A. Eduardo Sáez

A review on the importance of metals and metalloids in atmospheric dust and aerosol from mining operations

Contaminants can be transported rapidly and over relatively long distances by atmospheric dust and aerosol relative to other media such as water, soil and biota; yet few studies have explicitly evaluated the environmental implications of this pathway, making it a fundamental but understudied transport mechanism. Although there are numerous natural and anthropogenic activities that can increase dust and aerosol emissions and contaminant levels in the environment, mining operations are notable with respect to the quantity of particulates generated, the global extent of area impacted, and the toxicity of contaminants associated with the emissions. Here we review (i) the environmental fate and transport of metals and metalloids in dust and aerosol from mining operations, (ii) current methodologies used to assess contaminant concentrations and particulate emissions, and (iii) the potential health and environmental risks associated with airborne contaminants from mining operations. The review evaluates future research priorities based on the available literature and suggest that there is a particular need to measure and understand the generation, fate and transport of airborne particulates from mining operations, specifically the finer particle fraction. More generally, our findings suggest that mining operations play an important but underappreciated role in the generation of contaminated atmospheric dust and aerosol and the transport of metal and metalloid contaminants, and highlight the need for further research in this area. The role of mining activities in the fate and transport of environmental contaminants may become increasingly important in the coming decades, as climate change and land use are projected to intensify, both of which can substantially increase the potential for dust emissions and transport.

Shear rheology and porous media flow of wormlike micelle solutions formed by mixtures of surfactants of opposite charge

The rheology of solutions of wormlike micelles formed by oppositely charged surfactant mixtures (cationic cetyl trimethylammonium p-toluene sulfonate, CTAT, and anionic sodium dodecyl sulfate, SDS), in the dilute and semi-dilute regimes, were studied under simple shear and porous media flows. Aqueous mixtures of CTAT and SDS formed homogeneous solutions for SDS/CTAT molar ratios below 0.12. Solutions of mixtures exhibited a strong synergistic effect in shear viscosity, especially in the semi-dilute regime with respect to wormlike micelles, reaching a four order of magnitude increase in the zero-shear rate viscosity for solutions with 20 mM CTAT. Oscillatory shear results demonstrated that the microstructure of CTAT wormlike micelles is sensitive to SDS addition. The cross-over relaxation times of wormlike micelles of 20 mM CTAT solutions increased by three orders of magnitude with the addition of up to 2 mM of SDS, and the solutions became increasingly elastic. The shear thickening process observed in shear rheology became more pronounced in porous media flow due to the formation of stronger cooperative structures induced by the extensional component of the flow.

Hygroscopic and Chemical Properties of Aerosols collected near a Copper Smelter: Implications for Public and Environmental Health

Particulate matter emissions near active copper smelters and mine tailings in the southwestern United States pose a potential threat to nearby environments owing to toxic species that can be inhaled and deposited in various regions of the body depending on the composition and size of the particles, which are linked by particle hygroscopic properties. This study reports the first simultaneous measurements of size-resolved chemical and hygroscopic properties of particles next to an active copper smelter and mine tailings by the towns of Hayden and Winkelman in southern Arizona. Size-resolved particulate matter samples were examined with inductively coupled plasma mass spectrometry, ion chromatography, and a humidified tandem differential mobility analyzer. Aerosol particles collected at the measurement site are enriched in metals and metalloids (e.g., arsenic, lead, and cadmium) and water-uptake measurements of aqueous extracts of collected samples indicate that the particle diameter range of particles most enriched with these species (0.18-0.55 μm) overlaps with the most hygroscopic mode at a relative humidity of 90% (0.10-0.32 μm). These measurements have implications for public health, microphysical effects of aerosols, and regional impacts owing to the transport and deposition of contaminated aerosol particles.

