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Norbert V Heeb

Publications and source records attributed to Norbert V Heeb.

9 recordsLinked to original sources
PubMed2007

The historical record of PCB and PCDD/F deposition at Greifensee, a lake of the Swiss plateau, between 1848 and 1999.

Dated sediment cores provide an excellent way to investigate the historical input of persistent organic pollutants into the environment and to identify possible sources of pollution. The vertical distribution of polychlorinated dibenzo-p-dioxins/polychlorinated dibenzofurans (PCDD/F) and polychlorinated biphenyls (PCB) was investigated in a sediment core from Greifensee to elucidate the historical trends of PCDD/F and PCB inputs between 1848 and 1999. Concentrations of PCB and PCDD/F increased by more than one order of magnitude between 1930 and 1960. PCB and PCDD/F concentrations were 5700 ng/kg dry weight (dw) and 160 ng/kg dw, respectively, in sediments originating from the late 1930s and reached a maximum of 130,000 ng/kg dw and 2400 ng/kg dw, respectively, in the early 1960s. From 1960 on, concentrations decreased to the 1930s level by the mid 1980s. A remarkable shift in the PCDD/F pattern was observed after the early 1940s. Before 1940, the PCDD/F pattern was PCDF dominated (ratio of PCDD to PCDF=0.41+/-0.11), while the PCDD started to be the major species after the early 1940s (ratio of PCDD to PCDF=1.46+/-0.38). The temporal trends of PCB and PCDD/F correlate surprisingly well with each other. This might be due to the coincidence of two factors. The introduction of PCB on the market in the 1930s resulted in emissions due to the widespread use of these industrial chemicals. In the same time period, waste incineration became an increasingly popular way to get rid of garbage, boosting the PCDD/F emissions significantly. The rapid decline of PCDD/F and PCB concentrations in the sediment starting in the early 1960s reflects the result of better emission control techniques in thermal processes and the improvement of waste water treatment in the catchment of Greifensee.

Benzofurans↗
PubMed2006

Crystal structure analysis of enantiomerically pure (+) and (-) beta-hexabromocyclododecanes.

The molecular structures of individual HBCD stereoisomers are not elucidated yet. Recently, we isolated 8 of the 16 possible stereoisomers from a technical HBCD mixture and tentatively assigned their relative configurations. Herein we report on the isolation of enantiomerically pure (+) and (-) beta-HBCDs, both obtained from preparative chiral-phase liquid chromatography, and we present their absolute configurations determined from X-ray diffraction analysis. The absolute configuration of (+) beta-HBCD was found to be (1S,2S,5S,6R,9S,10R), while the one of (-) beta-HBCD was assigned to (1R,2R,5R,6S,9R,10S). The given structural information allows, for the first time, the unambiguous identification of these two important HBCD stereoisomers, which are typically found in technical products at proportions of about 3-5% for each enantiomer.

Chromatography, Liquid↗
PubMed2006

Hexabromocyclododecanes (HBCDs) in the environment and humans: a review.

Hexabromocyclododecanes (HBCDs) are brominated aliphatic cyclic hydrocarbons used as flame retardants in thermal insulation building materials, upholstery textiles, and electronics. As a result of their widespread use and their physical and chemical properties, HBCDs are now ubiquitous contaminants in the environment and humans. This review summarizes HBCD concentrations in several environmental compartments and analyzes these data in terms of point sources versus diffuse sources, biomagnification potential, stereoisomer profiles, time trends, and global distribution. Generally, higher concentrations were measured in samples (air, sediment, and fish) collected near point sources (plants producing or processing HBCDs), while lower concentrations were recorded in samples from locations with no obvious sources of HBCDs. High concentrations were measured in top predators, such as marine mammals and birds of prey (up to 9600 and 19 200 ng/g lipid weight, respectively), suggesting a biomagnification potential for HBCDs. Relatively low HBCD concentrations were reported in the few human studies conducted to date (median values varied between 0.35 and 1.1 ng/g lipid weight). HBCD levels in biota are increasing slowly and seem to reflect the local market demand. One important observation is the shiftfrom the high percentage of the gamma-HBCD stereoisomer in the technical products to a dominance of the alpha-HBCD stereoisomer in biological samples. A combination of factors such as variations in solubility, partitioning behavior, uptake, and, possibly, selective metabolism of individual isomers may explain the observed changes in stereoisomer patterns. Recommendations for further work include research on how HBCDs are transferred from products into the environment upon production, use, and disposal. Time trends need to be analyzed more in detail, including HBCD stereoisomers, and more data on terrestrial organisms are needed, especially for humans. Whenever possible, HBCDs should be analyzed as individual stereoisomers in order to address their fate and effects.

