Alexander Neaman

Elemental release rates from dissolving basalt and granite with and without organic ligands

Bacteria, fungi, lichen and plants all produce organic acids, which can strongly affect weathering by increasing the solubility and mobility of elements. Leaching by organic acids may therefore produce trace element signatures which could record the presence of life in the rock record from early Earth. To elucidate this effect, long term column experiments were performed with powdered granite and basalt with and without 0.01 M citrate at pH=6 for 45 weeks. Both granite (8.44 × 10−13, 3.39 × 10−13) and basalt (2.94 × 10−14, 6.47 × 10−14) dissolution rates mol (Ca, Mg) (m−2 s−1 respectively) were enhanced in the presence of citrate relative to the organic-free controls: granite (3.17 × 10−14, 4.4 × 10−15) and basalt (1.01 × 10−14, 1.04 × 10−14). Enhanced release of individual elements in the presence of citrate was strongly correlated with the stability constant of the citrate-element complex. Elements which might be useful as biosignatures are those elements that showed a strong enrichment in the presence of citrate: Zr, Sc and Mn (basalt), V and Zn (granite), and Y, La, Ce, Th, Ti, Al, P, Pb, Ni and Fe (both basalt and granite). Release of these elements from the rock material in the columns is consistent with dissolution of apatite + Fe sulfides + Fe oxides + augite in basalt and apatite + sphene + hornblende in granite. Similar groups of elements have been reported to be enriched in organic-rich rivers, suggesting leaching of strongly-complexed elements could be useful as biosignatures and may have left mineralogical traces on early Earth.

Element mobility patterns record organic ligands in soils on early Earth

Considerable mobilization of Fe without mobilization of Al in Precambrian paleosols has been documented and attributed to either anoxic- or ligand-promoted dissolution. To elucidate these mechanisms, basalt was dissolved under oxic and anoxic conditions with and without citrate, and the mobility of several elements was analyzed. The extent of release of Fe and P was minor (in citrate-free conditions) or considerable (with citrate) regardless of oxygen pressure. Release of Al was minor in all cases, whereas release of Cu was minor (in anoxic conditions) or considerable (in oxic conditions). Release of Cu was enhanced by citrate. In comparison, in the weathered surface of two of the oldest-known basalt-derived paleosols—the Mount Roe (2.76 Ga) and the Hekpoort (2.25 Ga)— Fe and P were considerably depleted and Al retained, consistent with the presence of organic ligands. Cu, retained in the Mount Roe paleosol but considerably mobilized in the Hekpoort paleosol, documents formation under an anoxic atmosphere and an oxic atmosphere, respectively, as inferred by others on the basis of Fe mobility. The immobility of Al in both paleosols is consistent with formation under conditions in which the annual volume of rainwater was lower than the topsoil pore volume. Mobilization of P in such paleosols developed under low-rainfall conditions provides a new proxy for identification of ligands secreted by terrestrial organisms on early Earth.

