Search

Asbestos fibers are highly toxic (Group 1 carcinogen) due to their high aspect ratio, durability, and the presence of iron. In nature, plants, fungi, and microorganisms release exudates, which can alter the physical and chemical properties of soil minerals including asbestos minerals. We examined whether exudates from bacteria and fungi at environmentally relevant concentrations can alter chrysotile, the most widely used asbestos mineral, and lower its toxicity. We monitored the release of iron from chrysotile in the presence of organic acid ligands and iron-specific siderophores derived from bacteria and fungi and measured any change in fiber toxicity toward peritoneal macrophages harvested from mice. Both fungal and bacterial siderophores increased the removal of iron from asbestos fibers. In contrast, organic acid ligands at environmentally relevant concentrations neither released iron from fibers nor helped in siderophore-mediated iron removal. Removal of plant-available or exchangeable iron did not diminish iron dissolution by both types of siderophores, which indicates that siderophores can effectively remove structural iron from chrysotile fibers. Removal of iron by siderophore lowered the fiber toxicity; fungal siderophore appears to be more effective than bacterial siderophore in lowering the toxicity. These results indicate that prolonged exposure to siderophores, not organic acids, in the soil environment decreases asbestos fiber toxicity and possibly lowers the health risks. Thus, bioremediation should be explored as a viable strategy to manage asbestos-contaminated sites such as Brownfield sites, which are currently left untreated despite dangers to surrounding communities.

We examine the feasibility of phytoremediation as an alternative strategy to limit the exposure of asbestos in site with asbestos-containing materials. We collected soils from four locations from two sites-one with naturally occurring asbestos, and another, a superfund site, where asbestos-containing materials were disposed over decades-and performed ecotoxicology tests. We also performed two experiments with crop cultivar and two grasses from serpentine ecotype and cultivar to determined best choice for phytoremediation. Asbestos concentrations in different size fractions of soils varied by orders of magnitude. However, different asbestos concentrations had little effect on germination and root growth. Presence of co-contaminants such as heavy metals and lack of nutrients affected plant growth to different extents, indicating that several of these limiting factors should be considered instead of the primary contaminant of concern. Crop cultivar survived on asbestos-contaminated soil. Grasses from serpentine ecotype did not show higher biomass than the cultivar. Overall, these results showed that soil conditions play a critical role in screening different crop species for phytoremediation and that asbestos concentration has limited to no effect on plant growth. Our study provided a framework for phytoremediation of asbestos-contaminated sites to limit long-term asbestos exposure.

Background and aimsElemental uptake in serpentine floras in eastern North America is largely unknown. The objective of this study was to determine major and trace element concentrations in soil and leaves of three native pseudo-metallophyte C4 grasses in situ at five sites with three very different soil types, including three serpentine sites, in eastern USA.MethodsPseudo-total and extractible concentrations of 15 elements were measured and correlated from the soils and leaves of three species at the five sites.ResultsElement concentrations in soils of pseudo-metallophytes varied up to five orders of magnitude. Soils from metalliferous sites exhibited higher concentrations of their characteristic elements than non-metalliferous. In metallicolous populations, elemental concentrations depended on the element. Concentrations of major elements (Ca, Mg, K) in leaves were lower than typical toxicity thresholds, whereas concentrations of Zn were higher.ConclusionsIn grasses, species can maintain relatively low metal concentrations in their leaves even when soil concentrations are richer. However, in highly Zn-contaminated soil, we found evidence of a threshold concentration above which Zn uptake increases drastically. Finally, absence of main characteristics of serpentine soil at one site indicated the importance of soil survey and restoration to maintain serpentinophytes communities and avoid soil encroachment.

In many gravel-bedded rivers, floods that fill the channel banks create just enough shear stress to move the median-sized gravel particles on the bed surface (D50). Because this observation is common and is supported by theory, the coincidence of bankfull flow and the incipient motion of D50 has become a commonly used assumption. However, not all natural gravel channels actually conform to this simple relationship; some channels maintain bankfull stresses far in excess of the critical stress required to initiate sediment transport. We use a database of >300 gravel-bedded rivers and >600 10Be-derived erosion rates from across North America to explore the hypothesis that sediment supply drives the magnitude of bankfull shear stress relative to the critical stress required to mobilize the median bed surface grain size ([Formula: see text]). We find that [Formula: see text] is significantly higher in West Coast river reaches (2.35, n = 96) than in river reaches elsewhere on the continent (1.03, n = 245). This pattern parallels patterns in erosion rates (and hence sediment supplies). Supporting our hypothesis, we find a significant correlation between upstream erosion rate and local [Formula: see text] at sites where this comparison is possible. Our analysis reveals a decrease in bed surface armoring with increasing [Formula: see text], suggesting channels accommodate changes in sediment supply through adjustments in bed surface grain size, as also shown through numerical modeling. Our findings demonstrate that sediment supply is encoded in the bankfull hydraulic geometry of gravel bedded channels through its control on bed surface grain size.

