Effects of increasing concentrations of unamended and gypsum modified bauxite residues on soil microbial community functions and structure - A mesocosm study.

Bauxite residues (BR), commonly named red muds, are the saline-sodic waste produced during the extraction of alumina from bauxite. In this study, four kinds of BR were mixed at increasing concentrations with two soils in a mesososm experiment. Unamended BR from Provence (PRO) and Guinea (GUI) bauxite were selected, and Modified Bauxite Residues from PRO and GUI (MBR-PRO and MBR-GUI) were obtained by gypsum application and repeated leaching, in order to reduce their pH, electrical conductivity (EC) and exchangeable sodium percentage (ESP). Several indicators of microbial community functions and structure (growth of culturable bacteria; enzymatic activities; C-sourced substrates degradation (Biolog®); bacteria and fungi PCR-RFLP fingerprints) were measured after 35 days of incubation. Results showed that PRO residue had stronger negative effects than GUI on all the tested indicators. Residues modified by gypsum addition (MBR-PRO, MBR-GUI) were equally or sometimes less harmful compared to unamended residues. Microbial activities (bacterial growth and enzyme activities) were more inhibited than the diversity of microbial functions (Biolog®), and the structure of bacterial and fungal communities was not affected by increasing concentrations of bauxite residues. EC and ESP were the main factors explaining the inhibition of microbial activities, although the origin of bauxite residue is of great importance too.

Pollution and ecological risk assessment of heavy metals in the soil-plant system and the sediment-water column around a former Pb/Zn-mining area in NE Morocco.

This study discussed the environmental fate and ecological hazards of heavy metals in the soil-plant system and sediment-water column around the former Pb-Zn mining Zeïda district, in Northeastern Morocco. Spatial distribution, pollution indices, and cluster analysis were applied for assessing Pb, Zn, As, Cu and Cd pollution levels and risks. The geo-accumulation index (Igeo) was determined using two different geochemical backgrounds: i) the commonly used upper crust values, ii) local geochemical background calculated with exploratory data analysis. The soils in the vicinity of the tailings, as well as the sediments downstream of the latter, displayed much higher metal concentrations, Igeo, and potential ecology risk coefficient values than other sites, classifying these sites as highly contaminated and severely hazardous. The concentrations of Pb in contaminated sediment samples also exceeded the PEC limits and are expected to cause harmful effects on sediment-dwelling organisms. Based on the comparison with the toxicity limits, the most contaminated plant samples were found around the tailings piles. The metal concentrations in both raw and filtrated water samples were overall below the drinking water standards in samples upstream and downstream of the mining center, indicating that heavy metals levels in the Moulouya River surface waters were not affected by the tailings spill. Cluster analysis suggest that: i) Pb and Zn in sediments were derived from the abandoned tailings and are mainly stored and transported as particle-bound to the bedload, ii) Pb, Zn, and Cu in the soil-plant system were related to the dispersion of tailings materials while As and Cd originated primarily from natural geological background in both the soil-plant and the water-sediment systems.

Investigating palygorskite's role in the development of mesothelioma in southern Nevada: Insights into fiber-induced carcinogenicity.

Similar to asbestos fibers, nonregulated mineral fibers can cause malignant mesothelioma (MM). Recently, increased proportions of women and young individuals with MM were identified in southern Nevada, suggesting that environmental exposure to carcinogenic fibers was causing the development of MM. Palygorskite, a fibrous silicate mineral with a history of possible carcinogenicity, is abundant in southern Nevada. In this study, our aim was to determine whether palygorskite was contributing to the development of MM in southern Nevada. While palygorskite, in vitro, displayed some cytotoxicity toward primary human mesothelial (HM) cells and reduced their viability, the effects were roughly half of those observed when using similar amounts of crocidolite asbestos. No Balb/c (0/19) or MexTAg (0/18) mice injected with palygorskite developed MM, while 3/16 Balb/c and 13/14 MexTAg mice injected with crocidolite did. Lack of MM development was associated with a decreased acute inflammatory response, as injection of palygorskite resulted in lower percentages of macrophages (p = .006) and neutrophils (p = .02) in the peritoneal cavity 3 d after exposure compared to injection of crocidolite. Additionally, compared to mice injected with crocidolite, palygorskite-injected mice had lower percentages of M2 (tumor-promoting) macrophages (p = .008) in their peritoneal cavities when exposed to fiber for several weeks. Our study indicates that palygorskite found in the environment in southern Nevada does not cause MM in mice, seemingly because palygorskite, in vivo, fails to elicit inflammation that is associated with MM development. Therefore, palygorskite is not a likely contributor to the MM cases observed in southern Nevada.

