PFAS contaminated asphalt and concrete - Knowledge gaps for future research and management

Per- and polyfluoroalkyl substances (PFAS) are now widespread in the environment. Globally, airfields and paved firefighting training surfaces are particularly affected due to extensive use of aqueous film forming foams (AFFF). This PFAS contamination in exposed concrete and asphalt has not been widely addressed. This review focusses on PFAS interaction with concrete and asphalt, traversing extraction, analytical identification/quantification, PFAS fractionation via differential adsorption on organic and inorganic substrates, and reuse options for contaminated concrete and asphalt. A total of 24 knowledge gaps and management challenges for concrete and asphalt characterisation and management have been identified.

Correction: Method for extraction and analysis of per- and poly-fluoroalkyl substances in contaminated asphalt

Correction for 'Method for extraction and analysis of per- and poly-fluoroalkyl substances in contaminated asphalt' by Prashant Srivastava et al., Anal. Methods, 2022, 14, 1678-1689, https://doi.org/10.1039/D2AY00221C.

Method for extraction and analysis of per- and poly-fluoroalkyl substances in contaminated asphalt

The legacy use of aqueous film-forming foam (AFFF) has led to the generation of large volumes of per- and poly-fluoroalkyl substances (PFAS)-contaminated asphalt materials, especially at airports and fire training areas. The management of such PFAS-contaminated asphalt materials requires an understanding of PFAS concentrations in these materials. This study, therefore, aimed to develop a suitable extraction methodology for the analysis of 22 target PFAS (i.e., carboxylic acids, sulfonic acids and fluorotelomers) in asphalt materials. A series of experiments was conducted to optimise extraction solvent composition, as well as to assess the performance of the chosen method under various conditions (i.e., sonication temperature, PFAS contamination level, asphalt core composition and timing of stable isotope addition used as internal standard). The methanol-based extractants performed best due to their accuracy and precision, which were within the acceptable range (extraction efficiency between 70 and 130% and RSD < 20%). The method which involved three successive extractions with methanol/1% NH₃ by ultrasonication at 25 °C was selected due to its performance and ease of operation. The mean recovery of a vast majority of PFAS was found to be in the acceptable range. Tests on the timing of addition of stable isotope (SI)-labelled PFAS internal standards indicate that the recoveries obtained, regardless of when the stable isotopes were added, were within the acceptable range for PFAS. The accuracy and precision of PFAS recoveries were not affected by PFAS spike level (2 μg kg^-1 and 200 μg kg^-1), as well as sample composition (based on the location of asphalt material in the field). Low RSDs were achieved for asphalt cores collected from a contaminated site covering a wide range of concentrations (from LOQ to 2135 mg kg^-1), demonstrating the suitability of the sample preparation method for real-world samples. The results from the interlaboratory testing were also in good agreement and validated the proposed PFAS extraction and analytical approach.

The influence of salinity on the chronic toxicity of shale gas flowback wastewater to freshwater organisms

The potential environmental risk associated with flowback waters generated during hydraulic fracturing of target shale gas formations needs to be assessed to enable management decisions and actions that prevent adverse impacts on aquatic ecosystems. Using direct toxicity assessment (DTA), we determined that the shale gas flowback wastewater (FWW) from two exploration wells (Tanumbirini-1 and Kyalla 117 N2) in the Beetaloo Sub-basin, Northern Territory, Australia were chronically toxic to eight freshwater biota. Salinity in the respective FWWs contributed 16% and 55% of the chronic toxicity at the 50% effect level. The remaining toxicity was attributed to unidentified chemicals and interactive effects from the mixture of identified organics, inorganics and radionuclides. The most sensitive chronic endpoints were the snail (Physa acuta) embryo development (0.08-1.1% EC10), microalga (Chlorella sp. 12) growth rate inhibition (0.23-3.7% EC10) and water flea (Ceriodaphnia cf. dubia) reproduction (0.38-4.9% EC10). No effect and 10% effect concentrations from the DTA were used in a species sensitivity distribution to derive "safe" dilutions of 1 in 300 and 1 in 1140 for the two FWWs. These dilutions would provide site-specific long-term protection to 95% of aquatic biota in the unlikely event of an accidental spill or seepage.

Isotopic signatures reveal zinc cycling in the natural habitat of hyperaccumulator Dichapetalum gelonioides subspecies from Malaysian Borneo

BACKGROUND

Some subspecies of Dichapetalum gelonioides are the only tropical woody zinc (Zn)-hyperaccumulator plants described so far and the first Zn hyperaccumulators identified to occur exclusively on non-Zn enriched 'normal' soils. The aim of this study was to investigate Zn cycling in the parent rock-soil-plant interface in the native habitats of hyperaccumulating Dichapetalum gelonioides subspecies (subsp. pilosum and subsp. sumatranum). We measured the Zn isotope ratios (δ66Zn) of Dichapetalum plant material, and associated soil and parent rock materials collected from Sabah (Malaysian Borneo).

RESULTS

We found enrichment in heavy Zn isotopes in the topsoil (δ66Zn 0.13 ‰) relative to deep soil (δ66Zn -0.15 ‰) and bedrock (δ66Zn -0.90 ‰). This finding suggests that both weathering and organic matter influenced the Zn isotope pattern in the soil-plant system, with leaf litter cycling contributing significantly to enriched heavier Zn in topsoil. Within the plant, the roots were enriched in heavy Zn isotopes (δ66Zn ~ 0.60 ‰) compared to mature leaves (δ66Zn ~ 0.30 ‰), which suggests highly expressed membrane transporters in these Dichapetalum subspecies preferentially transporting lighter Zn isotopes during root-to-shoot translocation. The shoots, mature leaves and phloem tissues were enriched in heavy Zn isotopes (δ66Zn 0.34-0.70 ‰) relative to young leaves (δ66Zn 0.25 ‰). Thisindicates that phloem sources are enriched in heavy Zn isotopes relative to phloem sinks, likely because of apoplastic retention and compartmentalization in the Dichapetalum subspecies.

CONCLUSIONS

The findings of this study reveal Zn cycling in the rock-soil-plant continuum within the natural habitat of Zn hyperaccumulating subspecies of Dichapetalum gelonioides from Malaysian Borneo. This study broadens our understanding of the role of a tropical woody Zn hyperaccumulator plant in local Zn cycling, and highlights the important role of leaf litter recycling in the topsoil Zn budget. Within the plant, phloem plays key role in Zn accumulation and redistribution during growth and development. This study provides an improved understanding of the fate and behaviour of Zn in hyperaccumulator soil-plant systems, and these insights may be applied in the biofortification of crops with Zn.

Intensive cycling of nickel in a New Caledonian forest dominated by hyperaccumulator trees

The hyperaccumulator Pycnandra acuminata is a New Caledonian rainforest tree known to have the highest concentration of nickel in any living organism, with 25 wt% nickel in its latex. All trees (with a diameter of >10 cm) and soil profiles in a 0.25-hectare permanent plot were sampled to assess the biogeochemical compartmentalisation of nickel in a dense stand of P. acuminata trees. Nickel stable isotope analysis permitted insights into the cycling of nickel in this ecosystem. The total tree biomass of the plot was calculated to be 281 tonnes ha^-1 , which contained 0.44 kg of cobalt, 49.1 kg of manganese, 257 kg of nickel and 6.76 kg of zinc. Nickel stable isotope analysis identified the biotic origin of the nickel in the soil upper layers, with P. acuminata shoots enriched in lighter nickel isotopes. The δ⁶⁰ Ni latex signature suggests that long-distance transport, radial xylem and phloem loading are at play in P. acuminata.

