固相微萃取/气质联用测定水中五种异味有机物

采用固相微萃取（SPME）法富集、气相色谱/质谱定量测定水体中的五种痕量异味有机物：2-异丙基-3-甲氧基吡嗪（IPMP）、2-异丁基-3-甲氧基吡嗪（IBMP）、2-甲基异冰片（2-MIB）、2,4,6-三氯苯甲醚（2,4,6-TCA）、土味素（Geosmin）.对五种物质的检出限均在5.0ng/L以下,加标回收率为86.7%～96.2%,相对标准偏差为3.9%～7.1%.     

粉末炭去除饮用水中土霉味物质的影响因素研究

采用粉末活性炭（PAC）去除饮用水中2-甲基异莰醇（MIB）、2,4,6-三氯茴萫醚（TCA）、2-异丙基-3-甲氧基吡嗪（IPMP）和2-异丁基-3-甲氧基吡嗪（IBMP）等4种常见的土霉味物质,研究了PAC种类、PAC投加量、嗅味物质的初始浓度、余氯、水质等因素对PAC去除土霉味物质的影响。结果表明,PAC吸附对嗅味物质的去除主要发生在前1 h内;煤质PAC对MIB有更高的去除率;在一定的吸附时间和活性炭投加量下,PAC对痕量嗅味物质的去除率与其初始浓度无关;余氯和有机物的存在降低了PAC对嗅味物质的吸附容量,水质对去除嗅味物质也有很大的影响。     

Inhibitory effects of odor substances,geosmin and 2-methylisoborneol,on early development of sea urchins

Geosmin (1α,10β-dimethyl-9α-decanol) and 2-methylisoborneol ((1-R-exo)-1,2,7,7-tetramethyl-bicyclo-(2,2,1)-heptan-2-ol) (MIB) are volatile terpene derivatives, and have received a great deal of attention because they can cause musty/muddy off-flavor in water and food resources. By the Ames test, these metabolites showed no mutagenicity but antimicrobial activity toward tester strains. While these compounds are produced by various organisms living in aquatic environments, there are few reports of their effects on aquatic organisms. The effects of geosmin and MIB on sea urchin development were examined. The estimated IC₅₀ (50% inhibitory concentration) values for the formation of the fertilization membrane were 16.67 mg geosmin l⁻¹ and 68.77 mg MIB l⁻¹; those for the cell cleavage were 16.58 mg geosmin l⁻¹ and 66.86 mg MIB l⁻¹, suggesting that the toxicity of geosmin and MIB toward sea urchins are comparable to their toxicity toward Salmonella tester strains in the Ames test. These values are far greater than concentrations of these substances observed in aquatic environments with severe muddy off-flavor problems.     

GAC adsorber design protocol for the removal of off-flavors

This paper investigates the effectiveness of granular activated carbon (GAC) for removing off-flavor compounds of water—geosmin and 2-methylisoborneol (MIB). More specifically, it focuses on the development of an appropriate modeling approach and experimental protocol for the design of fixed-bed GAC adsorbers. Adsorption equilibrium, rate and long-term mini-column studies were conducted on a bench-scale for geosmin and MIB to estimate the equilibrium and mass-transfer parameters required for adsorber modeling. The dispersed flow homogeneous surface diffusion model (DFHSDM) was used for the prediction/simulation of the adsorber dynamics. Scale-up procedures based on dimensional analysis and similitude were employed for the design of full-scale adsorbers from bench-scale adsorbers, and for performance forecasting of full-scale adsorbers under different operating conditions. More importantly, operation and maintenance (O & M) costs were estimated for full-scale adsorbers directed at the removal of off flavor compounds, based on carbon utilization rates and disposal costs. These estimates were obtained for different plant capacities and empty bed contact times (EBCTs).     

