Uptake by foods of tetrachloroethylene, trichloroethylene, toluene, and benzene from air

Summary Transition rates from air into foods as well as equilibrium concentrations in air and critical foods were determined for tetrachloroethylene, trichloroethylene, benzene and toluene. From these data, maximum concentrations of the four substances in air were estimated that keep contamination of critical foods at an acceptable level. A simple and rapid method allowed us to determine the risk of food contamination from the air, e.g. in shops and kitchens, by the analysis of the air. Estimations showed that concentrations in the air of shops should not exceed 1 mg/m³ if tetrachloroethylene concentrations in foods are limited to 100 g/kg (slightly higher concentrations can be accepted for the other three compounds); in kitchens of restaurants and households, even 0.3 mg/m³ cause the target concentration to be exceeded rather frequently. If the limit in foods is 50 g/kg, recommended maximum concentrations in air are 0.5 and 0.15 mg/m³. The data also shows that the recommended limits for concentrations in air conflict with the accepted emission limits: If emission at the accepted limit occurs near shops or households, contamination of foods far exceeds that considered as tolerable.

---

Übergang von Tri- und Tetrachlorethylen, Benzol und Toluol aus der Luft in Lebensmittel

Zusammenfassung Für Tri- und Tetrachlorethylen, Benzol und Toluol wurden Übergangsgeschwindigkeiten aus der Luft in Lebensmittel sowie Gleichgewichtskonzentrationen in Luft und kritischen Lebensmitteln bestimmt. Aus diesen Daten ließen sich maximale Konzentrationen in der Luft abschätzen, welche die Verunreinigung kritischer Lebensmittel in akzeptablen Grenzen halten. Das erlaubt uns, das Risiko von Lebensmittelverunreinigung aus der Luft, z. B. in Läden und Küchen, durch Luftanalyse zu bestimmen, wofür eine einfache Methode benutzt wird. Unter der Annahme einer maximalen Tetrachlorethylen-Konzentration in Lebensmitteln von 100 g/kg (z. B. deutsche Höchstmengenverordnung) wird abgeschätzt, daß Konzentrationen in Läden 1 mg/m³ nicht überschreiten dürfen (die Gehalte der anderen drei Substanzen dürfen leicht höher sein). In Küchen von Gaststätten oder Haushalten wird die Zielkonzentration in Lebensmitteln bereits bei 0,3 mg/m³ ziemlich häufig überschritten. Für die Schweiz (50 g/kg für Lebensmittel) werden 0,5 und 0,15 mg/m³ vorgeschlagen. Die Resultate zeigen aber auch, daß die empfohlenen Maximalkonzentrationen in der Luft leicht mit den Emissionsgrenzwerten in Konflikt geraten: Bei legalen Emissionen in der Nähe von Läden oder Haushalten kann die Lebensmittelkontamination die Grenzwerte bei weitem übersteigen.

     

Distinguishing abiotic and biotic transformation of tetrachloroethylene and trichloroethylene by stable carbon isotope fractionation

Significant carbon isotope fractionation was observed during FeS-mediated reductive dechlorination of tetrachloroethylene (PCE) and trichloroethylene (TCE). Bulk enrichment factors (E(bulk)) for PCE were -30.2 +/- 4.3 per thousand (pH 7), -29.54 +/- 0.83 per thousand (pH 8), and -24.6 +/- 1.1 per thousand (pH 9). For TCE, E(bulk) values were -33.4 +/- 1.5 per thousand (pH 8) and -27.9 +/- 1.3 per thousand (pH 9). A smaller magnitude of carbon isotope fractionation resulted from microbial reductive dechlorination by two isolated pure cultures (Desulfuromonas michiganensis strain BB1 (BB1) and Sulfurospirillum multivorans (Sm)) and a bacterial consortium (BioDechlor INOCULUM (BDI)). The E(bulk) values for biological PCE microbial dechlorination were -1.39 +/- 0.21 per thousand (BB1), -1.33 +/- 0.13 per thousand (Sm), and -7.12 +/- 0.72 per thousand (BDI), while those for TCE were -4.07 +/- 0.48 per thousand (BB1), -12.8 +/- 1.6 per thousand (Sm), and -15.27 +/- 0.79 per thousand (BDI). Reactions were investigated by calculation of the apparent kinetic isotope effect for carbon (AKIEc), and the results suggest that differences in isotope fractionation for abiotic and microbial dechlorination resulted from the differences in rate-limiting steps during the dechlorination reaction. Measurement of more negative E(bulk) values at sites contaminated with PCE and TCE may suggest the occurrence of abiotic reductive dechlorination by FeS.     