Potential carcinogenic and non-carcinogenic health hazards of metal(loid)s in food grains

Metal(loid) contamination of vital food grains such as wheat and rice is a very serious problem throughout the world because consumption of such contaminated food can lead to severe health effects in humans. Metal(loid) contamination of food crops can occur from different sources such as contaminated soil, irrigation water, and aerial deposition. Therefore, the present study was conducted to analyze potential non-carcinogenic and carcinogenic health impacts posed by different metal(loid)s (As Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Se, and Zn) via consumption of wheat and rice grown on metal(loid)-contaminated soils in areas around rivers (Beas and Sutlej) of Punjab, India. Among the metal(loid)s analyzed in wheat and rice samples, contents of As, Cd, Cr, Ni, and Pb were found to be above the international (FAO/WHO and EU) maximum permissible limits. The non-carcinogenic and carcinogenic health risk assessment of individual metal(loid)s revealed that As posed highest risk followed by Cd, Cu, Fe, Mn, and Pb. The values of indices calculated for analysis of combined non-carcinogenic, i.e., (hazard index; range 3.49-15.94) and carcinogenic (total carcinogenic risk index; range 8.30 × 10^-4-131.62 × 10^-4) risks for both crops were found to be many fold higher than the prescribed limits of 1.0 and 1.0 × 10^-4, respectively. Thus, the analysis of combined risks posed by metal(loid)s indicated that human population consuming wheat and rice from the study area faced both non-carcinogenic and carcinogenic health risks. Therefore, immediate steps must be taken to reduce the levels of metal(loid)s in wheat and rice from the study area.

Microplastics in municipal mixed-waste organic outputs induce minimal short to long-term toxicity in key terrestrial biota

Sustainable alternatives to landfill disposal for municipal mixed wastes represents a major challenge to governments and waste management industries. In the state of New South Wales (NSW) Australia, mechanical biological treatment (MBT) is being used to reduce the volume and pathogen content of organic matter isolated from municipal waste. The product of this treatment, a compost-like output (CLO) referred to as mixed waste organic output (MWOO), is being recycled and applied as a soil amendment. However, the presence of contaminants in MWOO including trace organics, trace metals and physical contaminants such as microplastic fragments has raised concerns about potential negative effects on soil health and agriculture following land application. Here, we used multiple lines of evidence to examine the effects of land application of MWOO containing microplastics in three soils to a variety of terrestrial biota. Treatments included unamended soil, MWOO-amended soil and MWOO-amended soil into which additional high-density polyethylene (HDPE), polyethylene terephthalate (PET), or polyvinyl chloride (PVC) microplastics were added. Tests were conducted in soil media that had been incubated for 0, 3 or 9 months. Addition of microplastics had no significant negative effect on wheat seedling emergence, wheat biomass production, earthworm growth, mortality or avoidance behaviour and nematode mortality or reproduction compared to controls. There was also little evidence the microplastics affected microbial community diversity, although measurements of microbial community structure were highly variable with no clear trends.

Optimisation of phosphate loading on graphene oxide–Fe(iii) composites – possibilities for engineering slow release fertilisers

Engineering of a graphene-oxide based slow release P composite as an efficient, environmental friendly fertiliser.

Engineering the Slow Photon Effect in Photoactive Nanoporous Anodic Alumina Gradient-Index Filters for Photocatalysis

In this study, we explore for the first time the capabilities of nanoporous anodic alumina gradient-index filters (NAA-GIFs) functionalized with titanium dioxide (TiO₂) photoactive layers to enhance photon-to-electron conversion rates and improve the efficiency of photocatalytic reactions by "slow photon" effect. A set of NAA-GIFs was fabricated by sinusoidal pulse anodization, in which a systematic modification of various anodization parameters (i.e., pore widening time, anodization period, and anodization time) enables the fine-tuning of the photonic stopband (PSB) of these nanoporous photonic crystals (PCs) across the spectral regions. The surface of NAA-GIFs was chemically modified with photoactive layers of TiO₂ to create a composite photoactive material with precisely engineered optical properties. The photocatalytic performance of TiO₂-functionalized NAA-GIFs was assessed by studying the photodegradation of three model organic dyes (i.e., methyl orange, Rhodamine B, and methylene blue) with well-defined absorption bands across different spectral regions under simulated irradiation conditions. Our study demonstrates that when the edges of characteristic PSB of TiO₂-modified NAA-GIFs are completely or partially aligned with the absorption band of the organic dyes, the photodegradation rate is enhanced due to "slow photon" effect. A rational design of the photocatalyst material with respect to the organic dye is demonstrated to be optimal to speed up photocatalytic reactions by an efficient management of photons from high-irradiance spectral regions. This provides new opportunities to develop high-performing photocatalytic materials for efficient photocatalysis with broad applicability.

Ecotoxicology of manufactured graphene oxide nanomaterials and derivation of preliminary guideline values for freshwater environments

The unique physical and chemical properties of graphene-based nanomaterials (GNMs) have inspired a diverse range of scientific and industrial applications. The market value of GNMs is predicted to reach $US 1.3 billion by 2023. Common to many nanomaterials, an important and unresolved question is the environmental consequences of the increases in GNMs use. The current deficiencies in studies reporting ecotoxicology data for GNMs include differences in analytical methodologies for quantification, no standardized test guidelines, differences in morphology of GNMs, the lack of Chemical Abstract Service numbers, and the quality of the reported data. The assessment of potential adverse effects on aquatic organisms typically relies on guideline values based on species sensitivity distributions (SSDs) of toxicity data. We present preliminary water quality guideline values for graphene oxide NMs in freshwaters. Data include 10 species from 7 phyla (bacteria and fungi were not included). The most sensitive organism was found to be the freshwater shrimp Palaemon pandaliformis. The derived guideline values for 99, 95, 90, and 80% species protection were 350, 600, 830, and 1300 μg/L, respectively. These results will contribute to the regulatory derivations of future water quality guideline values for graphene-based NMs. Environ Toxicol Chem 2018;37:1340-1348. © 2018 SETAC.

Complementary Imaging of Silver Nanoparticle Interactions with Green Algae: Dark-Field Microscopy, Electron Microscopy, and Nanoscale Secondary Ion Mass Spectrometry

Increasing consumer use of engineered nanomaterials has led to significantly increased efforts to understand their potential impact on the environment and living organisms. Currently, no individual technique can provide all the necessary information such as their size, distribution, and chemistry in complex biological systems. Consequently, there is a need to develop complementary instrumental imaging approaches that provide enhanced understanding of these "bio-nano" interactions to overcome the limitations of individual techniques. Here we used a multimodal imaging approach incorporating dark-field light microscopy, high-resolution electron microscopy, and nanoscale secondary ion mass spectrometry (NanoSIMS). The aim was to gain insight into the bio-nano interactions of surface-functionalized silver nanoparticles (Ag-NPs) with the green algae Raphidocelis subcapitata, by combining the fidelity, spatial resolution, and elemental identification offered by the three techniques, respectively. Each technique revealed that Ag-NPs interact with the green algae with a dependence on the size (10 nm vs 60 nm) and surface functionality (tannic acid vs branched polyethylenimine, bPEI) of the NPs. Dark-field light microscopy revealed the presence of strong light scatterers on the algal cell surface, and SEM imaging confirmed their nanoparticulate nature and localization at nanoscale resolution. NanoSIMS imaging confirmed their chemical identity as Ag, with the majority of signal concentrated at the cell surface. Furthermore, SEM and NanoSIMS provided evidence of 10 nm bPEI Ag-NP internalization at higher concentrations (40 μg/L), correlating with the highest toxicity observed from these NPs. This multimodal approach thus demonstrated an effective approach to complement dose-response studies in nano-(eco)-toxicological investigations.

Incorporating Transgenerational Epigenetic Inheritance into Ecological Risk Assessment Frameworks

Chronic exposure to environmental contaminants can induce heritable "transgenerational" modifications to organisms, potentially affecting future ecosystem health and functionality. Incorporating transgenerational epigenetic heritability into risk assessment procedures has been previously suggested. However, a critical review of existing literature yielded numerous studies claiming transgenerational impacts, with little compelling evidence. Therefore, contaminant-induced epigenetic inheritance may be less common than is reported in the literature. We identified a need for multigeneration epigenetic studies that extend beyond what could be deemed "direct exposure" to F1 and F2 gametes and also include subsequent multiple nonexposed generations to adequately evaluate transgenerational recovery times. Also, increased experimental replication is required to account for the highly variable nature of epigenetic responses and apparent irreproducibility of current studies. Further, epigenetic end points need to be correlated with observable detrimental organism changes before a need for risk management can be properly determined. We suggest that epigenetic-based contaminant studies include concentrations lower than current "EC_10-20" or "Lowest Observable Effect Concentrations" for the organism's most sensitive phenotypic end point, as higher concentrations are likely already regulated. Finally, we propose a regulatory framework and optimal experimental design that enables transgenerational epigenetic effects to be assessed and incorporated into conventional ecotoxicological testing.

