Backyard aerosol pollution monitors: foliar surfaces, dust enrichment, and factors influencing foliar retention.

Air pollution is one of the leading causes of death from noncommunicable diseases globally, and in Arizona, both mining activities and abandoned agriculture can generate erodible dust. This dust is transported via wind and can carry high amounts of toxic pollutants. Industry-adjacent communities, or "fenceline communities," are generally closer to the pollution sources and are disproportionally impacted by pollution, or in this case, dust. The dust transported from the mine settles into nearby rivers, gardens, and homes, and increases the concentrations of elements beyond their naturally occurring amounts (i.e., enriched). This study was built upon previous community science work in which plant leaves were observed to collect similar concentrations to an accepted dust collection method and illustrated promise for their use as low-cost air quality monitors in these communities. This work investigated the concentration of Na, Mg, Al, K, Ca, Mn, Co, Cu, Zn, Mo, and Ba in dust from the leaves of community-collected backyard and garden plants (foliar dust), as well as if certain variables affected collection efficacy. This assessment evaluated (1) foliar concentration versus surface area for 11 elements, (2) enrichment factor (EF) values and ratios, (3) comparisons of foliar, garden, and yard samples to US Geological Survey data, and (4) what variable significantly affected dust collection efficacy. The EF results indicate that many of the samples were enriched (anthropogenically contaminated) and that the foliar samples were generally more contaminated than the yard and garden soil samples. Leaf surface area was the most influential factor for leaf collection efficiency (p < 0.05) compared to plant family or sampling location. Further studies are needed that standardize the plant species and age and include multiple replicates of the same plant species across partnering communities. This study has demonstrated that foliar dust is enriched in the participating partnering communities and that plant leaf samples can serve as backyard aerosol pollution monitors. Therefore, foliar dust is a viable indicator of outdoor settled dust and aerosol contamination and this is an adoptable monitoring technique for "fenceline communities."

Phytoremediation Reduces Dust Emissions from Metal(loid)-Contaminated Mine Tailings.

Environmental and health risk concerns relating to airborne particles from mining operations have focused primarily on smelting activities. However, there are only three active copper smelters and less than a dozen smelters for other metals compared to an estimated 500000 abandoned and unreclaimed hard rock mine tailings in the US that have the potential to generate dust. The problem can also extend to modern tailings impoundments, which may take decades to build and remain barren for the duration before subsequent reclamation. We examined the impact of vegetation cover and irrigation on dust emissions and metal(loid) transport from mine tailings during a phytoremediation field trial at the Iron King Mine and Humboldt Smelter Superfund (IKMHSS) site. Measurements of horizontal dust flux following phytoremediation reveals that vegetated plots with 16% and 32% canopy cover enabled an average dust deposition of 371.7 and 606.1 g m-2 y-1, respectively, in comparison to the control treatment which emitted dust at an average rate of 2323 g m-2 y-1. Horizontal dust flux and dust emissions from the vegetated field plots are comparable to emission rates in undisturbed grasslands. Further, phytoremediation was effective at reducing the concentration of fine particulates, including PM1, PM2.5, and PM4, which represent the airborne particulates with the greatest health risks and the greatest potential for long-distance transport. This study demonstrates that phytoremediation can substantially decrease dust emissions as well as the transport of windblown contaminants from mine tailings.

Hygroscopic Properties and Respiratory System Deposition Behavior of Particulate Matter Emitted By Mining and Smelting Operations.

This study examines size-resolved physicochemical data for particles sampled near mining and smelting operations and a background urban site in Arizona with a focus on how hygroscopic growth impacts particle deposition behavior. Particles with aerodynamic diameters between 0.056-18 µm were collected at three sites: (i) an active smelter operation in Hayden, AZ, (ii) a legacy mining site with extensive mine tailings in Iron King, AZ, and (iii) an urban site, inner-city Tucson, AZ. Mass size distributions of As and Pb exhibit bimodal profiles with a dominant peak between 0.32 and 0.56 µm and a smaller mode in the coarse range (>3 µm). The hygroscopicity profile did not exhibit the same peaks owing to dependence on other chemical constituents. Submicrometer particles were generally more hygroscopic than supermicrometer ones at all three sites with finite water-uptake ability at all sites and particle sizes examined. Model calculations at a relative humidity of 99.5% reveal significant respiratory system particle deposition enhancements at sizes with the largest concentrations of toxic contaminants. Between dry diameters of 0.32 and 0.56 µm, for instance, ICRP and MPPD models predict deposition fraction enhancements of 171%-261% and 33%-63%, respectively, at the three sites.

