Andrew S. Kinsela

The aqueous phase speciation and chemistry of cobalt in terrestrial environments

The solution speciation of a metal has a critical influence on its biological activity in the environment and is now an important focus of research. In this review, pertinent aspects related to the aqueous speciation and chemistry of cobalt (Co) in terrestrial environments are critically assessed. Although there is a lack of comprehensive data on aqueous Co concentrations in soil porewaters, groundwaters and surface waters, existing reports indicate that natural Co concentrations vary within a picomolar to micromolar range. Cobalt chemistry is dominated by the Co(II) oxidation state in the aqueous phase of terrestrial environments primarily due to the extremely low solubility of Co(III). There is no universal agreement on the importance of Co(II) complexation in the solution phase of terrestrial environments and, furthermore, on the nature of the major binding organic ligands. The kinetics of Co(II) complexation to, and dissociation from, natural organic complexing ligands are such that the speciation of Co is likely to significantly diverge from estimates based on thermodynamic equilibrium calculations. As a result, an accurate understanding of Co bioavailability, toxicity and transport in terrestrial aquatic environments will only be achieved when thermodynamics can be reconciled with reaction kinetics.

Microbial communities reflect temporal changes in cyanobacterial composition in a shallow ephemeral freshwater lake

The frequency of freshwater cyanobacterial blooms is at risk of increasing as a consequence of climate change and eutrophication of waterways. It is increasingly apparent that abiotic data are insufficient to explain variability within the cyanobacterial community, with biotic factors such as heterotrophic bacterioplankton, viruses and protists emerging as critical drivers. During the Australian summer of 2012–2013, a bloom that occurred in a shallow ephemeral lake over a 6-month period was comprised of 22 distinct cyanobacteria, including Microcystis, Dolichospermum, Oscillatoria and Sphaerospermopsis. Cyanobacterial cell densities, bacterial community composition and abiotic parameters were assessed over this period. Alpha-diversity indices and multivariate analysis were successful at differentiating three distinct bloom phases and the contribution of abiotic parameters to each. Network analysis, assessing correlations between biotic and abiotic variables, reproduced these phases and assessed the relative importance of both abiotic and biotic factors. Variables possessing elevated betweeness centrality included temperature, sodium and operational taxonomic units belonging to the phyla Verrucomicrobia, Planctomyces, Bacteroidetes and Actinobacteria. Species-specific associations between cyanobacteria and bacterioplankton, including the free-living Actinobacteria acI, Bacteroidetes, Betaproteobacteria and Verrucomicrobia, were also identified. We concluded that changes in the abundance and nature of freshwater cyanobacteria are associated with changes in the diversity and composition of lake bacterioplankton. Given this, an increase in the frequency of cyanobacteria blooms has the potential to alter nutrient cycling and contribute to long-term functional perturbation of freshwater systems.

Pedogenic factors and measurements of the plant uptake of cobalt

Understanding the factors which affect plant uptake of cobalt (Co) across a range of soil types is essential for both continued agricultural productivity as well as for possible remediation of contaminated sites. This review examines the relevant pedogenic processes contributing to plant uptake of Co from soils based on a critical evaluation of existing numerical data. Numerous pedogenic factors have been put forward in the scientific literature to account for the plant uptake of Co, including total, extractable and isotopically exchangeable soil Co concentrations, pH and other soil chemical parameters (e.g. manganese concentrations), microbial variations as well as anthropogenic inputs. Despite there being certain instances where significant correlations occur between these parameters and plant uptake of Co, an examination of multiple data sets shows that these relationships are spatially isolated. With the measureable parameters showing only weak correlations at best, there should be a degree of scepticism regarding the interpretation of reported data sets. Newly evolving techniques which assess kinetically-bioavailable in-situ soil concentrations, such as diffusive gradient thin-films, offer the potential to better address plant Co uptake across a range of soil types.

