Po Neng Chiang

Cr(VI) Removal on Fungal Biomass of Neurospora crassa: the Importance of Dissolved Organic Carbons Derived from the Biomass to Cr(VI) Reduction

Interactions of toxic Cr(VI) with renewable biomaterials are considered an important pathway for Cr(VI) removal in ecosystems. Biomaterials are susceptible to dissolution, and their dissolved derivatives may provide an alternative to surface-involved pathway for scavenging of Cr(VI). In this study, dissolved organic carbon (DOC) derived from Neurospora crassa biomass was investigated. The proportion of Cr(VI) reduction by DOC to that on biomass was determined to evaluate the importance of DOC to Cr(VI) reduction. A rapid increase in DOC concentration from 145.6 to 193.7 mg L(-1) was observed when N. crassa-biomass was immersed in 0.01 M KCl solution at pH of 1-5, and polysaccharides, peptides, and glycoproteins with carboxyl, amide, and -NH functional groups, are the major compositions of DOC. On reaction of 96.2 microM Cr(VI) with N. crassa-biomass or DOC, it was estimated that DOC contributed approximately 53.8-59.5% of the total Cr(VI) reduction on biomass in the dark. Illumination enhanced Cr(VI) reduction via photo-oxidation of biomass/DOC under aeration conditions, which formed superoxide for Cr(VI) reduction. At pH 1, photoinduced Cr(VI) reduction by DOC proceeded more rapidly than reduction on the biomass surface. However, at pH >3, with a decrease in Cr(VI) reduction by DOC, photon-excited biomass may become an important electron source for Cr(VI) photoreduction.

Chromate reduction on humic acid derived from a peat soil – Exploration of the activated sites on HAs for chromate removal

Humic substances are a major component of soil organic matter that influence the behavior and fate of heavy metals such as Cr(VI), a toxic and carcinogenic element. In the study, a repetitive extraction technique was used to fractionate humic acids (HAs) from a peat soil into three fractions (denoted as F1, F2, and F3), and the relative importance of O-containing aromatic and aliphatic domains in humic substances for scavenging Cr(VI) was addressed at pH 1. Spectroscopic analyses indicated that the concentrations of aromatic C and O-containing functional groups decreased with a progressive extraction as follows: F1>F2>F3. Cr(VI) removal by HA proceeded slowly, but it was enhanced when light was applied due to the production of efficient reductants, such as superoxide radical and H(2)O(2), for Cr(VI). Higher aromatic- and O-containing F1 fraction exhibited a greater efficiency for Cr(VI) reduction (with a removal rate of ca. 2.89 mmol g(-1) HA under illumination for 3 h). (13)C NMR and FTIR spectra further demonstrated that the carboxyl groups were primarily responsible for Cr(VI) reduction. This study implied the mobility and fate of Cr(VI) would be greatly inhibited in the environments containing such organic groups.

Cesium and strontium sorption by selected tropical and subtropical soils around nuclear facilities.

The dynamics of Cs and Sr sorption by soils, especially in the subtropics and tropics, as influenced by soil components are not fully understood. The rates and capacities of Cs and Sr sorption by selected subtropical and tropical soils in Taiwan were investigated to facilitate our understanding of the transformation and dynamics of Cs and Sr in soils developed under highly weathering intensity. The Langmuir isotherms and kinetic rates of Cs and Sr sorption on the Ap1 and Bt1 horizons of the Long-Tan (Lt) and the A and Bt1 horizons of the Kuan-Shan (Kt), Mao-Lin (Tml) and Chi-Lo (Cl) soils were selected for this study. Air-dried soil (<2mm) samples were reacted with of 7.5 x 10(-5) to 1.88 x 10(-3)M of CsCl (pH 4.0) or 1.14 x 10(-4) to 2.85 x 10(-3)M of SrCl(2) (pH 4.0) solutions at 25 degrees C. The sorption maximum capacity (q(m)) of Cs by the Ap1 and Bt1 horizons of the Lt soil (62.24 and 70.70 mmol Cs kg(-1) soil) were significantly (p<0.05) higher than those by the A and Bt1 horizons of the Kt and Cl soils (26.46 and 27.49 mmol Cs kg(-1) soil in Kt soil and 34.83 and 29.96 mmol Cs kg(-1) soil in Cl soil, respectively), however, the sorption maximum capacity values of the Lt and Tml soils did not show significant differences. The amounts of pyrophosphate extractable Fe (Fe(p)) were correlated significantly with the Cs and Sr sorption capacities (for Cs sorption, r(2)=0.97, p<1.0 x 10(-4); for Sr sorption, r(2)=0.82, p<2.0 x 10(-3)). The partition coefficient of radiocesium sorbed on soil showed the following order: Cl soil>>Kt soil>Tml soil>Lt soil. It was due to clay minerals. The second-order kinetic model was applied to the Cs and Sr sorption data. The rate constant of Cs or Sr sorption on the four soils was substantiality increased with increasing temperature. This is attributable to the availability of more energy for bond breaking and bond formation brought about by the higher temperatures. The rate constant of Cs sorption at 308 K was 1.39-2.09 times higher than that at 278K in the four soils. The activation energy of Cs and Sr sorbed by the four soils ranged from 7.2 to 16.7 kJ mol(-1) and from 15.2 to 22.4 kJ mol(-1), respectively. Therefore, the limiting step of the Cs(+) or Sr(2+) sorption on the soils was diffusion-controlled processes. The reactive components, which are significantly correlated with the Langmuir sorption maxima of Cs and Sr by these soils, substantially influenced their kinetic rates of Cs and Sr sorption. The data indicate that among components of the subtropical and tropical soils studied, short-range ordered sesquioxides especially Al- and Fe-oxides complexed with organics play important roles in influencing their capacity and dynamics of Cs and Sr sorption.

