Abstract-The recent advances in nanotechnology and the corresponding increase in the use of nanomaterials in products in every sector of society have resulted in uncertainties regarding environmental impacts. The objectives of this review are to introduce the key aspects pertaining to nanomaterials in the environment and to discuss what is known concerning their fate, behavior, disposition, and toxicity, with a particular focus on those that make up manufactured nanomaterials. This review critiques existing nanomaterial research in freshwater, marine, and soil environments. It illustrates the paucity of existing research and demonstrates the need for additional research. Environmental scientists are encouraged to base this research on existing studies on colloidal behavior and toxicology. The need for standard reference and testing materials as well as methodology for suspension preparation and testing is also discussed.

Metal oxide nanoparticles are finding increasing application in various commercial products, leading to concerns for their environmental fate and potential toxicity. It is generally assumed that nanoparticles will persist as small particles in aquatic systems and that their bioavailability could be significantly greater than that of larger particles. The current study using nanoparticulate ZnO (ca. 30 nm) has shown that this is not always so. Particle characterization using transmission electron microscopy and dynamic light scattering techniques showed that particle aggregation is significant in a freshwater system, resulting in flocs ranging from several hundred nanometers to several microns. Chemical investigations using equilibrium dialysis demonstrated rapid dissolution of ZnO nanoparticles in a freshwater medium (pH 7.6), with a saturation solubility in the milligram per liter range, similar to that of bulk ZnO. Toxicity experiments using the freshwater alga Pseudokirchneriella subcapitata revealed comparable toxicity for nanoparticulate ZnO, bulk ZnO, and ZnCl2, with a 72-h IC50 value near 60 microg Zn/ L, attributable solely to dissolved zinc. Care therefore needs to be taken in toxicity testing in ascribing toxicity to nanoparticles per se when the effects may be related, at least in part, to simple solubility.

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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 a...

The Australian and New Zealand Guidelines for Fresh and Marine Water Quality are a key document in the Australian National Water Quality Management Strategy. These guidelines released in 2000 are currently being reviewed and updated. The revision is being co-ordinated by the Australian Department of Sustainability, Environment, Water, Population and Communities, while technical matters are dealt with by a series of Working Groups. The revision will be evolutionary in nature reflecting the latest scientific developments and a range of stakeholder desires. Key changes will be: changing the guidelines to an electronic format; increasing the types and sources of data that can be used; working collaboratively with industry to permit the use of commercial-in-confidence data; increasing the minimum data requirements; including a measure of the uncertainty of the trigger value; improving the software used to calculate trigger values; increasing the rigour of site-specific trigger values; improving the method for assessing the reliability of the trigger values; providing guidance of measures of toxicity and toxicological endpoints that may, in the near future, be appropriate for trigger value derivation. These changes will markedly improve the number and quality of the trigger values that can be derived and will increase end-users' ability to understand and implement the Guidelines in a scientifically rigorous manner.

The effects of the short-term resuspension of a contaminated anoxic estuarine sediment on solid-phase metal speciation have been studied. Preliminary experiments investigated the oxidation rates of model metal sulfide phases to provide mechanistic information for interpreting the observations on the natural sediment. FeS and MnS model phases were particularly labile and oxidized rapidly in aerated waters. In contrast, CdS, CuS, PbS, and ZnS model phases were kinetically stable over periods of several hours. The oxidation rate of free sulfide (HS -) was significantly slower than that of FeS and MnS. Upon sediment resuspension, the rapid decrease in acid volatile sulfide (AVS) could be accounted for by the oxidation of iron monosulfide phases. Over prolonged resuspension periods (>300 min), AVS decreased to values lower than the simultaneously extracted metals [SEM ) ∑Cd, Cu, Ni, Pb, Zn (1 M HCl extraction, 30 min)] concentration, indicating that a significant fraction of trace metal sulfide phases may be oxidized during resuspension events. During 8-h sediment resuspension experiments, SEM(Cu) increased from 0.1 to ca. 2 µmol/g while the SEM measured for the other metals remained constant. The increase in SEM(Cu) was shown to be an artifact of the AVS/SEM analytical procedure. Fe(OH) 3 , formed through the oxidation of FeS, dissolved upon acidification to produce Fe 3+ (aq), which subsequently oxidized acid-insoluble copper sulfide mineral phases in the sediment. The implications of these observations for natural systems and for the assessment of metal toxicity using AVS/SEM procedures are discussed.

The present review covers developments in studies of nanomaterials (NMs) in the environment since our much cited review in 2008. We discuss novel insights into fate and behavior, metrology, transformations, bioavailability, toxicity mechanisms, and environmental impacts, with a focus on terrestrial and aquatic systems. Overall, the findings were that: 1) despite substantial developments, critical gaps remain, in large part due to the lack of analytical, modeling, and field capabilities, and also due to the breadth and complexity of the area; 2) a key knowledge gap is the lack of data on environmental concentrations and dosimetry generally; 3) substantial evidence shows that there are nanospecific effects (different from the effects of both ions and larger particles) on the environment in terms of fate, bioavailability, and toxicity, but this is not consistent for all NMs, species, and relevant processes; 4) a paradigm is emerging that NMs are less toxic than equivalent dissolved materials but more toxic than the corresponding bulk materials; and 5) translation of incompletely understood science into regulation and policy continues to be challenging. There is a developing consensus that NMs may pose a relatively low environmental risk, but because of uncertainty and lack of data in many areas, definitive conclusions cannot be drawn. In addition, this emerging consensus will likely change rapidly with qualitative changes in the technology and increased future discharges.

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