The effects of in situ chemical oxidation on microbiological processes: A review

The effects of in situ chemical oxidation (ISCO) on biological processes, as reported in the literature, were researched to determine if coupling ISCO with in situ bioremediation could be achieved in field and laboratory experiments. Literature was compiled concerning the effect of ISCO on microbial communities following addition of a chemical oxidant at a range of concentrations designed to treat a variety of subsurface contaminants. The results indicate that although microbial communities may potentially be adversely affected by chemical oxidation in the short term, a rebound of microbial biomass and/or bioremediation activity can be expected. Successfully coupling ISCO with bioremediation in field applications may be a cost‐effective method of achieving risk‐based site remediation goals. © 2006 Wiley Periodicals, Inc.     

Anaerobic ammonium oxidation by Nitrosomonas spp. and anammox bacteria in a sequencing batch reactor

A sequencing batch reactor (SBR) was inoculated with mixed nitrifying bacteria from an anoxic tank at the conventional activated sludge wastewater treatment plant in Nongkhaem, Bangkok, Thailand. This enriched nitrifying culture was maintained under anaerobic conditions using ammonium (NH(4)(+)) as an electron donor and nitrite (NO(2)(-)) as an electron acceptor. Autotrophic ammonium oxidizing bacteria survived under these conditions. The enrichment period for anammox culture was over 100 days. Both ammonium and nitrite conversion rates were proportional to the biomass of ammonium oxidizing bacteria; rates were 0.08 g N/gV SS/d and 0.05 g N/g VSS/d for ammonium and nitrite, respectively, in a culture maintained for 3 months at 42 mg N/L ammonium. The nitrogen transformation rate at a ratio of NH(4)(+)-N to NO(2)(-)-N of 1:1.38 was faster, and effluent nitrogen levels were lower, than at ratios of 1:0.671, 1:2.18, and 1:3.05. Fluorescent in situ hybridization (FISH) was used to identify specific autotrophic ammonium oxidizing bacteria (Nitrosomonas spp., Candidatus Brocadia anammoxidans, and Candidatus Kuenenia stuttgartiensis). The ammonium oxidizing culture maintained at 42 mg N/L ammonium was enriched for Nitrosomonas spp. (30%) over Candidati B. anammoxidans and K. stuttgartiensis (2.1%) while the culture maintained at 210 mg N/L ammonium was dominated by Candidati B. anammoxidans and K. stuttgartiensis (85.6%). The specific nitrogen removal rate of anammox bacteria (0.6 g N/g anammox VSS/d) was significantly higher than that of ammonium oxidizing bacteria (0.4 g N/g Nitrosomonas VSS/d). Anammox bacteria removed up to 979 mg N/L/d of total nitrogen (ammonium:nitrite concentrations, 397:582 mg N/L). These results suggest significant promise of this approach for application to wastewater with high nitrogen but low carbon content, such as that found in Bangkok.     

The effect of oxygen on chemical dechlorination of dieldrin using iron sulphides

The degradation of dieldrin by ferric sulphide (FeS₂) in aqueous solution was investigated when shielded against sunlight. An oxidative dechlorination process was observed under aerobic and anaerobic conditions; oxygen volume changed the degradation rate of dieldrin and the generation rate of reaction products. The dechlorination rate under microaerophilic conditions was fastest among the anaerobic to air oxygen concentrations. For this experiment, over 99% of the dieldrin was degraded, and 90% of the released chloride was detected after 30 d under 10 μmol oxygen. The major reaction products were different depending on the dose of oxygen. In the case of aerobic conditions, low molecular weight organic acids, such as formic acid, lactic acid, and oxalic acid, were generated as major reaction products. However, under anaerobic conditions, C₁₆H₂₂O₄ (dibutyl phthalate) and C₆H₁₃ClO (3-chloro-4-methyl-2-pentanol) were detected as reaction intermediates, and small amounts of succinic acid, malonic acid, and formic acid were also generated. These reactions proceed by FeS₂ interface reactions with H₂O under anaerobic condition, or O₂ under aerobic condition.     

