S. M. Imamul Huq

Comparison of extractability of Cd, Cu, Pb and Zn with sequential extraction in contaminated and non-contaminated soils

Various extraction procedures were employed for measuring extractable concentrations of potential toxic elements in soil. The extractability of Cd, Cu, Pb and Zn in four contaminated and four non-contaminated soils of Japan, was compared by single extraction (CaCl2, DTPA, NH4Cl, 0.1 M HCl and 1 M HCl ) and sequential extraction procedures [(six operationally defined chemical phases, viz. water soluble (Fl), exchangeable (F2), carbonate (F3), oxide (F4), organic (F5) and residual (F6) fractions)]. Extractability of metals from soils samples varied depending on metals and/or extradants used. Among the extradants, 1 M HCl extracted the largest proportion of Cd (79 to 96% of total), Cu (61 to 83%), Pb (51 to 99%) and Zn (23 to 52%) from soils followed by 0.1 M HCl, NH4Cl, DTPA and CaCl2. In all the extradants, the proportion of extractability of metals was higher in the contaminated soils than the non-contaminated soils. Regardless of soils and extradants, relative extractability was higher for Cd as compared to other three metals. The use of 1 M HCl may be recommended for first-level screening of soil contamination with heavy metals. The other four weak extradants are believed to provide a better assessment of bioavailable/mobile metals content in soils than 1 M HCl extradant. However, 0.1 M HCl mobilized all four metals irrespective of soil types, therefore, might be the best choice if only one extradant is to be used. The sequential extraction procedures showed 22 to 64% of total Cd was in the mobile fraction (sum of Fl to F3), while the corresponding values for Cu, Pb and Zn in this fractions were 2 to 23% suggesting higher mobility of Cd than other three metals. The single extraction procedures are simple and easy to perform and obtained results are comparable with sequential extraction procedure.

Physiological and mineralogical properties of arsenic‐induced chlorosis in rice seedlings grown hydroponically

Abstract A hydroponic experiment was conducted to observe the effect of arsenic (As) on a number of physiological and mineralogical properties of rice (Oryza sativa L. cv. Akihikari) seedlings. Seedlings were treated with 0, 6.7, 13.4 and 26.8 µmol L−1 As (0, 0.5, 1.0 and 2.0 mg As L−1) for 14 days in a greenhouse. Shoot dry matter yield decreased by 23, 56 and 64%; however, the values for roots were 15, 35 and 42% for the 6.7, 13.4 and 26.8 µmol L−1 As treatments, respectively. Shoot height decreased by 11, 35 and 43%, while that of the roots decreased by 6, 11 and 33%, respectively. These results indicated that the shoot was more sensitive to As than the root in rice. Leaf number and width of leaf blade also decreased with As toxicity. Arsenic toxicity induced chlorosis symptoms in the youngest leaves of rice seedlings by decreasing chlorophyll content. Concentrations and accumulations of K, Mg, Fe, Mn, Zn and Cu decreased significantly in shoots in the 26.8 µmol L−1 As treatment. However, the concentration of P increased in shoots at 6.7 and 13.4 µmol L−1 As levels, indicating a cooperative rather than antagonistic relationship. Arsenic and Fe concentration increased in roots at higher As treatments. Arsenic translocation (%) decreased in the 13.4 and 26.8 µmol L−1 As treatments compared with the 6.7 µmol L−1 As treatment. Arsenic and Fe were mostly concentrated in the roots of rice seedlings, assuming co-existence of these two elements. Roots contained an almost 8–16-fold higher As concentration than shoots in plants in the As treatments. Considering the concentration of Mn, Zn and Cu, it was suggested that chlorosis resulted from Fe deficiency induced by As and not heavy-metal-induced Fe deficiency.

Groundwater chemistry and arsenic mobilization in the Holocene flood plains in south-central Bangladesh

A comparative study of arsenic enrichment in the Bengal Delta (BD) was carried out in three alluvial aquifers in south-central Bangladesh. Investigated sites included Sonargaon in Narayanganj, Chandina in Comilla and Sirajdikhan in Munshiganj districts. At all sites samples from different depths were collected, and water chemistry and redox status vs. depth trends were determined. The concentrations of DOC and HCO3− were highest at Sirajdikhan site, while at the Sonargaon and Chandina sites the concentrations were lower. On the contrary, the NH4+ concentration was high at the Chandina site as compared to the other sites. There was a good match between dissolved As and Fe at the Sirajdikhan and Sonargaon sites, but not at the Chandina site. The dissolved aqueous concentration of Mn was low at the Chandina site, which suggested that the Mn(IV) redox buffering step was missing. Speciation modeling indicated a possibility of siderite precipitation at all sites, but precipitation of rhodochrosite only at the Sonargaon and Sirajdikhan sites. At the Sirajdikhan site, the log

Effects of applying calcium salts to coastal saline soils on growth and mineral nutrition of rice varieties

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Effect of arsenic on phytosiderophores and mineral nutrition of barley seedlings grown in iron-depleted medium

values were very high (−1.37), which revealed the production of CO2 in redox processes. Principal component analysis (PCA) indicated an impact of sea water and redox status of different samples. These results suggest that the dissolved As is de-coupled from dissolved Mn because when released, As is re-adsorbed onto the Fe(III) minerals in solid phase, as well as from dissolved Fe when precipitation of Fe(II) minerals controls the aqueous concentrations of Fe. In addition, several other concurrent redox processes may exert kinetic constraints depending on refractory characteristics of Fe(III) minerals.