Low-molecular-weight Organic Acids Exuded by Millet ( setaria italica (l.) Beauv.) Roots and Their Effect on the Remediation of Cadmium-contaminated Soil

Cadmium (Cd)-contaminated soils are of concern because of their possible effects on ecosystems and human health. Millet (Setaria italica (L.) Beauv.) is moderately tolerant to salinity and poor soil fertility as well as pristine soils contaminated with trace elements. It has been hypothesized that low-molecular-weight organic acids (LMWOA) exuded into the rhizosphere may play important roles in Cd uptake by millet. Thus the objectives of this study were to assess the LMWOA exudations of millet in Cd-contaminated soils and to evaluate the capacity of millet to remove Cd for phytoremediation. Millet was grown for 3 weeks in soils containing between 0 and 1,000 mg Cd kg−1. These soils and plant tissues were analyzed for Cd content after harvest. The Cd accumulated in millet tissues was significantly increased with increasing Cd-amended rate. The total LMWOA concentrations in root exudates were significantly correlated with the amount of Cd accumulated in millet shoots and roots. High levels of Cd amendment stimulated secretion of LMWOA, a process capable of reducing Cd toxicity via the formation of Cd-organic complexes (Cd-LMWOA), thereby detoxifying the contaminated soil.

LOW-MOLECULAR-WEIGHT ORGANIC ACID EXUDATION OF RAPE (BRASSICA CAMPESTRIS) ROOTS IN CESIUM-CONTAMINATED SOILS

Cesium is an emission element from nuclear energy generation easily transferred to food chain. More evidence has been found that Brassica crops take up pollutants from soils. The objective of this study was to investigate the correlation between soil bioavailability of cesium and low-molecular-weight organic acids (LMWOAs) in rape (Brassica campestris) root exudates. Longtan (LT) red (Typic Hapladox) and Kuanshan (KS) iron-rich calcareous soils (Typic Paleudalf) were collected for this study. The pot experiments of rape were conducted with cesium-amended soils and plants grown in the soils (4 weeks). Cesium concentration in shoots and roots correlated well with Cs concentration in the amended soils. Within the amended range of 50 to 300 mg Cs kg−1 soil, Cs did not inhibit rape growth. The bioaccumulation ratio ([Cs]root/[Cs]soil] or [Cs]shoot/[Cs]soil) for Cs in shoots of pot grown plants ranged between 9 and 31 and showed significant differences (P < 0.05). Plant roots can exude LMWOAs, which are important components in root exudation. The total amounts of volatile and nonvolatile LMWOAs in all Cs-amended soils were higher than those in nonamended soils. Meanwhile, the LMWOA concentrations of the rape root exudates showed good correlation with Cs concentrations in the applied range of 50 to 300 mg Cs kg−1 soil.

Influence of chemical compositions and molecular weights of humic acids on Cr(VI) photo-reduction

Humic acids (HA) strongly affect the fate of trace metals in soils and aquatic environments. One of the remarkable properties of HA is its ability to reduce Cr(VI), an extremely toxic anion. However, it is unclear which HA components are involved in Cr(VI) reduction and possess the photo-induced properties. In this study, an ultrafiltration technique was used to fractionate HAs into four fractions of different nominal molecular weights (M(w)): >100, 50-100, 10-50 and <10 kDa. Each HA fraction was characterized by spectroscopic analyses followed by examining Cr(VI) removal on each fraction of HA at pH 1-5. Spectroscopic results indicated that low-M(w) HA was enriched with polar and aromatic domains. These polar, including polar C in aliphatic region, and aromatic groups were the major sites for Cr(VI) reduction because they disappeared rapidly upon interaction with Cr(VI). As a result, low M(w) of HA exhibited greater efficiency of Cr(VI) reduction. Light induced the rapid transfer of electrons between chromate-phenol/carboxyl ester, or the formation of peroxide radicals or H(2)O(2) through the ready decay of peroxy radicals associated with polar substituents, explained the rapid scavenging of Cr(VI) on polar and aromatic groups of HAs under illumination.