Removal of individual off-flavour compounds in water during artificial groundwater recharge and during treatment by alum coagulation/sand filtration

The removal of individual off-flavour compounds during artificial groundwater recharge has been compared to the removal of such compounds during conventional alum coagulation/sand filtration. By using an evaluation technique based on gas chromatography with both instrumental and sensory detection (“column sniffing”) it was shown that alum coagulation/sand filtration had no significant effect on any of the off-flavour compounds that could be detected in the raw water samples (geosmin, 2-methylisoborneol, 2-isopropyl-3-methoxypyrazine, 2,4,6-trichloroanisole, 1-octen-3-one, 1-nonen-3-one, dimethyl trisulphide and a number of unidentified muddy or musty odours). During artificial groundwater recharge in sand and gravel ridges, however, the concentrations of all these compounds were substantially reduced, thus proving that artificial groundwater recharge is not only a suitable method for water storage but can also be an effective method for removing muddy and musty odours. The successful use of the column-sniffing technique for evaluating water treatment methods has shown the potential of this technique in resolving some of the present disagreements concerning the effectiveness of different treatment methods for removing tastes and odours from water.     

Removal of MIB and geosmin using granular activated carbon with and without MIEX pre-treatment

This study assessed the impact of MIEX pre-treatment, followed by either coagulation or microfiltration (MF), on the effectiveness of pilot granular activated carbon (GAC) filters for the removal of the taste and odour compounds, 2-methylisoborneol (MIB) and geosmin, from a surface drinking water source over a 2-year period. Complete removal of MIB and geosmin was achieved by all GAC filters for the first 10 months, suggesting that the available adsorption capacity was sufficient to compensate for differences in dissolved organic carbon (DOC) entering the GAC filters.Reduction of empty bed contact time (EBCT), in all but one GAC filter, resulted in breakthrough of spiked MIB and geosmin, with initial results inconclusive regarding the impact of MIEX pre-treatment. MIB and geosmin removal increased over the ensuing 12 months until complete removal of both MIB and geosmin was again achieved in all but one GAC filter, which had been pre-chlorinated. Autoclaving and washing the GAC filters had minimal impact on geosmin removal but reduced MIB removal by 30% in all but the pre-chlorinated filter, confirming that biodegradation impacted MIB removal. The impact of biodegradation was greater than any impact on GAC adsorption arising from DOC differences due to MIEX pre-treatment. It is not clear whether, at a lower initial EBCT, MIEX pre-treatment may have impacted on the adsorption capacity of the virgin GAC.The GAC filter maintained at the longer EBCT, which was also pre-chlorinated, completely removed MIB and geosmin for the period of the study, suggesting that the greater adsorption capacity was compensating for any decrease in biological degradation.     

Influence of the character of NOM on the ozonation of MIB and geosmin

Tastes and odours (T&Os) are a major concern in drinking water as they are not efficiently removed by conventional water treatment. Ozonation has been effective for their destruction in some studies. However, the natural organic matter (NOM) in waters can affect the ozonation process and subsequently affect the destruction of T&Os. Five NOM fractions were isolated and ozonated in synthetic waters. The fraction containing the more highly coloured, higher molecular weight compounds exhibited the highest ozone (O3) demand, whereas the low aromatic fraction exhibited the lowest O3 demand. The character of the NOM fractions influenced the ozonation of MIB and geosmin. The destruction of MIB and geosmin was significantly higher in the fraction with the highest colour and UV/visible absorbance at all O3 doses. The destruction of the compounds in the other fractions showed the same trends, increasing MIB and geosmin destruction with increasing UV/visible absorbing character of the NOM. MIB was also ozonated in two real waters. with results showing a competing effect between NOM concentration and NOM character. The O3 reaction time was shown to be important for the destruction of both compounds.     

The management of undesirable cyanobacteria blooms in channel catfish ponds using a constructed wetland: Contribution to the control of off-flavor occurrences

