Parameters known to influence mercury (Hg) release from soils include substrate and air Hg concentration, light, atmospheric oxidants, temperature, and soil moisture. However, for low Hgcontaining soils, the influence of these parameters has been shown to vary across space and time. Here, we expand upon previous work by investigating whether soil-water evaporative loss, which integrates the influence of multiple parameters, could be applied for predicting Hg flux from soil with low Hg concentrations when bare and planted. To investigate our hypothesis, Hg flux was measured from three soil types (<100 ng Hg g-1). When these soils were saturated, flux was suppressed. Soil moisture evaporative stage was used to partition the parameters most important for controlling Hg flux as the soils dried. Classification and regression tree (CART) analyses showed that soil moisture was the most important parameter predicting Hg flux. Results also showed an important predictor for Hg flux was whether actual evaporation (Ea) was equal to potential evaporation (Ep) or Ea < Ep. Depending on evaporative stage, the parameters with the next highest correlation to Hg flux were light, temperature, and soil moisture evaporation rate. The presence of vegetation also influenced flux with lower Hg flux when the plants were transpiring. Results indicate for those developing models that estimate Hg flux from low Hg-containing soils, soil moisture and evaporative stage are useful tools for predicting flux. © Springer Science+Business Media Dordrecht 2013.

Kinetics and mechanism on discoloration of an azo dye, methyl orange (MO), by heterogeneous Fenton-like reaction using natural schorl as catalyst were investigated in this study. Among the three kinetic models (the first-order, the second-order, and the Behnajady-Modirshahla-Ghanbery (BMG)), the BMG kinetic model was the best one to describe MO discoloration at different reaction conditions, due to its highest determination coefficients. The BMG model parameter, 1/m, increased with initial hydrogen peroxide (H2O 2) concentration, and schorl dosage and reaction temperature increased while the pH solution decreased. The phenomenon indicated that the initial MO discoloration rate increased with the ascending of the initial H 2O2 concentration, schorl dosage, and reaction temperature and the descending of the pH solution. Meanwhile, another BMG parameter, 1/b, except for the one at pH=5, were all around 1, implying that the schorl-catalyzed Fenton-like reaction had high capacity for MO discoloration. The possible reason for these phenomena was interpreted from the point of view of OH generation and Fe dissolution. Generally speaking, the amount of hydroxyl radicals increased with initial H2O2 concentration, increased schorl dosage and reaction temperature, and decreased pH solution, playing an important role in the change of 1/m values. The concentration of soluble iron ions at all adopted experimental conditions ranged from 0.23 to 1.14 mg/L, much lower than the European Union directive (2 mg/L), which demonstrated that natural schorl would be a promising heterogeneous catalyst for the Fenton-like reaction. Finally, a possible mechanism for this process was put forward. © Springer Science+Business Media Dordrecht 2013.

Acid mine drainage (AMD) generated by some coal mines in New Zealand is currently treated by the addition of alkaline reagents which neutralize acidity, triggering the precipitation of dissolved metals as insoluble hydroxides. Some trace metals (Ni, Zn, Cu, Cd, and Pb) are discharged into receiving water bodies due to incomplete hydroxide precipitation at circum-neutral pH. This study investigated the incorporation of lignite-derived humic substances (HS) for metal complexation and removal during AMD treatment by Ca(OH)₂ and CaCO₃ neutralization. For Ca(OH)₂ neutralization, addition of HS (regardless of dosing sequence) enhanced the removal of Zn, Cu, and Cd, probably due to the incorporation of metal–humate complex into settling flocs (via aggregation, co-precipitation, and adsorption) that were subsequently removed by sedimentation. However, additional removal of Ni and Pb was statistically indeterminate, which was ascribed to the low complexation affinity of Ni and high removal of Pb by adsorption onto Fe/Al hydroxides. Conversely, for CaCO₃ neutralization, addition of HS only marginally enhanced Cd removal, with the removal of metals probably dominated by adsorption onto the abundant undissolved calcite. Equilibrium speciation modelling showed that about 25% and 38% of the remaining Cu and Pb in the treated AMD were complexed with HS, while only 5% of remaining Cd and less than 1 wt% of remaining Ni and Zn were organically complexed. In the AMD-receiving water bodies, about 20 mg l⁻¹ of HS would be required for complete complexation (>95%) of Cu and Pb and 50 mg l⁻¹ for Cd, whereas Zn and Ni complexation would not occur at natural stream HS concentrations.