Fate of radiolabeled C60 fullerenes in aged soils

Fullerenes (e.g. C₆₀, C₇₀, etc.) present in soil may undergo changes in its retention with aging. In this study, the partitioning behavior of (¹⁴C)-C₆₀ aged up to 12 weeks was investigated in biosolids-amended soil. Spiked samples were subjected to sequential partitioning using water, methanol, and toluene followed by total combustion of solids; the distribution of ¹⁴C across solvents and matrices were used to provide insights on C₆₀ behavior. In most samples, ¹⁴C only partitioned in toluene with the remaining (non-extractable) activity detected in the solid phase. In all biosolids-amended soil samples, an increase in non-extractable ¹⁴C were observed for those exposed to light (vs dark) with the greatest difference observed in biosolids + sand samples. Possible processes that contribute to the observed ¹⁴C distribution, i.e. retention and potential transformation of C_60, were discussed. Over-all, results suggest that environmental exposure to C₆₀ and potentially transformed C₆₀ species, as a result of their release from soils, is likely to be low.

Aseptic hydroponics to assess rhamnolipid-Cd and rhamnolipid-Zn bioavailability for sunflower (Helianthus annuus): a phytoextraction mechanism study

The availability of cadmium (Cd) and zinc (Zn) to sunflower (Helianthus annuus) was investigated in rhamnolipid- and ethylenediaminetetraacetic acid (EDTA)-buffered solutions in order to evaluate the influence of aqueous speciation of the metals on their uptake by the plant, in relation to predictions of uptake by the free ion activity model (FIAM). Free metal ion activity was estimated using the chemical equilibrium program MINTEQ or measured by Donnan dialysis. The uptake of Cd followed the FIAM for the EDTA-buffered solution at EDTA concentrations below 0.4 μM; for the rhamnolipid-buffered solution, the uptake of both metals in roots was not markedly affected by increasing rhamnolipid concentrations in solution. This suggests rhamnolipid enhanced metal accumulation in plant roots (per unit free metal in solution) possibly through formation and uptake of lipophilic complexes. The addition of normal Ca concentrations (low millimetre range) to the rhamnolipid uptake solutions reduced Cd accumulation in shoots by inhibiting Cd translocation, whereas it significantly increased Zn accumulation in shoots. This study confirms that although rhamnolipid could enhance accumulation of Cd in plants roots at low Ca supply, it is not suitable for Cd phytoextraction in contaminated soil environments where Ca concentrations in soil solution are orders of magnitude greater than those of Cd.

Quantifying the Sensitivity of Soil Microbial Communities to Silver Sulfide Nanoparticles Using Metagenome Sequencing

Soils are a sink for sulfidised-silver nanoparticles (Ag₂S-NPs), yet there are limited ecotoxicity data for their effects on microbial communities. Conventional toxicity tests typically target a single test species or function, which does not reflect the broader community response. Using a combination of quantitative PCR, 16S rRNA amplicon sequencing and species sensitivity distribution (SSD) methods, we have developed a new approach to calculate silver-based NP toxicity thresholds (HCx, hazardous concentrations) that are protective of specific members (operational taxonomic units, OTUs) of the soil microbial community. At the HC20 (80% of species protected), soil OTUs were significantly less sensitive to Ag₂S-NPs compared to AgNPs and Ag⁺ (5.9, 1.4 and 1.4 mg Ag kg^-1, respectively). However at more conservative HC values, there were no significant differences. These trends in OTU responses matched with those seen in a specific microbial function (rate of nitrification) and amoA-bacteria gene abundance. This study provides a novel molecular-based framework for quantifying the effect of a toxicant on whole soil microbial communities while still determining sensitive genera/species. Methods and results described here provide a benchmark for microbial community ecotoxicological studies and we recommend that future revisions of Soil Quality Guidelines for AgNPs and other such toxicants consider this approach.

Symbiosis between nitrogen-fixing bacteria and Medicago truncatula is not significantly affected by silver and silver sulfide nanomaterials

Silver (Ag) engineered nanomaterials (ENMs) are being released into waste streams and are being discharged, largely as Ag2S aged-ENMs (a-ENMs), into agroecosystems receiving biosolids amendments. Recent research has demonstrated that biosolids containing an environmentally relevant mixture of ZnO, TiO2, and Ag ENMs and their transformation products, including Ag2S a-ENMs, disrupted the symbiosis between nitrogen-fixing bacteria and legumes. However, this study was unable to unequivocally determine which ENM or combination of ENMs and a-ENMs was responsible for the observed inhibition. Here, we examined further the effects of polyvinylpyrollidone (PVP) coated pristine Ag ENMs (PVP-Ag), Ag2S a-ENMs, and soluble Ag (as AgSO4) at 1, 10, and 100 mg Ag kg(-1) on the symbiosis between the legume Medicago truncatula and the nitrogen-fixing bacterium, Sinorhizobium melliloti in biosolids-amended soil. Nodulation frequency, nodule function, glutathione reductase production, and biomass were not significantly affected by any of the Ag treatments, even at 100 mg kg(-1), a concentration analogous to a worst-case scenario resulting from long-term, repeated biosolids amendments. Our results provide additional evidence that the disruption of the symbiosis between nitrogen-fixing bacteria and legumes in response to a mixture of ENMs in biosolids-amended soil reported previously may not be attributable to Ag ENMs or their transformation end-products. We anticipate these findings will provide clarity to regulators and industry regarding potential unintended consequences to terrestrial ecosystems resulting from of the use of Ag ENMs in consumer products.

Bioavailability of silver and silver sulfide nanoparticles to lettuce (Lactuca sativa): Effect of agricultural amendments on plant uptake

Silver nanoparticles (AgNPs) can enter terrestrial systems as sulfidised AgNPs (Ag2S-NPs) through the application of biosolids to soil. However, the bioavailability of Ag2S-NPs in soils is unknown. The two aims of this study were to investigate (1) the bioavailability of Ag to lettuce (Lactuca sativa) using a soil amended with biosolids containing Ag2S-NPs and (2) the effect of commonly used agricultural fertilisers/amendments on the bioavailability of Ag, AgNPs and Ag2S-NPs to lettuce. The study used realistic AgNP exposure pathways and exposure concentrations. The plant uptake of Ag from biosolids-amended soil containing Ag2S-NPs was very low for all Ag treatments (0.02%). Ammonium thiosulfate and potassium chloride fertilisation significantly increased the Ag concentrations of plant roots and shoots. The extent of the effect varied depending on the type of Ag. Ag2S-NPs, the realistic form of AgNPs in soil, had the lowest bioavailability. The potential risk of AgNPs in soils is low; even in the plants that had the highest Ag concentrations (Ag(+)+thiosulfate), only 0.06% of added Ag was found in edible plant parts (shoots). Results from the study suggest that agricultural practises must be considered when carrying out risk assessments of AgNPs in terrestrial systems; such practises can affect AgNP bioavailability.

Complex Forms of Soil Organic Phosphorus-A Major Component of Soil Phosphorus

Phosphorus (P) is an essential element for life, an innate constituent of soil organic matter, and a major anthropogenic input to terrestrial ecosystems. The supply of P to living organisms is strongly dependent on the dynamics of soil organic P. However, fluxes of P through soil organic matter remain unclear because only a minority (typically <30%) of soil organic P has been identified as recognizable biomolecules of low molecular weight (e.g., inositol hexakisphosphates). Here, we use (31)P nuclear magnetic resonance spectroscopy to determine the speciation of organic P in soil extracts fractionated into two molecular weight ranges. Speciation of organic P in the high molecular weight fraction (>10 kDa) was markedly different to that of the low molecular weight fraction (<10 kDa). The former was dominated by a broad peak, which is consistent with P bound by phosphomonoester linkages of supra-/macro-molecular structures, whereas the latter contained all of the sharp peaks that were present in unfractionated extracts, along with some broad signal. Overall, phosphomonoesters in supra-/macro-molecular structures were found to account for the majority (61% to 73%) of soil organic P across the five diverse soils. These soil phosphomonoesters will need to be integrated within current models of the inorganic-organic P cycle of soil-plant terrestrial ecosystems.

