Determination of trace element concentrations in natural freshwaters: how low is "low", and how low do we need to go?

Resolving Uncertainties in the Quantification of Trace Elements within Organic-Rich Boreal Rivers for AF4-UV-ICP-MS Analysis

Over the past few decades, asymmetric flow field-flow fractionation (AF4) has emerged as a robust technique for the separation of colloid-associated trace elements (TEs) in aqueous samples. Nevertheless, little is known about potential artifacts and how to control them when measuring the concentrations of colloid-associated elements at low (μg L-1) or ultralow concentrations (ng L-1) using AF4-UV-ICP-MS. Water from a boreal river was selected as a challenging test material due to its high concentrations of dissolved organic matter (DOM) and Fe-rich colloids. These colloids are expected to be significant contributors to artifact occurrence, even in a metal-free, ultraclean laboratory. The results show that the adsorption of Mn, Co, Ni, Cu, and Pb onto acid-cleaned, non-channel surfaces (such as connection tubing and autosampler) accounted for up to 48% of TE loss. These losses on non-channel surfaces also represent potential sources of cross-contamination for Co, Ni, Cu, and Pb. New, uncleaned poly(ether sulfone) membranes are also sources of contamination for Ni and Cu. Analytical bias may exist in the measured concentrations of TEs, primarily due to the potential carryover of weakly adsorbed TEs (e.g., Ni and Cu) on the system surfaces by colloids in the samples (e.g., DOM). On the other hand, colloids in the samples can also act to gradually remove contaminants from the surfaces. For these types of DOM-rich waters, preconditioning the AF4 system using 40 mg C L-1 of Suwannee River Natural Organic Matter (SRNOM, pH = 7) is recommended to mitigate the impact of membrane fouling and carryover. A comprehensive strategy for minimizing instrumental artifacts is presented and discussed.

Natural enrichment of Cd and Tl in the bark of trees from a rural watershed devoid of point sources of metal contamination

To help understand the bioaccumulation of Cd and Tl in beaver tissue, we examined the enrichment of these metals in vegetation available to the animals. Bark was collected from 40 species of trees and shrubs, along with a complete soil weathering profile, within a small watershed devoid of trace metal contamination. Weathering resulted in a 5x enrichment of Cd in the soils relative to the underlying sediments, and a 6x Tl depletion: while Cd was lost from calcite and accumulates in the organic matter and oxyhydroxide fractions, Tl occurred only in the residual fraction. Soil processes alone, however, cannot explain the anomalous concentrations and enrichments of Cd in willow and poplar which contain up to 8.5 mg/kg Cd. The concentrations of Cd and Tl in the dissolved fraction (<0.45 μm) of the Wye River are similar (1.2 ± 0.4 and 1.6 ± 0.1 ng/L, respectively), and are taken to estimate their bioavailability in soil solutions. Normalizing the Cd/metal ratios in bark to the corresponding ratios in water yields the Stream Enrichment Factor: this novel approach shows that all plant species are enriched in Cd relative to Ni; 33 relative to Cu, 13 relative to Zn, and 7 relative to Mn. Thus, many plants preferentially accumulate Cd, especially willow and poplar, over these essential micronutrients. Clearly, the enrichment of Cd over Tl in bark is not a reflection of differences in bioavailability, but rather on the preferential uptake of Cd by the plants. The profound natural bioaccumulation of Cd in the bark of willow and poplar, the two favourite foods of the beaver, has ramifications for the use of these aquatic mammals as biomonitors of environmental contamination, as well as for the direct and indirect consumption of bark for traditional food and medicine.