To measure the toxic potential of asbestos fibers-a known cause of asbestosis, lung cancer, and malignant mesothelioma-asbestos minerals are generally first ground down to small fibers, but it is unknown whether the grinding condition itself changes the fiber toxicity. To evaluate this, we ground chrysotile ore with or without water for 5-30 min and quantified asbestos-induced reactive oxygen species generation in elicited murine peritoneal macrophages as an indicator of fiber toxicity. The toxicity of dry-ground fibers was higher than the toxicity of wet-ground fibers. Grinding with or without water did not materially alter the mineralogical properties. However, dry-ground fibers contained at least 7 times more iron than wet-ground fibers. These results indicate that grinding methods significantly affect the surface concentration of iron, resulting in changes in fiber-induced reactive oxygen species generation or toxicity. Therefore, fiber preparation conditions should be accounted for when comparing the toxicity of asbestos fibers between reported studies.

Environmental contextBeryllium is a toxic environmental contaminant but has many industrial and scientific applications. Our work explores the effects of soil composition on beryllium retention, focussing on organic matter, mineralogy and pH and concludes that phosphorus and sulfur oxides in addition to soil acidity are strong controls on beryllium mobility. These results aid in future predictions regarding the fate of beryllium in the environment.AbstractUnderstanding the chemical controls on beryllium sorption is fundamental when assessing its mobility as a pollutant and interpreting its concentration as a geochemical tracer of erosion, weathering and landscape surface stability. In order to evaluate the interactions of beryllium with soil- and aquatic-related materials, we selected model organic compounds and minerals to perform sorption experiments. The retention of beryllium by each of these compounds and minerals was evaluated over a pH range of 3–6 and at various equilibration times to determine which conditions allowed the greatest retention of beryllium. We conclude that most beryllium sorption occurred within 24h for both organic and mineral materials. However, equilibration required longer periods of time and was dependent on the solution pH and sorbent material. The pH exhibited a strong control on beryllium sorption with distribution coefficient (Kd) values increasing non-linearly with increasing pH. A system with a pH of 6 is likely to retain 79–2270% more beryllium than the same system at a pH of 4. Phosphonate retained the greatest amount of beryllium, with Kd values 2–30× greater than all other materials tested at a pH of 6. Therefore, soils containing larger amounts of phosphorus-bearing minerals could result in greater retention of beryllium relative to phosphorus-limited soils. Overall, soil composition, with an emphasis on phosphorus oxide content and pH, is an important property to consider when evaluating the capacity of a system to retain beryllium.

The modern Antarctic Dry Valleys are locked in a hyper-arid, polar climate that enables the East Antarctic Ice Sheet (EAIS) to remain stable, frozen to underlying bedrock. The duration of these dry, cold conditions is a critical prerequisite when modeling the long-term mass balance of the EAIS during past warm climates and is best examined using terrestrial paleoclimatic proxies. Unfortunately, deposits containing such proxies are extremely rare and often difficult to date. Here, we apply a unique dating approach to tundra deposits using concentrations of meteoric beryllium-10 ((10)Be) adhered to paleolake sediments from the Friis Hills, central Dry Valleys. We show that lake sediments were emplaced between 14-17.5 My and have remained untouched by meteoric waters since that time. Our results support the notion that the onset of Dry Valleys aridification occurred ~14 My, precluding the possibility of EAIS collapse during Pliocene warming events. Lake fossils indicate that >14 My ago the Dry Valleys hosted a moist tundra that flourished in elevated atmospheric CO2 (>400 ppm). Thus, Dry Valleys tundra deposits record regional climatic transitions that affect EAIS mass balance, and, in a global paleoclimatic context, these deposits demonstrate how warming induced by 400 ppm CO2 manifests at high latitudes.