Effect of ionic environment on the rheology of wormlike micelle solutions of mixtures of surfactants with opposite charge

This work reports on the rheological characterization of aqueous solutions of mixtures of a cationic surfactant (hexadecyltrimethylammonium p-toluenesulfonate, CTAT), capable of forming wormlike micelles, and an anionic surfactant (sodium dodecylsulfate, SDS) when the ionic environment of the solution is altered by the addition of electrolytes. Previous work showed that mixtures CTAT/SDS exhibit a strong rheological synergy in shear flows caused by promotion of interaction between wormlike micelles by the presence of the dodecylsulfate anion. In this work, we explore the CTAT/SDS synergy in the presence of electrolytes. The effect of the added electrolyte varies with wormlike micelle concentration range and type of flow. In simple shear flows and relatively low wormlike micelle concentrations (dilute regime), electrolyte addition inhibits the shear thickening effect observed in CTAT/SDS solution. In porous media flows, which have an important elongational component, electrolyte addition results in an appreciable increase in apparent viscosity at low electrolyte concentrations. In the semi-dilute regime, electrolyte addition at low concentrations strengthens the synergy between CTAT and SDS, leading to higher shear viscosities, especially at low-shear rates. An important consequence of these results is the potential for manipulation of the rheology of solutions of wormlike micelles by induction of intermicelle associations and/or promotion of conformational changes by electrolyte addition.

Size-resolved dust and aerosol contaminants associated with copper and lead smelting emissions: implications for emission management and human health.

Mining operations, including crushing, grinding, smelting, refining, and tailings management, are a significant source of airborne metal and metalloid contaminants such as As, Pb and other potentially toxic elements. In this work, we show that size-resolved concentrations of As and Pb generally follow a bimodal distribution with the majority of contaminants in the fine size fraction (<1 μm) around mining activities that include smelting operations at various sites in Australia and Arizona. This evidence suggests that contaminated fine particles (<1 μm) are the result of vapor condensation and coagulation from smelting operations while coarse particles are most likely the result of windblown dust from contaminated mine tailings and fugitive emissions from crushing and grinding activities. These results on the size distribution of contaminants around mining operations are reported to demonstrate the ubiquitous nature of this phenomenon so that more effective emission management and practices that minimize health risks associated with metal extraction and processing can be developed.

Assessment of the Effectiveness of Secondary Wastewater Treatment Technologies to Remove Trace Chemicals of Emerging Concern

This work presents the results of a literature review and statistical analysis of removals of chemicals of emerging concern (CECs) during conventional wastewater treatment. Process-dependent attenuations are examined for the 42 most frequently measured and reported CECs. Biological treatment processes contributing to the review include conventional activated sludge, membrane bioreactors, trickling filters, sequencing batch reactors, and lagoons. Also summarized are compound-specific physical characteristics and biodegradability data that are potential determinants of removal. As anticipated, results of the statistical analysis point to biodegradability and hydrophobicity as the most important contributing factors for removal. Supplemental materials are available for this article. Go to the publishers online edition of Critical Reviews in Environmental Science and Technology to view the supplemental file.

Toward Identifying the Next Generation of Superfund and Hazardous Waste Site Contaminants

Background This commentary evolved from a workshop sponsored by the National Institute of Environmental Health Sciences titled “Superfund Contaminants: The Next Generation” held in Tucson, Arizona, in August 2009. All the authors were workshop participants. Objectives Our aim was to initiate a dynamic, adaptable process for identifying contaminants of emerging concern (CECs) that are likely to be found in future hazardous waste sites, and to identify the gaps in primary research that cause uncertainty in determining future hazardous waste site contaminants. Discussion Superfund-relevant CECs can be characterized by specific attributes: They are persistent, bioaccumulative, toxic, occur in large quantities, and have localized accumulation with a likelihood of exposure. Although still under development and incompletely applied, methods to quantify these attributes can assist in winnowing down the list of candidates from the universe of potential CECs. Unfortunately, significant research gaps exist in detection and quantification, environmental fate and transport, health and risk assessment, and site exploration and remediation for CECs. Addressing these gaps is prerequisite to a preventive approach to generating and managing hazardous waste sites. Conclusions A need exists for a carefully considered and orchestrated expansion of programmatic and research efforts to identify, evaluate, and manage CECs of hazardous waste site relevance, including developing an evolving list of priority CECs, intensifying the identification and monitoring of likely sites of present or future accumulation of CECs, and implementing efforts that focus on a holistic approach to prevention.

