Wood pellet fly ash and bottom ash as an effective liming agent and nutrient source for rye grass (Lolium perenne L.) and oats (Avena sativa)

Fly ash (FA) and bottom ash (BA) from a softwood pellet boiler were characterized and evaluated as soil amendments. In a greenhouse study, two plant species (rye grass, Lolium perenne L. and oats, Avena sativa) were grown in three different treatments (1% FA, 1% BA, non-amended control) of a silty loam soil. Total concentrations of plant nutrients Ca, K, Mg, P and Zn in both ashes were elevated compared to conventional wood ash. Concentrations of Cd, Cr, Pb, Se and Zn were found to be elevated in the FA relative to BA and the non-amended soil. At 28 d, oat above-ground biomass was found to be significantly greater in soil amended with FA. Potassium and Mo plant tissue concentrations were significantly increased by addition of either ash, and FA significantly increased Zn tissue concentrations. Cadmium and Hg tissue concentrations were elevated in some cases. As soil amendments, either pellet ash is an effective liming agent and nutrient source, but high concentrations of Cd and Zn in FA may preclude its use as an agricultural soil amendment in some jurisdictions. Lower ash application rates than those used in this study (i.e. <1%) may still provide sufficient nutrients and effective neutralization of soil acidity.     

Variably saturated flow and multicomponent biogeochemical reactive transport modeling of a uranium bioremediation field experiment

Three-dimensional, coupled variably saturated flow and biogeochemical reactive transport modeling of a 2008 in situ uranium bioremediation field experiment is used to better understand the interplay of transport and biogeochemical reactions controlling uranium behavior under pulsed acetate amendment, seasonal water table variation, spatially variable physical (hydraulic conductivity, porosity) and geochemical (reactive surface area) material properties. While the simulation of the 2008 Big Rusty acetate biostimulation field experiment in Rifle, Colorado was generally consistent with behaviors identified in previous field experiments at the Rifle IFRC site, the additional process and property detail provided several new insights. A principal conclusion from this work is that uranium bioreduction is most effective when acetate, in excess of the sulfate-reducing bacteria demand, is available to the metal-reducing bacteria. The inclusion of an initially small population of slow growing sulfate-reducing bacteria identified in proteomic analyses led to an additional source of Fe(II) from the dissolution of Fe(III) minerals promoted by biogenic sulfide. The falling water table during the experiment significantly reduced the saturated thickness of the aquifer and resulted in reactants and products, as well as unmitigated uranium, in the newly unsaturated vadose zone. High permeability sandy gravel structures resulted in locally high flow rates in the vicinity of injection wells that increased acetate dilution. In downgradient locations, these structures created preferential flow paths for acetate delivery that enhanced local zones of TEAP reactivity and subsidiary reactions. Conversely, smaller transport rates associated with the lower permeability lithofacies (e.g., fine) and vadose zone were shown to limit acetate access and reaction. Once accessed by acetate, however, these same zones limited subsequent acetate dilution and provided longer residence times that resulted in higher concentrations of TEAP reaction products when terminal electron donors and acceptors were not limiting. Finally, facies-based porosity and reactive surface area variations were shown to affect aqueous uranium concentration distributions with localized effects of the fine lithofacies having the largest impact on U(VI) surface complexation. The ability to model the comprehensive biogeochemical reaction network, and spatially and temporally variable processes, properties, and conditions controlling uranium behavior during engineered bioremediation in the naturally complex Rifle IFRC subsurface system required a subsurface simulator that could use the large memory and computational performance of a massively parallel computer. In this case, the eSTOMP simulator, operating on 128 processor cores for 12h, was used to simulate the 110-day field experiment and 50 days of post-biostimulation behavior.     

Effects of sulfur dioxide pollution on the translocation and accumulation of heavy metals in soybean grain

Background  

Open-top chambers were used to study the impact of simultaneous exposure to atmospheric SO₂ pollution and heavy metal contamination in soils on the metal contents and productivity of soybean plant.     

Blood dioxin biomonitoring to assess local residents' exposure from a large urban remediation project

Background

A total of 265 000 m³ of dioxin contaminated soil and sediments from past industrial activity was treated on site in an urban setting in Sydney, Australia. To respond to local community concerns about potential dioxin exposure from fugitive emissions a human biomonitoring study was undertaken.