Three-dimensional computational fluid dynamics modeling of particle uptake by an occupational air sampler using manually-scaled and adaptive grids.

This work presents fluid flow and particle trajectory simulation studies to determine the aspiration efficiency of a horizontally oriented occupational air sampler using computational fluid dynamics (CFD). Grid adaption and manual scaling of the grids were applied to two sampler prototypes based on a 37-mm cassette. The standard k-ε model was used to simulate the turbulent air flow and a second order streamline-upwind discretization scheme was used to stabilize convective terms of the Navier-Stokes equations. Successively scaled grids for each configuration were created manually and by means of grid adaption using the velocity gradient in the main flow direction. Solutions were verified to assess iterative convergence, grid independence and monotonic convergence. Particle aspiration efficiencies determined for both prototype samplers were undistinguishable, indicating that the porous filter does not play a noticeable role in particle aspiration. Results conclude that grid adaption is a powerful tool that allows to refine specific regions that require lots of detail and therefore better resolve flow detail. It was verified that adaptive grids provided a higher number of locations with monotonic convergence than the manual grids and required the least computational effort.

Flow Field Penetration in Thin Nanoporous Polymer Films under Laminar Flow by Förster Resonance Energy Transfer Coupled with Total Internal Reflectance Fluorescence Microscopy.

Polymer-fluid interfaces are used widely in a variety of applications, including separations, which require exposure of the polymer to dynamic flow conditions. Despite the ubiquity of such interfaces, the importance of convective mass transport within the near-interface region of a polymer is a fundamental process that is still poorly defined. As a step toward better defining mass transport behavior within the near-interface portion of a polymer, in this work, a new application of a spectroscopic method based on the combination of Förster resonance energy transfer (FRET) and total internal reflectance fluorescence microscopy (TIRFM) is reported that allows quantification of the penetration depth of a laminar flow field (i.e., the slip length) in a densely grafted, thin poly(N-isopropylacrylamide) (pNIPAM) film as a model polymer system. Specifically, decay curves from FRET of an acceptor with a donor attached at the substrate surface are fit to a combined Taylor-Aris-Fickian mass transport model to extract apparent linear diffusion coefficients of acceptor molecules for different flow rates. Apparent diffusion coefficients range from 1.9 × 10(-12) to 9.1 × 10(-12) cm(2)/s for near-surface flow linear velocities ranging from 192 to 2952 µm/s. This increase in apparent diffusion coefficient with fluid flow rate suggests increasing contributions from convective mass transport that are indicative of flow field penetration into the polymer film. The depth of penetration of the flow field is estimated to range from ∼6% of the polymer film thickness in a good solvent at ∼192 µm/s to ∼60% of the film thickness at ∼2952 µm/s. Thus, flow field penetration into polymer thin films, with its concomitant contributions from convective mass transport within the near-interface region of the polymer, is demonstrated and quantified experimentally.

Modeling the emission, transport and deposition of contaminated dust from a mine tailing site.

Mining operations are potential sources of airborne particulate metal and metalloid contaminants through both direct smelter emissions and wind erosion of mine tailings. The warmer, drier conditions predicted for the Southwestern US by climate models may make contaminated atmospheric dust and aerosols increasingly important, due to potential deleterious effects on human health and ecology. Dust emissions and dispersion of contaminants from the Iron King Mine tailings in Dewey-Humboldt, Arizona, a Superfund site, are currently being investigated through in situ field measurements and computational fluid dynamics modeling. These tailings are significantly contaminated with lead and arsenic with an average soil concentration of 1616 and 1420 ppm, respectively. Similar levels of these contaminants have also been measured in soil samples taken from the area surrounding the mine tailings. Using a computational fluid dynamics model, we have been able to model dust transport from the mine tailings to the surrounding region. The model includes a distributed Eulerian model to simulate fine aerosol transport and a Lagrangian approach to model fate and transport of larger particles. In order to improve the accuracy of the dust transport simulations both regional topographical features and local weather patterns have been incorporated into the model simulations.

