Chemical extractions have been shown to measure the biodegradable fraction of aromatic contaminants in soil; however, there is little research on the chemical prediction of aliphatic hydrocarbon degradation. The aim of this study was to investigate the potential for cyclodextrin extractions to predict hexadecane biodegradation in soil. Soils were amended with 10 or 100 mg kg−1 of a model alkane n-hexadecane and 100 Bq g−1 14C-n-hexadecane. Correlations between the extents of mineralisation and extractions of the 14C-contaminant were determined. Solvent shake extractions and aqueous CaCl2 extractions were poor predictors of hexadecane bioaccessibility. However, the novel HP-α-CD shake extraction showed close correlation (r2 = 0.90, n = 36, p < 0.05) to the mineralisation data. This novel extraction technique has the potential to be used to assess the biodegradable aliphatic hydrocarbon fraction in contaminated soils. Cyclodextrin shake extractions have the potential to predict the bioaccessibility of aliphatic hydrocarbons in soil.

Variations in the soil/sediment organic matter (SOM)-hydrophobic organic contaminant (HOC) bindings upon microbially mediated redox conditions were examined. While the extractability of pyrene associated with soil declined after its biodegradation began during aerobic incubation, its variations were almost constant (±3.0-4.4%) during anoxic/anaerobic incubations. The dissolved organic matter released from the soil incubated under highly reduced conditions became more humified and aromatic, had a higher average molecular weight, and was more polydispersed compared to that obtained from oxic incubation, similar to the SOM alterations in the early stage of diagenesis (humification). The concentrations of pyrene in the aqueous phase increased significantly during the soil incubations under highly reduced conditions due to its favorable interaction with the altered DOM. Our results suggest that the microbially mediated redox conditions have significant impacts on SOM and should be considered for the transport, fate, bioavailability, and exposure risk of HOCs in the geo-environments. HOC association within soil/sediment matrix can be controlled by microbially mediated redox conditions.

Loss of nitrogen from the soil-plant system has raised environmental concern. This study assessed the fluxes of nitrous oxide (N2O) in the subsurface flow constructed wetlands (CWs). To better understand the mechanism of N2O emission, spatial distribution of ammonia-oxidizing bacteria (AOB) in four kinds of wetlands soil were compared. N2O emission data showed large temporal and spatial variation ranging from -5.5 to 32.7 mg N2O m-2 d-1. The highest N2O emission occurred in the cell planted with Phragmites australis and Zizania latifolia. Whereas, the lower emission rate were obtained in the cell planted with P. australis and Typha latifolia. These revealed that Z. latifolia stimulated the N2O emission. Transportation of more organic matter and oxygen for AOB growth may be the reason. The study of AOB also supported this result, indicating that the root structure of Z. latifolia was favored by AOB for N2O formation. Zizania latifolia has a large contribution to global warming.

The evaluation of microbial availability of contaminants is of high importance for better reflecting the processes governing contaminant fate in soil and for establishing the risk associated with contaminated sites. A sub-critical water extraction technique was assessed for its potential to determine the microbially degradable fraction of [14C]phenanthrene-associated activity in two dissimilar soils at three different ageing times (14, 28 and 49 days). For the majority of determinations, no significant (p > 0.05) difference between sub-critical water-extracted 14C-activity at 160 °C and the fraction mineralized by catabolically active Pseudomonas sp. was observed. Collectively, the results suggested that the sub-critical water extraction technique was an appropriate technique for predicting the biodegradable fraction of phenanthrene-associated 14C-activity in dissimilar soils following increasing soil-contaminant contact time. Sub-critical water extraction reflects phenanthrene bioaccessibility in the soil.

We studied the short- and medium-term effects of experimental nitrogen fertilization (3 and 15 months after the treatment) on the arthropods of Calluna vulgaris heathlands in NW Spain. Three heathland sites were selected with two permanent plots per site: control and fertilized. Ammonium nitrate fertilizer (56 kg N ha-1 yr-1) was applied monthly and insects were caught using pitfall traps. We found mainly species-level responses to nitrogen addition. Seven species (e.g. Lochmaea suturalis) showed a consistent trend (benefited or harmed) in both periods and were proposed as possible reliable indicators of the effects of nitrogen deposition in these ecosystems. We also found variable arthropod trophic-group responses: (a) herbivores (leaf beetles, true bugs) increased in abundance on a short-term scale; (b) predators (carabid beetles, true bugs) showed opposite and less clear responses in both periods. Further long-term studies are needed to determine the mechanisms underlying the observed arthropod responses. We observed consistent species-level and variable trophic-group responses to nitrogen addition in one of the southern-most locations for Calluna vulgaris heathlands within Europe.