Sediment pollution: An assessment of anthropogenic and geogenic trace element contributions along the central Algerian coast.

Sediment cores from the central Algerian coast were collected to investigate the distribution, sources and risk of trace metals. The local geochemical background of metals was defined from the core S collected in an uncontaminated area of the coast. The anthropogenic inputs in Algiers Bay elevated Ag, Cd, Pb and Zn concentrations as their maximum were 3.1, 3, 2.1 and 1.8 times the background values, respectively. Meanwhile, increased contents of Arsenic (up to 21.1 mg/kg) were detected in all sites. Correlations and PCA suggest that lithogenic sources controlled metal deposition, while most sediment arsenic was agriculture-derived. Organic matter acted as a sink or source for some trace metals. According to EFs, the study area showed slight to moderate enrichment with respect to Ag, As, Pb, Cd, Zn and Cu, whereas they remained uncontaminated with Cr, V, Co and Ni. This study provides a needed baseline for future environmental investigations.

Occurrence, contamination level and ecological risk assessment of dissolved and particulate trace elements in rivers entering the southwestern Mediterranean Sea.

Metal pollution in rivers should not be overlooked before their entry into the sea. However, there are few studies for estimating such contamination in rivers entering the Algerian coastal waters. Semimonthly quantification of dissolved and particulate metals, near the mouths of two industrial-tainted rivers, El Harrach and Mazafran rivers, was carried out during a period of one year. All the trace metals analyzed are originating from anthropogenic sources (EF > 1.5), with higher contamination of dissolved Pb, Cd, Zn and Ni and a slight degree of contamination of particulate Cu and Zn (0 < Igeo < 1). Particulate metals show a stable complex with the particulate phase (e.g. 2 < LogKd < 6). The risk assessment results indicate that particulate Pb and Zn have a 33% likelihood of toxicity for adverse biological effects. A significant toxicity effect (ΣTUi >4) of the combined particulate metals (Pb, Cd, Cu, Zn, Cr, Ni and As) was primarily due to the higher particulate Cd, Zn, and Cr availability.

Concentrations and transportation of metal and organochlorine pollutants in vegetables and risk assessment of human exposure in rural, urban and industrial environments (Bouches-du-Rhône, France).

The bioaccumulation of metals (As, Cd, Co, Cr, Cu, Ni, Pb, Sb, V, Zn, Al, Fe) and organochlorine compounds (PCDD-Fs and PCBs) was assessed in soils and vegetables of 3 sites of contrasted anthropogenic influence (rural and industrial-urban areas). Cultivated soils in industrial areas exhibited diffuse pollution in organochlorine pollutants (PCBs and PCDD-Fs). The pollutant levels encountered in vegetables were always lower than the EU regulatory or recommended values. However, the contents measured in vegetables cultivated near industrialized areas were significantly higher than those observed in rural areas. This was notably the case for Co, Cd, Cr, Ni, Pb, V, NDL- and DL-PCB, PCDD, and PCDF. The leaf pathway appeared as the main absorption pathway for many contaminants. The results suggested that population exposure to pollutants was mainly caused by vegetable ingestion. In the vegetables and soils, the toxicity was mainly caused by the V, Co, Cd, and Pb contents to which can be added As and PCDD-Fs for soils. Therefore, the proximity of vegetable crops to highly anthropised areas has led to long-term exposure of vegetables and soils to air pollutants, leading to an accumulation in the food chain and thus a risk for human health.

Modelling geochemical and kinetic processes involved in lead (Pb) remobilization during resuspension events of contaminated sediments.