Mechanisms of acid sulfate soil oxidation and leaching under sugarcane cropping

Analysis of acid sulfate soils (ASS) under sugarcane cropping at a site on the Tweed River, north-eastern New South Wales, showed that the majority of the acidity and higher valence ions generated through pyrite oxidation was retained within an individual caneblock. It appears that the oxidation products generated >1 m away from the field drain edge primarily remain where they were formed, and are not exported to the adjacent field drain. Capillary rise and diffusion control the transfer of oxidation products within this area. Leaching and mass movement dominate the transport of ionic species in the topsoil and close to the field drain edge (~1 m). Soluble ion movement within the unsaturated zone also appears to be influenced by nutrient uptake of the growing sugarcane, adsorption and exchange reactions, and convective/dispersive forces. The almost ubiquitous degree and depth of oxidation of ASS profiles along most of the coast, even where no artificial drainage has occurred, leads us to propose natural hydrological and pedogenic processes as the cause. While artificial drainage systems may not have caused the acidity that is stored in backswamps, they do provide the conduit for acidity export. Therefore, management regimes should focus on maximising the retention of acidity in the backswamp and treating that which is exported. Whilst a reduction in the drain frequency appears a logical solution to a reduction in the acidity export from the site, consideration must be given to the benefits field drainage provides before any subsequent changes can be made. An integrated approach of drain minimisation, laser levelling, and active watertable control would appear to be the most appropriate policy in containing the acidity within the soil profile. This approach, combined with the strategic application of lime, offers a means for minimising acid export from the sampled site.

Speciation and transport of arsenic in an acid sulfate soil-dominated catchment, eastern Australia

Factors controlling the transport of geogenically-derived arsenic from a coastal acid sulfate soil into downstream sediments are identified in this study with both solid-phase associations and aqueous speciation clearly critical to the mobility and toxicity of arsenic. The data from both sequential extractions and X-ray adsorption spectroscopy indicate that arsenic in the unoxidised Holocene acid sulfate soils is essentially non-labile in the absence of prolonged oxidation, existing primarily as arsenopyrite or as an arsenopyrite-like species, likely arsenian pyrite. Anthropogenically-accelerated pedogenic processes, which have oxidised this material over time, have greatly enhanced the potential bioavailability of arsenic, with solid-phase arsenic almost solely present as As(V) associated with secondary Fe(III) minerals present. Analyses of downstream sediments reveal that a portion of the arsenic is retained as a mixed As(III)/As(V) solid-phase, though not at levels considered to be environmentally deleterious. Determination of arsenic speciation in pore waters using high performance liquid chromatography/Inductively Coupled Plasma-Mass Spectrometry shows a dominance of As(III) in upstream pore waters whilst an unidentified As species reaches comparative levels within the downstream, estuarine locations. Pore water As(V) was detected at trace concentrations only. The results demonstrate the importance of landscape processes to arsenic transport and availability within acid sulfate soil environments.

The reduction of 4-chloronitrobenzene by Fe(II)-Fe(III) oxide systems - correlations with reduction potential and inhibition by silicate.

Recent studies have demonstrated that the rate at which Fe(II)-Fe(III) oxyhydroxide systems catalyze the reduction of reducible contaminants, such as 4-chloronitrobenzene, is well correlated to their thermodynamic reduction potential. Here we confirm this effect in the presence of Fe(III) oxyhydroxide phases not previously assessed, namely ferrihydrite and nano-goethite, as well as Fe(III) oxyhydroxide phases previously examined. In addition, silicate is found to decrease the extent of Fe(II) sorption to the Fe(III) oxyhydroxide surface, increasing the reduction potential of the Fe(II)-Fe(III) oxyhydroxide suspension and, accordingly, decreasing the rate of 4-chloronitrobenzene reduction. A linear relationship between the reduction potential of the Fe(II)-Fe(III) oxyhydroxide suspensions and the reduction rate of 4-chloronitrobenzene (normalized to surface area and concentration of sorbed Fe(II)) was obtained in the presence and absence of silicate. However, when ferrihydrite was doped with Si (through co-precipitation) the reduction of 4-chloronitrobenzene was much slower than predicted from its reduction potential. The results obtained have significant implications to the likely effectiveness of naturally occurring contaminant degradation processes involving Fe(II) and Fe(III) oxyhydroxides in groundwater environments containing high concentrations of silicate, or other species which compete with Fe(II) for sorption sites.

Fodinomyces uranophilus gen. nov. sp. nov. and Coniochaeta fodinicola sp. nov., two uranium mine-inhabiting Ascomycota fungi from northern Australia

Seven acidophilic/acidotolerant fungal strains were characterized from samples of process waters (raffinate) at one of Australia’s largest uranium mines, the Ranger Mine in Northern Territory. They were isolated from raffinate, which typically were very acidic (pH 1.7–1.8) and contained high concentrations of total dissolved/colloidal salts (> 100 g/L). Five of the isolates correspond to two new acidotolerant Ascomycota fungi. The first is a member of a new genus, here described as Fodinomyces (Teratosphaeriaceae, Capnodiales, Dothideomycetes) and does not show clear close affiliation with any other described fungus in the scientific literature. The second belongs to the genus Coniochaeta (Coniochaetaceae, Coniochaetales, Sordariomycetes) and is closely related to Coniochaeta hansenii.