Concentration of trichloroethylene in breast milk and household water from Nogales, Arizona.

The United States Environmental Protection Agency has identified quantification of trichloroethylene (TCE), an industrial solvent, in breast milk as a high priority need for risk assessment. Water and milk samples were collected from 20 households by a lactation consultant in Nogales, Arizona. Separate water samples (including tap, bottled, and vending machine) were collected for all household uses: drinking, bathing, cooking, and laundry. A risk factor questionnaire was administered. Liquid-liquid extraction with diethyl ether was followed by GC-MS for TCE quantification in water. Breast milk underwent homogenization, lipid hydrolysis, and centrifugation prior to extraction. The limit of detection was 1.5 ng/mL. TCE was detected in 7 of 20 mothers' breast milk samples. The maximum concentration was 6 ng/mL. TCE concentration in breast milk was significantly correlated with the concentration in water used for bathing (ρ = 0.59, p = 0.008). Detection of TCE in breast milk was more likely if the infant had a body mass index <14 (RR = 5.2, p = 0.02). Based on average breast milk consumption, TCE intake for 5% of the infants may exceed the proposed U.S. EPA Reference Dose. Results of this exploratory study warrant more in depth studies to understand risk of TCE exposures from breast milk intake.

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.

The status of water and sanitation among Pacific Rim nations.

Analysis of relationships among national wealth, access to improved water supply and sanitation facilities, and population health indices suggests that the adequacy of water resources at the national level is a poor predictor of economic development--namely, that low water stress is neither necessary nor sufficient for economic development at the present state of water stress among Pacific Rim nations. Although nations differ dramatically in terms of priority provided to improved water and sanitation, there is some level of wealth (per capita GNP) at which all nations promote the development of essential environmental services. Among the Pacific Rim countries for which there are data, no nation with a per capita GNP > US$18,000 per year has failed to provide near universal access to improved water supply and sanitation. Below US$18,000/person-year, however, there are decided differences in the provision of sanitary services (improved water supply and sanitation) among nations with similar economic success. There is a fairly strong relationship between child mortality/life expectancy and access to improved sanitation, as expected from the experiences of developed nations. Here no attempt is made to produce causal relationships among these data. Failure to meet Millennium Development Goals for the extension of improved sanitation is frequently evident in nations with large rural populations. Under those circumstances, capital intensive water and sanitation facilities are infeasible, and process selection for water/wastewater treatment requires an adaptation to local conditions, the use of appropriate materials, etc., constraints that are mostly absent in the developed world. Exceptions to these general ideas exist in water-stressed parts of developed countries, where water supplies are frequently augmented by water harvesting, water reclamation/reuse, and the desalination of brackish water resources. Each of these processes involves public acceptance of water resources that are at least initially of inferior quality. Despite predictions of looming increases in water stress throughout the world, adaptation and resourcefulness generally allow us to meet water demand while pursuing rational economic development, even in the most water-stressed areas of the Pacific Rim.

Assessing Children's Lead Exposure in an Active Mining Community Using the Integrated Exposure Uptake Biokinetic Model.

Lead exposure has been shown to be harmful to humans in various settings and there are no safe levels of blood lead in children. At an Alternative Superfund site in Hayden-Winkelman, Arizona, with an active copper smelter and concentrator, lead exceedances in air and soil have been measured in the past 20 years. In this work, the U.S. Environmental Protection Agency's Integrated Exposure Uptake Biokinetic (IEUBK) model was used to estimate Hayden-Winkelman children's (age 6 months-7 years) blood lead levels (BLLs) using site-specific lead concentrations measured in indoor and outdoor air, soil, indoor dust, and drinking water. Values used by a state agency's airborne lead risk forecast program were also evaluated to determine whether their forecasting program is useful in protecting children's public health. Using site-specific values in the model, the results demonstrated that lead ingested via indoor dust was the major contributor to children's BLLs. In addition, the output of the IEUBK model overestimated actual BLLs of children sampled in the community. The IEUBK model was particularly sensitive to high indoor dust levels, and these site-specific measures increased modeled BLL values. This finding is of significance as the IEUBK model is used worldwide in communities with industrial contamination. This study confirmed that the chief contributor to lead exposure in children is household dust. Thus, for lead exposure risk reduction, agencies working at Superfund sites should focus efforts on decontaminating outdoor soil and dust and indoor lead decontamination.