Effects of low molecular weight organic acids on 137Cs release from contaminated soils

Radio pollutant removal is one of several priority restoration strategies for the environment. This study assessed the effect of low molecular weight organic acid on the lability and mechanisms for release of (137)Cs from contaminated soils. The amount of (137)Cs radioactivity released from contaminated soils reacting with 0.02 M low molecular weight organic acids (LMWOAs) specifically acetic, succinic, oxalic, tartaric, and citric acid over 48 h were 265, 370, 760, 850, and 1002 Bq kg(-1), respectively. The kinetic results indicate that (137)Cs exhibits a two-step parabolic diffusion equation and a good linear relationship, indicating that the parabolic diffusion equation describes the data quite well, as shown by low p and high r(2) values. The fast stage, which was found to occur within a short period of time (0.083-3 h), corresponds to the interaction of LMWOAs with the surface of clay minerals; meanwhile, during the slow stage, which occurs over a much longer time period (3-24 h), desorption primarily is attributed to inter-particle or intra-particle diffusion. After a fifth renewal of the LMWOAs, the total levels of (137)Cs radioactivity released by acetic, succinic, oxalic, tartaric, and citric acid were equivalent to 390, 520, 3949, 2061, and 4422 Bq kg(-1) soil, respectively. H(+) can protonate the hydroxyl groups and oxygen atoms at the broken edges or surfaces of the minerals, thereby weakening Fe-O and Al-O bonds. After protonation of H(+), organic ligands can attack the OH and OH(2) groups in the minerals easily, to form complexes with surface structure cations, such as Al and Fe. The amounts of (137)Cs released from contaminated soil treated with LMWOAs were substantially increased, indicating that the LMWOAs excreted by the roots of plants play a critical role in (137)Cs release.

Chromate removal as influenced by the structural changes of soil components upon carbonization at different temperatures.

Surface fire could induce heat transferring into the soil, creating a carbonized environment, which may alter the chemical compositions of soil organic matters (SOM). In the study, a surface soil was carbonized at up to 600 °C with limited air to simulate soils experiencing a surface fire, and Cr(VI) removal on the carbonized soils was investigated. NMR and FTIR analyses demonstrated a remarkable change of SOM structures at 300-400 °C. TGA-MS spectra indicated that (e.g. C(2)H(4), CH(3)OH and C(3)H(8)) were the major components in the evolved gases from the pyrolyzed soil. A maximum amount of Cr(VI) removal (ca. 4 mg g(-1) soil) occurred for the 200 °C-carbonized soils, attributed mainly to a significant increase of Cr(VI) reduction by 0.1 M KCl extractable organic carbon (EOC) with abundant carboxylic groups. Nonetheless, the formation of aromatic C upon carbonization of the soil at >400 °C may be responsible for Cr(VI) reduction.

ORIGIN AND MINERALOGY OF SEPIOLITE AND PALYGORSKITE FROM THE TULUANSHAN FORMATION, EASTERN TAIWAN

The Tuluanshan Formation of the eastern Coastal Range of Taiwan overlies an andesitic core complex presumed to be the source of hydrothermal fluids responsible for the Si- and Mg-rich mineralization of sepiolite and palygorskite (attapulgite) which are found in veins within fissures and in fracture zones of the volcanic rocks of the region. This study was undertaken in order to understand these relationships better by characterizing sepiolite and palygorskite in this Formation and by examining their occurrence and distribution in the Tungho (TH) and Chunjih (CJ) areas. Samples were analyzed using X-ray diffraction (XRD), thermal analysis, Fourier-transform infrared (FTIR) spectroscopy, and petrographic, scanning (SEM), and transmission (TEM) electron microscopic methods. Sepiolite and palygorskite are blocky and earthy-type materials that display fibrous characteristics when viewed using TEM and SEM and occurred alone or with chalcedony in veins. The fibers of blocky sepiolite are commonly intercalated with smectite but the earthy type of sepiolite and palygorskite observed in this study displayed precipitation from fluid enriched in Si, Al, Mg, and minor Fe and depleted in other ions at an earlier stage of offset of the andesitic veins. Continuation of reverse faulting and high shearing stress caused the precipitation of a significant quantity of interlaminated sepiolite. Sepiolite and palygorskite were formed at an earlier stage of fluid interaction relative to smectite in the Tuluanshan Formation.