The objective of this paper is to present a model simulating and predicting the exchange kinetics of lead (Pb) between contaminated sediments and water during resuspension events potentially occurring in reservoirs. We developed an innovative model that combines thermodynamic speciation of particulate surfaces (oxides and Particulate Organic Carbon (POC)), thermodynamic Pb speciation in water, and kinetic modelling of exchanges between free Pb and particulate sites (i.e., dissolution of a carbonate carrier phase, adsorption/coprecipitation and desorption/dissolution to/from oxides, and adsorption and desorption/degradation to/from particulate organic particles). We used results from laboratory resuspension experiments performed on sediments from three contaminated dam reservoirs to calibrate a new chemical speciation model. Uptake and release processes to/from sediments were found to be controlled by at least two successive reactions that are associated with two particulate pools (here oxides and POC). Kinetic adsorption and desorption rates were calibrated for seven experimental conditions. Variability in kinetic rates allowed evaluation of the effect of the solid-to-liquid ratio and sediment origin on exchange kinetics at the water-particle interface. The kinetic release of dissolved Pb by desorption or dissolution from the oxides was reproduced almost identically between the experiments, regardless of the solid-to-liquid ratio or sediment origin. Long-term readsorption on POC sites is more variable, even if ranges of variation in the adsorption and desorption kinetic rates related to POC remain limited, considering that tested sediments vary significantly. CAPSULE: A kinetic model simulating the dynamics of lead (Pb) during sediment resuspension was developed and calibrated to laboratory experiments performed on three contaminated sediments.

Differences in bulk and microscale yttrium speciation in coal combustion fly ash.

Coal combustion ash is a promising alternative source of rare earth elements (REE; herein defined as the 14 stable lanthanides, yttrium, and scandium). Efforts to extract REE from coal ash will depend heavily on the location and speciation of these elements in the ash. This study sought to identify the major chemical forms of yttrium (Y), as a representative REE in coal fly ash samples selected from major coal sources in the United States. Y speciation was evaluated using both bulk scale analyses (sequential extractions, Y K-edge X-ray absorption near-edge spectroscopy - XANES) and complementary analyses at the micron scale (micro-focus X-ray fluorescence and micro-XANES). Sequential selective extractions revealed that the REE were primarily in the residual (unextracted fraction) of coal fly ash samples. Extraction patterns for yttrium resembled those of the lanthanides, indicating that these elements were collectively dispersed throughout the aluminosilicate glass in fly ash. Bulk XANES analysis indicated that Y coordination states resembled a combination of Y-oxides, Y-carbonate, and Y-doped glass, regardless of ash origin. However, in the microprobe analysis, we observed "hotspots" of Y (∼10-50 µm) in some samples that included different Y forms (e.g., Y-phosphate) not observed in bulk measurements. Overall, this study demonstrated that yttrium (and potentially other REEs) are entrained in the glass phase of fly ash and that microscale investigations of individual high-REE regions in fly ash samples do not necessarily capture the dominant speciation.

Diurnal evolution of the temperature sensitivity of CO2 efflux in permafrost soils under control and warm conditions.

Cryosols contain ~33% of the global soil organic carbon. Cryosol warming and permafrost degradation may enhance the CO2 release to the atmosphere through the microbial decomposition. Despite the large carbon pool, the permafrost carbon feedback on the climate remains uncertain. In this study, we aimed at better understanding the diurnal evolution of the temperature sensitivity of CO2 efflux in Cryosols. A Histic Cryosol and a Turbic Cryosol were instrumented in tussock tundra ecosystems near Salluit (Nunavik, Canada). Open top chambers were installed during summer 2011 and the ground temperature, the soil moisture and meteorological variables were recorded hourly while the ecosystem respiration was measured three times per day every second day with opaque and closed dynamic chambers in control and warm stations. Despite warmer conditions, the average CO2 efflux at the control stations at the Histic site (1.29±0.45µmolCO2m-2s-1) was lower than at the Turbic site (2.30±0.74µmolCO2m-2s-1). The increase in CO2 efflux with warming was greater in the Histic Cryosol (~39%) than in the Turbic Cryosol (~16%). Our study showed that the temperature sensitivity of the ecosystem respiration evolved during the day and decreased with the experimental warming. Both sites exhibited diurnal hysteresis loops between CO2 efflux and the soil surface temperature. The width of hysteresis loops increased with the solar radiation and decreased along the growing season. We developed simple linear models that took into account the diurnal evolution of the temperature sensitivity of CO2 efflux and we estimated the seasonal cumulative carbon release to the atmosphere. The calculation using solely diurnal measurements significantly differed from the seasonal carbon release modelled hourly. Our study highlighted that the time of the day when measurements are performed should be taken into account to accurately estimate the seasonal carbon release from tundra ecosystems.