Sulfur and oxygen isotope fractionation during benzene, toluene, ethyl benzene, and xylene degradation by sulfate-reducing bacteria

We examined the oxygen and sulfur isotope fractionation of sulfate during anaerobic degradation of toluene by sulfate-reducing bacteria in culture experiments with Desulfobacula toluolica as a type strain and with an enrichment culture Zz5-7 obtained from a benzene, toluene, ethylbenzene, and xylene (BTEX)-contaminated aquifer. Sulfur isotope fractionation can show considerable variation upon sulfate reduction and may react extremely sensitively to changes in environmental conditions. In contrast, oxygen isotope fractionation seems to be less sensitive to environmental changes. Our results clearly indicate that oxygen isotope fractionation is dominated by isotope exchange with ambient water. To verify our experimental results and to test the applicability of oxygen and sulfur isotope investigations under realistic field conditions, we evaluated isotope data from two BTEX-contaminated aquifers presented in the recent literature. On a field scale, bacterial sulfate reduction may be superimposed by processes such as dispersion, adsorption, reoxidation, or mixing. The dual isotope approach enables the identification of such sulfur transformation processes. This identification is vital for a general qualitative evaluation of the natural attenuation potential of the contaminated aquifer.     

Rapid gas-chromatographic determination of trichloroethylene and/or tetrachloroethylene in lettuce by direct head-space analysis

A direct head-space method has been developed for the rapid investigation of the contamination of large numbers of individual lettuce plants as a consequence of local ground water and soil pollution with trichloroethylene and/or tetrachloroethylene. The plants were divided into several anatomically and physiologically distinct parts with different chemico-physical properties.     

Rapid gas-chromatographic determination of trichloroethylene and/or tetrachloroethylene in lettuce by direct head-space analysis

Summary A direct head-space method has been developed for the rapid investigation of the contamination of large numbers of individual lettuce plants as a consequence of local ground water and soil pollution with trichloroethylene and/or tetrachloroethylene. The plants were divided into several anatomically and physiologically distinct parts with different chemicophysical properties.

---

Eine rasche gaschromatographische Bestimmung von Trichlorethen und Tetrachlorethen in Salatpflanzen durch direkte Kopfraum-Analyse

Zusammenfassung Eine rasche direkte Kopfraum-Methode wurde entwickelt, um die Kontamination großer Mengen individueller Salatpflanzen als Folge der lokalen Grundwasser- und Bodenverunreinigung mit Trichlorethen und/oder Tetrachlorethen zu untersuchen. Die Pflanzen wurden in anatomisch und physiologisch unterschiedliche Teile mit verschiedenen chemo-physikalischen Eigenschaften aufgeteilt.

     

Trichloroethylene and tetrachloroethylene elimination from the air by means of a hybrid bioreactor with immobilized biomass

Two-phase bioreactors consisting of bacterial consortium in suspension and sorbents with immobilized biomass were used to treat waste air containing chlorinated ethenes, trichloroethylene (TCE) and tetrachloroethylene (PCE). Synthetic municipal sewage was used as the medium for bacterial growth. The system was operated with loadings in the range 1.48-4.76 gm(-3)h(-1) for TCE and 1.49-5.96 gm(-3)h(-1) for PCE. The efficiency of contaminant elimination was 55-86% in the bioreactor with wood chips and 33-89% in the bioreactor filled with zeolite. The best results were observed 1 week after the pollutant loading was increased. However, in these conditions, the stability of the process was not achieved. In the next 7 days the effectiveness of the system decreased. Contaminant removal efficiency, enzymatic activity and the biomass content were all diminished. The system was working without being supplied with additional hydrocarbons as the growth-supporting substrates. It is assumed that ammonia produced during the transformation of wastewater components induced enzymes for the cometabolic degradation of TCE and PCE. However, the evaluation of nitrogen compound transformations in the system is difficult due to the sorption on carriers and the combined processes of nitrification and the aerobic denitrification. An applied method of air treatment is advantageous from both economic and environmental point of views.     