Effects of silver sulfide nanomaterials on mycorrhizal colonization of tomato plants and soil microbial communities in biosolid-amended soil

We investigated effects of Ag2S engineered nanomaterials (ENMs), polyvinylpyrrolidone (PVP) coated Ag ENMs (PVP-Ag), and Ag(+) on arbuscular mycorrhizal fungi (AMF), their colonization of tomato (Solanum lycopersicum), and overall microbial community structure in biosolids-amended soil. Concentration-dependent uptake was measured in all treatments. Plants exposed to 100 mg kg(-1) PVP-Ag ENMs and 100 mg kg(-1) Ag(+) exhibited reduced biomass and greatly reduced mycorrhizal colonization. Bacteria, actinomycetes and fungi were inhibited by all treatment classes, with the largest reductions measured in 100 mg kg(-1) PVP-Ag ENMs and 100 mg kg(-1) Ag(+). Overall, Ag2S ENMs were less toxic to plants, less disruptive to plant-mycorrhizal symbiosis, and less inhibitory to the soil microbial community than PVP-Ag ENMs or Ag(+). However, significant effects were observed at 1 mg kg(-1) Ag2S ENMs, suggesting that the potential exists for microbial communities and the ecosystem services they provide to be disrupted by environmentally relevant concentrations of Ag2S ENMs.

Influence of soil properties and soil leaching on the toxicity of ionic silver to plants

Silver (Ag) has been shown to exhibit antimicrobial properties; as a result, it is being used increasingly in a wide range of consumer products. With these uses, the likelihood that Ag may enter the environment has increased, predominately via land application of biosolids or irrigation with treated wastewater effluent. The aim of the present study was to investigate the toxicity of Ag to 2 plant species: barley (Hordeum vulgare L. CV Triumph) and tomato (Lycopersicum esculentum) in a range of soils under both leached and unleached conditions. The concentrations that resulted in a 50% reduction of plant growth (EC50) were found to vary up to 20-fold across the soils, indicating a large influence of soil type on Ag toxicity. Overall, barley root elongation was found to be the least sensitive to added Ag, with EC50 values ranging from 51 mg/kg to 1030 mg/kg, whereas the tomato plant height showed higher sensitivity with EC50 values ranging from 46 mg/kg to 486 mg/kg. The effect of leaching was more evident in the barley toxicity results, where higher concentrations of Ag were required to induce toxicity. Variations in soil organic carbon and pH were found to be primarily responsible for mitigating Ag toxicity; therefore, these properties may be used in future risk assessments for Ag to predict toxicity in a wide range of soil types.

Complexation of silver and dissolved organic matter in soil water extracts

An important aspect of the behaviour and fate of silver (Ag) in soils is the interaction with dissolved organic matter (DOM). The complexation and strength of binding of Ag(+) with DOM in soil water extracts was examined and modelled based on a range of chemical and quality DOM measurements. Silver ion binding measured by addition of the (110m)Ag radioisotope in addition to a cation exchange resin technique were used to determine strongly complexed Ag in solutions. Silver was found to be up to 70% strongly complexed. The variability in Ag(+) binding by DOM across different soils was closely related (R(2) = 0.8) to the mid-infrared spectra of these extracts. The affinity of Ag(+) for DOM was stronger in solutions containing a greater content of humic and aromatic structures. The ability of Ag(+) to complex with DOM could result in increased mobilisation of this metal in the soil environment.

Distribution and speciation of bromine in mammalian tissue and fluids by X-ray fluorescence imaging and X-ray absorption spectroscopy

Bromine is one of the most abundant and ubiquitous trace elements in the biosphere and until recently had not been shown to perform any essential biological function in animals. A recent study demonstrated that bromine is required as a cofactor for peroxidasin-catalysed formation of sulfilimine crosslinks in Drosophila. In addition, bromine dietary deficiency is lethal in Drosophila, whereas bromine replenishment restores viability. The aim of this study was to examine the distribution and speciation of bromine in mammalian tissues and fluids to provide further insights into the role and function of this element in biological systems. In this study we used X-ray fluorescence (XRF) imaging and inductively coupled plasma-mass spectrometry (ICP-MS) to examine the distribution of bromine in bovine ovarian tissue samples, follicular fluid and aortic serum, as well as human whole blood and serum and X-ray absorption spectroscopy (XAS) to identify the chemical species of bromine in a range of mammalian tissue (bovine, ovine, porcine and murine), whole blood and serum samples (bovine, ovine, porcine, murine and human), and marine samples (salmon (Salmo salar), kingfish (Seriola lalandi) and Scleractinian coral). Bromine was found to be widely distributed across all tissues and fluids examined. In the bovine ovary in particular it was more concentrated in the sub-endothelial regions of arterioles. Statistical comparison of the near-edge region of the X-ray absorption spectra with a library of bromine standards led to the conclusion that the major form of bromine in all samples analysed was bromide.

GEMAS: prediction of solid-solution phase partitioning coefficients (Kd) for oxoanions and boric acid in soils using mid-infrared diffuse reflectance spectroscopy

The authors' aim was to develop rapid and inexpensive regression models for the prediction of partitioning coefficients (Kd), defined as the ratio of the total or surface-bound metal/metalloid concentration of the solid phase to the total concentration in the solution phase. Values of Kd were measured for boric acid (B[OH]3(0)) and selected added soluble oxoanions: molybdate (MoO4(2-)), antimonate (Sb[OH](6-)), selenate (SeO4(2-)), tellurate (TeO4(2-)) and vanadate (VO4(3-)). Models were developed using approximately 500 spectrally representative soils of the Geochemical Mapping of Agricultural Soils of Europe (GEMAS) program. These calibration soils represented the major properties of the entire 4813 soils of the GEMAS project. Multiple linear regression (MLR) from soil properties, partial least-squares regression (PLSR) using mid-infrared diffuse reflectance Fourier-transformed (DRIFT) spectra, and models using DRIFT spectra plus analytical pH values (DRIFT + pH), were compared with predicted log K(d + 1) values. Apart from selenate (R(2)  = 0.43), the DRIFT + pH calibrations resulted in marginally better models to predict log K(d + 1) values (R(2)  = 0.62-0.79), compared with those from PSLR-DRIFT (R(2)  = 0.61-0.72) and MLR (R(2)  = 0.54-0.79). The DRIFT + pH calibrations were applied to the prediction of log K(d + 1) values in the remaining 4313 soils. An example map of predicted log K(d + 1) values for added soluble MoO4(2-) in soils across Europe is presented. The DRIFT + pH PLSR models provided a rapid and inexpensive tool to assess the risk of mobility and potential availability of boric acid and selected oxoanions in European soils. For these models to be used in the prediction of log K(d + 1) values in soils globally, additional research will be needed to determine if soil variability is accounted on the calibration.

GEMAS: prediction of solid-solution partitioning coefficients (Kd) for cationic metals in soils using mid-infrared diffuse reflectance spectroscopy

Partial least squares regression (PLSR) models, using mid-infrared (MIR) diffuse reflectance Fourier-transformed (DRIFT) spectra, were used to predict distribution coefficient (Kd) values for selected added soluble metal cations (Ag(+), Co(2+), Cu(2+), Mn(2+), Ni(2+), Pb(2+), Sn(4+), and Zn(2+)) in 4813 soils of the Geochemical Mapping of Agricultural Soils (GEMAS) program. For the development of the PLSR models, approximately 500 representative soils were selected based on the spectra, and Kd values were determined using a single-point soluble metal or radioactive isotope spike. The optimum models, using a combination of MIR-DRIFT spectra and soil pH, resulted in good predictions for log Kd+1 for Co, Mn, Ni, Pb, and Zn (R(2) ≥ 0.83) but poor predictions for Ag, Cu, and Sn (R(2)  < 0.50). These models were applied to the prediction of log Kd+1 values in the remaining 4313 unknown soils. The PLSR models provide a rapid and inexpensive tool to assess the mobility and potential availability of selected metallic cations in European soils. Further model development and validation will be needed to enable the prediction of log K(d+1) values in soils worldwide with different soil types and properties not covered in the existing model.