An exploratory study on the management of undesirable cyanobacteria blooms with respect to off-flavor problems using an integrated vertical-flow constructed wetland (CW) was performed at a small commercial-scale channel catfish farm from 2004 to 2007. The results of the three-year experiment indicated that water treatment by the CW could reduce the possibility of dominance by undesirable cyanobacteria species that often cause off-flavor problems. A detailed investigation in 2007, showed that the concentrations of geosmin, MIB (2-methylisoborneol), and β-cyclocitral in the water of the recirculating pond (4.3 ng L⁻¹, U.D. (undetected) and 0.2 ng L⁻¹, respectively) treated by the CW were significantly lower than those in the control pond (152.6 ng L⁻¹, 63.3 ng L⁻¹ and 254.8 ng L⁻¹, respectively). In addition, the relationships among the cyanobacteria species, the off-flavor compounds and ten environmental variables were explored by canonical correspondence analysis (CCA). The results showed that Oscillatoria sp., Oscillatoria kawamurae and Microcystis aeruginosa were the main sources of off-flavor compounds in the catfish ponds. The successful manipulation of undesirable cyanobacteria species potentially resulted in lower concentrations of odorous compounds in the water of the recirculating pond. An investigation of the concentrations of geosmin and MIB in catfish fillets showed that the levels of odorous compounds were below the OTC (odor threshold concentration) values in the recirculating pond but were above the OTC values from July to October in the control pond. Water recycling by the CW could potentially be one of the best management practices to control off-flavor occurrences in aquaculture.     

A planktonic Oscillatoria species from Mississippi catfish ponds that produces the off-flavor compound 2-methylisoborneol

A planktonic, gas-vacuolate Oscillatoria species was isolated from catfish ponds in Mississippi during an episode of off-flavor and high 2-methylisoborneol (MIB) levels. Volatile compounds from unialgal cultures were isolated using closed-loop stripping, liquid-liquid extraction, and analyzed by gas chromatography and mass spectroscopy. The organism produced MIB at 75–87 μg 1⁻¹ after 2–3 wk of incubation at 25°C. The alga was found in moderate to high numbers in three pond water samples with high MIB levels, and low numbers in two other samples with low MIB levels. The organism was not present (less than one organism/10 ml) in nine other samples characterized by a “woody” or “swampy” odor and no detectable MIB. This Oscillatoria strain is believed to be the first blue-green alga that produces MIB ever isolated from Mississippi catfish ponds, and may be a cause of the off-flavor problem associated with MIB in those systems.     

Cyanobacteria and earthy/musty compounds found in commercial catfish (Ictalurus punctatus) ponds in the Mississippi Delta and Mississippi--Alabama Blackland Prairie

The compounds responsible for earthy and musty "off-flavors" in farm-raised channel catfish (Ictalurus punctatus) in the southeastern United States of America are geosmin and 2-methylisoborneol (MIB), respectively. These compounds are produced by certain species of cyanobacteria (blue-green algae) that grow in the aquaculture ponds. Previous research has focused on the species of cyanobacteria found in catfish ponds in west Mississippi (the leading region of catfish production in the USA), while the species responsible for earthy/musty off-flavors in catfish produced in the Mississippi-Alabama Blackland Prairie (MABP) region (second greatest region of catfish production) have not been described. We examined water samples from commercial catfish ponds in both regions to contrast the different types of cyanobacteria and assess the prevalence of geosmin and MIB. Results established that filamentous cyanobacteria are more common in west Mississippi compared to the MABP region. Also, the MIB-producing cyanobacterium Oscillatoria perornata is present in catfish ponds in both geographic locations, and geosmin is more prevalent in catfish ponds in the MABP region than in west Mississippi.     

Seasonal occurrence and degradation of 2-methylisoborneol in water supply reservoirs

Methylisoborneol (MIB) and geosmin are cyanobacterial metabolites that occur at nanograms per liter levels in surface water supplies and are responsible for many taste and odor complaints about the aesthetics of drinking water. This study evaluated three water supply reservoirs with bottom-release (hypolimnion) outlet structures in Arizona. MIB concentrations were always higher than geosmin concentrations, but both followed similar seasonal trends. MIB concentrations increased from spring to late summer, and stratified vertically with depth in the water column; the highest concentrations were always in the upper 10 m of the water column. Thermal destratification in the autumn increased MIB concentrations released from the outlet of reservoirs and impacted downstream utilities for several months. By winter of each year MIB concentrations were non-detectable. Mass balance analyses on MIB indicated that in-reservoir reactions were more important in changing MIB concentrations than conservative hydraulic "flushing" of the reservoir. Maximum net loss rates for MIB in the field (R(F,max)) were on the order of 0.23-1.7 ng/L-day, and biodegradation appeared more important than volatilization, photolysis or adsorption. Using lake water in laboratory experiments, bacterial biodegradation rates (R(L)) ranged from 0.5-1 ng/L-day and were comparable to R(F,max) values. Based upon these rates, MIB concentrations in a reservoir would decrease by approximately 30 ng/L over a period of 1 month. This was the magnitude change in MIB concentrations commonly observed after autumn thermal destratification of the reservoirs.     