Atmospheric deposition and trajectories of antimony in Central Europe

Antimony (Sb) concentrations were measured in wet atmospheric deposition at 10 high-elevation sites in the Czech Republic (Central Europe) during three winter seasons (2009-2011). Soluble and insoluble Sb forms were quantified in snow (vertical deposition) and rime (horizontal deposition) on mountain summits located equidistantly near the Czech borders with Austria, Germany and Poland. The highest Sb concentrations were found in the soluble form in rime (0.47 μg L^-1), while the lowest Sb concentrations were those in the insoluble form in snow (0.017 μg L^-1). The estimated average Sb deposition rate in Central Europe amounted to 1.3. 10^-4 g m^-2 yr^-1. Most Sb was deposited in the soluble form in snow (7.9. 10^-5 g m^-2 yr^-1), followed by the soluble form in rime (3.5. 10^-5 g m^-2 yr^-1). The corresponding insoluble fraction contained less Sb, namely 1.2. 10^-5 g m^-2 yr^-1 in snow and 2.3. 10^-6 g m^-2 yr^-1 in rime. The average Sb deposition in Central Europe, measured at an altitude of 1000 m a.s.l., was by six orders of magnitude higher compared to Sb deposition in the Arctic (7. 10^-10 g m^-2 yr^-1), and by four orders of magnitude lower compared to Sb deposition in a Sb-Hg mining district in China (7 g m^-2 yr^-1). Using the HYSPLIT model, backward trajectories of air masses indicated that the Sb sources were predominantly situated in Upper and Lower Silesia.

Cadmium contents of vertically and horizontally deposited winter precipitation in Central Europe: Spatial distribution and long-term trends

Cadmium (Cd) and its forms has recently been a focus of attention due to its toxic effects on human health and the environment. We evaluated the atmospheric deposition of Cd during three consecutive winter seasons (2009-2011) at 10 mountain-top locations in the Czech Republic along the borders with Poland, Germany, Austria and Slovakia. Cadmium concentrations of soluble and insoluble forms in both horizontal (rime) and vertical (snow) deposition were determined using sector-field ICP-MS. Across the sites, 94% of the total winter Cd deposition occurred in the soluble (environmentally available) Cd form. Mean concentrations of soluble Cd in rime were six times higher than in snow (398 vs. 66 ng L^-1). Vertical deposition contributed as much as 41% to the total winter Cd input. Between-site variability in Cd deposition was large, ranging between 13 and 108 μg m^-2 winter^-1. Overall, Cd concentrations in winter deposition did not reach the drinking water limits and did not pose a direct threat for human health. Long-term trends (1996-2017) in winter Cd deposition were evaluated at six GEOMON sites (a monitoring network of small forested catchments). Since 1996, Cd input in winter atmospheric deposition decreased by 73-93%. Simultaneously, we found declines in between-site variability in winter Cd inputs. The highest recent winter Cd inputs were found at sites located in the northeast of the country. A north-south pollution gradient, which has frequently been mentioned in the literature, was not observed, with both northwestern sites and southern sites being among those with the lowest Cd pollution. Backward trajectories of the HYSPLIT model for fresh snow samples identified Poland and Germany as major transboundary Cd pollution sources for the Czech Republic.

Hydride generation coupled with thioglycolic acid coated gold nanoparticles as simple and sensitive headspace colorimetric assay for visual detection of Sb(III)

Antimony (Sb) is a toxic element which causes different health problems including cardiac problems and lung cancer in humans, and its levels in surface water can be noticeably increased to 100 μg/L typically in the proximity of anthropogenic sources. Thus, besides instrumental techniques, it is of great significance to develop a simple, sensitive and selective analytical method for direct analysis of Sb(III) at trace level without the need of any expensive and/or complicated instrumentations and sample preparation processes. Herein, a simple and sensitive headspace colorimetric assay was developed for the detection of Sb(III) by hydride generation coupled with thioglycolic acid functionalized gold nanoparticles (TGA-AuNPs). Sb(III) in the 30 mL sample solution was converted into its volatile form (SbH₃) through hydride generation reaction and headspace extracted into 100 μL chromogenic reagent, which contains methanol as extractant and TGA-AuNPs as nanosensors, leading to aggregation of TGA-AuNPs and therefore a red-to-blue color change. Parameters influencing the chromogenic and hydride generation reactions were optimized. Addition of 300 μM ethylenediamine tetraacetic acid (EDTA) as masking agent largely suppressed the inferences from mercury and arsenic. The proposed method can tolerate at least 10-fold As(III) and 100-fold other metal ions including Hg(II). The detection limits were 6.0 and 1.2 μg/L Sb(III) by naked-eye and UV-Vis spectrometer, respectively, which meet the maximum admissible level in drinking water (6 μg/L) set by the United States Environmental Protection Agency. The feasibility of the proposed method was demonstrated by rapid detection of Sb(III) in river water, lake water, ground water and sea water samples by naked-eye at a spiking level of 6 μg/L Sb(III).