Air pollution and young children's inhalation exposure to organophosphorus pesticide in an agricultural community in Japan

Assessment of airborne organophosphorus pesticides in houses of young children (1-6 years old) and childcare facilities was conducted following pesticide applications in an agricultural community in Japan. Trichlorfon and fenitrothion, applied in two separate periods, were frequently detected from outdoor and indoor air. Dichlorvos, the primary degradation product of trichlorfon, was also detected after the application of trichlorfon. Both the outdoors and indoor concentration of applied pesticide were shown to increase with decreasing distance from the pesticide-applied farm. Indoor concentration of these pesticides significantly correlated with outdoor concentration (p=0.001 for trichlorfon and p=0.001 for fenitrothion), indicating infiltration of applied pesticide inside. Ratio of indoor to outdoor concentration (I/O ratio) of fenitrothion was higher for houses with windows open during the application than those with closed windows (median value: 0.74 vs. 0.16, p=0.003). However, a similar trend was not observed for trichlorfon as well as dichlorvos in the first period. Dichlorvos was found to have a higher I/O ratio than trichlorfon during the period, and clear correlation between indoor concentrations of dichlorvos and those of trichlorfon suggested increased decomposition of trichlorfon in the indoor environment. Daily inhalation exposure estimated by using the fixed measurement data and time-activity questionnaire ranged from 0 to 35 ng/kg/day for trichlorfon, from 0 to 26 ng/kg/day for dichlorvos, and from 0 to 44 ng/kg/day for fenitrothion. Median inhalation exposure from indoor air accounted for 74%, 86.3%, and 45% of the daily inhalation exposure, respectively. For kindergarteners or nursery school children, inhalation exposure at childcare facilities was comparable with or more than that at home, indicating that pollution level at childcare facilities had potential of high impact on children's exposure. Estimated daily inhalation exposures were inversely correlated to the proximity of their activity location to the pesticide-applied farm.     

Ranking the risks of 12 major environmental pollutants that occur in Japan

The risks posed by 12 major environmental pollutants in Japan were evaluated and ranked on the same scale. These were arsenic, benzene, cadmium, chlordane, chlorpyrifos, DDTs, dioxins, formaldehyde, methylmercury, radon, toluene, and xylenes. Approximately half of these substances are carcinogenic while the other half are non-carcinogenic. We applied a risk estimation framework that can evaluate both cancer and non-cancer risks on the same scale. The framework consists of two parts: the calculation of the probability of adverse health effects, and the evaluation of the severity of the effects. In order to calculate the probability of adverse health effects, individual variabilities in exposure level, metabolizing rate, and sensitivity were taken into account. Loss of life expectancy (LLE; days) was used as a measure of severity of the adverse health effects and of the resulting risk level. The risk level of the substances in terms of LLE ranged from approximately 0.01 to 10 days. The risks from radon and formaldehyde were found to be the highest, while those from DDT and chlordane were the lowest. Our findings also suggested that the risk levels posed by non-carcinogenic substances were comparable to those posed by carcinogenic substances.     

Simulation of dioxin accumulation in human tissues and analysis of reproductive risk

Polychlorinated dibenzo-p-dioxin, polychlorinated dibenzofuran and dioxin-like polychlorinated biphenyl concentrations in human liver, kidney, fat, blood, muscle, richly perfused tissue (brain, lung etc.) and skin were simulated to assess the health risk for Japanese fetuses. A 40-year time course of dioxin accumulation via food ingestion was simulated using a physiologically based pharmacokinetic (PBPK) model. In richly perfused tissue, the concentration estimated by the PBPK model showed better agreement with measured concentrations than that calculated by the one-compartment model. Fetal dioxin concentration was simulated based on the assumption that the fetal concentration was almost equal to the concentration in the mother's richly perfused tissue. To assess the reproductive risk, the estimated concentration in human fetus was compared with that in rat fetus in which reproductive function showed signs of alteration by 2,3,7,8-TCDD in previous reports [Toxicol. Appl. Pharmacol. 114 (1992) 118; 146 (1997) 11; Toxicol. Sci. 53 (2000) 411; 57 (2000) 275]. The present daily intake of 2,3,7,8-TCDD is approximately 1/50 of the amount that leads to possible reproductive toxicity in the next generation. However, when 29 kinds of dioxin congeners are considered, the present level is 1/5 of the hazardous levels. For species extrapolation of dioxin risk, further study on tissue concentration versus toxicity is required.     