We studied the effectiveness of remediation on microbial endpoints, namely microbial biomass and activity, microbial and plant species richness, of an As-contaminated mine spoil, amended with compost (C) alone and in combination with beringite (B) or zerovalent iron grit (Z), to increase organic matter content and reduce trace elements mobility, and to allow Holcus lanatus and Pinus pinaster growth. Untreated spoil showed the lowest microbial biomass and activity and hydrolase activities, and H. lanatus as sole plant species, whereas the presented aided phytostabilisation option, especially CBZ treatment, significantly increased microbial biomass and activity and allowed colonisation by several plant species, comparable to those of an uncontaminated sandy soil. Microbial species richness was only increased in spoils amended with C alone. No clear correlation occurred between trace element mobility and microbial parameters and plant species richness. Our results indicate that the choice of indicators of soil remediation practices is a bottleneck. Organo-mineral amendment and revegetation of a gold mine spoil increased microbial activity but did not increase microbial species richness.

The biodegradation of different peat types was studied with a manometric respirometric test. Compaction peat and sphagnum peat samples were analysed, and the effect of peat pH on biodegradation behaviour was evaluated. Only minor (BOD/ThOD < 0.4%) biodegradation was observed with compaction peat samples, and the stable state, in which biodegradation stopped, was achieved during a two month period. As expected, sphagnum peat samples with a lower decomposition rate degraded more than compaction peat samples. Alkalinity (pH between ca. 4-9) of the peat was noticed to reduce the degree of biodegradation and accelerate the achievement of the stable state.

Hyperaccumulating plants are increasingly investigated in combination with EDTA addition to soil for phytoremediation of heavy metal contaminated soils. A 60-day incubation experiment was carried out to investigate the effects of heavy metal release during the decomposition of Zn-rich (15.7 mg g-¹ dry weight) Arabidopsis halleri litter on C mineralization, microbial biomass C, biomass N, ATP, and adenylate energy charge (AEC). These effects were investigated in two soils with different Zn, Cu, and Pb levels, with and without EDTA addition to soil. The sole addition of Zn-rich A. halleri litter to the two soils did not increase the contents of NH₄NO₃ extractable Zn, only with the combined additions of EDTA and litter was there a considerable increase, being equivalent to three times the added amount in the low metal soil and to 50% in the high metal soil. Litter amendment increased the CO₂ evolved; being equivalent to 44% of the added C in the two soils, but EDTA addition had no significant effect on CO₂ evolution. Litter amendment resulted also in an 18% increase in microbial biomass C, 27% increase in ATP and 6% increase in AEC in the two soils, but EDTA had again no effect on these indices at both metal levels. In contrast, the sole addition of litter had no effect on microbial biomass N, but EDTA addition increased microbial biomass N on average by 49%. The application of EDTA for chelate-assisted phytoextraction should in the future consider the risk of groundwater pollution, which is intensified by resistance of EDTA to microbial decomposition.

An improved understanding of factors that influence the survival and/or growth of Escherichia coli (E. coli) in soil is essential to allow the formation of land management practices to control the spread of the pathogenic strains of the bacteria, whose transmission to fresh produce is a threat to food safety. Persistence of E. coli in soils held at different water potentials and with carbon additions then subjected to post-freezing incubation temperatures and in the presence of Klebsiella terrigena (K. terrigena) were investigated. Soil samples adjusted to different water potentials (-0.03, -0.1 and -1.5 MPa) were inoculated with a multi-antibiotic resistant strain of E. coli (E. coli 2+), which allowed recovery of the organism from soil samples. In addition to manipulation of water content, different C levels were added and samples were frozen for varying lengths of time, thawed and incubated. In freezing studies, initial soil moisture content significantly affected E. coil 2+ survival in soils following thawing, resulting in lower survival rate (k) at water potential of -0.03 than at -0.1 and -1.5 MPa. The effect of length of freezing time was significant only at -0.03 MPa. Glucose addition at 1.25 mg C g⁻¹ improved survival rate versus glucose at 0.125. The low level glucose increased die-off rate versus no addition, suggesting that unless amendments provide C above a certain threshold level, they might facilitate the death of the bacteria. E. coli 2+ survival improved in the presence of K. terrigena at 6°C but not at 23°C. Persistence of E. coli under the interactive influence of various environmental factors highlights the urgency and importance of understanding its potential for transmission to fresh produce and water bodies.

A conceptual model of solute transport with bioremediation processes using sawdust as a matrix to improve the efficiency of bioremediation in porous media is presented. The transport part of the model solves the advection dispersion differential equations and the reaction part describes the heterotrophic metabolisms of several groups of bacteria. The bacterial growth is formulated using the double Monod kinetic equation. The model depicts the utilization of oxygen, nitrate, manganese, iron oxides and sulfate as electron acceptors for oxidation of organic carbon in porous media. Exchange between the different phases (mobile pore water phase, bio phase and matrix phase) is also considered in this model. Model parameters were adopted from literature on bioremediation processes. Feasibility and applicability of parameters were assessed by conducting a laboratory soil-sawdust columns experiments and comparing the simulated results with the experimental data. The results indicate that sawdust could be employed as low-cost materials to enhance the bioremediation processes in porous media. While the availability of organic carbon is one of the most important factors that affect bacterial activity in porous media, this study demonstrates that using sawdust as a carbon source can improve the bacterial activity and increase the column permeability.