Thermostability and reversibility of silver nanoparticle-protein binding

The interactions between nanoparticles (NPs) and proteins in living systems are a precursor to the formation of a NP-protein "corona" that underlies cellular and organism responses to nanomaterials. However, the thermodynamic properties and reversibility of NP-protein interactions have rarely been examined. Using an automated, high-throughput and temperature-controlled dynamic light scattering (DLS) technique we observed a distinct hysteresis in the hydrodynamic radius of branched polyethyleneimine (BPEI) coated-silver nanoparticles (bAgNPs) exposed to like-charged lysozyme during the processes of heating and cooling, in contrast to the irreversible interactions between bAgNPs and oppositely charged alpha lactalbumin (ALact). Our discrete molecular dynamics (DMD) simulations offered a new molecular insight into the differential structure, dynamics and thermodynamics of bAgNPs binding with the two protein homologs and further revealed the different roles of the capping agents of citrate and BPEI in NP-protein interactions. This study facilitates our understanding of the transformation of nanomaterials in living systems, whose implications range from the field study of nanotoxicology to nanomaterials synthesis, nanobiotechnology and nanomedicine.

Remobilisation of silver and silver sulphide nanoparticles in soils

Manufactured nanoparticles (NPs) present in consumer products could enter soils through re-use of biosolids. Among these NPs are those based on silver (Ag), which are found sulphidised (e.g. silver sulphide, Ag2S) in biosolids. Herein, our aim was to examine the release of retained Ag(0) and Ag2S NPs in soils and biosolids as facilitated by environmentally and agriculturally relevant ligands. Under natural soil conditions, exemplified by potassium nitrate and humic acid experiments, release of Ag retained in soil was limited. The highest total Ag release was facilitated by ligands that simulated root exudates (citrate) or fertilisers (thiosulphate). Released Ag was predominantly present in the colloidal phase (>3 kDa-< 0.45 μm); intact NPs only identified in Ag2S-NP extracts. For biosolids containing nanoparticulate-Ag-S, release was also enhanced by thiosulphate, though mostly as colloidal-Ag - not intact NPs. These results suggest that exposure to NPs as a result of its release from soils or biosolids will be low.

Dermal absorption and short-term biological impact in hairless mice from sunscreens containing zinc oxide nano- or larger particles

Previous studies have shown no, or very limited, skin penetration of metal oxide nanoparticles following topical application of sunscreens, yet concerns remain about their safety compared to larger particles. Here, we assessed the comparative dermal absorption of a traceable form of Zn ((68)Zn) from (68)ZnO nano-sized and larger particles in sunscreens. Sunscreens were applied to the backs of virgin or pregnant hairless mice over four days. Control groups received topical applications of the sunscreen formulation containing no ZnO particles, or no treatment. Major organs were assessed for changes in (68)Zn/(64)Zn ratios, (68)Zn tracer and total Zn concentrations. Short-term biological impact was assessed by measuring levels of serum amyloid A in blood, and by performing whole-genome transcriptional profiling on livers from each group. Increased concentrations of (68)Zn tracer were detected in internal organs of mice receiving topical applications of (68)ZnO (nano-sized and larger particles), as well as in fetal livers from treated dams, compared with controls. Furthermore, concentrations of (68)Zn in organs of virgin mice treated with sunscreen containing (68)ZnO nanoparticles were found to be significantly higher than in mice treated with sunscreen containing larger (68)ZnO particles. However, no ZnO-mediated change in total Zn concentration in any of the major organs was observed. Thus, despite (68)Zn absorption, which may have been in the form of soluble (68)Zn species or (68)ZnO particles (not known), Zn homeostasis was largely maintained, and the presence of ZnO particles in sunscreen did not elicit an adverse biological response in the mice following short-term topical applications.

Fate and lability of silver in soils: effect of ageing

The fate and lability of added soluble Ag in soils over time was examined by measurement of labile metal (E-value) by isotopic dilution using the (110m)Ag radioactive isotope and the solid-phase speciation of Ag by X-ray absorption near edge structure (XANES) spectroscopy. After two weeks of ageing the E-values for Ag decreased by 20-90% with a further decrease of 10-40% after six months. The overall decrease in labile Ag for all soils after the 6 month ageing period was 50-100%. The ageing was more rapid and pronounced in the alkaline soils. XANES results for Ag in soils indicated that for the majority of soils the added Ag(+) was reduced to metallic Ag over time, and associations with Fe-oxohydroxides and reduced S groups in organic matter also decreased Ag lability. Strong positive correlations were found between metallic Ag and non-labile Ag and between organic carbon and Ag bonded with S species.

The effect of soil properties on the toxicity of silver to the soil nitrification process

Silver (Ag) is being increasingly used in a range of consumer products, predominantly as an antimicrobial agent, leading to a higher likelihood of its release into the environment. The present study investigated the toxicity of Ag to the nitrification process in European and Australian soils in both leached and unleached conditions. Overall, leaching of soils was found to have a minimal effect on the final toxicity data, with an average leaching factor of approximately 1. Across the soils, the toxicity was found to vary by several orders of magnitude, with concentrations of Ag causing a 50% reduction in nitrification relative to the controls (EC50) ranging from 0.43 mg Ag/kg to >640 mg Ag/kg. Interestingly, the dose-response relationships in most of the soils showed significant stimulation in nitrification at low Ag concentrations (i.e., hormesis), which in some cases produced responses up to double that observed in the controls. Soil pH and organic carbon were the properties found to have the greatest influence on the variations in toxicity thresholds across the soils, and significant relationships were developed that accounted for approximately 90% of the variability in the data. The toxicity relationships developed from the present study will assist in future assessment of potential Ag risks and enable the site-specific prediction of Ag toxicity.

Copper isotope fractionation during equilibration with natural and synthetic ligands

As copper (Cu) stable isotopes emerge as a tool for tracing Cu biogeochemical cycling, an understanding of how Cu isotopes fractionate during complexation with soluble organic ligands in natural waters and soil solutions is required. A Donnan dialysis technique was employed to assess the isotopic fractionation of Cu during complexation with the soluble synthetic ligands ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), iminodiacetic acid (IDA) and desferrioxamine B (DFOB), as well as with Suwannee River fulvic acid (SRFA). The results indicated enrichment of the heavy isotope ((65)Cu) in the complexes, with Δ(65)Cu complex-free values ranging from +0.14 to +0.84‰. A strong linear correlation was found between the logarithms of the stability constants of the Cu complexes and the magnitudes of isotopic fractionation. These results show that complexation of Cu by organic ligands can affect the isotopic signature of the free Cu ion. This free Cu is considered the most bioavailable species, and hence, our results highlight the importance of understanding fractionation processes in the uptake medium when using Cu isotopes to study the uptake mechanisms of organisms. These data contribute a vital piece to the emerging picture of Cu isotope cycling in the natural environment, as organic complexation plays a key role in the Cu cycle.

Behaviour of fullerenes (C60) in the terrestrial environment: potential release from biosolids-amended soils

Owing of their wide-range of commercial applications, fullerene (C60) nanoparticles, are likely to reach environments through the application of treated sludge (biosolids) from wastewater treatment plants to soils. We examined the release behaviour of C60 from contaminated biosolids added to soils with varying physicochemical characteristics. Incubation studies were carried out in the dark for up to 24 weeks, by adding biosolids spiked (1.5mg/kg) with three forms of C60 (suspended in water, in humic acid, and precipitated/particulate) to six contrasting soils. Leaching of different biosolids+soil systems showed that only small fractions of C60 (<5% of applied amount) were released, depending on incubation time and soil properties (particularly dissolved organic carbon content). Release of C60 from unamended soils was greater (at least twice as much) than from biosolids-amended soils. The form of C60 used to spike the biosolids had no significant effect on the release of C60 from the different systems. Contact time of C60 in these systems only slightly increased the apparent release up to 8 weeks, followed by a decrease to 24 weeks. Mass balance analysis at the completion of the experiment revealed that 20-60% of the initial C60 applied could not be accounted for in these systems; the reasons for this are discussed.