Effects of organic ligands on granite dissolution in batch experiments at pH 6

Yosemite granite from the Tuolumne River series was dissolved under oxic and anoxic conditions in the presence (0.001 or 0.01 M) and absence of organic ligands in batch experiments at pH 6. Release of all elements was enhanced considerably in the presence of organic ligands. Citrate (tridentate) and gallate (tetradentate) increased element release to the greatest extent among the aliphatic and aromatic ligands, respectively. The extent of element mobilization observed for the aliphatic ligands decreased in the order citrate > oxalate ≈ malonate and for the aromatic ligands gallate > salicylate ≈ phthalate. The effects of the ligands generally followed trends in cation-ligand stability constants, but aromatic ligands were less effective in element mobilization than aliphatic ligands. This was attributed to protonation of the functional groups of aromatic ligands at pH 6. Rock dissolution was non-stoichiometric regardless of the presence or absence of organic ligands. Release of P and Cu (% of total element content in the unweathered rock) in the presence of organic ligands was considerably greater than that of other elements. Findings of the present study were compared to the findings of our previous study on dissolution of basalt. Differences in the mobility patterns of Y, Fe, Cu, Ti, and Zr during dissolution of granite and basalt were observed. In basalt, release of Y was enhanced considerably in the presence of citrate. In contrast, in the present study, release of Y from granite with and without citrate was at the detection limit. This difference was attributed to the difference in Y-hosting parent minerals: apatite (basalt) and sphene (granite). With and without organic ligands, no significant differences were observed in the extent of Fe released from granite under oxic versus anoxic conditions, while the extent of Fe release from basalt was considerably greater under anoxic versus oxic conditions with and without organic ligands. These differences can be attributed to the difference in major Fe-hosting phases in the rocks: biotite (granite) versus glass and augite (basalt). In the granite, concentrations of Cu released increased considerably in the presence of organic ligands under both oxic and anoxic conditions. In contrast, concentrations of Cu released from basalt were increased considerably only under oxic conditions, especially in the presence of organic ligands. This difference was attributed to the different extent of Fe release from basalt and granite that affected dissolution of Cu/Fe-sulfides. Although both Ti and Zr can be mobilized in the presence of organic ligands, in the rock where zircons hosted Zr (granite), this element was the most immobile, while in the rock where Fe/Ti oxides hosted Zr (basalt), Ti was the most immobile.

Acumulación de cobre en una comunidad vegetal afectada por contaminación minera en el valle de Puchuncaví, Chile central

Las especies hiperacumuladoras son capaces de acumular mas de 1.000 mg kg-1 de metal en su biomasa aerea y son utiles en procesos de fitoextraccion de metales en suelos contaminados por actividades mineras. Con el fin de identificar especies hiperacumuladoras representativas de las condiciones chilenas, se realizo una prospeccion dentro de la diversidad vegetal en el area afectada por las emisiones de la Fundicion Ventanas (90-900 mg kg-1 de Cu total en suelos), asi como en un area cercana a una pila de escorias de fundicion (500-3.000 mg kg-1 de Cu total en suelos). Se determinaron las concentraciones de Cu en la biomasa aerea de las plantas. Los resultados indican que dentro de la diversidad del sitio existen al menos veintidos especies pseudometalofitas, es decir, ecotipos de especies comunes que son capaces de tolerar concentraciones de cobre en el suelo que para una planta normal serian toxicas. Las especies fueron clasificadas segun su concentracion de cobre y mostraron en su mayoria media (200-600 mg kg-1) o baja (< 200 mg kg-1) acumulacion de cobre. La especie con la concentracion mas alta de cobre fue Oenothera affinis (614 mg kg-1). Sin embargo, no se identificaron hiperacumuladoras. Oenothera affinis podria considerarse como una buena candidata para iniciativas de remediacion en Chile, ya que es una hierba nativa perenne, resistente a la sequia, facil de propagar y que produce una gran biomasa. Sin embargo, es necesario comprobar que no hubo alguna sobreestimacion de las concentraciones de Cu en las plantas, debido a la adherencia de particulas contaminantes en los tricomas. Ademas, se realizaron dos nuevos muestreos mas tarde en la temporada, para Argemone subfusiformis y Oenothera affinis. Existe una disminucion en la concentracion de Cu en la biomasa aerea al avanzar la temporada causada por el desarrollo de estructuras de baja acumulacion de Cu (flores, frutos y hojas de verano) en el estado reproductivo y a l

Amendments Promote the Development of Lolium Perenne in Soils Affected by Historical Copper Smelting Operations

