Simon C. Apte

Transformations of Nanomaterials in the Environment

Increasing use of engineered nanomaterials with novel properties relative to their bulk counterparts has generated a need to define their behaviors and impacts in the environment. The high surface area to volume ratio of nanoparticles results in highly reactive and physiochemically dynamic materials in environmental media. Many transformations, e.g. reactions with biomacromolecules, redox reactions, aggregation, and dissolution, may occur in both environmental and biological systems. These transformations and others will alter the fate, transport, and toxicity of nanomaterials. The nature and extent of these transformations must be understood before significant progress can be made toward understanding the environmental risks posed by these materials.

The biotic ligand model: a historical overview

During recent years, the biotic ligand model (BLM) has been proposed as a tool to evaluate quantitatively the manner in which water chemistry affects the speciation and biological availability of metals in aquatic systems. This is an important consideration because it is the bioavailability and bioreactivity of metals that control their potential to cause adverse effects. The BLM approach has gained widespread interest amongst the scientific, regulated and regulatory communities because of its potential for use in developing water quality criteria (WQC) and in performing aquatic risk assessments for metals. Specifically, the BLM does this in a way that considers the important influences of site-specific water quality. This journal issue includes papers that describe recent advances with regard to the development of the BLM approach. Here, the current status of the BLM development effort is described in the context of the longer-term history of advances in the understanding of metal interactions in the environment upon which the BLM is based. Early developments in the aquatic chemistry of metals, the physiology of aquatic organisms and aquatic toxicology are reviewed first, and the degree to which each of these disciplines influenced the development of water quality regulations is discussed. The early scientific advances that took place in each of these fields were not well coordinated, making it difficult for regulatory authorities to take full advantage of the potential utility of what had been learned. However, this has now changed, with the BLM serving as a useful interface amongst these scientific disciplines, and within the regulatory arena as well. The more recent events that have led to the present situation are reviewed, and consideration is given to some of the future needs and developments related to the BLM that are envisioned. The research results that are described in the papers found in this journal issue represent a distinct milestone in the ongoing evolution of the BLM approach and, more generally, of approaches to performing ecological assessments for metals in aquatic systems. These papers also establish a benchmark to which future scientific and regulatory developments can be compared. Finally, they demonstrate the importance and usefulness of the concept of bioavailability and of evaluative tools such as the BLM.

Bioaccumulation and biomagnification of mercury in Lake Murray, Papua New Guinea

The bioaccumulation of mercury in the food webs incorporating the major piscivorous fish species of Lake Murray, Papua New Guinea, has been characterised. Methylmercury concentrations increased with trophic level and the proportion of total mercury present as methylmercury increased from <1% in plants to 94% in piscivorous fish. Methylmercury bioaccumulation factors (BAFs) were similar to those found in temperate environments, with a typical increase of 1 log unit between planktivore and piscivore trophic levels. The greatest bioaccumulation of methylmercury occurred between seston and the water column (log BAF of 5.36). The bioaccumulation of mercury to levels of regula tory concern by the lake’s piscivores was attributable to the biomagnification power of the plankton-based food chain comprising four trophic levels (phytoplankton, zooplankton, planktivore, piscivore) rather than any elevated concentra tions of mercury in waters or sediments. The methylmercury concentrations of individual piscivores were positively correlated with both trophic position, as indicated by d15N measurements, and fish size. Stable-isotope measurements were used to identify fish species where dietary changes occurring with age significantly augmented age-related bioaccumulation of mercury. Résumé: La bioaccumulation du mercure a été étudiée dans le réseau alimentaire reliant les principales espèces de poissons piscivores du lac Murray en Papouasie-Nouvelle-Guinée. Les concentrations de méthylmercure croissent avec le niveau trophique et le pourcentage du mercure total présent sous la forme méthylée augmente de <1% chez les plantes à 94% chez les poissons piscivores. Les facteurs de bioaccumalation du méthylmercure (BAFs) sont semblables à ceux que l’on retrouve dans les milieux tempérés et i l y a typiquement une augmentation d’une unité logarithmique entre les niveaux trophiques planctonophage et piscivore. La bioaccumulation la plus considérable a lieu entre le seston et la colonne d’eau (log BAF de 5,36). La bioaccumulation du mercure à des niveaux inquiétants (d’après les normes actuelles) par les piscivores du lac est causée par le pouvoir de bioamplification de la chaîne alimentaire à base de plancton qui couvre quatre niveaux (phytoplanctonique, zooplanctonique, planctonophage, piscivore) plutôt qu’à une augmentation des concentrations de mercure dans les eaux ou dans les sédiments. Les concentrations de méthylmercure chez les différents piscivores sont en corrélation positive à la fois avec leur position trophique, telle que déterminée par les mesures de d15N, et avec leur taille. Les analyses à l’aide d’isotopes stables ont permis de reconnaître les espèces de poissons chez lesquelles des changements de régime alimentaire au cours de la vie augmentent significativement la bioaccumulation du mercure reliée à l’âge. [Traduit par la Rédaction] Bowles et al. 897

