Precipitation as the Primary Driver of Variability in River Nitrogen Loads in the Midwest United States

Nitrogen (N) losses from agricultural lands in the Midwest United States are contributing to the expansion of the hypoxic zone in the Gulf of Mexico. This study evaluated the importance of inter‐annual variability in precipitation, land cover, and N fertilizer use on NO₃ + NO₂‐N loads in seven United States Midwestern Rivers using the backward stepwise regression analysis. At the annual scale, fluctuations in the current and previous years’ precipitations explained much of the variation in streamflow, baseflow, and N‐load. Previous years precipitation effects were associated with fillable soil porosity. In some years, higher residual soil N from previous dry years also contributed to an increase in N‐load. Area under soybean production (SOY), a surrogate for replacement of prairies and small grains was generally not a significant explanatory variable. Fertilizer use from 1987 to 2012 was also not a significant explanatory variable in the annual analysis. Precipitation in both the current and previous months and previous year were important in explaining variation in monthly streamflow, baseflow, and N‐load. SOY was significant in one or two months from June to August, but had a higher p‐value than precipitation. We conclude recent increases in river N‐loads are primarily due to wet climate and minimally due to the changes in land cover or N fertilizer use. Under current cropping systems and agronomic N application rates, tile water remediation will be necessary to reduce river N‐loads.     

Moderate phosphorus application enhances Zn mobility and uptake in hyperaccumulator Sedum alfredii

While phytoextraction tools are increasingly applied to remediation of contaminated soils, strategies are needed to optimize plant uptake by improving soil conditions. Mineral nutrition affects plant growth and metal absorption and subsequently the accumulation of heavy metal through hyper-accumulator plants. Microcosm experiments were conducted in greenhouse to examine the effect of different phosphorus (P) sources on zinc (Zn) phytoextraction by Sedum alfredii in aged Zn-contaminated paddy soil. The Zn accumulation, soil pH, microbial biomass and enzyme activity, available Zn changes. and Zn phytoremediation efficiency in soil after plant harvest were determined. Upon addition of P, Zn uptake of S. alfredii significantly increased. Mehlich-3 extractable or the fractions of exchangeable and carbonate-bound soil Zn were significantly increased at higher P applications. Soil pH significantly decreased with increasing P application rates. Soil microbial biomass in the P-treated soils was significantly higher (P?<?0.05) than those in the control. Shoot Zn concentration was positively correlated with Mehlich-3 extractable P (P?<?0.0001) or exchangeable/carbonate-bound Zn (P?<?0.001), but negatively related to soil pH (P?<?0.0001). These results indicate that application of P fertilizers has the potential to enhance Zn mobility and uptake by hyperaccumulating plant S. alfredii, thus increasing phytoremediation efficiency of Zn-contaminated soils.     

Zerovalent iron encapsulated chitosan nanospheres - a novel adsorbent for the removal of total inorganic arsenic from aqueous systems

Evaluation of Chitosan zerovalent Iron Nanoparticle (CIN) towards arsenic removal is presented. Addition of chitosan enhances the stability of Fe(0) nano particle. Prepared adsorbent was characterized by FT-IR, SEM EDX, BET and XRD. It was found that, with an initial dose rate of 0.5 g L⁻¹, concentrations of As (III) and As (V) were reduced from 2 mg L⁻¹ to <5 μg L⁻¹ in less than 180 min and the adsorbent was found to be applicable in wide range of pH. Langmuir monolayer adsorption capacity was found to be 94 ± 1.5 mg g⁻¹ and 119 ± 2.6 mg g⁻¹ at pH 7 for As (III) and As (V) respectively. Major anions including sulfate, phosphate and silicate did not cause significant interference in the adsorption behavior of both arsenite and arsenate. The adsorbent was successfully recycled five times and applied to the removal of total inorganic arsenic from real life groundwater samples.     

