Xiulan Yan

Effect and mechanism of persulfate activated by different methods for PAHs removal in soil

The influence of persulfate activation methods on polycyclic aromatic hydrocarbons (PAHs) degradation was investigated and included thermal, citrate chelated iron, and alkaline, and a hydrogen peroxide (H₂O₂)-persulfate binary mixture. Thermal activation (60 °C) resulted in the highest removal of PAHs (99.1%) and persulfate consumption during thermal activation varied (0.45-1.38 g/kg soil). Persulfate consumption (0.91-1.22 g/kg soil) and PAHs removal (73.3-82.9%) varied using citrate chelated iron. No significant differences in oxidant consumption and PAH removal was measured in the H₂O₂-persulfate binary mixture and alkaline activated treatment systems, relative to the unactivated control. Greater removal of high molecular weight PAHs was measured with persulfate activation. Electron spin resonance spectra indicated the presence of hydroxyl radicals in thermally activated systems; weak hydroxyl radical activity in the H₂O₂-persulfate system; and superoxide radicals were predominant in alkaline activated systems. Differences in oxidative ability of the activated persulfate were related to different radicals generated during activation.

The Arsenic Hyperaccumulator Fern Pteris vittata L.

Arsenic (As) contaminated soils and waters are becoming major global environmental and human health risks. The identification of natural hyperaccumulators of As opens the door for phytoremediation of the arsenic contaminant. Pteris vittata is the first identified naturally evolving As hyperaccumulator. More than a decade after its discovery, we have made great progress in understanding the uptake, transport, and detoxification of As in the fern. The molecular mechanisms controlling As accumulation in P. vittata are now beginning to be recognized. In this review, we will try to summarize what we have learned about this As accumulator, with particular emphasis on the current knowledge of the physiological and molecular mechanisms of arsenic phytoremediation. We also discuss the potential strategies to further enhance phytoextraction abilities of P. vittata.

Regional assessment of cadmium pollution in agricultural lands and the potential health risk related to intensive mining activities: A case study in Chenzhou City, China

The purpose of this study was to assess the extent of cadmium (Cd) contamination in agricultural soil and its potential risk for people. Soils, rice, and vegetables from Chenzhou City, Southern China were sampled and analyzed. In the surface soils, the 95% confidence interval for the mean concentration of Cd varied between 2.72 and 4.83 mg/kg (P < 0.05) in the survey, with a geometric mean concentration of 1.45 mg/kg. Based on the GIS map, two hot spot areas of Cd in agricultural soils with high Cd concentrations were identified to be located around the Shizhuyuan, Jinshiling, and Yaogangxian mines, and the Baoshan and Huangshaping mines, in the center of the city. About 60% of the total investigated area, where the agricultural soil Cd concentration is above 1 mg/kg, is distributed in a central belt across the region. The critical distances, at which the soil Cd concentration were increased by the mining activities, from the mines of the soils were 23 km for the Baoshan mine, 46 km for the Huangshaping mine, and 63 km for the Shizhuyuan mine, respectively. These are distances calculated from models. The Cd concentrations in rice samples ranged from 0.01 to 4.43 mg/kg and the mean dietary Cd intake from rice for an adult was 191 microg/d. Results of risk indexes showed that soil Cd concentrations possessed risks to local residents whose intake of Cd from rice and vegetables grown in soils in the vicinity of the mine was 596 microg/d.

Evaluation of heavy metal and polycyclic aromatic hydrocarbons accumulation in plants from typical industrial sites: potential candidate in phytoremediation for co-contamination

The heavy metal and polycyclic aromatic hydrocarbons (PAHs) contents were evaluated in surface soil and plant samples of 18 wild species collected from 3 typical industrial sites in South Central China. The accumulative characteristics of the plant species for both heavy metal and PAHs were discussed. The simultaneous accumulation of heavy metal and PAHs in plant and soil was observed at all the investigated sites, although disparities in spatial distributions among sites occurred. Both plant and soil samples were characterized by high accumulation for heavy metal at smelting site, moderate enrichment at coke power and coal mining sites, whereas high level of PAHs (16 priority pollutants according to US Environmental Protection Agency) at coke power site, followed sequentially by coal mining and smelting sites. Based on the differences of heavy metal and PAH accumulation behaviors of the studied plant species, heavy metal and PAH accumulation strategies were suggested: Pteris vittata L. and Pteris cretica L. for As and PAHs, Boehmeria nivea (L.) Gaud for Pb, As, and PAHs, and Miscanthus floridulu (Labnll.) Warb for Cu and PAHs. These native plant species could be proposed as promising materials for heavy metal and PAHs combined pollution remediation.