Animals↗
PubMed2006

Anaerobic degradation of brominated flame retardants in sewage sludge.

Tetrabromobisphenol A (TBBPA), hexabromocyclododecane (HBCD), and decabromodiphenyl ether (DecaBDE) are high production volume chemicals used as flame retardants in plastics for products such as electronic equipment, insulation panels, and textiles. The environmental safety of brominated flame retardants, especially their persistence, bioaccumulation, and toxicity is a controversial topic. Here, we studied and compared the degradation of TBBPA, HBCD, and DecaBDE under anaerobic conditions in digested sewage sludge. The half-lives of TBBPA and a technical HBCD mixture were 0.59 and 0.66 d, respectively. The fact that (+/-)-alpha-HBCD exhibited an almost doubled half-life compared to (+/-)-beta-HBCD and (+/-)-gamma-HBCD is an important finding with respect to the discussion on the persistence of individual HBCD stereoisomers and the recent reports on strong relative enrichment of alpha-HBCD in biota. We found no statistically significant enantioselective degradation of alpha-, beta-, or gamma-HBCD. Half-lives of TBBPA and a technical HBCD mixture were not dependent on the presence of additional nutrients or primers. Concentrations of TBBPA and a technical HBCD mixture decreased also in sterile control samples, however, at a rate that was more than a factor of 50 smaller than in incubations under non-sterile conditions. Compared to TBBPA and a technical HBCD mixture, DecaBDE exhibited a much longer half-life of 7 x 10(2)d in the same system. Pseudo-first-order degradation rate constants decreased according to the following sequence: TBBPA congruent with(+/-)-gamma-HBCD congruent with(+/-)-beta-HBCD>(+/-)-alpha-HBCD>>DecaBDE. Preliminary investigations suggest that degradation of TBBPA, HBCD, and DecaBDE occurs in full-scale anaerobic digesters, as well.

Anaerobiosis↗
PubMed2005

Anaerobic degradation of decabromodiphenyl ether.

The environmental safety of decabromodiphenyl ether (BDE-209), a widely used flame retardant, has been the topic of controversial discussions during the past several years. Degradation of BDE-209 into lower brominated diphenyl ether congeners, exhibiting a higher bioaccumulation potential, has been a critical issue. Here, we report on the degradation of BDE-209 and the formation of octa- and nonabromodiphenyl ether congeners under anaerobic conditions. Sewage sludge collected from a mesophilic digester was used as the inoculum and incubated up to 238 days with and without a set of five primers. Following Soxhlet extraction and a liquid chromatography cleanup procedure, parent compounds and debromination products were analyzed by GC/HRMS. In experiments with primers, concentrations of BDE-209 decreased by 30% within 238 days. This corresponds to a pseudo-first-order degradation rate constant of 1 x 10(-3) d(-1). Without primers, the degradation rate constant was 50% lower. Formation of two nonabromodiphenyl ether and six octabromodiphenyl ether congeners proved that BDE-209 underwent reductive debromination in these experiments. Debromination occurred at the para and the meta positions, whereas debromination at the ortho position was not statistically significant. All three nonabromodiphenyl ether congeners (BDE-206, BDE-207, and BDE-208) were found to undergo reductive debromination as well. No significant change of the BDE-209 concentration and no formation of lower brominated congeners was observed in sterile control experiments. To our knowledge, this is the first report demonstrating microbially mediated reductive debromination of BDE-209 under anaerobic conditions.

Animals↗
PubMed2005

Benzene: a secondary pollutant formed in the three-way catalyst.