Agricultural acid sulfate soils: a potential source of volatile sulfur compounds?

Environmental context. Acid sulfate soils are important contributors to global environmental problems. Agricultural acid sulfate soils have recently been shown to emit sulfur dioxide, an important gas in global issues of acid rain, cloud formation and climate change. This emission is surprising because these soils tend to be wet and the gas is extremely water-soluble. The potential origins of this gas are not yet understood within the context of acid sulfate soils. Our new study reports the measurement of two potential precursors of sulfur dioxide, dimethylsulfide and ethanethiol, from both a natural and an agricultural acid sulfate soil in eastern Australia. Abstract. Most agricultural soils are generally considered to be a sink for sulfur gases rather than a source; however, recent studies have shown significant emissions of sulfur dioxide and hydrogen sulfide from acid sulfate soils. In the current study, acid sulfate soil samples were taken in northern New South Wales from under sugarcane cropping, as well as from an undisturbed nature reserve. Using gas chromatography/flame photometric detection in conjunction with headspace solid-phase microextraction, we have now determined that these soils are a potential source of the low molecular weight volatile sulfur compounds, dimethylsulfide and ethanethiol. Although the mechanism for their production remains unclear, both compounds are important in the transfer and interconversions of atmospheric and terrestrial sulfur. Therefore, these novel findings have important implications for refining local and regional atmospheric sulfur budgets, as well as for expanding our understanding of sulfur cycling within acid sulfate soils and other sediments.

Enrichment, inter-relationship, and fractionation of heavy metals in road-deposited sediments of Sydney, Australia

Urban road-deposited sediments (RDS) are potential sources of heavy metal pollution of both terrestrial and aquatic environments. We determined the heavy metals enrichments, their possible sources, and potential bioavailability and mobility in RDS from nine sites along major motorways of Sydney, the largest city with highest road traffic density in Australia. Mean total concentrations of metals in the RDS decreased in the order: Fe > Mn > Zn > Cu > Cr > Pb > Ni > Cd. The corresponding order in the background soils (minimally contaminated from roads) was: Fe > Mn > Zn ~ Ni > Cu ~ Pb > Cr > Cd. Both the pollution index (PI) and metal enrichment factor (EF), which are comparative measures between contaminated and uncontaminated sites, were highest for Cu and Zn. Inputs of Cu and Zn to RDS were likely to be mainly the result of brake and tyre wear, respectively. Cluster and correlation analyses showed that while the concentrations of these two metals were related in the soil, they were not correlated in RDS. Low PI and EF values as well as the close inter-relationships of Fe, Mn, Cr, and Ni in both RDS and soils suggest that these metals were derived mainly from natural sources. Metal fractionation data showed 50–95% of Cr and Fe in RDS to be present in the immobile and bio-unavailable residual fraction, whereas 15–65% of Zn was contained in the exchangeable fraction, which is considered to be mobile and bioavailable.

Uranium Binding Mechanisms of the Acid-Tolerant Fungus Coniochaeta fodinicola

The uptake and binding of uranium [as (UO2)(2+)] by a moderately acidophilic fungus, Coniochaeta fodinicola, recently isolated from a uranium mine site, is examined in this work in order to better understand the potential impact of organisms such as this on uranium sequestration in hydrometallurgical systems. Our results show that the viability of the fungal biomass is critical to their capacity to remove uranium from solution. Indeed, live biomass (viable cells based on vital staining) were capable of removing ∼16 mg U/g dry weight in contrast with dead biomass (autoclaved) which removed ∼45 mg U/g dry weight after 2 h. Furthermore, the uranium binds with different strength, with a fraction ranging from ∼20-50% being easily leached from the exposed biomass by a 10 min acid wash. Results from X-ray absorption spectroscopy measurements show that the strength of uranium binding is strongly influenced by cell viability, with live cells showing a more well-ordered uranium bonding environment, while the distance to carbon or phosphorus second neighbors is similar in all samples. When coupled with time-resolved laser fluorescence and Fourier transformed infrared measurements, the importance of organic acids, phosphates, and polysaccharides, likely released with fungal cell death, appear to be the primary determinants of uranium binding in this system. These results provide an important progression to our understanding with regard to uranium sequestration in hydrometallurgical applications with implications to the unwanted retention of uranium in biofilms and/or its mobility in a remediation context.