Evaluating the Mobility of Arsenic in Synthetic Iron-containing Solids Using a Modified Sequential Extraction Method.

Many water treatment technologies for arsenic removal that are used today produce arsenic-bearing residuals which are disposed in non-hazardous landfills. Previous works have established that many of these residuals will release arsenic to a much greater extent than predicted by standard regulatory leaching tests (e.g. the toxicity characteristic leaching procedure, TCLP) and, consequently, require stabilization to ensure benign behavior after disposal. In this work, a four-step sequential extraction method was developed in an effort to determine the proportion of arsenic in various phases in untreated as well as stabilized iron-based solid matrices. The solids synthesized using various potential stabilization techniques included: amorphous arsenic-iron sludge (ASL), reduced ASL via reaction with zero valent iron (RASL), amorphous ferrous arsenate (PFA), a mixture of PFA and SL (M1), crystalline ferrous arsenate (HPFA), and a mixture of HPFA and SL (M2). The overall arsenic mobility of the tested samples increased in the following order: ASL > RASL > PFA > M1 > HPFA > M2.

Environmental monitoring and exposure science dataset to calculate ingestion and inhalation of metal(loid)s through preschool gardening.

Metal(loid) contamination may pose an increased risk of exposure to children residing near legacy and active resource extraction sites. Children may be exposed to arsenic, cadmium, and/or lead by ingestion and/or inhalation while engaging in school or home outdoor activities via environmental media including water, soil, dust, and locally grown produce. It is thus critical to collect site-specific data to best assess these risks. This data article provides gastric and lung in-vitro bioaccessibility assay (IVBA) data, as well as environmental monitoring data for water, soil, dust, and garden produce collected from preschools (N = 4) in mining communities throughout Nevada County, California in 2018. Arsenic, cadmium, and lead concentrations in the aforementioned media and synthetic gastric and lung fluids were measured by inductively coupled plasma-mass spectrometry (ICP-MS). This dataset provides useful metal(loid) concentrations for future risk assessments for similar settings.

Ingestion and inhalation of metal(loid)s through preschool gardening: An exposure and risk assessment in legacy mining communities.

Children residing in mining towns are potentially disproportionately exposed to metal(loid)s via ingestion and dust inhalation, thus, increasing their exposure when engaging in school or home gardening or playing outside. This citizen science study assessed preschool children's potential arsenic (As), cadmium (Cd), and lead (Pb) exposure via locally grown produce, water, incidental soil ingestion, and dust inhalation at four sites. Participants were trained to properly collect water, soil, and vegetable samples from their preschools in Nevada County, California. As, Cd, and Pb concentrations in irrigation sources did not exceed the U.S. EPA's maximum contaminant and action levels. In general, garden and playground As and Pb soil concentrations exceeded the U.S. EPA Regional Screening Level, CalEPA Human Health Screening Level, and California Department of Toxic Substances Control Screening Level. In contrast, all Cd concentrations were below these recommended screening levels. Dust samples (<10 µm diameter) were generated from surface garden and playground soil collected at the preschools by a technique that simulated windblown dust. Soil and dust samples were then analyzed by in-vitro bioaccessibility assays using synthetic lung and gastric fluids to estimate the bioaccessible fraction of As, Cd, and Pb in the body. Metal(loid) exposure via grown produce revealed that lettuce, carrot, and cabbage grown in the preschool gardens accumulated a higher concentration of metal(loid) than those store-bought nation-wide. None of the vegetables exceeded the respective recommendation maximum levels for Cd and Pb set by the World Health Organization Codex Alimentarius Commission. The results of this study indicate that consumption of preschool-grown produce and incidental soil ingestion were major contributors to preschool-aged children's exposure to As, Cd, and Pb. Traditionally, this level of site- and age-specific assessment and analyses does not occur at contaminated sites. The results of this holistic risk assessment can inform future risk assessment and public health interventions related to childhood metal(loid) exposures.