Seismic detection of CO2 leakage along monitoring wellbores

A pilot carbon dioxide (CO₂) sequestration experiment was carried out in the Michigan Basin in which ～10,000 tonnes of supercritical CO₂ was injected into the Bass Island Dolomite (BILD) at 1050 m depth. A passive seismic monitoring (PSM) network was operated before, during and after the ～17-day injection period. The seismic monitoring network consisted of two arrays of eight, three-component sensors, deployed in two monitoring wells at only a few hundred meters from the injection point. 225 microseismic events were detected by the arrays. Of these, only one event was clearly an injection-induced microearthquake. It occurred during injection, approximately 100 m above the BILD formation. No events, down to the magnitude ?3 detection limit, occurred within the BILD formation during the injection. The observed seismic waveforms associated with the other 224 events were quite unusual in that they appear to contain dominantly compressional (P) but no (or extremely weak) shear (S) waves, indicating that they are not associated with shear slip on faults. The microseismic events were unusual in two other ways. First, almost all of the events occurred prior to the start of injection into the BILD formation. Second, hypocenters of the 94 locatable events cluster around the wells where the sensor arrays were deployed, not the injection well. While the temporal evolution of these events shows no correlation with the BILD injection, they do correlate with CO₂ injection for enhanced oil recovery (EOR) into the 1670 m deep Coral Reef formation that had been going on for ～2.5 years prior to the pilot injection experiment into the BILD formation. We conclude that the unusual microseismic events reflect degassing processes associated with leakage up and around the monitoring wells from the EOR-related CO₂ injection into the Coral Reef formation, ～700 m below the depth of the monitoring arrays. This conclusion is also supported by the observation that as soon as injection into the Coral Reef formation resumed at the conclusion of the BILD demonstration experiment, seismic events (essentially identical to the events associated with the Coral Reef injection prior to the BILD experiment) again started to occur close to a monitoring arrays. Taken together, these observations point to vertical migration around the casings of the monitoring wellbores. Detection of these unusual microseismic events was somewhat fortuitous in that the arrays were deployed at the depth where the CO₂ undergoes a strong volume increase during transition from a supercritical state to a gas. Given the large number of pre-existing wellbores that exist in depleted oil and gas reservoirs that might be considered for CO₂ sequestration projects, passive seismic monitoring systems could be deployed at appropriate depths to systematically detect and monitor leakage along them.     

Nanoporous activated carbon fluidized bed catalytic oxidations of aqueous o, p and m-cresols: kinetic and thermodynamic studies

Nanoporous activated carbon prepared from rice husk through precarbonisation at 400 °C and phosphoric acid activation at 800 °C was used as fluidized bed in Fenton oxidation of the o, p and m-cresols in aqueous solution. The efficiencies of homogeneous Fenton oxidation, fluidized Fenton oxidation and aerobic biological oxidation systems for the removal of o, p and m-cresols in aqueous solution have been compared. The kinetic constants and the thermodynamic parameters for the homogeneous Fenton, heterogeneous Fenton and aerobic biological oxidations of o, p and m-cresols in synthetic wastewater were determined. The degradation of cresols in synthetic wastewater was confirmed using FT-IR, ¹H-NMR and UV–visible spectroscopy.     

Genotoxic effect of ciprofloxacin during photolytic decomposition monitored by the in vitro micronucleus test (MNvit) in HepG2 cells

Purpose

Ciprofloxacin (CIP), a broad-spectrum, second-generation fluoroquinolone, has frequently been found in hospital wastewaters and effluents of sewage treatment plants. CIP is scarcely biodegradable, has toxic effects on microorganisms and is photosensitive. The aim of this study was to assess the genotoxic potential of CIP in human HepG2 liver cells during photolysis.

Methods

Photolysis of CIP was performed in aqueous solution by irradiation with an Hg lamp, and transformation products were monitored by HPLC-MS/MS and by the determination of dissolved organic carbon (DOC). The cytotoxicity and genotoxicity of CIP and of the irradiated samples were determined after 24?h of exposure using the WST-1 assay and the in vitro micronucleus (MN) test in HepG2 cells.

Results

The concentration of CIP decreased during photolysis, whereas the content of DOC remained unchanged. CIP and its transformation products were not cytotoxic towards HepG2 cells. A concentration-dependent increase of MN frequencies was observed for the parent compound CIP (lowest observed effect level, 1.2???mol?L^?1). Furthermore, CIP and the irradiated samples were found to be genotoxic with a significant increase relative to the parent compound after 32?min (P?P?Conclusions Photolytic decomposition of aqueous CIP leads to genotoxic transformation products. This proves that irradiated samples of CIP are able to exert heritable genotoxic effects on human liver cells in vitro. Therefore, photolysis as a technique for wastewater treatment needs to be evaluated in detail in further studies, not only for CIP but in general.     

Superior photodecomposition of pyrene by metal ion-loaded TiO₂ catalyst under UV light irradiation

BACKGROUND: The photocatalytic degradation of pyrene under UV (125 W Hg-Arc, 10.4 mW/cm2) irradiation of TiO2 aqueous suspension has been found to be highly improved with the dissolved transition metal ions like Cu2+, Fe3+, Ag+, and Au3+, etc. As the reduction potential of these metals lies below the conduction band (CB) position (?0.1 eV) of TiO2, the photoexcited electron transfer occurs more readily and reduces electron–hole recombination rate. Therefore, it has a beneficial influence on the photocatalytic ability of TiO2 because of rapid Fermi energy equilibrium between the CB of TiO2 and its surface adsorbed metal ions. RESULTS AND DISCUSSION: The Fermi level is referred to as the electrochemical potential and plays an important role in the band theory of solids. When metal and semiconductor are in contact, electron migration from photoirradiated semiconductor to the deposited metal occurs at the interface until two Fermi levels equilibrate and enhanced the photocatalytic activity of semiconductor photocatalyst. Ni2+ having more negative reduction potential (?0.25 eV) than the CB of TiO2 imparts negligible co-catalytic activity to TiO2 photoreaction. It also revealed that loading of Au3+ ions displayed higher degradation rate of pyrene than Au photodeposition. Furthermore, when the amount of dissolved Fe+3 and Au3+ ions gradually increases from 0.1 to 2 wt.%, the pyrene photodecomposition rate also become faster.     

