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Microbial denitrification occurs in anaerobic soil microsites and aquatic environments leading to production of N 2 O and N 2 gases, which eventually escape to the atmosphere. Atmospheric concentrations of N 2 O have been on the rise since the beginning of the industrial revolution due to large-scale manipulations of the N cycle in managed ecosystems, especially the use of synthetic nitrogenous fertilizer. Here we document and test a microbial denitrification model identified as IMWJ and implemented as a submodel in the EPIC terrestrial ecosystem model. The IMWJ model is resolved on an hourly time step using the concept that C oxidation releases electrons that drive a demand for electron acceptors such as O 2 and oxides of N (NO 3 − , NO 2 − , and N 2 O). A spherical diffusion approach is used to describe O 2 transport to microbial surfaces while a cylindrical diffusion method is employed to depict O 2 transport to root surfaces. Oxygen uptake by microbes and roots is described with Michaelis-Menten kinetic equations. If insufficient O 2 is present to accept all electrons generated, the deficit for electron acceptors may be met by oxides of nitrogen, if available. The movement of O 2 , CO 2 and N 2 O through the soil profile is modeled using the gas transport equation solved on hourly or sub-hourly time steps. Bubbling equations also move N 2 O and N 2 through the liquid phase to the soil surface under highly anaerobic conditions. We used results from a 2-yr field experiment conducted in 2007 and 2008 at a field site in southwest Michigan to test the ability of EPIC, with the IMWJ option, to capture the non-linear response of N 2 O fluxes as a function of increasing rates of N application to maize [ Zea mays L.]. Nitrous oxide flux, soil inorganic N, and ancillary data from 2007 were used for EPIC calibration while 2008 data were used for independent model validation. Overall, EPIC reproduced well the timing and magnitude of N 2 O fluxes and NO 3 − mass in surficial soil layers after N fertilization. Although similar in magnitude, daily and cumulative simulated N 2 O fluxes followed a linear trend instead of the observed exponential trend. Further model testing of EPIC + IMWJ, alone or in ensembles with other models, using data from comprehensive experiments will be essential to discover areas of model improvement and increase the accuracy of N 2 O predictions under a wide range of environmental conditions. [ABSTRACT FROM AUTHOR]

Quantification of risks to the ecosystem is necessary for cost-effective remediation strategies. Contaminant endpoints need to be established that consider the bioavailability of toxicants in soil. The challenge is to develop methods that assign risk to the bioavailable toxic contaminants, thereby protecting ecosystems, while balancing remediation costs. Our objective was to evaluate changes in bioavailability of creosote constituents in soils to earthworms. An acute ecotoxicological investigation of three weathered creosote-contaminated and two slurry-phase-biotreated soils was conducted using a 14-d earthworm (Eisenia fetida) survival bioassay. Soil characterization (physical and chemical) and contaminant concentration data (polycyclic aromatic hydrocarbons [PAH] and total dichloromethane extractable organics [DEO]) were also determined. The toxicity of the soils could not always be predicted based on chemical concentrations alone. Soils having a low PAH:DEO ratio had higher cumulative earthworm survival times as measured by earthworm-days. We propose that the DEO fraction may regulate toxicity by altering bioavailability of toxicants. [ABSTRACT FROM AUTHOR]

Reports on a method for predicting partition coefficients of nonionic chemicals onto soils and geologic materials. Properties of sorbents and sorbates; Use of commercial biopolymers and humic acids extracted from soils; Limitations associated with the proposed cross-relation method.

Reports on phenol sorption by soil organic compounds cellulose, chitin, collagen, lignin and activated carbon. Reaction of phenol with soil minerals; Relation of phenol uptake to polarity and heat of wetting of biopolymers; Energetics of uptake of phenol by ligning and activated carbon.