Physico-chemical behaviour and algal toxicity of nanoparticulate CeO2 in freshwater

In assessing the risks posed by nanomaterials in the environment, the overriding research challenges are to determine if nanomaterials are more toxic than the bulk forms of the same material, and the extent to which toxicity is governed by particle size and reactivity. In this study, the toxicity of nanoparticulate CeO2 (nominally 10-20 nm) to the freshwater alga Pseudokirchneriella subcapitata was compared to the same material at the micron size (nominally <5 µm). Growth inhibition experiments revealed inhibitory concentration values, giving 50% reduction in algal growth rate after 72 h (IC50), of 10.3 ± 1.7 and 66 ± 22 mg L −1 for the nanoparticles and bulk materials respectively. Cells exposed to CeO2 particles were permeable to the DNA-binding dye SYTOX ® Green in a concentration-dependent manner indicating damage to the cell membrane. Screening assays to assess the oxidative activity of the particles showed that the light illumination conditions used during standard assays are sufficient to stimulate photocatalytic activity of CeO2 particles, causing the generation of hydroxyl radicals and peroxidation of a model plant fatty acid. No oxidative activity or lipid peroxidation was observed in the dark. These findings indicate that inhibitory mode of action of CeO2 to P. subcapitata is mediated by a cell-particle interaction causing membrane damage. The effect is most likely photochemically induced and is enhanced for the nanoparticulate form of the CeO2.

Speciation and Bioavailability of Trace Metals in Water: Progress Since 1982

The advances in studies of trace metal speciation and bioavailability since Mark Florence’s 1982 review of the topic, published in Talanta, have been comprehensively reviewed. While the relative merits of kinetic and equilibrium approaches are still being determined, advances in the applications of stripping voltammetry, including the application of microelectrodes and an appreciation of detection windows in both CSV and ASV, have been matched by the introduction of new dynamic techniques including diffusive gradients in thin films (DGTs), permeation liquid membranes (PLMs), and improved applications of chelating resins. There have also been improvements in equilibrium techniques such as ion-selective electrodes and Donnan dialysis. The ability of geochemical speciation models to predict metal complexation by natural organic matter has greatly improved, yet the models still require validation against field measurements. More reliable and relevant bioassays have been developed using sensitive species such as algae and bacteria, and improved protocols are eliminating uncertainties particularly due to problems with high cell densities, and are allowing more useful comparisons with chemically estimated bioavailability. While the free-ion activity model has provided an improved interpretation of the relative toxicities observed with different metal species, its extension to the biotic ligand model is leading to better predictions of acute effects at least on higher organisms. The extension of such approaches to studies of chronic effects at ‘natural’ concentrations using unicellular organisms remains a challenge, as does the evaluation of whether such approaches are simplified limiting cases of a more dynamic natural situation where chemical reactivity and rates of metal transport could be important.

Dissolved trace metal distributions in Port Jackson estuary (Sydney Harbour), Australia

Concentrations of dissolved metals (Cd, Cu, Ni, Mn and Zn) were determined for summer and winter, under low-flow conditions in Port Jackson, a microtidal, well-mixed estuary in south-east Australia. Mean concentrations of Cd (0.04+/-0.02 microg/l), Ni (0.86+/-0.40 microg/l), Mn (20.0+/-25 microg/l) and Zn (6.47+/-2.0 microg/l) were below water quality guidelines. Concentrations of Cu (1.68+/-0.37 microg/l), however, slightly exceeded recommended values. Dissolved Ni and Mn behaved mostly conservatively, whereas Cd, Cu and Zn showed mid-estuarine maxima. Peaks in Cd, Cu and Zn concentrations were located in the upper estuary, independent of the salinity and suspended particulate matter loading, and were consistent with anthropogenic inputs of metals in the estuary. Concentrations of dissolved Cu were highest in summer, whereas concentrations of Cd, Ni and Mn were significantly lower in summer than winter (P< or =0.05). The increase in temperature and biological activity during summer explained the seasonal variation. The sequence of log K(d) values (20-30 salinity) was Mn>Zn>Cu>Ni. These results give unique information concerning the contemporaneous distribution of dissolved trace metals in the Port Jackson estuary and they provide a data set against which the long-term contamination may be assessed.