Interactions of arsenic and phenanthrene on their uptake and antioxidative response in Pteris vittata L.

The interactions of arsenic and phenanthrene on plant uptake and antioxidative response of Pteris vitatta L. were studied hydroponically. The combination of arsenic and phenanthrene decreased arsenic contents in fronds by 30-51%, whereas increased arsenic concentrations 1.2-1.6 times in roots, demonstrating the suppression of arsenic translocation compared to the corresponding treatment without phenanthrene. Under the co-exposure, As(III) concentrations in fronds deceased by 12-73%, and at higher arsenic exposure level (≥ 10 mg/L), As(V) in fronds and As(III) in roots increased compared to the single arsenic treatment. Arsenic exposure elevated phenanthrene concentrations in root by 39-164%. The co-existence of arsenic and phenanthrene had little impact on plant arsenic accumulation, although synergistic effect on antioxidants was observed, suggesting the special physiological process of P. vitatta in the co-exposure and application potential of P. vitatta in phytoremediation of arsenic and PAHs co-contamination.

Identification of persulfate oxidation products of polycyclic aromatic hydrocarbon during remediation of contaminated soil

The extent of PAH transformation, the formation and transformation of reaction byproducts during persulfate oxidation of polycyclic aromatic hydrocarbons (PAHs) in coking plant soil was investigated. Pre-oxidation analyses indicated that oxygen-containing PAHs (oxy-PAHs) existed in the soil. Oxy-PAHs including 1H-phenalen-1-one, 9H-fluoren-9-one, and 1,8-naphthalic anhydride were also produced during persulfate oxidation of PAHs. Concentration of 1,8-naphthalic anhydride at 4h in thermally activated (50°C) persulfate oxidation (TAPO) treatment increased 12.7 times relative to the oxidant-free control. Additionally, the oxy-PAHs originally present and those generated during oxidation can be oxidized by unactivated or thermally activated persulfate oxidation. For example, 9H-fluoren-9-one concentration decreased 99% at 4h in TAPO treatment relative to the control. Thermally activated persulfate resulted in greater oxy-PAHs removal than unactivated persulfate. Overall, both unactivated and thermally activated persulfate oxidation of PAH-contaminated soil reduced PAH mass, and oxidized most of the reaction byproducts. Consequently, this treatment process could limit environmental risk related to the parent compound and associated reaction byproducts.

Arsenic accumulation and resistance mechanism in Panax notoginseng, a traditional rare medicinal herb

Panax notoginseng, a traditional rare Chinese medicinal herb, was recently found to bring health risk to consumers, mainly because soil in its major plantation area was contaminated by arsenic (As). We investigated the effect of soil As pollution on the growth and As uptake of pot-cultured P. notoginseng, and the associated mechanisms of As stressed response. Results showed that, comparing with P. notoginseng growing in a low-As soil, the root, stem, and leaf biomasses of those growing in a high-As soil significantly reduced by 0.75, 0.09 and 0.21 g seedling(-1), respectively. Arsenic concentrations in roots, stems and leaves of the seedlings growing in high-As soil were 22, 15 and 3 times higher than those growing in low-As soil, respectively. Regardless of the soil As concentration, As existed in plants mainly as As(III), suggesting that the reduction of As(V) is a key step in As metabolism. Arsenic was distributed primarily in cell walls (51.7% for plants growing in the low-As soil, and 51.5% in the high-As soil), followed by cytoplasm supernatant, with cell organelles containing the least As. Compared with plants growing in the low-As soil, those in the high-As soil had increased superoxide dismutase and peroxidase activities in their roots, stems, and leaves, which would be associate with improving the resistance of P. notoginseng to As stress. The results suggest that there exists some special mechanisms of As-tolerance in P. notoginseng and the study is of significance in developing measures to reduce As in the herb.