New standards for the determination of geosmin and methylisoborneol in water by gas chromatography/mass spectrometry

Deuterium labelled geosmin and methylisoborneol (MIB) have been synthesized and evaluated as internal standards in the determination of geosmin and MIB in water by closed loop stripping followed by gas chromatography/mass spectrometry (GC/MS). The labelled standards were compared with chloroalkanes added as internal standards either at the time of sampling or immediately before closed loop stripping. When added at sampling time, the new standards enabled accurate determination of the geosmin and MIB present initially, even when the samples were analysed as much as 3 weeks later. The new standards gave better precision and accuracy than the chloroalkanes and overcame the underestimation of initial analyte concentration which usually results from losses of analyte through adsorption, volatilisation, biodegradation etc. during sample storage. Geosmin had a limit of detection of<0.1ng/l and 1 ng/lwas determined with a coefficient of variation (CV) of 1.2% (n = 5). MIB was determined at 1 ng/l with a CV of 3.5% (n = 5).     

2-Methylisoborneol and geosmin uptake by organic sludge derived from a recirculating aquaculture system

In a previous study on a recirculating fish culture system, levels of geosmin and 2-methylisoborneol were found to decrease when culture water was recirculated through the anaerobic sludge digestion treatment stage of the system. This finding led us to the present study in which the geosmin and 2-methylisoborneol removal capacity of the sludge derived from this treatment stage was examined in vitro. It was found that reduction of off-flavor compounds by the sludge was mediated by both chemical/physical sorption and biological degradation. At geosmin and 2-methylisoborneol concentrations within the range of those experienced in fish culture systems, chemical/physical sorption by the sludge was found to account for a 93% reduction in geosmin and a 79% reduction in 2-methylisoborneol from the overlying water within 48 h of incubation. Combined with the biological degradation taking place in the sludge, a complete removal of these compounds from the water phase occurred within 9 days of incubation. By means of repeated washing of the geosmin and 2-methylisoborneol contaminate sludge with clean water, relatively small amounts of these compounds were released from the sludge, a possible indication for the fact that absorption, rather than adsorption, underlies the chemical/physical removal process.     

The application of powdered activated carbon for MIB and geosmin removal: predicting PAC doses in four raw waters

Blooms of blue-green algae in reservoirs often produce the musty-earthy taste and odour algal metabolites 2-methylisoborneol (MIB) and geosmin. MIB and geosmin are not removed by conventional water treatment and their presence in the distribution system, even at low ng L-1 levels, can result in consumer complaints. Powdered activated carbon (PAC) can effectively remove MIB and geosmin when the correct dose is applied. The homogeneous surface diffusion model (HSDM) was used to predict PAC doses required to reduce MIB and geosmin concentrations to below 10 ng L-1 at four water treatment plants in Adelaide, South Australia. In jar tests, undertaken under treatment plant conditions, the predicted doses were found to produce water of the desired quality in three of the four waters. The poor predictions found in the fourth water, which had a considerably higher turbidity, were attributed to the incorporation of PAC in a larger, denser floc, leading to a reduced effective contact time of the adsorbent. It was found that higher doses of PAC were required for both compounds to produce acceptable quality water when turbidities rose above 26 NTU.     