Susceptibility of epigeic earthworm Eisenia fetida to agricultural application of six insecticides

Ecotoxicological risks of agricultural application of six insecticides to soil organisms were evaluated by acute toxicity tests under laboratory condition following OECD guidelines using the epigeic earthworm Eisenia fetida as the test organism. The organochlorine insecticide endosulfan (LC₅₀ - 0.002 mg kg⁻¹) and the carbamate insecticides aldicarb (LC₅₀ - 9.42 mg kg⁻¹) and carbaryl (LC₅₀ - 14.81 mg kg⁻¹) were found ecologically most dangerous because LC₅₀ values of these insecticides were lower than the respective recommended agricultural dose (RAD). Although E. fetida was found highly susceptible to the pyrethroid insecticide cypermethrin (LC₅₀ - 0.054 mg kg⁻¹), the value was higher than its RAD. The organophosphate insecticides chlorpyrifos (LC₅₀ - 28.58 mg kg⁻¹), and monocrotophos (LC₅₀ - 39.75 mg kg⁻¹) were found less toxic and ecologically safe because the LC₅₀ values were much higher than their respective RAD.     

Epibrassinolide ameliorates Cr (VI) stress via influencing the levels of indole-3-acetic acid, abscisic acid, polyamines and antioxidant system of radish seedlings

The present investigation determined the effects of epibrassinolide (EBL) on the levels of indole-3-acetic acid (IAA), abscisic acid (ABA), and polyamine (PA) and antioxidant potential of 7-d old Raphanus sativus L. cv. ‘Pusa chetki’ seedlings grown under Cr (VI) metal stress. Reduced titers of free (0.767 μg g⁻¹ FW) and bound (0.545 μg g⁻¹ FW) IAA in Cr (VI) stressed seedlings were observed over untreated control. Supplementations of EBL to Cr (VI) stressed seedlings were able to enhance both free (2.14-5.68 μg g⁻¹ FW) and bound IAA (2.45-7.78 μg g⁻¹ FW) concentrations in comparison to Cr (VI) metal treatment alone. Significant rise in free (13.49 μg g⁻¹ FW) and bound (12.17 μg g⁻¹ FW) ABA contents were noticed for Cr (VI) stressed seedlings when compared to untreated control. No significant increase in ABA contents were recorded for Cr (VI) stressed seedlings upon supplementation with EBL over Cr (VI) treatment alone. A significant increase in Put (18.40 μg g⁻¹ FW) and Cad (9.08 μg g⁻¹ FW) contents were found for 10⁻⁹ M EBL plus Cr (VI) metal treatments when compared to Cr (VI) treatment alone. Spermidine (Spd) contents were found to decline significantly for EBL treatment alone or when supplemented with Cr (VI) treatments over untreated controls and Cr (VI) treatment alone. Antioxidant levels were found to enhance, with glutathione (57.98 mg g⁻¹ FW), proline (4.97 mg g⁻¹ FW), glycinebetaine (39.01 μmol mL⁻¹), ascorbic acid (3.17 mg g⁻¹ FW) and phytochelatins (65.69 μmol g⁻¹ FW) contents noted for EBL supplemented to Cr (VI) metal solution over Cr (VI) treatment alone. Reduced activities of guaiacol peroxidase (0.391 U mg⁻¹ protein) and catalase (0.221 U mg⁻¹ protein) and enhanced activities of glutathione reductase (7.14 U mg⁻¹ protein), superoxide dismutase (15.20 U mg⁻¹ protein) and ascorbate peroxidase (4.31 U mg⁻¹ protein) were observed in seedlings treated with EBL plus Cr (VI) over Cr metal treatment alone. Reduced MDA (2.55 μmol g⁻¹ FW) and H₂O₂ (33.24 μmol g⁻¹ FW) contents were recorded for 10⁻⁹ M EBL supplemented to Cr (VI) stress over Cr (VI) treatment alone. Enhancement in free radical scavenging potential as indicated by higher values of 1,1-diphenylpicrylhydrazyl, deoxyribose and reducing power activity assays, and increased levels of phenols and soluble sugars also showed significant influence of EBL in alleviating Cr (VI) stress in radish seedlings.