Objective

To determine whether local residents were exposed to significant amounts of dioxin from the remediation process.Methods: Blood samples were collected from local residents around the site and a representative metropolitan control group. They were pooled within age and sex strata and the change in dioxin concentrations over the remediation period and a summary of the mid point and post remediation dioxin concentrations were compared between groups. Information on dietary intake was collected to look for possible confounding.

Results

The mean dioxin Toxic Equivalent concentrations (TeQ) decreased among both the local resident and control groups over the remediation period by 1.9 and 2.1 pg gm⁻¹ lipid respectively. Modelled blood concentrations adjusting for age and sex did not detect a significant difference between groups for changes in either TeQ or 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8 TCDD). The summary measure approach did however demonstrate that the 2,3,7,8 TCDD concentrations among the local resident group was approximately 0.7 pg g⁻¹ lipid higher compared to the control group post remediation. There were no significant changes in dietary intake sources of dioxin.

Conclusion

Biomonitoring demonstrated that local residents were not exposed to significant quantities of dioxin. Large scale remediation of dioxin contaminated land can be safely undertaken in an urban setting.     

Using a physiologically based pharmacokinetic model to link urinary biomarker concentrations to dietary exposure of perchlorate

Exposure to perchlorate is widespread in the United States and many studies have attempted to character the perchlorate exposure by estimating the average daily intakes of perchlorate. These approaches provided population-based estimates, but did not provide individual-level exposure estimates. Until recently, exposure activity database such as CSFII, TDS and NHANES become available and provide opportunities to evaluate the individual-level exposure to chemical using exposure surveillance dataset. In this study, we use perchlorate as an example to investigate the usefulness of urinary biomarker data for predicting exposures at the individual level. Specifically, two analyses were conducted: (1) using data from a controlled human study to examine the ability of a physiologically based pharmacokinetic (PBPK) model to predict perchlorate concentrations in single-spot and cumulative urine samples; and (2) using biomarker data from a population-based study and a PBPK model to demonstrate the challenges in linking urinary biomarker concentrations to intake doses for individuals. Results showed that the modeling approach was able to characterize the distribution of biomarker concentrations at the population level, but predicting the exposure-biomarker relationship for individuals was much more difficult. The type of information needed to reduce the uncertainty in estimating intake doses, for individuals, based on biomarker measurements is discussed.     

Modelling the dissipation kinetics of six commonly used pesticides in two contrasting soils of New Zealand

We used three non-linear bi-phasic models, bi-exponential (BEXP), first-order double exponential decay (FODED), and first-order two-compartment (FOTC), to fit the measured degradation data for six commonly used pesticides (atrazine, terbuthylazine, bromacil, diazinon, hexazinone and procymidone) in two New Zealand soils. Corresponding DT₅₀ and DT₉₀ values for each compound were numerically obtained and compared against those estimated by simple first-order kinetic (SFOK) model. All 3 non-linear models gave good fit of the measured data under both soil depths and were well supported by the values obtained for the respective statistical indices (RMSE, CRM and r ²). The FOTC model gave by far the best fit for most compounds, followed by the FODED and BEXP models. Overall, DT₅₀ values derived by non-linear models for the six compounds in soils from both sites were lower than the values obtained by the SFOK model. Differences in the SFOK and the three non-linear models derived DT₉₀were, however, an order of magnitude higher for some compounds, while for others differences were very small. Although all three non-linear models described most data by giving excellent fits, in a few instances > 5–10% asymptotes hindered the estimation of DT₉₀ values. This work shows that when degradation deviates from first-order kinetic, application of non-linear decay models to describe the kinetics of degradation becomes important in order to derive the true end-points for pesticides in soil.     

Why geodiversity matters in valuing nature's stage

Geodiversity—the variability of Earth's surface materials, forms, and physical processes—is an integral part of nature and crucial for sustaining ecosystems and their services. It provides the substrates, landform mosaics, and dynamic physical processes for habitat development and maintenance. By determining the heterogeneity of the physical environment in conjunction with climate interactions, geodiversity has a crucial influence on biodiversity across a wide range of scales. From a literature review, we identified the diverse values of geodiversity; examined examples of the dependencies of biodiversity on geodiversity at a site‐specific scale (for geosites <1 km² in area); and evaluated various human‐induced threats to geosites and geodiversity. We found that geosites are important to biodiversity because they often support rare or unique biota adapted to distinctive environmental conditions or create a diversity of microenvironments that enhance species richness. Conservation of geodiversity in the face of a range of threats is critical both for effective management of nature's stage and for its own particular values. This requires approaches to nature conservation that integrate climate, biodiversity, and geodiversity at all spatial scales.