Oxidative weathering decreases bioaccessibility of toxic metal(loid)s in PM10 emissions from sulfide mine tailings.

Environmental contamination from legacy mine-waste deposits is a persistent problem due to the long history of hard-rock mining. Sulfide ore deposits can contain elevated levels of toxic metal(loid)s that, when mobilized by weathering upon O2 and H2O infusion, can result in groundwater contamination. Dry-climate and lack of vegetative cover result in near-surface pedogenic processes that produce fine-particulate secondary minerals that can be translocated as geo-dusts leading to ingestion or inhalation exposure in nearby communities. In this study, in vitro bioassays were combined with synchrotron-based x-ray spectroscopy and diffraction to determine the potential risk for toxic element release from dust (PM10) samples into biofluid simulants. PM10 were isolated from across the oxidative reaction front in the top meter of tailings subjected to 50 years of weathering under semi-arid climate, and introduced to synthetic gastric- and alveolar-fluids. Aqueous concentrations were measured as a function of reaction time to determine release kinetics. X-ray diffraction and absorption spectroscopy analyses were performed to assess associated changes in mineralogy and elemental speciation. In vitro bioaccessibility of arsenic and lead was highest in less-weathered tailings samples (80-110 cm) and lowest in samples from the sub-oxic transition zone (40-52 cm). Conversely, zinc release to biofluids was greatest in the highly-weathered near-surface tailings. Results indicate that bioaccessibility of As and Pb was controlled by (i) the solubility of Fe2+-bearing solids, (ii) the prevalence of soluble SO4 2-, and (iii) the presence of poorly-crystalline Fe(III) oxide sorbents, whereas Zn bioaccessibility was controlled by the pH-dependent solubility of the stable solid phase.

Effect of ionic strength on the rheological behavior of aqueous cetyltrimethylammonium p-toluene sulfonate solutions.

The influence of ionic environment on the rheological properties of aqueous cetyltrimethylammonium p-toluene sulfonate (CTAT) solutions has been studied under three different flow fields: simple shear, opposed-jets flow and porous media flow. Emphasis was placed in the experiments on a range of CTAT concentration in which wormlike micelles were formed. It is known that these solutions exhibit shear thickening in the semi-dilute regime, which has been explained in terms of the formation of shear-induced, cooperative structures involving wormlike micelles. In simple shear flow, the zero shear viscosity exhibits first an increase with salt addition followed by a decrease, while the critical shear rate for shear thickening increases sharply at low salt contents and tends to saturate at relatively high ionic strengths. The results are explained in terms of a competition between micellar growth induced by salt addition and changes in micellar flexibility caused by ionic screening effects. Dynamic light scattering results indicate that micelles grow rapidly upon salt addition but eventually achieve a constant size under static conditions. These observations suggest that the wormlike micelles continuously grow with salt addition, but, as they become more flexible due to electrostatic screening, the wormlike coils tend to adopt a more compact conformation. The trends observed in the apparent viscosities measured in porous media flows seem to confirm these hypotheses-but viscosity increases in the shear thickening region-and are magnified by micelle deformation induced by the elongational nature of the local flow in the pores. In opposed-jets flow, the solutions have a behavior that is close to Newtonian, which suggests that the range of strain rates employed makes the flow strong enough to destroy or prevent the formation of cooperative micellar structures.

Changes in estrogen/anti-estrogen activities in ponded secondary effluent.

Total estrogenic activity, measured using the yeast estrogen screen reporter gene bioassay, decreased from 60 pM (equivalent 17alpha-ethinylestradiol concentration) to an estimated 1.4 pM during a 24-hour period in which secondary effluent was held in a shallow infiltration basin. Over the same period, anti-estrogenic activity, measured as an equivalent concentration of tamoxifen, increased from 35 to 260 nM, suggesting that antagonists produced during secondary effluent storage played a role in the apparent loss of estrogenic activity. Androgenic activity, measured over the same 24-hour period using the yeast androgen screen, was near or below the method detection limit (0.7 pM as testosterone). However, the same pond samples were clearly anti-androgenic. When whole-sample extracts were separated via adsorption and stepwise elution in alcohol/water solutions consisting of 20, 40 and 100% ethanol, the sum of estrogenic activities in derived fractions was always lower than the measured estrogenic activity in the whole-sample extracts. Summed anti-estrogenic activities in the same fractions, however, always exceeded values for corresponding whole-sample extracts. Results reinforce the importance of sample preparation steps (concentration of organics followed by estrogen/anti-estrogen separation) when measuring endocrine-related activities in chemically complex samples such as wastewater effluent. The potential complexity of relationships among estrogens, anti-estrogens and matrix organics suggests that additive models are of questionable validity for estimating whole-sample estrogenic activity from measurements involving sample fractions.