Determination of tissue-blood partition coefficients for a physiological model for humans, and estimation of dioxin concentration in tissues

The tissue-blood partition coefficients for a physiologically based pharmacokinetic (PBPK) model were determined, and the concentrations of 17 congeners of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) in tissues in Japanese people were estimated using the model. According to the PBPK model established by Lawrence and Gobas [Chemosphere 35 (1997) 427-452], we assumed a steady-state fugacity model for Japanese people in general, and set the route of PCDD/Fs exposure only from food intake. The required partition coefficients for liver, kidney, adipose, muscle, skin, bile, gut and viscera (richly perfused tissue) were calculated using available autopsy data from eight Japanese men and women who were not accidentally exposed to PCDD/Fs. For validation of the partition coefficients, estimated PCDD/F concentrations in liver, kidney, fat, blood and muscle using the model were compared to other two sets of measured concentration data in Japanese tissues. Good agreement was obtained between estimated data and measured data, and most of the measured data were within the simulated concentration range in liver, kidney, blood and muscle. From these results, our model and calculated partition coefficients seem applicable for the estimation of congener-specific concentrations in human tissues.     

Leaching of bisphenol A (BPA) to seawater from polycarbonate plastic and its degradation by reactive oxygen species

In this study, (1) change in the concentration of bisphenol A (BPA) leached from polycarbonate (PC) tube to control water (BPA free), seawater and river water at 20 and 37 degrees C as a function of time, (2) the fate of BPA caused by addition of H(2)O(2) and Fe(3+) to seawater containing BPA leached from PC tube were assessed. BPA leached from PC tube to all water samples increased with the ascendant of temperature and with the passage of time. The BPA leaching velocity in seawater was the fastest in three samples (11 ng/day for seawater, 4.8 ng/day for river water 0.8 ng/day for control water at 37 degrees C).BPA leaching velocity from PC tube was significantly high at pH 8 (50 mM Na(2)HPO(4)) and increased dose-dependently. There was no difference in the velocity of BPA among the 50 mM phosphate-buffers at pH 6.5, 7.0 and 7.5. BPA was leached three times higher by addition of Na(+) than K(+). However, the higher the K(+) concentration, the larger the BPA leached from PC tube. Na(+) mixed with PO(4)(-) was effective on BPA leaching from PC tube, but not with SO(4)(-) or Cl(-). The results suggested that BPA leaching from PC tube would be attributed to the concentration of bibasic phosphate such as Na(2)HPO(4) and K(2)HPO(4) in water samples. BPA was degraded in both control water and seawater in the presence of radical oxygen species, but the degradation rate was lower in seawater than in control water, suggesting that anti-oxidative system exists in seawater. Neo-synthesized substance in both control water and seawater in the presence of reactive oxygen species was identified as BPA-quinone by LC-MS.     

Validation of modeling approach to evaluate congener-specific concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans in air and soil near a solid waste incinerator.

A concise modeling approach using long-term averaged meteorological data was developed to estimate site-specific concentrations of congeners of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) near a solid waste incinerator. This approach consists of calculation of atmospheric dispersion, dry and wet deposition of gaseous and particle-bound congeners, and non-steady-state concentrations in soil. The predictability of this approach was evaluated by comparison of calculated concentrations of congeners in soil with those measured at eight locations near a municipal solid waste incinerator (MSWI). The variation of these concentrations due to variability of meteorological parameters is small. A considerable number of mean values show good agreement with measured concentrations within a factor of three. The reasonable agreement between calculated and measured concentrations indicates that algorithms for the calculation of vapor-phase deposition and non-steady-state concentrations in soil must be included in the modeling approach for an accurate estimation of the concentrations of congeners of PCDD/Fs emitted from MSWIs to the atmosphere. For a detailed estimation of site-specific concentrations, it is important to specify the bulk density of soil in the evaluated area, together with meteorological parameters.