Reductive dechlorination of tetrachloroethylene and trichloroethylene by mackinawite (FeS) in the presence of metals: reaction rates

Reductive dechlorination by mackinawite (FeS) is an important transformation pathway for chloroethylenes in anoxic environments. Yet, the impact of metals on reductive dechlorination is not well understood, despite their frequent cooccurrence with chloroethylenes. Fe(II), Co(II), Ni(II), and Hg(II) were evaluated for their impact on the dechlorination rates of PCE and TCE by FeS. Compared with unamended FeS batches, the dechlorination rates of both chloroethylenes decreased by addition of 0.01 M Fe(II). Relative to 0.01 M Fe(II)-added FeS batches, the dechlorination rates increased in FeS batches amended with 0.01 M of Co(II) and Hg(II), whereas the rates decreased in 0.01 M Ni(II)-added batches. While significantly impacting the dechlorination rates, the amended metals were quantitatively sequestered by FeS mainly because of formation of metal sulfides. Comparison of the dechlorination rates between metal-added FeS batches and metal sulfide batches suggests that discrete metal sulfides do not form in metal-added FeS batches. The observed exceptionally high reactivity of CoS suggests that it may be useful in reactive permeable barrier applications because of its stability in anoxic waters. The dechlorination rates of PCE and TCE significantly varied with Fe(ll) amendment concentrations (Fe(II)0), indicating the presence of different types of solid-bound Fe phases with Fe(II)o.     

Biofiltration and inhibitory interactions of gaseous benzene, toluene, xylene, and methyl tert-butyl ether

This study evaluated the individual and combined removal capacities of benzene, toluene, and xylene (B, T, and X) in the presence and absence of methyl tert-butyl ether (MTBE) in a polyurethane biofilter inoculated with a BTX-degrading microbial consortium, and further examined their interactive effects in various mixtures. In addition, Polymerase chain reaction-denaturing gradient gel electrophoresis and phylogenetic analysis of 16S rRNA gene sequences were used to compare the microbial community structures found in biofilters exposed to the various gases and gas mixtures. The maximum individual elimination capacities (MECs) of B, T, and X were 200, 238, and 400 g m(-3) h(-1), respectively. There was no significant elimination of MTBE alone. Addition of MTBE decreased the MECs of B,T, and X to 75, 100, and 300 g m(-3) h(-1), respectively, indicating that benzene was most strongly inhibited by MTBE. When the three gases were mixed (B + T + X), the removal capacities of individual B, T, and X were 50, 90, and 200 g m(-3) h(-1), respectively. These capacities decreased to 40, 50, and 100 g m(-3) h(-1) when MTBE was added to the mix. The MEC of the three-gas mixture (B + T + X) was 340 g m(-3) h(-1), and that of the four-gas mixture was 200 g m(-3) h(-1). Although MTBE alone was not degraded by the biofilter, it could be co-metabolically degraded in the presence of toluene, benzene, or xylene with the MECs of 34, 23, and 14 g m(-3) h(-1), respectively. The microbial community structure analysis revealed that two large groups could be distinguished based on the presence or absence of MTBE, and many of the dominant bacteria in the consortia were closely related to bacteria isolated from aromatic hydrocarbon-contaminated sites and/ or oil wastewaters. These findings provide important new insights into biofiltration and may be used to improve the rational design of biofilters for remediation of petroleum gas-contaminated airstreams according to composition types of mixed gases.     