Effect of pH, competitive anions and NOM on the leaching of arsenic from solid residuals.

Implementation of the new arsenic MCL in 2006 will lead to the generation of an estimated 6 million pounds of arsenic-bearing solid residuals (ABSRs) every year, which will be disposed predominantly in non-hazardous landfills. The Toxicity Characteristic Leaching Procedure (TCLP) is typically used to assess whether a waste is hazardous and most solid residuals pass the TCLP. However, recent research shows the TCLP significantly underestimates arsenic mobilization in landfills. A variety of compositional dissimilarities between landfill leachates and the TCLP extractant solution likely play a role. Among the abiotic factors likely to play a key role in arsenic remobilization/leaching from solid sorbents are pH, and the concentrations of natural organic matter (NOM) and anions like phosphate, bicarbonate, sulfate and silicate. This study evaluates the desorption of arsenic from actual treatment sorbents, activated alumina (AA) and granular ferric hydroxide (GFH), which are representative of those predicted for use in arsenic removal processes, and as a function of the specific range of pH and concentrations of the competitive anions and NOM found in landfills. The influence of pH is much more significant than that of competing anions or NOM. An increase in one unit of pH may increase the fraction of arsenic leached by 3-4 times. NOM and phosphate replace arsenic from sorbent surface sites up to three orders of magnitude more than bicarbonate, sulfate and silicate, on a per mole basis. Effects of anions are neither additive nor purely competitive. Leaching tests, which compare the fraction of arsenic mobilized by the TCLP vis-a-vis an actual or more realistic synthetic landfill leachate, indicate that higher pH, and greater concentrations of anions and NOM are all factors, but of varying significance, in causing higher extraction in landfill and synthetic leachates than the TCLP.

Modeling the oxidation of phenolic compounds by hydrogen peroxide photolysis.

Hydrogen peroxide UV photolysis is among the most widely used advanced oxidation processes (AOPs) for the destruction of trace organics in waters destined for reuse. Previous kinetic models of hydrogen peroxide photolysis focus on the dynamics of hydroxyl radical production and consumption, as well as the reaction of the target organic with hydroxyl radicals. However, the rate of target destruction may also be affected by radical scavenging by reaction products. In this work, we build a predictive kinetic model for the destruction of p-cresol by hydrogen peroxide photolysis based on a complete reaction mechanism that includes reactions of intermediates with hydroxyl radicals. The results show that development of a predictive kinetic model to evaluate process performance requires consideration of the complete reaction mechanism, including reactions of intermediates with hydroxyl radicals.

Use of lead isotopes to identify sources of metal and metalloid contaminants in atmospheric aerosol from mining operations.

Mining operations are a potential source of metal and metalloid contamination by atmospheric particulate generated from smelting activities, as well as from erosion of mine tailings. In this work, we show how lead isotopes can be used for source apportionment of metal and metalloid contaminants from the site of an active copper mine. Analysis of atmospheric aerosol shows two distinct isotopic signatures: one prevalent in fine particles (<1µm aerodynamic diameter) while the other corresponds to coarse particles as well as particles in all size ranges from a nearby urban environment. The lead isotopic ratios found in the fine particles are equal to those of the mine that provides the ore to the smelter. Topsoil samples at the mining site show concentrations of Pb and As decreasing with distance from the smelter. Isotopic ratios for the sample closest to the smelter (650m) and from topsoil at all sample locations, extending to more than 1km from the smelter, were similar to those found in fine particles in atmospheric dust. The results validate the use of lead isotope signatures for source apportionment of metal and metalloid contaminants transported by atmospheric particulate.

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.