Photodegradation of dioxin in contaminated soil in the presence of solvents and nanoscale TiO2 particles.

Decomposition of 2,3,7,8-Tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) present in soil under ultraviolet (UV) illumination (350-400nm) was investigated using a combination of nontoxic solvents mixed in soil and nanoscale anatase TiO2 (nTiO2) distributed on 2mm top soil surface. Three types of UV-exposure experiments were conducted: intermittent exposure (8 h/day) for 90 days and 120 days, sequential intermittent (120 days) and continuous (24 h/day) for the next 55 days, and continuous exposure for 55 days. The influence of several factors on dioxin photodegradation efficiency was investigated, including the UV absorption by the targeted dioxin, presence of catalytic nTiO2 on soil surface, solvent evaporation rate, as well as vertical gradients of solvents added into the soil columns. Results of dioxin analysis for the soil samples collected at the end of every experiment condition show that the photodegradation enhanced by the nTiO2 presence on the soil surface considerably increased the dioxin removal. Higher removal efficiencies were found for treatments with 15%wt of nTiO2 mixed in the 2-mm surface soil as compared to the 5%wt nTiO2 treatments. The highest removal efficiency (79.6%) was for the sequential intermittent-continuous UV-exposure experiment with nTiO2. Dechlorinated products of 2,3,7,8-TCDD were generally not detected which suggests degradation of targeted dioxin by C-Cl cleavage was negligible. Further modifications to improve removal efficiencies were proposed. Large-scale engineered systems may employ this integrated treatment approach which can also incorporate the reuse of the top soil containing nTiO2 and solvent vapours. With the utilization of natural sunlight such systems would be promisingly suitable for tropical conditions.

Air pollution and risk of respiratory and cardiovascular hospitalizations in the most populous city in Vietnam.

Air pollution has become an alarming issue in Vietnam recently; however, there was only one study so far on the effects of ambient air pollution on population health. Our study aimed to investigate the short-term effects of air pollutants including PM10, NO2, SO2, and O3 on respiratory and cardiovascular hospitalizations in Ho Chi Minh City (HCMC), the largest city in Vietnam. Data on hospitalization from the two largest hospitals in HCMC and daily records of PM10, NO2, SO2, O3 and meteorological data were collected from February 2004 to December 2007. A time-series regression analysis with distributed lag model was applied for data analysis. Changes in levels of NO2 and PM10 were strongly associated with hospital admissions for both respiratory and cardiovascular diseases (CVD); whereas levels of SO2 were only moderately associated with respiratory and CVD hospital admissions and O3 concentration was not associated with any of them. For a 10µg/m(3) increase of each air pollutant, the risk of respiratory admissions increased from 0.7% to 8% while the risk of CVD admissions increased from 0.5% to 4%. Females were found to be more sensitive than males to exposure to air pollutants in regard to respiratory diseases. In regard to CVD, females (RR, 1.04, 95% CI, 1.01-1.07) had a slightly higher risk of admissions than males (RR, 1.03, 95% CI, 1-1.06) to exposure to NO2. In contrast, males (RR, 1.007, 95%CI, 1-1.01) had a higher risk of admission than females (RR, 1.004, 95%CI, 1.001-1.007) to exposure to PM10. People in the age group of 5-65year-olds had a slightly higher risk of admissions caused by air pollutants than the elderly (65+years old) except for a significant effect of PM10 on the risk of cardiovascular admissions was found for the elderly only.

Sequential anaerobic-aerobic biodegradation of 2,3,7,8-TCDD contaminated soil in the presence of CMC-coated nZVI and surfactant.

Enriched microorganisms in sediment collected from a dioxin-contaminated site in Vietnam (Bien Hoa airbase) were used for examining the effectiveness in biological treatment of 2,3,7,8-Tetrachlorodibenzo-p-dioxin in soil. Four bio-treatments were investigated using a sequential anaerobic (17 weeks) followed by an aerobic (6 weeks) incubation. The maximum removal efficiency was approximately 60% even at an extremely low pH (approx. 3.6) condition. Surfactant Tween-80 was added to enhance the bioavailability of dioxin in two treatments, but it appeared to biostimulate methanogens rather than dechlorinators. As a result, methane production was the highest while the dioxin removal efficiency was the lowest, as compared with the other bio-treatments. Carboxymethylcellulose (CMC) coated on nanoscale zero valent iron (nZVI) surface used in two treatments could prevent the direct contact between bacterial cell surface and nZVI which prevented cell death and lysis, hence enhancing dioxin removal. The presence of CMC--_nZVI in bio-treatments gradually released H2 required for microbiological processes, but the amount used in the experiments were likely too high to maintain optimum H2 levels for biostimulating dechlorinators rather than methanogens.