Fabrication of Sb3+sensor based on 1,1′-(-(naphthalene-2,3-diylbis(azanylylidene))bis(methanylylidene))bis(naphthalen-2-ol)/nafion/glassy carbon electrode assembly by electrochemical approach

A new Schiff base named 1,1′-(-(naphthalene-2,3-diylbis(azanylylidene))bis(methanylylidene))bis(naphthalen-2-ol) (NDNA) was synthesized by condensation reaction and then characterized by spectroscopic techniques for structure elucidation.

Arsenic speciation in the lower Athabasca River watershed: A geochemical investigation of the dissolved and particulate phases

Human and ecosystem health concerns for arsenic (As) in the lower Athabasca River downstream of Athabasca Bituminous Sands (ABS) mining (Alberta, Canada) prompted an investigation to determine its forms in surface and groundwater upstream and downstream of industry. Dissolved As species, together with total and particulate As, were used to evaluate the potential bioavailability of As in water as well as to decipher inputs from natural geological processes and ABS mining and upgrading activities. Water samples were collected from the river in October at 13 locations in 2014 and 19 locations in 2015, spanning up to 125 km. Additional samples were collected from groundwater, tributaries and springs. "Dissolved" (<0.45 μm) As was consistently low in the Athabasca River (average 0.37 ± 0.01 and 0.34 ± 0.01 μg L^-1 in 2014 and 2015, respectively) as well as tributaries and springs (<1 μg L^-1), with As(V) as the predominant form. The average total As concentration was higher in 2014 (12.7 ± 2.8 μg L^-1) than 2015 (3.3 ± 0.65 μg L^-1) with nearly all As associated with suspended solids (>0.45 μm). In 2014, when total As concentrations were greater, a significant correlation (p < 0.05) was observed with thorium in particles > 0.45 μm, suggesting that mineral material is an important source of As. Naturally saline groundwater contained low dissolved As (<2 μg L^-1) and did not appear to be a significant source to the river. Arsenic in shallow groundwater near a tailings pond exceeded 50 μg L^-1 predominantly as As(III) warranting further investigation.

Trace metals in the dissolved fraction (<0.45μm) of the lower Athabasca River: Analytical challenges and environmental implications

Water samples were collected on the Athabasca River (AR), upstream and downstream from bitumen mines and upgrading facilities, to identify changes in water quality due to industrial activities in this region of northern Alberta, Canada. Starting upstream of Fort McMurray and proceeding downstream ca. 100km, waters were collected in duplicate at 13 locations on the main stem of the river, as well as 5 tributary streams, using ultraclean sampling protocols developed for polar snow and ice. To estimate potential bioaccessibility, trace elements of concern (Ag, Cd, Pb, Sb, Tl) were determined in the dissolved fraction (<0.45μm) along with metals known for their enrichments in bitumen (V, Ni, Mo, Re) and those found mainly in ionic (Li, Sr) or colloidal forms (Al, Co, Cr, Fe, Ga, Mn, Th, Y). Analyses were performed in the metal-free, ultraclean SWAMP lab using quadrupole and sector-field ICP-MS. Concentrations of Ag, Cd, Pb, Sb and Tl were extremely low, not significantly more abundant downstream of industry and probably reflect "background" values. In contrast, V, Ni, Mo and Re concentrations were all significantly (p<0.05) greater downstream of industry. However, chloride also increased downstream, due to natural inputs of saline groundwaters and it is unclear whether the increases in V, Ni, Mo and Re are due to natural or anthropogenic inputs to the river. Although it had been claimed that the industrial development of the Athabasca Bituminous Sands (ABS) is a significant source of Ag, Cd, Pb, Sb and Tl to the river, our study failed to find any evidence to support this. Here we provide a first, robust (accurate and precise) description of baseline values for these trace elements in the AR, and suggest that V, Ni, Mo and Re are more valuable tracers for environmental monitoring and source assessment.