Transport of silver nanoparticles in saturated columns of natural soils

With industrialization and urbanization soils are increasingly exposed to engineered nanoparticles (ENP), yet knowledge regarding the transport of ENP in natural soils is lacking, a process that was examined further in the current study. Saturated columns of 11 natural soils with varying physical and chemical properties were spiked with two pore volumes of a solution containing 1.7 mg Ag L(-1) as polyvinylpyrrolidone (PVP)-coated silver nanoparticles (AgNP) (40 nm actual diameter) and eluted at a constant flow rate of 1 ml min(-1). Breakthrough of Ag was analyzed using filtration theory and a HYDRUS-1D transport model that incorporated two-site kinetic attachment-detachment. Separate kinetic batch studies suggested fast heteroaggregation between negatively charged AgNP and positively charged sites on the common soil colloids maghemite or montmorillonite. The concentration of such sites in the soil correlates positively with the oxalate-extractable aluminum concentration of the soils, a measure that correlated positively with collision efficiency. This correlation thus suggested favorable deposition of AgNP and/or enhanced straining following heteroaggregation of AgNP with mobile soils colloids. Occurrence of heteroaggregation was supported by the batch studies, enhanced size-exclusion in the soil with the highest porosity, and reversible attachment-detachment predicted from HYDRUS modeling, whereas straining and favorable deposition were suggested by irreversible attachment. Our study suggests that under similar experimental conditions, PVP-coated AgNP would rapidly interact with natural colloids in soils significantly reducing their mobility and hence potential risk from off-site transport.

Characterization and ecological risk assessment of nanoparticulate CeO2 as a diesel fuel catalyst

Nanoparticulate cerium dioxide (nano-CeO2 ), when combusted as an additive to diesel fuel, was transformed from 6 nm to 14 nm sizes into particles near 43 nm, with no obvious change in the unit cell dimensions or crystalline form. Cerium sulfate, if formed during combustion, was below detection limits. Ceria nanoparticles were agglomerated within the soot matrix, with a mean aerodynamic diameter near 100 nm. The dissolution of cerium from the dried ceria catalyst in synthetic soft water was extremely small (<0.0006% or <0.2 µg Ce/L), with particles being highly agglomerated (<450 nm). Agglomeration was reduced in the presence of humic acid. In the combusted samples, soot was dominant, and the solubility of cerium in soft water showed an almost 100-fold increase in the <1 nm fraction compared to that before combustion. It appeared that the nano-CeO2 remained agglomerated within the soot matrix and would not be present as dispersed nanoparticles in aquatic or soil environments. Despite the increased dissolution, the solubility was not sufficient for the combusted ceria to represent a risk in aquatic ecosystems. The predicted environmental concentrations were still orders of magnitude below the predicted no effects concentration of near 1 mg/L. In the soil environment, any cerium released from soot materials would interact with natural colloids, decreasing cerium concentrations in soil solutions and further minimizing the potential risk to soil organisms.

Copper speciation and isotopic fractionation in plants: uptake and translocation mechanisms

The fractionation of stable copper (Cu) isotopes during uptake into plant roots and translocation to shoots can provide information on Cu acquisition mechanisms. Isotope fractionation ((65) Cu/(63) Cu) and intact tissue speciation techniques (X-ray absorption spectroscopy, XAS) were used to examine the uptake, translocation and speciation of Cu in strategy I (tomato-Solanum lycopersicum) and strategy II (oat-Avena sativa) plant species. Plants were grown in controlled solution cultures, under varied iron (Fe) conditions, to test whether the stimulation of Fe-acquiring mechanisms can affect Cu uptake in plants. Isotopically light Cu was preferentially incorporated into tomatoes (Δ(65) Cu(whole plant-solution ) = c. -1‰), whereas oats showed minimal isotopic fractionation, with no effect of Fe supply in either species. The heavier isotope was preferentially translocated to shoots in tomato, whereas oat plants showed no significant fractionation during translocation. The majority of Cu in the roots and leaves of both species existed as sulfur-coordinated Cu(I) species resembling glutathione/cysteine-rich proteins. The presence of isotopically light Cu in tomatoes is attributed to a reductive uptake mechanism, and the isotopic shifts within various tissues are attributed to redox cycling during translocation. The lack of isotopic discrimination in oat plants suggests that Cu uptake and translocation are not redox selective.

Fate and risks of nanomaterials in aquatic and terrestrial environments

Over the last decade, nanoparticles have been used more frequently in industrial applications and in consumer and medical products, and these applications of nanoparticles will likely continue to increase. Concerns about the environmental fate and effects of these materials have stimulated studies to predict environmental concentrations in air, water, and soils and to determine threshold concentrations for their ecotoxicological effects on aquatic or terrestrial biota. Nanoparticles can be added to soils directly in fertilizers orplant protection products or indirectly through application to land or wastewater treatment products such as sludges or biosolids. Nanoparticles may enter aquatic systems directly through industrial discharges or from disposal of wastewater treatment effluents or indirectly through surface runoff from soils. Researchers have used laboratory experiments to begin to understand the effects of nanoparticles on waters and soils, and this Account reviews that research and the translation of those results to natural conditions. In the environment, nanoparticles can undergo a number of potential transformations that depend on the properties both of the nanoparticle and of the receiving medium. These transformations largely involve chemical and physical processes, but they can involve biodegradation of surface coatings used to stabilize many nanomaterial formulations. The toxicity of nanomaterials to algae involves adsorption to cell surfaces and disruption to membrane transport. Higher organisms can directly ingest nanoparticles, and within the food web, both aquatic and terrestrial organisms can accumulate nanoparticles. The dissolution of nanoparticles may release potentially toxic components into the environment. Aggregation with other nanoparticles (homoaggregation) or with natural mineral and organic colloids (heteroaggregation) will dramatically change their fate and potential toxicity in the environment. Soluble natural organic matter may interact with nanoparticles to change surface charge and mobility and affect the interactions of those nanoparticles with biota. Ultimately, aquatic nanomaterials accumulate in bottom sediments, facilitated in natural systems by heteroaggregation. Homoaggregates of nanoparticles sediment more slowly. Nanomaterials from urban, medical, and industrial sources may undergo significant transformations during wastewater treatment processes. For example, sulfidation of silver nanoparticles in wastewater treatment systems converts most of the nanoparticles to silver sulfides (Ag₂S). Aggregation of the nanomaterials with other mineral and organic components of the wastewater often results in most of the nanomaterial being associated with other solids rather than remaining as dispersed nanosized suspensions. Risk assessments for nanomaterial releases to the environment are still in their infancy, and reliable measurements of nanomaterials at environmental concentrations remain challenging. Predicted environmental concentrations based on current usage are low but are expected to increase as use increases. At this early stage, comparisons of estimated exposure data with known toxicity data indicate that the predicted environmental concentrations are orders of magnitude below those known to have environmental effects on biota. As more toxicity data are generated under environmentally-relevant conditions, risk assessments for nanomaterials will improve to produce accurate assessments that assure environmental safety.

Transformation of PVP coated silver nanoparticles in a simulated wastewater treatment process and the effect on microbial communities

Background

Manufactured silver nanoparticles (AgNPs) are one of the most commonly used nanomaterials in consumer goods and consequently their concentrations in wastewater and hence wastewater treatment plants are predicted to increase. We investigated the fate of AgNPs in sludge that was subjected to aerobic and anaerobic treatment and the impact of AgNPs on microbial processes and communities. The initial identification of AgNPs in sludge was carried out using transmission electron microscopy (TEM) with energy dispersive X-ray (EDX) analysis. The solid phase speciation of silver in sludge and wastewater influent was then examined using X-ray absorption spectroscopy (XAS). The effects of transformed AgNPs (mainly Ag-S phases) on nitrification, wastewater microbial populations and, for the first time, methanogenesis was investigated.

Results

Sequencing batch reactor experiments and anaerobic batch tests, both demonstrated that nitrification rate and methane production were not affected by the addition of AgNPs [at 2.5 mg Ag L^-1 (4.9 g L^-1 total suspended solids, TSS) and 183.6 mg Ag kg ^-1 (2.9 g kg^-1 total solids, TS), respectively].