Pleural mesothelioma in New Caledonia: associations with environmental risk factors.

BACKGROUND: High incidences of malignant mesothelioma (MM) have been observed in New Caledonia. Previous work has shown an association between MM and soil containing serpentinite. OBJECTIVES: We studied the spatial and temporal variation of MM and its association with environmental factors. METHODS: We investigated the 109 MM cases recorded in the Cancer Registry of New Caledonia between 1984 and 2008 and performed spatial, temporal, and space-time cluster analyses. We conducted an ecological analysis involving 100 tribes over a large area including those with the highest incidence rates. Associations with environmental factors were assessed using logistic and Poisson regression analyses. RESULTS: The highest incidence was observed in the Houaïlou area with a world age-standardized rate of 128.7 per 100,000 person-years [95% confidence interval (CI), 70.41-137.84]. A significant spatial cluster grouped 18 tribes (31 observed cases vs. 8 expected cases; p = 0.001), but no significant temporal clusters were identified. The ecological analyses identified serpentinite on roads as the greatest environmental risk factor (odds ratio = 495.0; 95% CI, 46.2-4679.7; multivariate incidence rate ratio = 13.0; 95% CI, 10.2-16.6). The risk increased with serpentinite surface, proximity to serpentinite quarries and distance to the peridotite massif. The association with serpentines was stronger than with amphiboles. Living on a slope and close to dense vegetation appeared protective. The use of whitewash, previously suggested to be a risk factor, was not associated with MM incidence. CONCLUSIONS: Presence of serpentinite on roads is a major environmental risk factor for mesothelioma in New Caledonia.

XANES evidence for oxidation of Cr(III) to Cr(VI) by Mn-oxides in a lateritic regolith developed on serpentinized ultramafic rocks of New Caledonia.

Although several laboratory studies showed that Mn-oxides are capable of oxidizing Cr(II) to Cr(VI), very few have reported evidence for such a reaction in natural systems. This study presents new evidence for this redox reaction between Cr(III) and Mn-oxides in a lateritic regolith developed on ultramafic rocks in New Caledonia. The studied lateritic regolith presents several units with contrasting amounts of major (Fe, Al, Si, and Mg) and trace (Mn, Cr, Ni, Co) elements, which are related to varying mineralogical compositions. Bulk XANES analyses show the occurrence of Cr(VI) (up to 20 wt % of total chromium) in the unit of the regolith which is also enriched in Mn (up to 21.7 wt % MnO), whereas almost no Cr(VI) is detected elsewhere. X-ray powder diffraction indicates that the large amounts of Mn in this unit of the regolith are due to the occurrence of Mn-oxides (identified as a mixture of asbolane, lithiophorite and birnessite) and Mn K-edge XANES data indicate that Mn occurs mainly as Mn(IV) in this unit, although small amounts of Mn(III) could also be detected. These results strongly suggest a direct role of the Mn-oxides on the occurrence of Cr(VI) through a redox reaction between Cr(III) and Mn(IV) and/or Mn(III). Owing to the much larger toxicity and solubility of Cr(VI), such a co-occurrence of Cr and Mn-oxides in these soils could then represent an important risk for the environment. However, the significant amounts of Cr(VI) released after reacting the samples from the studied sequence with a 0.1 M (NH)4H2PO4 solution, designed to remove tightly sorbed chromate species, suggest that Cr(VI) mainly occurs as sorption complexes. This hypothesis is reinforced by spatially resolved XANES analyses, which show that Cr(VI) is associated with both Mn- and Fe-oxides, and especially at the boundary between these two mineral species. Such a distribution of Cr(VI) suggests a possible readsorption of Cr(VI) onto surrounding Fe-oxyhydroxides (mainly goethite) after oxidation by the Mn(IV)-oxides. These results, added to leaching tests with a 0.01 M CaCl2 solution indicative of low exchangeability of Cr in the investigated samples, suggest that secondary sorption reactions onto Fe-oxides might significantly decrease the environmental impact of the oxidation of Cr(III) to Cr(VI) by Mn-oxides.