On the origin of benzene, toluene, ethylbenzene and xylene in extra virgin olive oil

Concentrations of benzene, toluene, C₂-benzenes and styrene were determined in olives and the oils produced thereof, as well as at various intermediate steps during production. Concentrations were compared to those found in samples of air taken from the olive grove and the olive mills. In an exposition experiment in the laboratory, olives absorbed aromatic compounds, approaching saturation corresponding to the partition coefficient between air and oil. However, concentrations in olives delivered to the mills were 4–10 times higher than expected from the analysis of the air in the olive grove. In the olive mills, concentrations were increased further by a factor of up to 2 because of uptake from air which contained high concentrations of aromatics. Styrene concentrations strongly increased during storage of crushed olives at ambient temperature, which confirms the hypothesis that styrene is a product of metabolism.

---

Über die Herkunft von Benzol, Toluol, Ethylbenzol und Xylol in nativen Olivenölen

Zusammenfassung Gehalte von Benzol, Toluol, C₂-Benzolen und Styrol wurden in Oliven, den daraus gewonnenen Ölen sowie Zwischenstufen der Ölproduktion gemessen und mit den Konzentrationen in der Luft des Olivenhains und der Ölmühlen verglichen. In Expositionsversuchen im Labor nahmen Oliven annähernd soviel Aromaten auf, wie Sättigung gemäß dem Verteilungskoeffizienten zwischen Luft und Öl entspricht. Die Konzentrationen in den an die Mühlen gelieferten Oliven lagen jedoch 4–10mal höher als die Gehalte in der Luft des Olivenhains erwarten ließen. In der Ölmühle erhöhten sich die Konzentrationen nochmals um einen Faktor bis zu zwei wegen höheren Aromatengehalten in jener Luft. Styrol stieg bei der Lagerung zerquetschter Oliven bei Raumtemperatur stark an, was die Vermutung bestätigt, daß es sich um ein Metabolisierungsprodukt handelt.

     

On the origin of benzene, toluene, ethylbenzene, and the xylenes in virgin olive oil-further results

Investigations into the sources of contamination of virgin olive oil by gasoline components were concluded. Olives on the tree contained volatile aromatic hydrocarbons at concentrations exceeding those corresponding to the equilibrium with the environment. Present knowledge indicates that up to 10 g/kg of benzene and 250 g/kg for the sum of benzene, toluene, and the C₂-benzenes must be considered as possible background concentrations. Aside from the oil mills, the rooms for intermediate storage of the olives were found to be an important source of contamination by gasoline vapours, since they often contain vehicles and other gasoline-driven engines. Parking of a small, hot grass mower into a similar room released an amount of gasoline that was sufficient to contaminate the oil in olives above the proposed limit by a factor of 100. Recommendations are derived for the producers to avoid contamination of olive oil with gasoline components.     

Reductive dechlorination pathways of tetrachloroethylene and trichloroethylene and subsequent transformation of their dechlorination products by mackinawite (FeS) in the presence of metals

Because of frequent co-occurrence of metals with chlorinated organic pollutants, Fe(II), Co(II), Ni(II), and Hg(II) were evaluated for their impact on the dechlorination pathways of PCE and TCE and the subsequent transformation of the initial dechlorination products by FeS. PCE transforms to acetylene via beta-elimination, TCE via hydrogenolysis, and 1,1-DCE via alpha-elimination, while TCE transforms to acetylene via beta-elimination and cis-DCE and 1,1-DCE via hydrogenolysis. Acetylene subsequently transforms in FeS batches, but little transformation of cis-DCE and 1,1-DCE was observed. Branching ratio calculations indicate that the added metals decrease the reductive transformation of PCE and TCE via beta-elimination relative to hydrogenolysis, resulting in a higher production of the toxic DCE byproducts. Nonetheless, acetylene is generally the dominant product. Production of highly water-soluble compound(s) is suspected as a significant source for incomplete mass recoveries. In the transformation of PCE and TCE, the formation of unidentified product(s) is most significant in Co(II)-added FeS batches. Although nearly complete mass recoveries were observed in the other FeS batches, the subsequent transformation of acetylene would lead to the formation of unidentified product(s) over long time periods.     

