Nabeel Khan Niazi

Arsenic speciation and phytoavailability in contaminated soils using a sequential extraction procedure and xanes spectroscopy

In this study, a sequential extraction procedure (SEP) and X-ray absorption near edge structure (XANES) spectroscopy were used to determine the solid-phase speciation and phytoavailability of arsenic (As) of historically contaminated soils from As containing pesticides and herbicides and soils spiked with As in the laboratory. Brassica juncea was grown in the contaminated soils to measure plant available As in a glasshouse experiment. Arsenic associated with amorphous Fe oxides was found to be the dominant phase using both SEP and XANES spectroscopy. Arsenic predominantly existed in arsenate (As(V)) form in the soils; in a few samples As was also present in arsenite (As(III)) form or in scorodite mineral. Arsenic concentration in shoots showed significant (p < 0.001-0.05) correlations with the exchangeable As (r = 0.85), and amorphous Fe oxides associated As evaluated by the SEP (r = 0.67), and As associated with amorphous Fe oxides as determined by XANES spectroscopy (r = 0.51). The results show that As in both fractions was readily available for plant uptake and may pose a potential risk to the environment. The combination of SEP and XANES spectroscopy allowed us the quantitative speciation of As in the contaminated soils and the identification of valence and mineral forms of As. Such detailed knowledge on As speciation and availability is vital for management and rehabilitation of As-contaminated soils.

Phytoremediation of an arsenic-contaminated site using Pteris vittata L. and Pityrogramma calomelanos var. austroamericana : a long-term study

This field study investigated the phytoremediation potential of two arsenic (As) hyperaccumulating fern species, Pityrogramma calomelanos var. austroamericana and Pteris vittata over 27-month duration at a disused As-contaminated cattle-dip site located at Wollongbar, NSW, Australia. Ferns planted in January 2009 were harvested following 10, 22 and 27xa0months of growth. A detailed soil sampling was undertaken in June 2009 (initial, nu2009=u200942 per plot) and limited sampling in April 2011 (after 27xa0months, nu2009=u200915 per plot) to measure total and phosphate-extractable As concentrations in soil at 0u2009−u200920-, 20u2009−u200940- and 40u2009−u200960-cm depths. The choice of the limited number of samples was considered sufficient to estimate the changes in soil As concentration following phytoremediation based on a geostatistical model. The average frond dry biomass, As concentration and As uptake were significantly (Pu2009<u20090.001u2009−u20090.05) greater in P. calomelanos var. austroamericana than P. vittata, at all three harvests (1.6u2009−u20094.3, 1.3u2009−u20091.5 and 2.2u2009−u20095.7 times, respectively). After 27-months of growth, P. calomelanos var. austroamericana removed 8,053xa0mg As (i.e. cumulative over three harvests) in plot B (25.4xa0kg As ha−1) that was 2.65 times higher than that depleted by P. vittata (3,042xa0mg As in plot A (9.7xa0kg As ha−1)). The cumulative frond As uptake data of the two fern species revealed that P. calomelanos var. austroamericana extracted 1.7u2009−u20093.9xa0% and P. vittata removed 0.53u2009−u20091.5xa0% of total As from soil at three depths. However, for the surface (0u2009−u200920xa0cm) and subsurface (40u2009−u200960xa0cm) layers, the (post-experiment) soil As data indicated that total As concentration in soil was reduced by 49 and 63xa0% (Pu2009<u20090.05), respectively, using P. calomelanos var. austroamericana; and 17 and 15xa0% (Pu2009>u20090.05), respectively, by P. vittata. Our results show that phytoremediation time based on observed changes in soil As based on limited sampling is not reliable; hence, it is recommended that the frond As uptake should be considered in order to evaluate the phytoremediation efficiency of the two fern species at the experimental site. Using As uptake of the two fern species, we estimate that with P. calomelanos var. austroamericana it would take 55u2009−u2009125xa0years to decrease mean total As content below the ecological investigation level (20xa0mgxa0kg−1) in the surface and subsurface soils, whereas with P. vittata 143u2009−u2009412xa0years would be required to achieve this target.

Mid-infrared spectroscopy and partial least-squares regression to estimate soil arsenic at a highly variable arsenic-contaminated site

AbstractnThe potential of mid-infrared spectroscopy in combination with partial least-squares regression was investigated to estimate total and phosphate-extractable arsenic contents in soil samples collected from a highly variable arsenic-contaminated disused cattle-dip site. Principal component analysis was performed prior to mid-infrared partial least-squares analysis to identify spectral outliers in the absorbance spectra of soil samples. The mid-infrared partial least-squares calibration model (nxa0=xa0149) excluding spectral outliers showed an acceptable reliability (coefficient of determination,

Arsenic hyperaccummulation by ferns: A field study in northern NSW

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Using mid infrared spectroscopy and partial-least squares regression to estimate soil arsenic content at an arsenic-contaminated site

Rc2xa0=xa00.75 (Pxa0<xa00.01); ratio of performance to interquartile distance, RPIQcxa0=xa02.20) to estimate total soil arsenic. For total soil arsenic, the validation of final calibration model using 149 unknown samples also resulted in a good acceptability with

Letter to the editor regarding, “First evidence on different transportation modes of arsenic and phosphorus in arsenic hyperaccumulator Pteris vittata” by Lei et al. (2012)

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