Over geologic timescales, C[O.sub.2] is emitted from the Earth's interior and is removed from the atmosphere by silicate rock weathering and organic carbon burial. This balance is thought to have stabilized greenhouse conditions within a range that ensured habitable conditions (1). Changes in this balance have been attributed to changes in topographic relief, where varying rates of continental rock weathering and erosion (1,2) are superimposed on fluctuations in organic carbon burial (3). Geological strata provide an indirect yet imperfectly preserved record of this change through changing rates of sedimentation (1,2,4). Widespread observations of a recent (0-5-Myr) fourfold increase in global sedimentation rates require a global mechanism to explain them (4-6). Accelerated uplift and global cooling have been given as possible causes (2,4,6,7), but because of the links between rates of erosion and the correlated rate of weathering (8,9), an increase in the drawdown of C[O.sub.2] that is predicted to follow may be the cause of global climate change instead (2). However, globally, rates of uplift cannot increase every where in the way that apparent sedimentation rates do (4,10). Moreover, proxy records of past atmospheric C[O.sub.2] provide no evidence for this large reduction in recent C[O.sub.2] concentrations (11,12). Here we question whether this increase in global weathering and erosion actually occurred and whether the apparent increase in the sedimentation rate is due to observational biases in the sedimentary record (13). As evidence, we recast the ocean dissolved [sup.10]Be/[sup.9]Be isotope system as a weathering proxy spanning the past ~12 Myr (ref. 14). This proxy indicates stable weathering fluxes during the late-Cenozoic era. The sum of these observations shows neither clear evidence for increased erosion nor clear evidence for a pulse in weathered material to the ocean. We conclude that processes different from an increase in denudation caused Cenozoic global cooling, and that global cooling had no profound effect on spatially and temporally averaged weathering rates., Studies of both the suspended and the dissolved loads of the world's largest rivers and of hill-slope denudation have shown a strong link between physical erosion and chemical weathering (8,9). [...]

Along the South Fork of the Eel River in northern California, paleoerosion rates derived from [sup.10]Be concentrations in late Pleistocene strath terrace sediment are a factor of 2 greater than erosion rates derived from modern stream sediment and 3.5 times greater than paleoerosion rates from the Pleistocene-Holocene transition. Using these results as a proxy for sediment supply, we provide quantitative field-based evidence that extensive strath planation is linked to elevated sediment supply conditions. We have used optically stimulated luminescence (OSL) to date strath terrace sediment and find that the highest erosion rates and most extensive period of strath planation occurred during a period of increased precipitation in the late Pleistocene. Based on our OSL data, we estimate that bedrock channel lowering rates have outpaced basin-averaged erosion rates by a factor of three since abandonment of the extensive late Pleistocene strath surface. Thus, our data indicate that hillslope relief has been increasing for the past ~20 ka.

Meteoric 10Be (10Bemet) concentrations in soil profiles have great potential as a geochronometer and a tracer of Earth surface processes, particularly in fine-grained soils lacking quartz that would preclude the use of in situ produced 10Be (10Bein situ). One prerequisite for using this technique for accurately calculating rates and dates is constraining the delivery, or flux, of 10Bemet to a site. However, few studies to date have quantified long-term (i.e., millennial) delivery rates, and none have determined a delivery rate for an eroding soil. In this study, we compared existing concentrations of 10Bein situ with new measurements of 10Bemet in eroding soils sampled from the same depth profiles to calibrate a long-term 10Bemet delivery rate. We did so on the Pinedale (~21-25 kyr) and Bull Lake (~140 kyr) glacial moraines at Fremont Lake, Wyoming (USA), where age, grain sizes, weathering indices, and soil properties are known, as are erosion and denudation rates calculated from 10Bein situ. After ensuring sufficient beryllium retention in each profile, solving for the delivery rate of 10Bemet, and normalizing for paleomagnetic and solar intensity variations over the Holocene, we calculate 10Bemet fluxes of 1.46 (±0.20) x 106 atoms cm-2 yr-1 and 1.30 (±0.48) x 106 atoms cm-2 yr-1 to the Pinedale and Bull Lake moraines, respectively, and compare these values to two widely used 10Bemet delivery rate estimation methods that substantially differ for this site. Accurately estimating the 10Bemet flux using these methods requires a consideration of spatial scale and temporally varying parameters (i.e., paleomagnetic field intensity, solar modulation) to ensure the most realistic estimates of 10Bemet-derived erosion rates in future studies. [ABSTRACT FROM AUTHOR]