The Puchuncaví valley, central Chile, has been exposed to aerial emissions from a copper smelter. Nowadays, soils in the surroundings are sparsely-vegetated, acidic, and metal-contaminated, and their remediation is needed to reduce environmental risks. We assessed effectiveness of lime, fly ash, compost, and iron grit as amendments to immobilize Cu in soils and promote plant growth. Amended soils were cultivated with Lolium perenne for 60 days under controlled conditions. Total dissolved Cu and Cu2+ activity in the soil solution, ryegrass biomass, and Cu accumulation in plant tissues were measured. Addition of lime and fly ash decreased Cu concentrations and Cu2+ activity in the soil solution, increased plant biomass, and reduced shoot Cu concentration below 22 mg kg−1 (the phytotoxicity threshold for the species). The most effective amendment with respect to the shoot biomass yield was a combination of lime and compost. Water content of the substrate and the K accumulation were positively correlated with the compost application rate. Compost combined with iron grit decreased dissolved Cu concentrations during the period of highest solubility, i.e. during the first 60 days after the compost application. However, iron grit incorporation into soils amended with lime and compost decreased the shoot biomass of ryegrass.

Spatial distribution of copper and pH in soils affected by intensive industrial activities in Puchuncaví and Quintero, central Chile

The soils of Puchuncavi and Quintero, in the coastal area of central Chile, have been exposed to atmospheric deposition of sulfur dioxide (SO 2 ) and metal-rich particles from the Ventanas Industrial Complex. The objective of this study was to determine, using geostatistical tools, the spatial distribution of copper and pH in these soils. Using Universal Kriging tool for geostatistical interpolation, we generated maps of continuous distribution of Cu and pH in the soils. The distribution of these variables was related to the distance from the industrial complex and to the direction of the winds. The concentrations of Cu and acidity were higher in the surroundings to the industrial complex and in the direction of the dominant winds. Although the distributions of both variables were similar, there was no correlation between the distribution of Cu and pH, which could be due to the distinct aerial dispersion dynamics of the compounds, which causes a divergence in their deposition on the soil. Specifically, this could be due to the fact that SO 2 is smaller than the particulate matter that contains copper, so that it is capable of being dispersed over greater distances without being deposited on the soil.

Effect of compost and biodegradable chelate addition on phytoextraction of copper by Oenothera picensis grown in Cu-contaminated acid soils.

Oenothera picensis plants (Fragrant Evening Primrose) grow in the acid soils contaminated by Cu smelting in the coastal region of central Chile. We evaluated the effects of compost, at application rate of 5 kg m(-2), and biodegradable chelate MGDA (methylglycinediacetic acid), at application rate of 6 mmol plant(-1), on Cu phytoextraction by O. picensis, in field plots. No significant differences were found between treatments regarding aboveground biomass, shoot Cu concentrations and Cu phytoextraction of O. picensis. This lack of effects of the treatments was provoked by the large variability of soil properties, prior to applying of the treatments. The shoot Cu concentration in O. picensis positively and significantly correlated to exchangeable Cu concentration in the soil. Likewise, the aboveground biomass of O. picensis positively and significantly correlated to soil organic matter content. The Cu phytoextraction by O. picensis, in turn, positively and significantly correlated to both variables, i.e. exchangeable Cu concentration and organic matter content. The average Cu phytoextraction was 1.1 mg plant(-1), which is equivalent to 90 g ha(-1) at planting rate of 8 plants m(-2). In the chelate treatment, Cu phytoextraction was 2.6±2.1 mg plant(-1), which is equivalent to 212±171 g ha(-1) at planting rate of 8 plants m(-2).