The low toxicity is most likely due to AgNP sulfidation. XAS analysis showed that sulfur bonded Ag was the dominant Ag species in both aerobic (activated sludge) and anaerobic sludge. In AgNP and AgNO₃ spiked aerobic sludge, metallic Ag was detected (~15%). However, after anaerobic digestion, Ag(0) was not detected by XAS analysis. Dominant wastewater microbial populations were not affected by AgNPs as determined by DNA extraction and pyrotag sequencing. However, there was a shift in niche populations in both aerobic and anaerobic sludge, with a shift in AgNP treated sludge compared with controls. This is the first time that the impact of transformed AgNPs (mainly Ag-S phases) on anaerobic digestion has been reported.

Conclusions

Silver NPs were transformed to Ag-S phases during activated sludge treatment (prior to anaerobic digestion). Transformed AgNPs, at predicted future Ag wastewater concentrations, did not affect nitrification or methanogenesis. Consequently, AgNPs are very unlikely to affect the efficient functioning of wastewater treatment plants. However, AgNPs may negatively affect sub-dominant wastewater microbial communities.

Aging effects on molybdate lability in soils

Aging reactions in soils can influence the lability and hence bioavailability of added metals in soils through their removal from labile pools into pools from which desorption is slow (non-labile pools). The aims of this study were to examine the effect of aging reactions on the lability of soluble molybdate (MoO(4)(2-)) added into soils with varying physical and chemical properties and develop models to predict changes in the labile pool of MoO(4)(2-) in soils with incubation time. Soils were spiked with soluble MoO(4)(2-) at quantities sufficient to inhibit barley root growth by 10% (EC(10)) or 90% (EC(90)) and incubated for up to 18 months. The labile pool of MoO(4)(2-) (E value) was observed to decrease in soils with incubation time, particularly in soils with high clay content. A strong relationship was observed between measures of MoO(4)(2-) lability in soils determined using E and L value techniques (R(2)=0.98) suggesting E values provided a good measure of the potential plant available pool of MoO(4)(2-) in soils. A regression model was developed that indicates clay content and incubation time were the most important factors affecting the labile pool of MoO(4)(2-) in soils with time after addition (R(2)=0.70-0.75). The aging model developed suggests soluble MoO(4)(2-) will be removed into non-labile pools more rapidly with time in neutral to alkaline clay soils than in acidic sandy soils. Labile MoO(4)(2-) concentrations in molybdenum (Mo) contaminated soils was found to be <10% of the total Mo concentrations in soils.

Selenate-enriched urea granules are a highly effective fertilizer for selenium biofortification of paddy rice grain

This study examined the effects of applied selenium (Se) species, time of application, method of application, and soil water management regimen on the accumulation of Se in rice plants. Plants were grown to maturity in a temperature- and humidity-controlled growth chamber using three water management methods: field capacity (FC), submerged until harvest, and submerged and drained 2 weeks before harvest. Two Se species, selenate (SeO4(2-)) and selenite (SeO3(2-)), were applied at a rate equivalent to 30 g ha(-1). Four application methods were employed as follows: (i) Se applied at soil preparation, (ii) Se-enriched urea granules applied to floodwater at heading; (iii) foliar Se applied at heading; and (iv) fluid fertilizer Se applied to soil or floodwater at heading. Total Se concentrations in rice grains, husks, leaves, culms, and roots were measured, as well as Se speciation in grains from the Se-enriched urea granule treatment. Highest Se concentrations in the grain occurred with SeO4(2-) and with fertilizer applied at heading stage; SeO4(2-)-enriched urea granules applied at heading increased grain Se concentrations 5-6-fold (by 450-600 μg kg(-1)) compared to the control (no fertilizer Se applied) in all water treatments. Under paddy conditions other Se fertilization strategies were much less effective. Drainage before harvesting caused Se to accumulate in/on rice roots, possibly through adsorption onto iron plaque on roots. Rice grains contained Se mainly in the organic form as selenomethionine (SeM), which comprised >90% of the total grain Se in treatments fertilized with SeO4(2-)-enriched urea granules. The results of this study clearly show that of the fertilizer strategies tested biofortification of Se in rice grains can best be achieved in lowland rice by broadcast application of SeO4(2-)-enriched urea granules to floodwater at heading stage.

Dissolution kinetics of macronutrient fertilizers coated with manufactured zinc oxide nanoparticles

The solubility of Zn in Zn fertilizers plays an important role in the agronomic effectiveness of the fertilizer. On the basis of thermodynamics, zinc oxide (ZnO) nanoparticles (NPs) should dissolve faster and to a greater extent than bulk ZnO particles (equivalent spherical diameter >100 nm). These novel solubility features of ZnO NPs might be exploited to improve the efficiency of Zn fertilizers. In this study, we compared the Zn solubility and dissolution kinetics of ZnO nanoparticles and bulk ZnO particles coated onto two selected granular macronutrient fertilizers, urea and monoammonium phosphate (MAP). The main Zn species on coated MAP and urea granules were zinc ammonium phosphate and ZnO, respectively. Coated MAP granules showed greater Zn solubility and faster dissolution rates in sand columns compared to coated urea granules, which may be related to pH differences in the solution surrounding the fertilizer granules. The kinetics of Zn dissolution was not affected by the size of the ZnO particles applied for coating of either fertilizer type, possibly because solubility was controlled by formation of the same compounds irrespective of the size of the original ZnO particles used for coating.

Cobalt distribution and speciation: effect of aging, intermittent submergence, in situ rice roots

The speciation and distribution of Co in soils is poorly understood. This study was conducted using x-ray absorption spectroscopy (XAS) techniques to examine the influence of soluble cobalt in the +2 oxidation state (Co[II]) aging, submergence-dried cycling, and the presence of in vivo rice roots on the speciation and distribution of added Co(II) in soils. In the aging and submerged-dried cycling studies, Co was found to be associated with Mn oxide fraction (23 to 100% of total Co) and Fe oxide fractions (0 to 77% of total Co) of the soils as either Co(II) species or a mixed Co(II), and Co in the +3 oxidation state (Co[III]) species. The surface speciation of Co in the Mn oxide fraction suggests an innersphere complex was present and the speciation of Co in the Fe oxide fraction was an innersphere surface complex. The in vivo root box experiments showed similar Co speciation in the Mn oxide fraction (13 to 76% of total Co) as the aging and submerged-dried cycling studies. However, the Fe oxide fraction of the soil was unimportant in Co retention. A significant amount (24 to 87% of total Co) of the Co in root box treatments was identified as a Co precipitate. The importance of this finding is that in the presence of rice roots, the Co is redistributed to a Co precipitate. This work confirmed earlier macroscopic work that Mn oxides are important in the sequestration of Co in soils and the influence of roots needs to be taken into account when addressing Co speciation. The information gained from this study will be used to improve models to predict the lability and hence the availability of Co in terrestrial environments.

Solubility and batch retention of CeO2 nanoparticles in soils

There is a paucity of information on the environmental fate of cerium oxide nanoparticles (CeO2 NPs) for terrestrial systems that may be exposed to CeO2 NPs by the application of biosolids derived from wastewater treatment systems. Using ultrafiltration (UF), dissolution, and nonequilibrium retention (Kr) values of citrate-coated (8 nm diameter) CeO2 NPs and partitioning (Kd) values of dissolved Ce(III) and Ce(IV) were obtained in suspensions of 16 soils with a diversity of physicochemical properties. Dissolution of CeO2 NPs studied in solutions was only significant at pH 4 and was less than 3.1%, whereas no dissolved Ce was detected in soils spiked with CeO2 NPs. Kr values of CeO2 NP were low (median Kr=9.6 L kg(-1)) relative to Kd values of dissolved CeIII and CeIV (median Kd=3763 and 1808 L kg(-1), respectively), suggesting low CeO2 NP retention in soils. Surface adsorption of phosphate to CeO2 NP caused a negative zeta potential, which may explain the negative correlation of log Kr values with dissolved phosphate concentrations and the significant reduction of Kr values upon addition of phosphate to soils. The positive correlation of Kr values with clay content suggested heterocoagulation of CeO2 NPs with natural colloids in soils. Co-addition of CeO2 NPs with biosolids, on the other hand, did not affect retention.