Benzene emissions from a relevant proportion of today's gasoline-driven passenger cars and light-duty vehicles can increase by up to 2 orders of magnitude when driving at high engine load (e.g., on highways). Under such conditions, post-catalyst benzene levels exceeded those found pre-catalyst. As a consequence, formation of benzene in the catalyst was postulated. To further reduce ambient air concentrations of benzene,these critical operating conditions must be carefully avoided. Here, we report in detail to what extent and at what operating conditions catalyst-induced benzene and toluene formation can occur. For that purpose, a EURO-1 passenger car (1.8 L, model year 1995)fulfilling the valid regulations, equipped with a new, two-layered, Pd-CeO2-Al2O3/Rh-ZrO2-Al2O3 three-way catalyst was operated at steady state on a chassis dynamometer at 100, 125, and 150 km/h at variable air to fuel ratios. Pre- and post-catalyst exhaust gas concentrations of benzene, toluene, C2-, and C3-benzenes were monitored at a time resolution of 0.5 Hz by means of chemical ionization mass spectrometry. A net benzene formation window, ranging from pre-catalyst exhaust gas temperatures of 600-730 degrees C and lambda-values of 0.83-0.95, with a pronounced minimum at 0.87, was observed. Dealkylation reactions of aromatic hydrocarbons are assumed to be the major pathway leading to benzene.

Air Pollutants↗
PubMed2005

Structure elucidation of hexabromocyclododecanes--a class of compounds with a complex stereochemistry.

Hexabromocyclododecanes (HBCDs) are high production volume chemicals (16700 t worldwide in 2001) used as flame-retardants for plastics and textiles. HBCDs exhibit typical properties of persistent organic pollutants (POPs). They are highly lipophilic and accumulate in biota. Increasing environmental concentrations of HBCDs, mostly reported as sum values, have been observed. As such, HBCDs have to be considered as potential emerging POPs, but their occurrence and environmental fate have not yet been addressed at the level of individual HBCD stereoisomers. Considering the six stereogenic centers of HBCDs, 16 stereoisomers, six diastereomeric pairs of enantiomers as well as four meso forms, can be deduced. Herein, we report spectroscopic and chromatographic data for eight out of 16 possible HBCD stereoisomers, which were isolated from a technical product. Six stereoisomers were identified as three pairs of enantiomers ((+/-) alpha-, beta-, and gamma-HBCDs), differing in optical rotation and chromatographic retention on a chiral phase. The crystal structures of these pairs of enantiomers were determined. Another two of these eight HBCD stereoisomers, not yet described in the literature, showed no optical rotation and are tentatively assigned as meso forms (delta- and epsilon-HBCD). The given spectroscopic and chromatographic information allows the unambiguous identification of eight HBCD stereoisomers and the occurrence, fate, and toxicology of these individual stereoisomers can now be studied.

Chromatography↗
PubMed2003

Determination of nitrated phenolic compounds in rain by liquid chromatography/atmospheric pressure chemical ionization mass spectrometry.

A sensitive, specific, and rapid analytical method based on liquid-liquid extraction and liquid chromatography/atmospheric pressure chemical ionization mass spectrometry has been developed for trace analysis of nitrated phenolic compounds in rain samples. Selective detection in the low nanogram-per-milliliter range was achieved on the basis of selected ion monitoring of the respective phenolate anions [M - H]-. The presence of alkylated (C1-C3) and nonalkylated nitrophenols (C0) was confirmed by their characteristic neutral loss of nitrogen dioxide upon collision-induced dissociation in tandem mass spectrometry mode. In individual rain samples, 27 C0-C3-nitrophenol isomers as well as 16 C0-C3-dinitrophenol isomers were detected. Total levels of nitro- and dinitrophenol isomers were estimated on the basis of 2-nitrophenol and 2,6-dinitrophenol. Concentrations between 0.66 and 2.0, 12-29, 12-36, and 5.5-12 microg/L were obtained for the C0-, C1-, C2-, and C3-nitrophenols, respectively. Lower levels of 0.19-1.4, 0.39-2.1, 0.053-0.55, and 0.081-0.10 microg/L were estimated for the corresponding C0-, C1-, C2-, and C3-dinitrophenols. The highest number of individual isomers was found in winter rain samples, and distinctive isomeric patterns were observed for individual samples. Mono- and dialkylated nitrophenols and non- and monoalkylated dinitrophenols represent the major part of nitro- and dinitrophenol species. Comparing the pattern of Co-, C1-, and C2-nitrophenols in rain with the corresponding Co-, C1-, and C2-benzene pattern in ambient air suggests that atmospheric oxidation and nitration processes of alkylbenzenes are favored, as compared to those of benzene.

Journal Article↗