Cu-Zn isotope constraints on the provenance of air pollution in Central Europe: Using soluble and insoluble particles in snow and rime

Copper (Cu) and zinc (Zn) isotope ratios can be used to fingerprint sources and dispersion pathways of pollutants in the environment. Little is known, however, about the potential of δ⁶⁵Cu and δ⁶⁶Zn values in liquid and solid forms of atmospheric deposition to distinguish between geogenic, industrial, local and remote sources of these potentially toxic base metals. Here we present Cu-Zn deposition fluxes at 10 mountain-top sites in the Czech Republic, a region affected by extremely high industrial emission rates 25 years ago. Additionally, we monitored isotope composition of Cu and Zn in vertical and horizontal atmospheric deposition at two sites. We compared δ⁶⁵Cu and δ⁶⁶Zn values in snow and rime, extracted by diluted HNO₃ and concentrated HF. Cu and Zn isotope signatures of industrial pollution sources were also determined. Cu and Zn deposition fluxes at all study sites were minute. The mean δ⁶⁵Cu value of atmospheric deposition (-0.07‰) was higher than the mean δ⁶⁵Cu value of pollution sources (-1.17‰). The variability in δ⁶⁵Cu values of atmospheric deposition was lower, compared to the pollution sources. The mean δ⁶⁶Zn value of atmospheric deposition (-0.09‰) was slightly higher than the mean δ⁶⁶Zn value of pollution sources (-0.23‰). The variability in δ⁶⁶Zn values of atmospheric deposition was indistinguishable from that of pollution sources. The largest isotope differences (0.35‰) were observed between the insoluble and soluble fractions of atmospheric deposition. These differences may result from different sources of Cu/Zn for each fraction. The difference in isotope composition of soluble and insoluble particles appears to be a promising tool for pollution provenance studies in Central Europe.

Isotopic Composition of Pb in Peat and Porewaters from Three Contrasting Ombrotrophic Bogs in Finland: Evidence of Chemical Diagenesis in Response to Acidification

The isotopic composition of Pb was determined in Finnish peat bogs and their porewaters from Harjavalta (HAR, near a Cu-Ni smelter), Outokumpu (OUT, near a Cu-Ni mine), and Hietajärvi (HIJ, a background site). At HIJ and OUT, the porewaters yielded similar concentrations (0.1-0.7 μg/L) and isotopic composition ((206)Pb/(207)Pb = 1.154-1.164). In contrast, the peat profile from HAR yielded greater concentrations of Pb in the porewaters (average 2.4 μg/L), and the Pb is less radiogenic ((206)Pb/(207)Pb = 1.121-1.149). Acidification of the bog surface waters to pH 3.5 by SO2 emitted from smelting (compared to pH 4.0 at the control site) apparently promotes the dissolution of Pb-bearing aerosols, as well as desorption of metals from the surfaces of these particles and from the peat matrix. Despite this, the chronology of anthropogenic, atmospheric deposition for the past millenium recorded by the isotopic composition of Pb in all three peat bogs is remarkably similar. While the immobility of Pb in the peat cores may appear inconsistent with the elevated porewater Pb concentrations, Pb concentrations in the aqueous phase never amount to more than 0.01% of the total Pb at any given depth so that the potential for migration remains small. The low rates of vertical water movement in bogs generally combined with the size of the metal-containing particles in solution may be additional factors limiting Pb mobilization.

Making waste management public (or falling back to sleep)

Human-produced waste is a major environmental concern, with communities considering various waste management practices, such as increased recycling, landfilling, incineration, and waste-to-energy technologies. This article is concerned with how and why publics assemble around waste management issues. In particular, we explore Noortje Marres and Bruno Latour's theory that publics do not exist prior to issues but rather assemble around objects, and through these assemblages, objects become matters of concern that sometimes become political. The article addresses this theory of making things public through a study of a small city in Ontario, Canada, whose landfill is closed and waste diversion options are saturated, and that faces unsustainable costs in shipping its waste to the United States, China, and other regions. The city's officials are undertaking a cost-benefit assessment to determine the efficacy of siting a new landfill or other waste management facility. We are interested in emphasizing the complexity of making (or not making) landfills public, by exploring an object in action, where members of the public may or may not assemble, waste may or may not be made into an issue, and waste is sufficiently routinized that it is not typically transformed from an object to an issue. We hope to demonstrate Latour's third and fifth senses of politics best account for waste management's trajectory as a persistent yet inconsistent matter of public concern.