Effects of lime and compost on earthworm (Eisenia fetida) reproduction in copper and arsenic contaminated soils from the Puchuncaví Valley, Chile

The Puchuncaví Valley in central Chile has been exposed to atmospheric depositions from a copper smelter. Nowadays, soils in the surrounding area are acidic and contaminated with Cu and As. The objective of this study was to determine the effectiveness of lime and compost for in situ immobilization of trace elements in the soils of the Puchuncaví Valley by using earthworms as bioindicators of toxicity. The lime and compost treatments significantly increased soil pH and decreased the soluble and exchangeable Zn, exchangeable Cu, and free Cu(2+) activity. However, the compost treatment increased soluble Cu, and soluble and exchangeable As. Lime application had no effect on earthworm reproduction in comparison with the unamended control, whereas the application of compost increased cocoon and juvenile production. There was a spatial variability of soil properties within treatments in the field plots. This allowed the identification of which soil properties were actually having an impact on earthworm reproduction. For both cocoon and juvenile production, soil organic matter (SOM) was a positive factor, i.e., more SOM increased cocoon or juvenile production. The toxicity (negative) factor was total soil As. However, total Cu and total As were well correlated (R(2)=0.80, p<0.001), hence some of the trends could have been masked. In summary, compost treatment was effective in improving the quality of soils of Puchuncaví Valley, increasing earthworm reproduction. Future Chilean legislation on maximum permissible concentrations of trace elements in soils should consider SOM content due to its effect on trace element solubility and bioavailability.

Biodegradable chelate enhances the phytoextraction of copper by Oenothera picensis grown in copper-contaminated acid soils

Oenothera picensis plants (Fragrant Evening Primrose) grow in the acid soils contaminated by copper smelting in the coastal region of central Chile. We evaluated the effects of the biodegradable chelate MGDA (methylglycinediacetic acid) on copper extraction by O. picensis and on leaching of copper through the soil profile, using an ex situ experiment with soil columns of varying heights. MGDA was applied in four rates: 0 (control), 2, 6 and 10 mmol plant(-1). MGDA application significantly increased biomass production and foliar concentration, permitting an effective increase in copper extraction, from 0.09 mg plant(-1) in the control, to 1.3mg plant(-1) in the 6 and 10 mmol plant(-1) treatments. With 10 mmol plant(-1) rate of MGDA, the copper concentration in the leachate from the 30 cm columns was 20 times higher than in the control. For the 60 cm columns, copper concentration was 2 times higher than the control. It can be concluded that at increased soil depths, copper leaching would be minimal and that MGDA applications at the studied rates would not pose a high risk for leaching into groundwater. It can thus be stated that applications of MGDA are an effective and environmentally safe way to improve copper extraction by O. picensis in these soils.

Thresholds of copper phytotoxicity in field-collected agricultural soils exposed to copper mining activities in Chile

It has been argued that the identification of the phytotoxic metal thresholds in soil should be based on field-collected soil rather than on artificially-contaminated soils. However, the use of field-collected soils presents several difficulties for interpretation because of mixed contamination and unavoidable covariance of metal contamination with other soil properties that affect plant growth. The objective of this study was to estimate thresholds of copper phytotoxicity in topsoils of 27 agricultural areas historically contaminated by mining activities in Chile. We performed emergence and early growth (21 days) tests (OECD 208 and ISO 11269-2) with perennial ryegrass (Lolium perenne L.). The total Cu content in soils was the best predictor of plant growth and shoot Cu concentrations, while soluble Cu and pCu(2+) did not well correlate with these biological responses. The effects of Pb, Zn, and As on plant responses were not significant, suggesting that Cu is a metal of prime concern for plant growth in soils exposed to copper mining activities in Chile. The effects of soil nutrient availability and shoot nutrient concentrations on ryegrass response were not significant. It was possible to determine EC10, EC25 and EC50 of total Cu in the soil of 327 mg kg(-1), 735 mg kg(-1) and 1144 mg kg(-1), respectively, using the shoot length as a response variable. However, the derived 95% confidence intervals for EC10, EC25 and EC50 values of total soil Cu were wide, and thus not allowing a robust assessment of metal toxicity for agricultural crops, based on total soil Cu concentrations. Thus, plant tests might need to be performed for metal toxicity assessment. This study suggests shoot length of ryegrass as a robust response variable for metal toxicity assessment in contaminated soils with different nutrient availability.