6 research outputs found
Biotransformation of Hexabromocyclododecanes (HBCDs) with LinBî—¸An HCH-Converting Bacterial Enzyme
Hexabromocyclododecanes (HBCDs) and hexachlorocyclohexanes
(HCHs)
are polyhalogenated hydrocarbons with similar stereochemistry. Both
classes of compounds are considered biologically persistent and bioaccumulating
pollutants. In 2009, the major HCH stereoisomers came under regulation
of the Stockholm convention. Despite their persistence, HCHs are susceptible
to bacterial biotransformations. Here we show that LinB, an HCH-converting
haloalkane dehalogenase from <i>Sphingobium indicum</i> B90A,
is also able to transform HBCDs. Racemic mixtures of α-, β-,
and γ-HBCDs were exposed to LinB under various conditions. All
stereoisomers were converted, but (−)Âα-, (+)Âβ-,
and (+)Âγ-HBCDs were transformed faster by LinB than their enantiomers.
The enantiomeric excess increased to 8 ± 4%, 27 ± 1%, and
20 ± 2% in 32 h comparable to values of 7.1%, 27.0%, and 22.9%
as obtained from respective kinetic models. Initially formed pentabromocyclododecanols
(PBCDOHs) were further transformed to tetrabromocyclododecadiols (TBCDDOHs).
At least, seven mono- and five dihydroxylated products were distinguished
by LC-MS so far. The widespread occurrence of HCHs has led to the
evolution of bacterial degradation pathways for such compounds. It
remains to be shown if LinB-catalyzed HBCD transformations in vitro
can also be observed in vivo, for example, in contaminated soils or
in other words if such HBCD biotransformations are important environmental
processes
Deconvolution of Mass Spectral Interferences of Chlorinated Alkanes and Their Thermal Degradation Products: Chlorinated Alkenes
Chlorinated
paraffins (CPs) are high production volume chemicals
and ubiquitous environmental contaminants. CPs are produced and used
as complex mixtures of polychlorinated <i>n</i>-alkanes
containing thousands of isomers, leading to demanding analytical challenges.
Due to their high degree of chlorination, CPs have highly complex
isotopic mass patterns that often overlap, even when applying high
resolution mass spectrometry. This is further complicated in the presence
of degradation products such as chlorinated alkenes (CP-enes). CP-enes
are formed by dehydrochlorination of CPs and are expected thermal
degradation products in some applications of CPs, for example, as
metal working fluids. A mathematical method is presented that allows
deconvolution of the strongly interfered measured isotope clusters
into linear combinations of isotope clusters of CPs and CP-enes. The
analytical method applied was direct liquid injection into an atmospheric
pressure chemical ionization source, followed by quadrupole time-of-flight
mass spectrometry (APCI-qTOF-MS), operated in full scan negative ion
mode. The mathematical deconvolution method was successfully applied
to a thermally aged polychlorinated tridecane formulation (Cl<sub>5</sub>–Cl<sub>9</sub>). Deconvolution of mass patterns allowed quantifying fractions of
interfering CPs and CP-enes. After exposure to 220 °C for 2,
4, 8, and 24 h, fractions of CP-enes within the respective interfering
clusters increased from 0–3% at 0 h up to 37–44% after
24 h. It was shown that thermolysis of CPs follows first-order kinetics.
The presented deconvolution method allows CP degradation studies with
mass resolution lower than 20000 and is therefore a good alternative
when higher resolution is not available
Corelease of Genotoxic Polycyclic Aromatic Hydrocarbons and Nanoparticles from a Commercial Aircraft Jet Engine – Dependence on Fuel and Thrust
Jet engines are important contributors to global CO2 emissions and release enormous numbers of ultrafine particles
into different layers of the atmosphere. As a result, aviation emissions
are affecting atmospheric chemistry and promote contrail and cloud
formation with impacts on earth’s radiative balance and climate.
Furthermore, the corelease of nanoparticles together with carcinogenic
polycyclic aromatic hydrocarbons (PAHs) affects air quality at airports.
We studied exhausts of a widely used turbofan engine (CFM56–7B26)
operated at five static thrust levels (idle, 7, 30, 65, and 85%) with
conventional Jet A-1 fuel and a biofuel blend composed of hydro-processed
esters and fatty acids (HEFA). The particles released, the chemical
composition of condensable material, and the genotoxic potential of
these exhausts were studied. At ground operation, particle number
emissions of 3.5 and 0.5 × 1014 particles/kg fuel
were observed with highest genotoxic potentials of 41300 and 8800
ng toxicity equivalents (TEQ)/kg fuel at idle and 7% thrust, respectively.
Blending jet fuel with HEFA lowered PAH and particle emissions by
7–34% and 65–67% at idle and 7% thrust, respectively,
indicating that the use of paraffin-rich biofuels is an effective
measure to reduce the exposure of airport personnel to nanoparticles
coated with genotoxic PAHs (Trojan horse effect)
Effects of a Combined Diesel Particle Filter-DeNOx System (DPN) on Reactive Nitrogen Compounds Emissions: A Parameter Study
The impact of a combined diesel particle filter-deNO<sub><i>x</i></sub> system (DPN) on emissions of reactive nitrogen
compounds
(RNCs) was studied varying the urea feed factor (α), temperature,
and residence time, which are key parameters of the deNO<sub><i>x</i></sub> process. The DPN consisted of a platinum-coated
cordierite filter and a vanadia-based deNO<sub><i>x</i></sub> catalyst supporting selective catalytic reduction (SCR) chemistry.
