmaceuticals, and are useful as biosensors to access contaminant toxicity information in wastewater treatment plants. Therefore, in order to assess the colistin acute toxicity to the microorganisms involved in the nitrification processes, the nitritation and nitratation kinetics were monitored under different colistin concentrations. The results showed that only ammonia-oxidizing bacteria are sensitive to the antibiotic, presenting an IC50 of 10.8 mg L⁻¹ of colistin when used as a commercial formulation and 67.0 mg L⁻¹ when used as raw colistin sulfate. For nitrite-oxidizing bacteria, even the highest colistin concentration used in the assays (316 mg L⁻¹) was not sufficient to inhibit the process. According to these results, the colistin concentrations expected in animal farming wastewater, when its dosage is used as a growth promoter, would not be enough to keep nitrification from taking place. Nevertheless, when used in higher concentrations, such as for therapeutic purposes, it could endanger the maintenance of the process.

Arsenic (As) adsorption onto metal oxide-precipitated clinoptilolite was investigated by using response surface methodology (RSM). Box-Behnken experimental design combined with RSM was used to examine and to optimize major process parameters. The quadratic statistical model was defined by three independent variables namely, pH (3-7), temperature (25-65 C), and initial arsenate (As(V)) concentration (0.5-9.5 mg L-1) while adsorption capacities of modified zeolites were designated as dependent variables. The iron oxide-precipitated zeolite (ZNa-Fe) was found to be more effective adsorbent when compared with aluminum oxide-modified one (ZNa-Al). The maximum As(V) adsorption capacities for ZNa-Fe and ZNa-Al were observed at pH 3.0 and pH 4.96, respectively. In the chosen range, higher adsorption capacities were achieved with increasing temperature, indicating the endothermic behavior of process for both samples. Initial As(V) concentration had a marked favorable effect on the amount of As(V) adsorbed onto adsorbents in the selected field. The constructed polynomial model was found significant, as was evident from the model F values (FZNa-Fe = 414.95 and F ZNa-Al = 167.17). The coefficients of determination values of second-order polynomial regression models were found as 0.9981 and 0.9953 for ZNa-Fe and ZNa-Al, respectively, indicating the accuracy and general availability of the model. © 2013 Springer Science+Business Media Dordrecht.

Total atmospheric bulk mercury (Hg) concentration and deposition were measured from August 2008 to November 2010 at nine locations in the Northern Great Plains, USA using passive bulk mercury samplers. Monthly mercury concentrations ranged from 1.3 to 51.0 ng L⁻¹ with an overall volume weighted mean of 12.9 ng L⁻¹. Normalized daily Hg fluxes ranged from 0.43 to 110 ng m⁻² day⁻¹ with higher rates occurring during high precipitation months as rainfall during spring and summer. Annual deposition rates ranged from 5.82 to 9.21 μg m⁻² year⁻¹ and were comparable to studies performed at similar latitudes and to estimates from the Mercury Deposition Network (MDN). There was no significant difference (p > 0.05) between measured atmospheric mercury for one colocated bulk Hg sampler and an existing MDN wet-only sampler at Eagle Butte, South Dakota, demonstrating measurement unity between the two sampling techniques in this geographic area.

In this work, photocatalytic degradation of two reactive dyes, Reactive Yellow 84 (RY 84) and Reactive Black 5 (RB 5), on FeTiO₃/TiO₂ heterojunction in the presence of UV–visible radiation and H₂O₂ has been reported. FeTiO₃/TiO₂ heterojunction has been prepared from ilmenite FeTiO₃ and anatase TiO₂ by employing oxalic acid as an organic linker. FeTiO₃/TiO₂ ratios have been varied from 1 to 5 wt.%, and the materials were characterized by X-ray diffraction, scanning electron microscope and diffused reflectance UV–visible spectroscopic analysis. The photocatalytic activity of FeTiO₃/TiO₂ heterojunction for the degradation of the organic dyes RY 84 and RB 5 in the presence of UV–visible light was found to be higher than that of pure TiO₂. The addition of H₂O₂ increases the rate of degradation of both dyes on FeTiO₃/TiO₂ heterojunction. It facilitates the fast degradation of dye solutions even when their concentration was above 100 mg/l, which is otherwise very slow due to the low transmittance of light by the dye solution. The extent of mineralisation of the reactive dye during photocatalytic degradation was estimated from chemical oxygen demand analysis. FeTiO₃/TiO₂ heterojunction photocatalyst was also found to have good photostability; the material retains almost 97 % of its initial activity even in the fifth cycle.

Although many studies have examined effects of metal mine effluents (MMEs) on receiving environments, few have compared the roles of individual and mixed metals relative to whole effluents. The objective of the present set of studies was to examine whether Cu, Ni, or Se, alone or in a mixture, causes comparable effects to those observed in fathead minnows (Pimephales promelas) exposed to an environmentally relevant MME (45 % process water effluent [PWE]). Metal bioaccumulation, fathead minnow (FHM) morphometrics, and egg production were compared between treatments over a 21-day exposure. FHMs were exposed to similar waterborne concentrations and species of metals in single and mixed metal treatments relative to 45 % PWE. FHMs were also exposed to similar concentrations of metals in single and mixed metal treatments relative to 45 % PWE through the diet (Chironomus dilutus — a representative prey species). However, only FHMs exposed to 45 % PWE had reduced egg production (60–80 % less than controls). Our findings indicate that Cu, Ni, and Se exposures and bioaccumulation did not contribute to decreased reproductive output in FHMs under the conditions that were examined. We also found no evidence to believe that these metals were responsible for decreased egg production in PWE. It is therefore reasonable to suggest that these metals have limited potential to cause reproductive effects in MMEs with similar composition and water chemistry conditions. Overall, this study highlights the importance of examining single and mixed metal exposures prior to suggesting that adverse effects in fish exposed to MMEs occur due to bioaccumulation of metal(s).