Cadmium solubility in paddy soils: effects of soil oxidation, metal sulfides and competitive ions

Cadmium (Cd) is a non-essential element for human nutrition and is an agricultural soil contaminant. Cadmium solubility in paddy soils affects Cd accumulation in the grain of rice. This is a human health risk, exacerbated by the fact that rice grains are deficient in iron (Fe) and zinc (Zn) for human nutrition. To find ways of limiting this potential risk, we investigated factors influencing Cd solubility relative to Fe and Zn during pre-harvest drainage of paddy soils, in which soil oxidation is accompanied by the grain-filling stage of rice growth. This was simulated in temperature-controlled "reaction cell" experiments by first excluding oxygen to incubate soil suspensions anaerobically, then inducing aerobic conditions. In treatments without sulfur addition, the ratios of Cd:Fe and Cd:Zn in solution increased during the aerobic phase while Cd concentrations were unaffected and the Fe and Zn concentrations decreased. However, in treatments with added sulfur (as sulfate), up to 34 % of sulfur (S) was precipitated as sulfide minerals during the anaerobic phase and the Cd:Fe and Cd:Zn ratios in solution during the aerobic phase were lower than for treatments without S addition. When S was added, Cd solubility decreased whereas Fe and Zn were unaffected. When soil was spiked with Zn the Cd:Zn ratio was lower in solution during the aerobic phase, due to higher Zn concentrations. Decreased Cd:Fe and Cd:Zn ratios during the grain filling stage could potentially limit Cd enrichment in paddy rice grain due to competitive ion effects for root uptake.

Copper lability in soils subjected to intermittent submergence

Reducing conditions in soils can have significant influences on the availability of nutrient and toxic metals, through their remobilization, their release through reductive dissolution of oxide phases, and from the formation of precipitates. In the literature, contrasting results are reported on the effects of temporary waterlogging conditions on the availability of metals. In the present study, changes in the "labile" or "potentially available" pool of copper (Cu) in soils as a consequence of up to three intermittent soil submergence cycles was investigated using isotopic dilution. The soils (an Oxisol and an Inceprisol) selected were amended in the field with both biosolids-Cu and salt-Cu. Intermittent soil submergence was found to have a significant effect on the lability of Cu in soils, with E(total) values generally increasing in all the treatments with the different submergence cycles, the highest lability of Cu observed in the Cu-salt treatment. The presence of nonexchangeable colloidal forms of Cu, influenced by treatments and submergence cycles, was also reported.

Influences of soil properties and leaching on copper toxicity to barley root elongation

The relationships developed between soil properties and phytotoxicity threshold values for copper require validation in a wide range of soils with different properties and climate characteristics before they can be applied for regulatory purposes in countries throughout the world. Seventeen soils, which are representative of the major soil types and properties in China, were spiked with Cu chloride. A subset of the Cu-spiked soils was leached with artificial rain water to compare toxicity with that in unleached soils. Barley root elongation tests were performed under controlled environmental conditions. The concentrations of added Cu causing a 50% inhibitory effect (EC50) ranged from 67 to 1,129 mg/kg in unleached soils and from 88 to 1,255 mg/kg in leached soil. Compared with the unleached toxicity thresholds, the leached EC10 (10% inhibition) and EC50 were higher by an average of 1.43- and 1.15-fold, respectively. Soil leaching significantly (p <or= 0.05) decreased the toxicity of Cu in approximately 35% of the soils. In this study, no single soil property was found to explain over 35% of the variance in (log transformed) EC50. However, stepwise multiple regressions using soil pH, organic carbon (OC) content, and effective cation exchange capacity (eCEC) were found to explain over 80% of the variance in Cu toxicity across soils. The model developed for Chinese soils based on these factors was found to predict significantly (r(2), 0.90) the phytotoxicity of Cu in European soils. These quantitative relationships between Cu toxicity and soil properties are helpful for developing soil-specific guidance on Cu toxicity thresholds.

Aging effects on cobalt availability in soils

Aging processes in soils can significantly affect the potential biological availability of introduced metals via incorporation into crystal lattices, diffusion into micropores, or formation of metal precipitates on the surfaces of soil minerals. Over time, metals in contact with the soil solid phase are less freely exchangeable with the soil solution and, hence, less available to soil biota. In the present study, the effects of aging on the fate and behavior of added divalent cobalt (Co2+) in a range of soils with varying physicochemical characteristics was assessed using isotope-exchange techniques, chemical extraction, and plant growth. Following addition to soil, the Co2+ salt rapidly partitioned to the soil solid phase. Particularly in soils with neutral to alkaline pH, a large percentage of the surface-bound Co was fixed in forms no longer in equilibrium with soil solution cobalt through aging reactions. Using techniques commonly applied to estimate metal bioavailability in soil, the lability (E values), plant availability (L values), and extractability of added Co2+ salts with the mild chemical extractants calcium chloride (CaCl2) and ammonium nitrate (NH4NO3) were observed to markedly decrease with time, particularly in soils with high pH or those containing appreciable quantities of iron/ manganese oxyhydroxide minerals. Results indicated rapid partitioning of added Co2+ into isotopically nonexchangeable pools, with more than 60% of the aging occurring within 15 d in most soils. Soil pH was the primary factor controlling the rate of cobalt aging and extent of exchangeability in the soils examined. Understanding the influence of long-term aging on cobalt availability in soils is necessary to accurately assess the potential risk associated with cobalt contamination of soil environments.

A predictive model of the effects of aging on cobalt fate and behavior in soil

Metal toxicity to terrestrial organisms is influenced by a number of factors including the organisms affected and ecotoxicological end points, soil properties, aging processes, and metal speciation. The toxicity of metals added to soils can change over time through aging processes, which may reduce availability of metals via diffusion into micropores, incorporation into crystal lattices, or Ostwald ripening of precipitates. Metals which have been in contact with soil for longer periods are less able to exchange with the soil solution, rendering them less available to soil biota. The objective of this work was to investigate and model the effects of long-term aging on cobalt(II) (Co2+) (isotopic) exchangeability and potential bioavailability in a wide range of soils, as this is the form of Co commonly used in ecotoxicological investigations. After addition to soil, added soluble Co(II) rapidly partitioned to the soil solid phase, and in alkaline soils a large percentage of this surface-bound Co was fixed through aging reactions in forms that were no longer in equilibrium with the soil solution Co. Analyses indicated that soil pH and incubation time were the most important factors affecting Co(II) aging. The rate and extent of aging of added Co(II) could be accurately predicted across all soils using a semi-mechanistic model that suggested Co was fixed through reactions that we postulate were related to surface oxidation/precipitation/nucleation as driven by hydrolysis reactions at the surface of soil minerals.

Selenium speciation and bioavailability in biofortified products using species-unspecific isotope dilution and reverse phase ion pairing-inductively coupled plasma-mass spectrometry

In some regions of the world, where the bioavailability of selenium (Se) in soil is low and/or declining (e.g., due to use of high-sulfur fertilizers), there is increased risk of adverse affects on animals and human health. In recent years, increased research attention has focused on understanding the relationships between Se contents in foods and supplements and their nutritional benefits for animal and humans. The objective of this study was to use a species-unspecific isotope dilution and reverse phase ion pairing-inductively coupled plasma-mass spectrometry techniques for the identification and quantification of Se species in biofortified grains (i.e., wheat and triticale), flour, and wheat biscuits. The information on Se species was used to gain an understanding of the bioavailability of Se in biofortified and process-fortified wheat biscuits used in a clinical trail. The major Se species identified in biofortified and process-fortified samples were selenomethionine (76-85%) and selenomethionine selenoxide (51-60%), respectively. Total plasma Se concentrations in the biofortified Se exposure group were found to increase throughout the 6 month trial period (mean=122 microg L(-1) at 0 months to 194 microg L(-1) at 6 months). In contrast, the trial group exposed to process-fortified Se biscuits showed little increase in mean total Se plasma concentrations until 4 months of exposure (mean=122 microg L(-1) at 0 months to 140 microg L(-1) at 4 months) that remained constant until the end of the trial period (mean=140 microg L(-1) at 4 months to 138 microg L(-1) at 6 months). The difference in total Se plasma concentrations may be due to the presence and bioavailability of different Se species in biofortified and process-fortified biscuits. An understanding of Se speciation in foods enables better understanding of pathways and their potential benefits for animals and humans.