The biofiltration of indoor air: air flux and temperature influences the removal of toluene, ethylbenzene, and xylene

An alternative approach to maintaining indoor air quality may be the biofiltration of air circulated within the space. A biofilter with living botanical matter as the packing medium reduced concentrations of toluene, ethylbenzene, and o-xylene concurrently present at parts per billion (volume) in indoor air. The greatest reduction in concentrations per pass was under the slowest influent air flux (0.025 m s(-1)); however, the maximum amount removed per unit time occurred under the most rapid flux (0.2 m s(-1)). There was little difference between the different compounds with removal capacities of between 1.3 and 2.4 micromol m(-3) biofilter s(-1) (between 0.5 and 0.9 g m(-3) biofilter h(-1)) depending on influent flux and temperature. Contrary to biofilters subjected to higher influent concentrations, the optimal temperatures for removal by this biofilter decreased to less than 20 degrees C at the most rapid flux for all three compounds. Microbial activity was decreased at these cooler temperatures suggesting the biofilter was not microbially limited but rather was limited by the availability of substrate. The cooler temperatures allowed greater partitioning of the VOCs into the water column which had a greater impact on removal than its reduction in microbial activity.     

Headspace analysis of benzene in food contact materials and its migration into foods from plastics cookware

Concentrations of benzene of 29 and 64 mg/kg were found in two samples of thermoset polyester compounded for the manufacture of plastic cookware. In collaboration with the suppliers of the materials, it was established that the benzene originated from the use of t-butyl perbenzoate used as an initiator in the manufacture of the polymer. Samples of thermoset polyester made to the original formulations and thus contaminated with benzene showed migration levels of 1.9 and 5.6 mg/kg in olive oil after extraction for 1 hour at 175 degrees C. Migration levels into olive oil at 175 degrees C for samples produced with non-aromatic initiator were less than 0.1 mg/kg. Concentrations of benzene in thermoset polyester cookware purchased from retail outlets were 0.3 to 84.7 mg/kg. Low amounts of benzene (less than 0.01 to 0.09 mg/kg) were detected in foods when the articles were used for cooking in microwave or conventional ovens. Other plastics used for retail food packaging, such as polystyrene and PVC, which might utilise t-butyl perbenzoate catalyst, were also analysed for benzene. Levels were mostly below 0.1 mg/kg, with the highest amounts detected being from 0.2 to 1.7 mg/kg, predominantly in articles of expanded polystyrene.     

Experimental confirmation of the dicarbonyl route in the photo-oxidation of toluene and benzene

The methodology of solid phase microextraction (SPME) with O-(2,3,4,5,6)-pentafluorobenzylhydroxylamine hydrochloride (PFBHA) on-fiber derivatization for the determination of carbonyls has been applied to the photo-oxidation of benzene and toluene carried out in the EUPHORE chambers. This work focuses on the results obtained for a number of highly reactive carbonyls, crucial in the determination of branching ratios and confirmation of the carbonylic route. The observed yields and kinetic behavior were compared to simulations with the Master Chemical Mechanism model, version 3.1 (MCMv3.1). The following yields were measured in the toluene system: glyoxal, (37 +/- 2)%; methylglyoxal, (37 +/- 2)%; 4-oxo-2-pentenal, > (13.8 +/- 1.5)%; and total butenedial, (13 +/- 7)% (cis-butenedial, (6 +/- 3)%; trans-butenedial, (7 +/- 4)%]. For benzene, the experimental glyoxal yields were (42 +/- 3) and (36 +/- 2)% for the two successive experiments (September 24 and 25, 2003), (17 +/- 9)% for total butenedial [(8 +/- 4)% cis-butenedial and (9 +/- 5)% trans-butenedial (September 24, 2003)] and (15 +/- 6)% total butenedial (September 25, 2003) [(7 +/- 3) and (7 +/- 3)% for the cis and trans isomers, respectively]. PTR-MS estimations for butenedial also allowed the two isomers of butenedial to be distinguished, but the measurements showed signs of interference from other products. The results presented confirm the fast ring cleavage and provide further experimental confirmation of the dicarbonylic route.     