固相微萃取法同时分析源水中54种挥发性有机物

建立了同时测定饮用水源水中54种挥发性有机物的前处理方法———顶空固相微萃取法。用65μm聚二甲基硅氧烷二乙烯基苯(PDMS-DVB)固相微萃取柱顶空萃取水样中的挥发性有机物,萃取物用气相色谱/质谱联用法(GC-MS)分析,采用质谱(MS)检测器的选择离子监测模式(SIM)和内标法进行定量分析。试验优化了顶空固相微萃取条件,如萃取柱涂层、盐度、萃取温度和萃取时间等。采用优化后的条件获得的方法检出限为0.01～0.37μg/L,在所测浓度范围内校准曲线的相关系数良好(除三氯甲烷和四氯化碳外均大于0.991),对0.60μg/L标准水样测得结果的RSD均小于15%;实际饮用水源水样加标回收率均值和RSD分别为73.1%～130%和1.4%～19%(n=6)。该方法适用于饮用水源水中挥发性有机物的监测分析。     

Earthy odor compounds production and loss in three cyanobacterial cultures

Geosmin and 2-methylisoborneol (MIB) related odor events caused by cyanobacteria have been a very common problem to water supply. This paper investigated the effects of temperature (18 and 25 °C) and light intensity (10 and 100 μmol photons m⁻² s⁻¹) on the production behaviors of earthy odor compounds by three odorous cyanobacteria, i.e., the geosmin-producing planktonic Anabaena circinalis (Ana 318), geosmin-producing benthic Phormidium amoenum (Pho 012) and MIB-producing benthic Phormidium sp. (Pho 689). At the same time, the effects of biodegradation and volatilization on the fates of the released odor compounds in water were also evaluated. The combination of high temperature (25 °C) and light intensity (100 μmol photons m⁻² s⁻¹) favored the growth of the three cyanobacteria and the production of chl-a and odor compounds. However, higher chl-a and odor yields (average odor compounds per cell) were achieved for the two benthic cyanobacteria at the temperature of 18 °C. Most of geosmin was included within the cells for Ana 318 (95-99%) and Pho 012 (85-60%), while only 20-40% MIB was bound to the cells for Pho 689. The half-life times of MIB and geosmin due to volatilization varied between 18.8 and 35.4 days, while 8 out of 10 samples exhibited a half-life time (t_1/2) for geosmin biodegradation shorter than 1 day (0.38-15.0 h), showing that biodegradation could affect the fate of geosmin significantly in aquatic environments. In comparison, biodegradation of MIB was much slower (t_1/2: 122-2166 h). Denaturing gradient gel electrophoresis (DGGE) analysis showed that Pseudomonas- and Sphingomonas-like bacteria coexisted with cyanobacteria in the cultures, and may have played an important role in geosmin/MIB biodegradation. The result of this study will be helpful for better understanding and managing the earthy odor problems caused by cyanobacteria in water supply.     

Establishment of a real-time PCR method for quantification of geosmin-producing Streptomyces spp. in recirculating aquaculture systems

Geosmin and 2-methylisoborneol (MIB) have been associated with off-flavour problems in fish and seafood products, generating a strong negative impact for aquaculture industries. Although most of the producers of geosmin and MIB have been identified as Streptomyces species or cyanobacteria, Streptomyces spp. are thought to be responsible for the synthesis of these compounds in indoor recirculating aquaculture systems (RAS). The detection of genes involved in the synthesis of geosmin and MIB can be a relevant indicator of the beginning of off-flavour events in RAS. Here, we report a real-time polymerase chain reaction (qPCR) protocol targeting geoA sequences that encode a germacradienol synthase involved in geosmin synthesis. New geoA-related sequences were retrieved from eleven geosmin-producing Actinomycete strains, among them two Streptomyces strains isolated from two RAS. Combined with geoA-related sequences available in gene databases, we designed primers and standards suitable for qPCR assays targeting mainly Streptomyces geoA. Using our qPCR protocol, we succeeded in measuring the level of geoA copies in sand filter and biofilters in two RAS. This study is the first to apply qPCR assays to detect and quantify the geosmin synthesis gene (geoA) in RAS. Quantification of geoA in RAS could permit the monitoring of the level of geosmin producers prior to the occurrence of geosmin production. This information will be most valuable for fish producers to manage further development of off-flavour events.     