A comparative long-term study of three subsurface horizontal-flow (HF) constructed wetlands (CW) treating winery wastewater was carried out. The water depth for HF1 was 0.3 m, while the depth for HF2 and HF3 was 0.6 m, respectively. Hydraulic loading rate ranged from 7 to 93 mm/d, while surface loading rates fell into the following ranges: 4–85 g COD/m²·d, 2–49 g BOD₅/m²·d and 0.5–6 g TSS/m²·d. The percentage of biological oxygen demand (BOD₅) removal clearly decreased when influent concentration increased, while surface removal rate increased and reached a maximum of approximately 8 g BOD₅/m²·d removed in the range of 10–20 g BOD₅/m²·d fed, depending on the CW depth. HF1 showed a worse performance than the other units, appearing to be more affected by high influent concentrations. Solids accumulation on gravel media, hydraulic conductivity and gas emissions were monitored over the 2.8 years of operation.

The fate and transport of emerging contaminants have been major concerns for ecoenvironment and human health. This study presents the adsorption behavior of an endocrine disrupting chemical estrone (E1) and its sulfate conjugate estrone-3-sulfate (E1-3S) that are released to the environment via animal waste in significant amounts and direct exposures in grazed pasture systems. Both compounds have been shown to potentially contribute to endocrine disruption in wildlife, and knowledge about the adsorption behavior of these compounds is necessary for a sound environmental risk assessment. For labile compounds such as E1 and E1-3S, however, the standard protocols might overestimate adsorption by not considering metabolite formation or allowing for equilibration that exceeds the commonly reported half-lives of these compounds. Modified batch adsorption experiments with mediator solution of 0.005 M calcium chloride (CaCl₂) and artificial urine (AU) solution were, therefore, conducted to determine the influence of these mediator solutions on the adsorption of E1 and E1-3S in three agricultural soils from Nasarawa State of Nigeria. Adsorption isotherms of both compounds were nonlinear, and the Freundlich equation was found adequate to describe the isotherms. The calculation of concentration-dependent effective distribution coefficients (K d ᵉᶠᶠ) revealed that for a range of realistic exposure concentrations in a grazed farming system, the common approach of using CaCl₂ would deliver incorrect information for a sound risk assessment.

The present study deals with the effect of trace metals on the endangered limpet Cymbula nigra. The Bay of Algeciras (Strait of Gibraltar) was used as the study site. Important industrial activity takes place in the area, including frequent oil spills. However, it is home to important populations of C. nigra. The objective of this work was to determine if these animals were being affected at a subcellular level by the pollutants present in their environment and to analyze the trace metal concentrations in the animal’s soft tissues. To determine the effects of water quality on the antioxidant activity and concentrations through field experimentation, a total of six sites were selected in Algeciras Bay, three located in the inner areas (environmentally degraded sites with higher levels of pollutants) and three in the outermost areas of the Bay. Stress associated to reactive oxygen species formation was assessed on digestive glands and gills as the enzymatic antioxidant activity of catalase (CAT), superoxide dismutase (SOD), and glutathione S-transferase (GST) and as the concentrations of lipid-soluble (α-tocopherol and β-carotene) and the water-soluble antioxidants (reduced and oxidized glutathione (GSH and GSSG)). Gills and digestive glands of those animals located in the inner areas of Algeciras Bay showed higher CAT activity values than those located in the outer areas. As a general pattern, we observed higher antioxidant activities and concentrations in digestive glands that in gills, suggesting the possibility that pollutants are mainly being incorporated by limpets through the food. As a general rule, larger animals showed greater concentrations of these compounds. Iron, zinc, and manganese, in this order, were present in the tissues at the highest concentrations. Chromium and manganese were found in significantly higher concentrations in those animals collected from the inner areas of the Bay. Through the present study, we provide the first data regarding the antioxidant defense levels and metal accumulation capacity of this species, and we reinforce the idea that this endangered species may be, in fact, relatively tolerant to degraded environments.

This study was aimed to examine the efficiency of a novel bacterial consortium on the reduction of toxic hexavalent chromium [Cr(VI)] to non-toxic trivalent Cr [Cr(III)]. Six Cr(VI)-resistant bacteria (IS1-IS6) were isolated from a tannery waste disposal site at Mount Barker, South Australia, of which three viz., IS1, IS2 and IS3 were selected based on Cr(VI) reduction ability in minimal salt medium. The isolates were identified as Bacillus endophyticus (IS1), Microbacterium paraoxydans (IS2) and Bacillus simplex (IS3) by 16S rRNA gene sequencing. All three isolates were able to tolerate chromium (Cr(VI), 300–400 mg L ⁻¹), arsenic (As(V), 1,000 mg L ⁻¹), copper (Cu(II), 300–400 mg L ⁻¹) and lead (Pb(II), 1,000 mg L ⁻¹). The isolates were evaluated both as an individual and as a consortia for Cr(VI) reduction in minimal salt medium and storm water, both spiked with 100 mg Cr(VI) L ⁻¹. In both cases, the rate of Cr(VI) reduction was found to be significantly higher in the bacterial consortium inoculation ( t_½ = 8.45 for minimal salt medium; 6.02 h for storm water), compared to inoculation with individual isolates ( t_½ = 53.3–115.5 h for minimal salt medium; 8.77–9.76 h for storm water). The rate of Cr(VI) reduction in both minimal salt medium and storm water was found to be higher in bacterial consortium inoculation (IS1 + IS2 + IS3) than in individual isolate inoculation. This experiment demonstrated that bacterial consortium prepared by using B. endophyticus, M. paraoxydans and B. simplex was more effective in Cr(VI) detoxification than application of individual bacterium. This experiment also proved that a bacterial consortium was more effective in Cr(VI) detoxification than the application of individual bacterial strain.

