Article pubs.acs.org/est
Mutagenicity of Diesel Engine Exhaust Is Eliminated in the Gas Phase by an Oxidation Catalyst but Only Slightly Reduced in the Particle Phase Götz A. Westphal,*,† Jürgen Krahl,‡ Axel Munack,§ Yvonne Ruschel,§ Olaf Schröder,§ Ernst Hallier,∥ Thomas Brüning,† and Jürgen Bünger† †
Institute for Prevention and Occupational Medicine of the German Social Accident InsuranceInstitute of the Ruhr-University Bochum (IPA), Bürkle-de-la-Camp-Platz 1, 44789 Bochum, Germany ‡ Coburg University of Applied Sciences and Arts, Friedrich-Streib-Strasse 2, 96450 Coburg, Germany § Institute for Agricultural Technology and Biosystems Engineering, Johann Heinrich von Thünen-Institute (vTI), Bundesallee 50, 38116 Braunschweig, Germany ∥ Institute of Occupational, Social, and Environmental Medicine, Georg-August-University Göttingen, Waldweg 37, 37073 Göttingen, Germany
ABSTRACT: Concerns about adverse health effects of diesel engine emissions prompted strong efforts to minimize this hazard, including exhaust treatment by diesel oxidation catalysts (DOC). The effectiveness of such measures is usually assessed by the analysis of the legally regulated exhaust components. In recent years additional analytical and toxicological tests were included in the test panel with the aim to fill possible analytical gaps, for example, mutagenic potency of polycyclic aromatic hydrocarbons (PAH) and their nitrated derivatives (nPAH). This investigation focuses on the effect of a DOC on health hazards from combustion of four different fuels: rapeseed methyl ester (RME), common mineral diesel fuel (DF), SHELL V-Power Diesel (V-Power), and ARAL Ultimate Diesel containing 5% RME (B5ULT). We applied the European Stationary Cycle (ESC) to a 6.4 L turbo-charged heavy load engine fulfilling the EURO III standard. The engine was operated with and without DOC. Besides regulated emissions we measured particle size and number distributions, determined the soluble and solid fractions of the particles and characterized the bacterial mutagenicity in the gas phase and the particles of the exhaust. continued...
Received: Revised: Accepted: Published: © 2012 American Chemical Society
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February 2, 2012 May 4, 2012 May 15, 2012 May 15, 2012 dx.doi.org/10.1021/es300399e | Environ. Sci. Technol. 2012, 46, 6417−6424
Environmental Science & Technology
Article
The effectiveness of the DOC differed strongly in regard to the different exhaust constituents: Total hydrocarbons were reduced up to 90% and carbon monoxide up to 98%, whereas nitrogen oxides (NOX) remained almost unaffected. Total particle mass (TPM) was reduced by 50% with DOC in common petrol diesel fuel and by 30% in the other fuels. This effect was mainly due to a reduction of the soluble organic particle fraction. The DOC caused an increase of the water-soluble fraction in the exhaust of RME, V-Power, and B5ULT, as well as a pronounced increase of nitrate in all exhausts. A high proportion of ultrafine particles (10−30 nm) in RME exhaust could be ascribed to vaporizable particles. Mutagenicity of the exhaust was low compared to previous investigations. The DOC reduced mutagenic effects most effectively in the gas phase. Mutagenicity of particle extracts was less efficiently diminished. No significant differences of mutagenic effects were observed among the tested fuels. In conclusion, the benefits of the DOC concern regulated emissions except NOX as well as nonregulated emissions such as the mutagenicity of the exhaust. The reduction of mutagenicity was particularly observed in the condensates of the gas phase. This is probably due to better accessibility of gaseous mutagenic compounds during the passage of the DOC in contrast to the particle-bound mutagens. Concerning the particulate emissions DOC especially decreased ultrafine particles.
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sensitive for PAH and nPAH.16,17 Although the test covers only a part of DEE toxicity, it enables an assessment of the alteration of the mutagenicity of DEE during recent years. Besides PAH the particle emissions of diesel engines themselves are a matter of concern, in particular the emission of fine and ultrafine particles. Approximately 50−90% of the DEE particles are in the ultrafine size range (nuclei-mode), with the majority of diesel particles ranging in size from 0.005 to 0.05 μm and the mode at about 0.02 μm. Ultrafine DEE particles comprise of vaporizable components. Approximately 80−95% of diesel particle mass is in the size range from 0.05 to 1.0 μm, with a mean particle diameter of about 0.2 μm (accumulation mode).25 Such particles are readily inhalable and associated with diseases of the respiratory tract and adverse cardiovascular effects.25 In this study, we investigated the influence of different diesel fuels and the exhaust after-treatment with a DOC on the genotoxicity of DEE using the bacterial reverse mutation assay (Ames test) and a detailed characterization of the emitted particles.
INTRODUCTION Diesel engine emissions (DEE) are classified as probably carcinogenic to humans.1 The classification is based on epidemiological studies of cohorts occupationally exposed to DEE, animal studies and strong mutagenic effects in vitro. Epidemiological studies revealed elevated relative risks for lung cancer ranging from 1.2 to 1.6 following long-term occupational exposure to high DEE concentrations. However, significance of the results was not always achieved2−4 and shortcomings in exposure assessment and consideration of confounders (smoking, asbestos) were noted.5−7 However, more recent reports have again supported the classification of DEE as a human carcinogen.8−10 Moreover, the induction of lung tumors by DEE was shown in long-term inhalation studies in the rat.11−13 The classification of DEE as carcinogenic is mechanistically supported by short-term genotoxicity assays, such as the bacterial reverse mutation test which showed strong mutagenicity of DEE. Genotoxic and carcinogenic DEE effects were mainly attributed to the particulate matter and the adherent polycyclic aromatic hydrocarbons (PAH). Recently in particular the fine