Effect of residual chlorine on the analysis of geosmin, 2-MIB and MTBE in drinking water using the SPME technique

The effect of chlorine on the analysis of three organic compounds (geosmin, 2-methylisoborneol (2-MIB) and methyl tert-butyl ether (MTBE)) in drinking water is elucidated. Three fibers for solid-phase microextraction (SPME) were employed for the extraction of the organic compounds from drinking water samples with and without free residual chlorine present. A gas chromatograph coupled with a mass spectrometer was used to analyze the compounds trapped by the fibers. The presence of chlorine substantially reduces the observed geosmin, 2-MIB, and MTBE concentrations. Depending on the analyte and chlorine concentrations, an experimental error of 10-70% may be observed due to the presence of free residual chlorine. The impact is larger for lower organic compound concentrations, and under higher residual chlorine conditions. To counteract the effect from residual chlorine, sodium thiosulfate was used to dechlorinate the water. After dechlorination the experimental error was less than 10%, suggesting that dechlorination is necessary when applying SPME for the extraction of organic compounds from chlorinated drinking water.     

Ultrasonically induced degradation of 2-methylisoborneol and geosmin

2-Methylisoborneol (MIB) and geosmin (GSM) are taste and odor compounds produced by cyanobacteria in surface waters. While the strong odors and musty flavors of MIB and GSM are generally associated with poor water quality, the removal of these semi-volatile compounds presents a significant challenge to drinking water providers. Likewise in aquaculture, accumulation of these compounds in fish meat leads to quality problems and reduces marketability. Conventional water treatments are ineffective at removing low concentration of odor compounds. We report herein ultrasonic irradiation at 640 kHz leads to rapid degradation of MIB and GSM. While radical processes generally dominate during ultrasonic-induced degradation, pyrolysis appears to be responsible for a significant fraction of the observed degradation. Several pyrolytic products from MIB and GSM have been identified and degradation pathways are elucidated. The degradation of MIB and GSM follows the first-order kinetics and the rate constants are 0.07 and 0.12 min(-1), respectively. These results suggest ultrasonic irradiation maybe applicable as an effective method for removal of taint compounds from potable water supplies and fish farms.     

Countercurrent liquid/liquid extraction for analysis of organic water pollutants by GC/MS

A continuous countercurrent liquid/liquid extractor was developed to concentrate trace organic pollutants from large water samples. Non-volatile hydrophobic pollutants were extracted using methylene chloride in a pulsed column system (1 m × 15 mm ID). The procedure follows EPA method 625 to separate the water sample into basic/neutral and acidic compounds.Methylene chloride was chosen from a number of possible solvents (di-isopropylether, chloroform, hexane, ethyl acetate). Solvent efficiencies were studied using ultrapure water containing different model compounds (dimethylphtalate, anthracene, diphenylamine, atrazine, lindane, heptachlor, methyl parathion, 2-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol, 2-chloro,4-nitrophenol). Methylene chloride was found to be the most efficient extractant of both non-polar and polar chemicals. Recoveries ranged between 75% and 96% after one step batch liquid/liquid extraction, except for dimethylphtalate (38%).Pulsed column efficiency was evaluated for a 10 litre ultrapure water sample spiked with the same organic compounds as mentioned above (0.4–1.3 μg/l concentration range). The average recovery was found to be 86%. Continuous countercurrent extractor efficiency was comparable with that observed after a three step batch liquid/liquid extraction. Further, method sensitivity and sample representativity were both improved (concentration factor of 10,000 after 10 litre water extraction). The pulsed column, especially when coupled with GC/MS, can be used to identify trace organic pollutants at the ng/l level in natural waters.Countercurrent liquid/liquid extraction was applied to the analysis of natural surface waters from the Rhône River (France). Results are discussed with regard to EPA and EEC priority lists. Pollutants (such as organochlorine pesticides, triazines, monoaromatic and polyaromatic hydrocarbons, nitrophenols and chlorophenols) were identified by GC/MS at the ng/l level together with several natural organic compounds. Pulsed column extraction can thus be considered as an appropriate multiresidue method for monitoring pollution in natural water.