Ammonia (NH<sub>3</sub>) is produced in situ from thermolysis of urea
and hydrolysis of isocyanic acid (HNCO). HNCO and NH<sub>3</sub> are
both toxic and highly reactive intermediates. The deNO<sub><i>x</i></sub> system was only part-time active in the ISO8178/4
C1cycle. Urea injection was stopped and restarted twice. Mean NO and
NO<sub>2</sub> conversion efficiencies were 80%, 95%, 97% and 43%,
87%, 99%, respectively, for α = 0.8, 1.0, and 1.2. HNCO emissions
increased from 0.028 g/h engine-out to 0.18, 0.25, and 0.26 g/h at
α = 0.8, 1.0, and 1.2, whereas NH<sub>3</sub> emissions increased
from <0.045 to 0.12, 1.82, and 12.8 g/h with maxima at highest
temperatures and shortest residence times. Most HNCO is released at
intermediate residence times (0.2–0.3 s) and temperatures (300–400
°C). Total RNC efficiencies are highest at α = 1.0, when
comparable amounts of reduced and oxidized compounds are released.
The DPN represents the most advanced system studied so far under the
VERT protocol achieving high conversion efficiencies for particles,
NO, NO<sub>2</sub>, CO, and hydrocarbons. However, we observed a trade-off
between deNO<sub><i>x</i></sub> efficiency and secondary
emissions. Therefore, it is important to adopt such DPN technology
to specific application conditions to take advantage of reduced NO<sub><i>x</i></sub> and particle emissions while avoiding NH<sub>3</sub> and HNCO slip
Biofuel-Promoted Polychlorinated Dibenzodioxin/furan Formation in an Iron-Catalyzed Diesel Particle Filter
Iron-catalyzed diesel particle filters
(DPFs) are widely used for
particle abatement. Active catalyst particles, so-called fuel-borne
catalysts (FBCs), are formed <i>in situ</i>, in the engine,
when combusting precursors, which were premixed with the fuel. The
obtained iron oxide particles catalyze soot oxidation in filters.
Iron-catalyzed DPFs are considered as safe with respect to their potential
to form polychlorinated dibenzodioxins/furans (PCDD/Fs). We reported
that a bimetallic potassium/iron FBC supported an intense PCDD/F formation
in a DPF. Here, we discuss the impact of fatty acid methyl ester (FAME)
biofuel on PCDD/F emissions. The iron-catalyzed DPF indeed supported
a PCDD/F formation with biofuel but remained inactive with petroleum-derived
diesel fuel. PCDD/F emissions (I-TEQ) increased 23-fold when comparing
biofuel and diesel data. Emissions of 2,3,7,8-TCDD, the most toxic
congener [toxicity equivalence factor (TEF) = 1.0], increased 90-fold,
and those of 2,3,7,8-TCDF (TEF = 0.1) increased 170-fold. Congener
patterns also changed, indicating a preferential formation of tetra-
and penta-chlorodibenzofurans. Thus, an inactive iron-catalyzed DPF
becomes active, supporting a PCDD/F formation, when operated with
biofuel containing impurities of potassium. Alkali metals are inherent
constituents of biofuels. According to the current European Union
(EU) legislation, levels of 5 μg/g are accepted. We conclude
that risks for a secondary PCDD/F formation in iron-catalyzed DPFs
increase when combusting potassium-containing biofuels
PCDD/F Formation in an Iron/Potassium-Catalyzed Diesel Particle Filter
Catalytic
diesel particle filters (DPFs) have evolved to a powerful
environmental technology. Several metal-based, fuel soluble catalysts,
so-called fuel-borne catalysts (FBCs), were developed to catalyze
soot combustion and support filter regeneration. Mainly iron- and
cerium-based FBCs have been commercialized for passenger cars and
heavy-duty vehicle applications. We investigated a new iron/potassium-based
FBC used in combination with an uncoated silicon carbide filter and
report effects on emissions of polychlorinated dibenzodioxins/furans
(PCDD/Fs). The PCDD/F formation potential was assessed under best
and worst case conditions, as required for filter approval under the
VERT protocol. TEQ-weighted PCDD/F emissions remained low when using
the Fe/K catalyst (37/7.5 μg/g) with the filter and commercial,
low-sulfur fuel. The addition of chlorine (10 μg/g) immediately
led to an intense PCDD/F formation in the Fe/K-DPF. TEQ-based emissions
increased 51-fold from engine-out levels of 95 to 4800 pg I-TEQ/L
after the DPF. Emissions of 2,3,7,8-TCDD, the most toxic congener
(TEF = 1.0), increased 320-fold, those of 2,3,7,8-TCDF (TEF = 0.1)
even 540-fold. Remarkable pattern changes were noticed, indicating
a preferential formation of tetrachlorinated dibenzofurans. It has
been shown that potassium acts as a structural promoter inducing the
formation of magnetite (Fe<sub>3</sub>O<sub>4</sub>) rather than hematite
(Fe<sub>2</sub>O<sub>3</sub>). This may alter the catalytic properties
of iron. But the chemical nature of this new catalyst is yet unknown,
and we are far from an established mechanism for this new pathway
to PCDD/Fs. In conclusion, the iron/potassium-catalyzed DPF has a
high PCDD/F formation potential, similar to the ones of copper-catalyzed
filters, the latter are prohibited by Swiss legislation