Fate of trace organics in a wastewater effluent dependent stream

Trace organic compounds (TOrCs) in municipal wastewater effluents that are discharged to streams are of potential concern to ecosystem and human health. This study examined the fate of a suite of TOrCs and estrogenic activity in water and sediments in an effluent-dependent stream in Tucson, Arizona. Sampling campaigns were performed during 2011 to 2013 along the Lower Santa Cruz River, where TOrCs and estrogenic activity were measured in aqueous (surface) and solid (riverbed sediment) phases. Some TOrCs, including contributors to estrogenic activity, were rapidly attenuated with distance of travel in the river. Those TOrCs that are not sufficiently attenuated and percolate to ground water have in common low biodegradation probabilities and low octanol-water distribution ratios. Independent experiments showed that attenuation of estrogenic compounds may be due in part to indirect photolysis caused by formation of organic radicals from sunlight absorption. Hydrophobic TOrCs may accumulate in riverbed sediments during dry weather periods, but riverbed sediment quality is periodically affected through storm-related scouring during periods of heavy rainfall and runoff. Taken together, evidence suggests that natural processes can attenuate at least some TOrCs, reducing potential impacts to ecosystem and human health.

Interactions between high-molecular-weight poly(ethylene oxide) and sodium dodecyl sulfate

In this work, we study interactions between poly(ethylene oxide) (PEO) and sodium dodecyl sulfate (SDS) in aqueous solutions, using surface tension, electrical conductivity and shear rheometry. The main distinguishing feature of this investigation with respect to previous works is the use of high-molecular-weight PEOs (up to 8 × 106 g/mol). The aggregation pattern of the surfactant in the form of micellar aggregates attached to the polymer chain causes specific changes in surface tension, electrical conductivity and zero-shear-rate viscosity that qualitatively resemble those found previously for lower-molecular-weight PEOs when no additional electrolytes are present in the solu tion. In the presence of 0.1 M NaCl and for PEOs with molecular weights of 600,000 g/mol and more, the electrical conductivity and surface tension of the solutions remain constant when surfactant is added beyond the critical aggregation concentration, until saturation of the polymer with micellar aggregates is achieved. This behavior indicates complete complexation of the dodecyl sulfate ions into micellar aggregates attached to the polymer, as well as a strong binding of the counterions to the PEO/SDS complex.

Laboratory dust generation and size-dependent characterization of metal and metalloid-contaminated mine tailings deposits.

The particle size distribution of mine tailings material has a major impact on the atmospheric transport of metal and metalloid contaminants by dust. Implications to human health should be assessed through a holistic size-resolved characterization involving multidisciplinary research, which requires large uniform samples of dust that are difficult to collect using conventional atmospheric sampling instruments. To address this limitation, we designed a laboratory dust generation and fractionation system capable of producing several grams of dust from bulk materials. The equipment was utilized in the characterization of tailings deposits from the arsenic and lead-contaminated Iron King Superfund site in Dewey-Humboldt, Arizona. Results show that metal and metalloid contaminants are more concentrated in particles of < 10 μm aerodynamic diameter, which are likely to affect surrounding communities and ecosystems. In addition, we traced the transport of contaminated particles from the tailings to surrounding soils by identifying Pb and Sr isotopic signatures in soil samples. The equipment and methods developed for this assessment ensure uniform samples for further multidisciplinary studies, thus providing a tool for comprehensive representation of emission sources and associated risks of exposure.