The competitive adsorption of organic pollutants—phenol, aniline and n-heptane—from biologically treated coking wastewater on powdered activated carbon (PAC) was studied. Firstly, batch adsorption experiments of coking wastewater were conducted to investigate the effect of pH and temperature on their adsorption. Results showed that long-chain alkanes, benzoic, halogenated and phenolic compounds were adsorbed well under acidic condition, while amines were adsorbed well under alkaline condition; maximum co-adsorption amount of all kinds of organic compounds occurred at around pH 5. Then, Lagergren kinetic model and pseudo-second-order kinetic model were used to describe the adsorption process of phenol and aniline on PAC. The data were fitted very well with pseudo-second-order kinetics, and the adsorption capacity decreased with an increase in temperature, belonging to Freundlich multi-layer physical adsorption. The adsorption speed and capacity of phenol were superior to aniline in unitary and binary solution. The adsorption amount of n-heptane decreased by 26.6 % from ternary competitive absorption system of phenol, aniline and n-heptane compared with that in unitary solutions, which showed that phenol and aniline caused spatial adsorption steric hindrance to n-heptane.

Spring/summer surface ozone concentrations, [O3], in coastal environments were investigated: (1) by comparison of coastal and inland monitoring stations with data from a small island >5 km off the coast of southwest Sweden, (2) as a gradient from the coast towards inland in southernmost Sweden. Further, results from the chemical transport model MATCH were used to assess the marine influence on [O3]. It was hypothesised that [O3] is higher on the small island compared to the coast, especially during night and in offshore wind. Another hypothesis was that [O3] declines from the coast towards inland. Our hypotheses were based on observations that the deposition velocity of O3 to sea surfaces is lower than to terrestrial surfaces, and that vertical air mixing is stronger in the marine environment, especially during night. The island experienced 10 % higher [O3] compared to the coast. This difference was larger with offshore (15 %) than onshore wind (9 %). The concentration difference between island and coast was larger during night, but prevailed during day and could not be explained by differences in [NO2] between the sites. The difference in [O3] between the island and the inland site was 20 %. Higher [O3] over the sea, especially during night, was reproduced by MATCH. In the gradient study, [O3] declined from the coast towards inland. Both [O3] and [NO2] were elevated at the coast, indicating that the gradient in [O3] from the coast was not caused by NO titration. The conclusions were that surface [O3] in marine environments is higher than in coastal, and higher in coastal than inland areas, especially during night. © 2013 Springer Science+Business Media Dordrecht.

Metaldehyde is a selective molluscicide used in the agricultural and residential sector to control slugs and snails for a wide variety of crops. In recent years, some water companies have started monitoring drinking water supply catchments for presence of this compound, with positive and concern results. Conventional techniques are yet to achieve complete efficient and feasible removal of metaldehyde. The aim of this study was to measure the efficiency of nano-sized zinc oxide/laponite composites (NZnC) in the effective removal of metaldehyde (influent concentration of 500 μg dm⁻³) through the interaction of photocatalysis. Reaction time, pH of sample solution and NZnC mass were tested against each other using a rotatable central composite design method of experimentation. Statistical tests showed that linear effects of time, quadratic/linear effects of NZnC mass and the interaction of pH and NZnC mass proved to be the most significant variables for degrading metaldehyde. Optimal values of each variable for the highest removal efficiency were achieved, being pH equal to 10.4 and NZnC mass added equal to 28 g. The rate of reaction was then predicted by non-linear regression of four models. The best fit was provided by the modified first-order with residual kinetic model, with the apparent degradation coefficient k equal to 0.0363 min⁻¹ and the lowest remaining metaldehyde concentration observed among all runs was 278.7 μg dm⁻³. NZnC has shown to be a prominent nanotechnology for metaldehyde removal.

Knowledge of the levels of both total metal content and metal bioavailability is critical for understanding the long-term effects of liming on soil chemistry and potential metal uptake by biota. In the present study, the long-term effects of liming on metal bioavailability in soils contaminated by smelter emissions were assessed in eroded and stable uplands in the Sudbury region, Ontario, Canada. Analytical results revealed that total metal and nutrient contents of the soil matrix are not dominantly in forms available for plant uptake for these soils. On average, only 1 and 1.1 % of total copper and nickel, respectively, were phytoavailable. Landscape topography, site stability, and smelter proximity all play an important role in metal accumulation in the surface organic and mineral horizons of regional soils. The levels of total and bioavailable elements for eroded sites were always smaller for stable and reference sites. The pH in limed sites was significantly higher, ranging from 4.12 to 6.75, in the humus form compared to unlimed areas, even 20 to 30 years following applications of the crushed dolostone (liming). No significant differences between limed and unlimed areas were found for total metal and nutrient contents. Interestingly, in the higher pH limed areas, the levels of bioavailable Al, Co, Cu, Fe, K, Mn, Ni, and Sr were lower than on unlimed areas. © 2013 Springer Science+Business Media Dordrecht.