Trace metals in upland headwater lakes in Ireland

Trace elements (n = 23) in Irish headwater lakes (n = 126) were investigated to determine their ambient concentrations, fractionation (total, dissolved, and non-labile), and geochemical controls. Lakes were generally located in remote upland, acid-sensitive regions along the coastal margins of the country. Total trace metal concentrations were low, within the range of natural pristine surface waters; however, some lakes (~20 %) had inorganic labile aluminum and manganese at levels potentially harmful to aquatic organisms. Redundancy analysis indicated that geochemical weathering was the dominant controlling factor for total metals, compared with acidity for dissolved metals. In addition, many metals were positively correlated with dissolved organic carbon indicating their affinity (or complexation) with humic substances (e.g., aluminum, iron, mercury, lead). However, a number of trace metals (e.g., aluminum, mercury, zinc) were correlated with anthropogenic acidic deposition (i.e., non-marine sulfate), suggesting atmospheric sources or elevated leaching owing to acidic deposition. As transboundary air pollution continues to decline, significant changes in the cycling of trace metals is anticipated.

Atmospheric deposition of beryllium in Central Europe: comparison of soluble and insoluble fractions in rime and snow across a pollution gradient

Little is known about atmospheric input of beryllium (Be) into ecosystems, despite its highly toxic behavior. For three consecutive winters (2009-2011), we measured Be concentrations in horizontal deposition (rime) and vertical deposition (snow) at 10 remote mountain-top locations in the Czech Republic, Central Europe. Beryllium was determined both in filtered waters, and in HF digests of insoluble particles. Across the sites, soluble Be concentrations in rime were 7 times higher, compared to snow (6.1 vs. 0.9ng·L(-1)). Rime scavenged the pollution-rich lower segments of clouds. The lowest Be concentrations were detected in the soluble fraction of snow. Across the sites, 34% of total Be deposition occurred in the form of soluble (bioavailable) Be, the rest were insoluble particles. Beryllium fluxes decreased in the order: vertical dry deposition insoluble>vertical dry deposition soluble>horizontal deposition soluble>vertical wet deposition insoluble>vertical wet deposition soluble>horizontal deposition insoluble. The average contributions of these Be forms to total deposition were 56, 21, 8, 7, 5 and 3%, respectively. Sites in the northeast were more Be-polluted than the rest of the country with sources of pollution in industrial Silesia.

Increasing arsenic concentrations in runoff from 12 small forested catchments (Czech Republic, Central Europe): patterns and controls

The 40-year long period of heavy industrialization in Central Europe (1950-1990) was accompanied by burning of arsenic-rich lignite in thermal power plants, and accumulation of anthropogenic arsenic in forest soils. There are fears that retreating acidification may lead to arsenic mobilization into drinking water, caused by competitive ligand exchange. We present monthly arsenic concentrations in surface runoff from 12 headwater catchments in the Czech Republic for a period of 13 years (1996-2008). The studied area was characterized by a north-south gradient of decreasing pollution. Acidification, caused mainly by SOx and NOx emissions from power plants, has been retreating since 1987. Between 1996 and 2003, maximum arsenic concentrations in runoff did not change, and were < 1 ppb in the rural south and < 2 ppb in the industrial north. During the subsequent two years, 2004-2005, maximum arsenic concentrations in runoff increased, reaching 60% of the drinking water limit (10 ppb). Starting in 2006, maximum arsenic concentrations returned to lower values at most sites. We discuss three possible causes of the recent arsenic concentration maximum in runoff. We rule out retreating acidification and a pulse of high industrial emission rates as possible controls. The pH of runoff has not changed since 1996, and is still too low (<6.5) at most sites for an As-OH(-) ligand exchange to become significant. Elevated arsenic concentrations in runoff in 2004-2005 may reflect climate change through changing hydrological conditions at some, but not all sites. Dry conditions may result in elevated production of DOC and sulfur oxidation in the soil. Subsequent wet conditions may be accompanied by acidification leading to faster dissolution of arsenic-bearing sulfides, dissolution of arsenic-bearing Fe-oxyhydroxides, and elevated transport of arsenic sorbed on organic matter. Anaerobic domains exist in normally well-aerated upland soils for hours-to-days following precipitation events.