Arsenic–iron interaction: Effect of additional iron on arsenic-induced chlorosis in barley grown in water culture

ABSTRACT The experiment was carried out to investigate the effects of arsenic (As) on the physiological and mineralogical properties of barley (Hordeum vulgare L. cv. ‘Minorimugi’). The plants were grown in nutrient solution treated with 0, 6.7, 33.5, and 67 μ M As (0, 0.5, 2.5, and 5 ppm As, respectively) in the phytotron. Dry matter yield of shoots and roots decreased significantly with the As treatments, indicating that barley plants are As-sensitive and As-toxicity depends on the As concentration in the rooting medium. Necrosis in older leaves and chlorosis symptoms (whitish color) in the fully developed young leaves were observed at the 33.5 and 67 μ M As treatments. Arsenic concentration, accumulation, and translocation increased with the increase of As concentration in the rooting medium. Arsenic was mostly concentrated in roots and a little amount was moved to shoots, indicating that As was not easily translocated to shoots of barley seedlings. Concentrations and accumulations of phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), manganese (Mn), zinc (Zn), and copper (Cu) decreased significantly in shoots for 33.5 and 67 μ M As treatments as compared to the 0 μ M As treatment. Concentrations of P, K, Ca, Mg, Mn, and Cu decreased in roots, but Zn concentration increased in roots at 67 μ M As treatment. Accumulations of P, K, Ca, Mg, Mn, Zn, and Cu in roots also decreased significantly at 67 μ M As treatment. Accumulation of P and the cations showed negative relationship with As. Concentration of Fe decreased in shoots at 33.5 and 67 μ M As treatments where chlorosis was induced in the young leaf but increased in roots at 33.5 and 67 μ M As treatments. It was suggested that As might induce iron (Fe)-chlorosis in the plants. Among the micronutrients, Fe translocation was more affected than others by As. Phytosiderophore (PS) accumulation in roots, which is a symptom of Fe-deficiency in grasses, did not change significantly between 0 and 33.5 μ M As treatments; indicating that As-induced chlorosis did not enhance PS accumulation in roots and decreased due to As-toxicity at 67 μ M As treatment.

Mechanism of Potassium Alleviation of Manganese Phytotoxicity in Barley

A greenhouse experiment was conducted with 3 coastal saline soils, viz. Ramgati (Aeric Fluvaquent), Nalchiti (Aeric Haplaquept), and Jhalakati (Typic Haplaquept), representing 3 salinity levels. Calcium (Ca) salts in the form of nitrate, chloride, sulfate, and phosphate (dibasic) were added to maintain the ratio of 1 : 5 for Na:Ca on the basis of the content of sodium (Na) and Ca in all soils. Two varieties of rice (Oryza sativa L.) (BR-11 and Pokkali) with varying salt tolerance were grown on the soils under submergence for 30 days. Salt injury symptoms such as chlorosis and necrosis on leaves of plants receiving no additional Ca (control) were observed and the severity of symptoms varied among the soils. Pokkali was less affected by salinity than BR-11 and produced greater dry matter yield on all soils. In comparison to control plants, application of calcium phosphate (CP) and calcium sulfate (CS) to soils tended to ameliorate the detrimental effects of salinity stress on dry matter yield. On the other hand, a decrease in dry matter yield was obtained with calcium chloride (CC) and calcium nitrate (CN). This suggests that maintaining a constant Na:Ca in the growth medium with Ca salts (CP and CS) having lower solubility seems to be effective in the amelioration of salinity stress regardless of its level. Concentrations of nitrogen (N), phosphorus (P), potassium (K), and Ca in shoots and roots of two varieties of rice plants decreased with increasing salinity levels, while results obtained with Na and magnesium (Mg) were opposite. Application of CP and CS increased N, P, K, and Ca and decreased Na and Mg concentrations when compared to control plants grown on all soils. The decrease in Na and Mg concentrations was less pronounced in BR-11 as compared to Pokkali. In general, CP was more effective than CS in the acquisition of essential macronutrient elements (except Mg), which was higher in Pokkali than BR-11.

Understanding bioenergy production and optimisation at the nanoscale - a review

Besides dissolution, particle dispersion and mobilization can substantially contribute to element transfer from soils to waters. The dispersibility of the fine particulate and the associated potential losses of P and As from Bangladesh soils of the Ganges and Meghna floodplains have been evaluated with a simple dispersion test. The dispersible fraction was greater for the coarse-textured soils from the Meghna floodplain and increased with particle charge density. Particulate phosphorus (PP) and As (PAs) were the dominant forms in the dispersion, dissolved P and As being scarce to negligible. The PP and PAs were related to the amount of dispersed particulate, oxalate-extractable iron and, respectively, to the water-extractable P or phosphate-extractable As. Although reductive dissolution is reported as the main mechanism of As mobilization during prolonged monsoon flooding, the transfer in particulate form could potentially represent a major pathway for P and As transfer from soils to waters in oxic environments after sudden, extreme events. Since the frequency of extreme rainfall and floods is increasing because of the climate changes, and the intensified land cultivation is enhancing soil disturbance, larger contributions of particulate runoff to element migration from soils to waters could be expected in the future.