Impact of ethanol on the natural attenuation of benzene, toluene, and o-xylene in a normally sulfate-reducing aquifer

Side-by-side experiments were conducted in a sulfate-reducing aquifer at a former fuel station to evaluate the effect of ethanol on biodegradation of other gasoline constituents. On one side, for approximately 9 months we injected groundwater amended with 1-3 mg/L benzene, toluene, and o-xylene (BToX). On the other side, we injected the same, adding approximately 500 mg/L ethanol. Initially the BToX plumes on both sides ("lanes") extended approximately the same distance. Thereafter, the plumes in the "No Ethanol Lane" retracted significantly, which we hypothesize to be due to an initial acclimation period followed by improvement in efficiency of biodegradation under sulfate-reducing conditions. In the "With Ethanol Lane", the BToX plumes also retracted, but more slowly and not as far. The preferential biodegradation of ethanol depleted dissolved sulfate, leading to methanogenic/acetogenic conditions. We hypothesize that BToX in the ethanol-impacted lane were biodegraded in part within the methanogenic/acetogenic zone and, in part, within sulfate-reducing zones developing along the plume fringes due to mixing with sulfate-containing groundwater surrounding the plumes due to dispersion and/or shifts in flow direction. Overall, this research confirms that ethanol may reduce rates of biodegradation of aromatic fuel components in the subsurface, in both transient and near steady-state conditions.     

Comparative assessments of benzene, toluene, and xylene natural attenuation by quantitative polymerase chain reaction analysis of a catabolic gene, signature metabolites, and compound-specific isotope analysis

A controlled-release study conducted at Vandenberg Air Force Base involved the injection of anaerobic groundwater amended with benzene, toluene, and o-xylene (BToX; 1-3 mg/L each) in two parallel lanes: lane A injectate contained no ethanol, whereas lane B injectate contained approximately 500 mg/L ethanol. As reported previously by Mackay and co-workers, ethanol led to slower BToX disappearance in lane B. Here, we report on assessments of BToX natural attenuation by three independent and specific monitoring approaches: signature metabolites diagnostic of anaerobic TX metabolism (benzysuccinates), compound-specific isotope analysis (CSIA), and quantitative polymerase chain reaction (qPCR) analysis of a catabolic gene involved in anaerobic TX degradation (bssA). In combination, the three monitoring methods provided strong evidence of in situ TX biodegradation in both lanes A and B; however, no single method provided strong evidence for TX biodegradation in both lanes. Benzylsuccinates were detected almost exclusively in lane B, where slower TX degradation and higher residual TX concentrations led to higher metabolite concentrations. In contrast, CSIA provided evidence of TX biodegradation almost exclusively in lane A, as greater degradation rates led to more pronounced isotopic enrichment. qPCR analyses of bssA were more complex. Evidence of increases in bssA copy number (up to 200-fold) after the release started was stronger in lane A, but higher absolute bssA copy number (and bacterial abundance, based on 16S rRNA genes) was observed in lane B, where bacteria genetically capable of anaerobic TX degradation may have been growing primarily on ethanol or its metabolites rather than TX.     

Characteristics of Rhodococcus pyridinovorans PYJ-1 for the biodegradation of benzene, toluene, m-xylene (BTX), and their mixtures

The degradation rates of benzene, toluene, and m-xylene (BTX) by Rhodococcus pyridinovorans PYJ-1, were highest at 30, 50, and 25 mg/l, respectively. The degradation rate was highest for toluene (0.106 mg/mg-protein x h) followed by benzene and m-xylene at the optimum pH and temperature of 7 and 32 degrees C, respectively. For BTX mixtures, toluene was the preferred substrate, but degradation of each BTX was competitively inhibited by other BTX compounds. The degradation rate of each component of in the BTX mixture decreased by 57-89% depending on the concentration (1-5 mg/l) of the component compared with that of the component as a single substrate.