Determination of potassium permanganate demand variation with depth for oxidation-remediation of soils from a PAHs-contaminated coking plant.

Bench-scale experiments were conducted to investigate the potassium permanganate demand, a key parameter for in situ chemical oxidation (ISCO) system design, and its variation with depth in PAHs-contaminated site of a coking plant. The concentrations of permanganate decreased rapidly during the first 8 d of the reaction process. The reaction follows first order kinetics, with rate constant ranging from 0.01 to 0.3/h. The total oxidant demand (TOD) is significantly higher for clayey silt fill than for soils of other lithology. The typical TOD is about 50 g MnO(4)(-)/kg soil for clayey silt fill, 20-40 g MnO(4)(-)/kg soil for silt, silty clay and 1-7 g MnO(4)(-)/kg soil for fine sand. Statistical analysis revealed that TOD was positively correlated with total organic carbon (TOC) content, clay content and PAHs concentrations, besides sand content, meanwhile TOC was the parameter with the strongest influence on oxidant demand. After 32 d duration of oxidation, PAHs in all tested soils were effectively removed, with total removal percent ranging from 78% to 99%, and small molecular weight PAHs were removed to a greater extent than high molecular weight PAHs. Parameters obtained in this study, combined with soil bulk density, soil porosity and soil moisture, can be used for full-scale ISCO system design and application in coking contaminated site.

Removal of heavy metals and arsenic from a co-contaminated soil by sieving combined with washing process

Batch experiments were conducted with a heavy metals and arsenic co-contaminated soil from an abandoned mine to evaluate the feasibility of a remediation technology that combines sieving with soil washing. Leaching of the arsenic and heavy metals from the different particle size fractions was found to decrease in the order: <0.1, 2-0.1, and >2mm. With increased contact time, the concentration of heavy metals in the leachate was significantly decreased for small particles, probably because of adsorption by the clay soil component. For the different particle sizes, the removal efficiencies for Pb and Cd were 75%-87%, and 61%-77% for Zn and Cu, although the extent of removal was decreased for As and Cr at <45%. The highest efficiency by washing for Pb, Cd, Zn, and As was from the soil particles >2mm, although good metal removal efficiencies were also achieved in the small particle size fractions. Through SEM-EDS observations and correlation analysis, the leaching regularity of the heavy metals and arsenic was found to be closely related to Fe, Mn, and Ca contents of the soil fractions. The remediation of heavy metal-contaminated soil by sieving combined with soil washing was proven to be efficient, and practical remediation parameters were also recommended.

Arsenic stabilization by zero-valent iron, bauxite residue, and zeolite at a contaminated site planting Panax notoginseng

Panax notoginseng (Burk.) F.H. Chen, a rare traditional Chinese medicinal herb, is a widely used phytomedicine used all over the world. In recent years, the arsenic contamination of the herb and its relative products becomes a serious problem due to elevated soil As concentration. This study aimed to evaluate the effects of different types and dosages of amendments on As stabilization in soil and its uptake by P. notoginseng. Results showed that comparing to control treatment, the As concentrations of P. notoginseng declined by 49-63%, 43-61% and 52-66% in 0.25% zero-valent iron (Fe(0)), 0.5% bauxite residue, and 1% zeolite treatment, respectively; whereas the biomasses were elevated by 62-116%, 45-152% and 114-265%, respectively. The As(III) proportions of P. notoginseng increased by 8%, 9%, and 8%, and the transfer factors of As from root to shoot increased by 37%, 42% and 84% in the optimal treatments of Fe(0), bauxite residue, and zeolite. For soil As, all the three amendments could transform the non-specifically adsorbed As fraction to hydrous oxides Fe/Al fractions (by Fe(0) and red mud) or specifically adsorbed As fraction (by zeolite), therefore reduced the bioavailability of soil As. With a comprehensive consideration of stabilization efficiency, plant growth, environmental influence, and cost, Fe(0) appeared to be the best amendment, and zeolite could also be a good choice. In conclusion, this study was of significance in developing As contamination control in P. notoginseng planting areas, and even other areas for medicinal herb growing.