To assess strategies for mitigating Pb and As transfer into leafy vegetables from contaminated garden soils, we conducted greenhouse experiments using two field-contaminated soils amended with materials expected to reduce metal phytoavailability. Lettuce and mustard greens grown on these soils were analyzed by ICP-MS, showing that some Pb and As transfer into the vegetables occurred from both soils tested, but plant Pb concentrations were highly variable among treatment replicates. Soil-to-plant transfer was more efficient for As than for Pb. Contamination of the leaves by soil particles probably accounted for most of the vegetable Pb, since plant Pb concentrations were correlated to plant tissue concentrations of the immobile soil elements Al and Fe. This correlation was not observed for vegetable As concentrations, evidence that most of the soil-to-plant transfer for this toxic metal occurred by root uptake and translocation into the above-ground tissues. A follow-up greenhouse experiment with lettuce on one of the two contaminated soils revealed a lower and less variable foliar Pb concentration than observed in the first experiment, with evidence of less soil particle contamination of the crop. This reduced transfer of Pb to the crop appeared to be a physical effect attributable to the greater biomass causing reduced overall exposure of the above-ground tissues to the soil surface. Attempts to reduce soil Pb and As solubility and plant uptake by amendment at practical rates with stabilizing materials, including composts, peat, Ca phosphate, gypsum, and Fe oxide, were generally unsuccessful. Only Fe oxide reduced soluble As in the soil, but this effect did not persist. Phosphate amendment rapidly increased soil As solubility but had no measurable effect on either soil Pb solubility or concentrations of Pb or As in the leafy vegetables. The ineffectiveness of these amendments in reducing Pb transfer into leafy vegetables is attributed in this study to the low initial Pb solubility of the studied soils and the fact that the primary mechanism of Pb transfer is physical contamination.

This study aimed to chemically and radiologically characterize the water resources influenced by a phosphogypsum stack in Imbituba, SC, Brazil and to identify the annual intake by ingestion. Surface water was collected at six points downstream of the phosphogypsum stack. Subsurface water samples were collected from a piezometer in the stack area. These samples were analyzed using a radiochemical method to determine the natural radionuclide content and an inductively coupled plasma optical emission spectrometry to determine the concentration of selected metals. The concentrations of radionuclides were also compared with current standards. The radionuclide concentrations in the surface waters samples were lower or similar to those found in other studies. The effective dose resulting from water ingestion is below the recommended reference levels for drinking water. Samples collected exhibited no increase in radioactivity, under the influence of phosphogypsum stacks.

The processes of wind erosion of fertile soil, dune movement in sand deserts, dust storms in arid and semi-arid regions, as well as the emission and dispersion of agricultural or industrial dusts create a lot of problems and dangers for human life, environment, and infrastructure. Conventional ways to suppress dust emission to the atmosphere are agricultural fixation in the case of fertile soil surface and application of chemical agents to immobilize dust particulates onto the surface of soil, desert sand, country roads, or mining areas. However, these methods are often too expensive to be applied for large-scale suppression of sand dust. Chemical methods of dust suppression are often environmentally unfriendly due to the release of toxic reagents in water, air, and soil. This paper examines, for the first time, the microbially mediated aggregation of fine sand particles to suppress the emission of sand dust and its chemical and bacteriological pollutants. The bioaggregation reagent was a solution of calcium chloride and urea sprayed over the sand surface, which was preliminarily treated with the suspension of urease-producing bacteria. Quantity of calcium used for sand dust suppression was 15.6 g of Ca/m2. After the biotreatment of fine sand, the release of sand dust and its artificial pollutants to the atmosphere decreased in comparison with control by 99.8 % for dust, 92.7 % for phenantherene, 94.4 % for led nitrate, and 99.8 % for bacterial cells of Bacillus megaterium. This immobilization of dust and dust pollutants was due to the bioaggregation of fine sand particles. The sizes of 90 % of the sand dust particles increased from 29 μm in control to 181 μm after bioaggregation. Bioaggregation treatment of the soil surface could be a useful method to prevent the dispersion of dust and dust-associated chemical and bacteriological pollutants in water, air, and soil. © 2013 Springer Science+Business Media Dordrecht.