The sorptive behavior of two surfactants (Triton X-100(R) and Dowfax(R) 8390) with two surface soil samples, a subsurface soil sample, a weathered black shale containing large amounts of aged organic matter, an aeolian sand, and two clay minerals (montmorillonite and kaolinite) was examined. Dowfax 8390 (dianionic surfactant) sorption was notdetected with any of the samples. In contrast, Triton X-100, an ethoxylated nonionic surfactant, sorbed to all the samples. The mole surfactant sorbed/g sorbent (mol surf/g sorbent) was greater for samples containing large amounts of smectite minerals and nonlinearity of theTriton X-100 isotherm increased in samples low in organic carbon. The X-ray diffraction analysis concluded that the ethoxylate group of Triton X-100 intercalates with montmorillonite. The weathered black shale sample also has a high mol surf/g sorbent value when reacted withTriton X-100 but contains less smectite clay. We suggest that TritonX-100 may be reacting via hydrophobic groups (branched alkyl chain) with the shale sample. Consequently, sorption of alcohol ethoxylate surfactants cannot be predicted solely on the basis of soil attributessuch as clay or organic matter content, for it appears that the organic matter-clay organization may predominate in these types of interactions. [ABSTRACT FROM AUTHOR]

• The oily sludge-derived char (OSDC) had more favorable sorption for Pb2+ than Cd2+. • The OSDC showed a Pb2+ sorption capacity as high as 373.2 mg/g. • Pb2+ and Cd2+ sorption fit the Elovich equation and Redlich-Peterson isotherm model. • Precipitation dominated Pb2+ sorption on OSDC. • Complexation and cation exchange were mainly responsible for Cd2+ removal by OSDC. The objective of this study was to investigate the physicochemical properties of oily sludge-derived char produced from pyrolysis at 500 °C (OS500) and its sorption behavior towards lead (Pb2+) and cadmium (Cd2+) in aqueous solution. The sorption kinetics and isotherm of Pb2+ and Cd2+ sorption on OS500 were determined. The results were fitted with four kinetic (pseudo first order, pseudo second order, Elovich equation, and intraparticle diffusion) and six isotherm (Langmuir, Freundlich, Sips, Redlich-Peterson, Temkin, and Dubinin-Radushkevich) models. The maximum sorption capacity (Q L) of Pb2+ obtained from the Langmuir model was 373.2 mg/g, while Q L of Cd2+ was 23.19 mg/g. The mechanisms of lead and cadmium sorption on OS500 and their quantitative contributions were further studied by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and sequential extraction test. The results indicated the chemical characteristics (e.g., alkaline minerals and effective cation exchange capacity (CEC)) but not microstructure of OS500 controlled its Pb2+ and Cd2+ sorption. New mineral precipitates (i.e., hydrocerussite (Pb 3 (CO 3) 2 (OH) 2) and cerussite (PbCO 3)) formed during Pb2+ sorption. The Pb2+-π interaction and complexation of Cd2+ with hydroxyl functional groups were evidenced by FTIR. Mineral precipitation with Pb2+ was the predominant mechanism for Pb2+ sorption on OS500 (accounted for 93.79%), whereas the complexation dominated Cd2+ sorption (accounted for 84.15%). The OS500 shows application potential in removing heavy metal contaminants from solution, especially Pb2+. [ABSTRACT FROM AUTHOR]

Chromium speciation in naturally contaminated soils appears more complex than spiked studies have shown. This study characterized Cr speciation (oxidation states; availability; molecular geometry) intended to highlight the genesis of immobile Cr(VI) species in long-term tannery waste-contaminated soils. In a series of samples obtained from Shuitou in China, chemical extraction methods showed that Cr(III) was dominant(>96.7% of total Cr), with Cr(VI) concentration up to 144 mg kg -1 . Of the total Cr(VI) present, immobile Cr(VI) represents >90%. Synchrotron-based X-ray near-edge structure spectroscopy (XANES) showed the occurrence of Cr(VI), which was not removed by phosphate buffer extraction, confirming a significant amount of immobile Cr(VI) fractions in soils. X-ray fluorescence maps exhibited the heterogeneous distribution of Cr in soils associated with both Mn and Fe. Such a distribution suggests Cr(III) oxidation to Cr(VI) by Mn oxides and a possible immobilization of both Cr(III) and Cr(VI) onto Fe (hydr)oxides. Linear combination fitting of XANES spectra revealed that fractional weights (%) in samples were CrFeO 3 (49.3-53.6), CrOOH (22.3-30.8), and CaCrO 4 (13.2-25.3). Our results demonstrate that (i) Cr(VI) is immobilized in soils and (ii) mechanisms of Cr(VI) immobilization are CaCrO 4 precipitation and recrystallization with Fe (hydr)oxides.