A microwave-assisted sequential extraction of water and dilute acid soluble arsenic species from marine plant and animal tissues

This paper describes the use of dilute nitric acid for the extraction and quantification of arsenic species. A number of extractants (e.g. water, 1.5M orthophosphoric acid, methanol-water and dilute nitric acid) were tested for the extraction of arsenic from marine biological samples, such as plants that have proved difficult to quantitatively extract. Dilute 2% (v/v) nitric acid was found to give the highest recoveries of arsenic overall and was chosen for further optimisation. The optimal extraction conditions for arsenic were 2% (v/v) HNO(3), 6 min(-1), 90 degrees C. Arsenic species were found to be stable under the optimised conditions with the exception of the arsenoriboses which degraded to a product eluting at the same retention time as glycerol arsenoribose. Good agreement was found between the 2% (v/v) HNO(3) extraction and the methanol-water extraction for the certified reference material DORM-2 (AB 17.1 and 16.2microg g(-1), respectively, and TETRA 0.27 and 0.25microg g(-1), respectively), which were in close agreement with the certified concentrations of AB 16.4+/-1.1microg g(-1) and TETRA 0.248+/-0.054microg g(-1). To preserve the integrity of arsenic species, a sequential extraction technique was developed where the previously methanol-water extracted pellet was further extracted with 2% (v/v) HNO(3) under the optimised conditions. Increases in arsenic recoveries between 13% and 36% were found and speciation of this faction revealed that only inorganic and simple methylated species were extracted.

Pore water sampling with sediment peepers

Abstract The use of in situ equilibrium dialysis samplers (peepers) for the collection of sediment pore waters for trace metal analysis is reviewed. Optimum peeper designs, construction and preparation procedures are described. Field deployment and sampling protocols are outlined with their utility illustrated by dissolved metal profiles obtained from field studies.

Geochemical cycling and speciation of copper in waters and sediments of Macquarie Harbour, Western Tasmania

The factors determining the concentration and speciation of copper in the waters and sediments of Macquarie Harbour, Tasmania were investigated. This harbour is the most extensively copper-contaminated estuarine water body in Australia owing to current and historical inputs of metal-rich waters and sediments from the nearby Mount Lyell copper mine. The dissolved copper concentrations in the harbour water column were highly variable (4–560l gl � 1 ) and displayed a north to south gradient, decreasing with distance from the King River, which carries the inputs from the mine. The most significant process affecting dissolved copper concentrations was the neutralisation of acidic river waters with seawater and the resulting coprecipitation with iron oxyhydroxide flocs. Approximately 60% of the riverine dissolved copper input was removed from solution by this process. Particulate copper concentrations in surficial benthic sediments were high in most regions of the harbour (typically 0.5–1 mg g � 1 ). In the north, sediments were dominated by fine, mine-derived material and showed uniform particulate copper concentrations with depth. Sediment acid-volatile sulphide concentrations were highest (11–142lmol g � 1 ) in the southern harbour and were barely detectable in the northern harbour region (<0.46lmol g � 1 ). A similar north–south gradient of sediment organic carbon concentrations was observed. Very high porewater concentrations of copper (up to 520l gl � 1 ) and iron (200 mg l � 1 ) were found at sites in the northern harbour. The high porewater copper concentrations are believed to result from the oxidation of porewater Fe(II), formation of amorphous iron oxyhydroxide and the associated pH-related dissolution of particulate copper. Calculations indicated a positive flux of dissolved copper from the sediments at sites in the northern harbour. However, in the southern harbour, the high acid volatile sulphide concentrations of the sediments meant that they acted as a sink for dissolved copper, resulting in low porewater copper concentrations (<1–10l gl � 1 ) and a significant copper flux from the overlying water to the sediment. The study illustrates the roles of iron redox chemistry, associated pH gradients, and acid volatile sulphide in controlling copper mobility in contaminated estuarine environments. 2003 Elsevier Science B.V. All rights reserved.

Dissolved metal concentrations in the Torres strait and Gulf of Papua

Dissolved copper, cadmium and nickel concentrations were accurately measured in surface water samples from the Torres Strait and the Gulf of Papua. The data indicated that there are significant inputs of dissolved metals to the region from the river systems that drain the mineralized areas of Papua New Guinea. The Purari River was identified as a major source of cadmium and nickel whereas the Fly River, which receives inputs from a large copper mine, was a major source of dissolved copper. Offshore, the concentrations of trace metals are close to background concentrations and were consistent with recent data for Australian coastal waters and the Pacific Ocean.