Willie C. Young

The Formation of Reactive Oxygen Species Catalyzed by Neutral, Aqueous Extracts of NIST Ambient Particulate Matter and Diesel Engine Particles

ABSTRACT It is important to characterize the chemical properties of particulate matter in order to understand how low doses, inhaled by a susceptible population, might cause human health effects. The formation of reactive oxygen species catalyzed by neutral, aqueous extracts of two ambient par-ticulate samples, National Institute of Standards & Technology (NIST) Standard Reference Materials (SRM) 1648 and 1649, and two diesel particulate samples, NIST SRM 1650 and SRM 2975, were measured. The formation of reactive oxygen species was estimated by measuring the formation of malondialdehyde from 2-deoxyribose in the presence of ascorbic acid; H2O2 was not added to this assay. SRM 1649, ambient particulate matter collected from Washington, DC, generated the most malondialdehyde, while SRM 2975, diesel particulate matter collected from a forklift, yielded the least amount. Desferrioxamine inhibited the formation of malondialdehyde from the par-ticulate samples providing additional data to support the observation that transition metals were involved in the generation of reactive oxygen species. Six transition metal sulfates (iron sulfate, copper sulfate, vanadyl sulfate, cobalt sulfate, nickel sulfate, and zinc sulfate) were assayed

Solvent extraction efficiencies of mutagenic components from diesel particles

In order to determine the efficiency of organic solvent extractions of fresh diesel-engine exhaust particles a series of Soxhlet extractions were set up using single and sequential extractions of fresh diesel particles with solvents of increasing polarities. Single extractions were carried out with methylene chloride, methanol, acetone and acetonitrile. A single filter was sequentially extracted with methylene chloride followed by methanol, acetone and acetonitrile. Methylene chloride extracted the most mutagenicity relative to the other three solvents. In addition, methylene chloride extracted 97% of the total extracted mutagenicity from a sequential series of extractions. Therefore, we conclude that of the solvents tested methylene chloride extracts the highest proportion of mutagens from fresh diesel exhaust and little mutagenicity is lost using methylene chloride as the only extraction solvent.

Direct-acting mutagenicity of diesel particulate extract is unchanged by addition of neat aromatic compounds to diesel fuel

While there appears to be no consistent evident to suggest that an increase in the aromatic content (compounds >C/sub 14/) of diesel fuel will have an adverse affect on the emission of mutagenic material the effect of adding a large amount of a single aromatic compound (less than or equal to C/sub 14/) is unknown. Compounds were selected for this study, in part, because they are among the major aromatic compounds present in diesel fuel and because they are at a concentration less than 1 percent. Fourteen aromatic compounds were used in this study. It was concluded that the addition of neat aromatic compounds containing less than fourteen carbon atoms, with a variety of structures, to diesel fuel did not significantly alter the direct-acting mutagenicity of extracts of particles or the emission rate. A mechanical factor, injectors, did affect the direct-acting mutagenicity of the samples. The sensitivity of direct-acting mutagenicity to specific injectors should be investigated.

Evidence from Ames assays of laboratory pulse-flame combustors samples that direct-acting mutagens are not an inevitable consequence of hydrocarbon fuel combustion

In order to investigate the chemistry that leads to the formation of direct-acting mutagens in vehicle exhaust, we have sought a laboratory combustion system that would simulate the particle-associated organic compounds of vehicle exhaust

Ames assay mutagenicity and electronic structure calculations of bromomethylfluoranthenes, chloromethylfluoranthenes, and hydroxymethylfluoranthenes.

The mutagenicities of the five possible isomers of bromomethylfluoranthene, chloromethylfluoranthene, and hydroxymethylfluoranthene were determined in the Ames assay using strains TA100 and TA98 without the addition of rat-liver S9 tissue extract. The mutagenicities of the bromomethyl and chloromethylfluoranthenes ranged from 25 to 6000 rev./nmol. The most mutagenic compound was 8-chloromethylfluoranthene in strain TA98 (6000 rev./nmol). The reactivities of the bromomethylfluoranthenes and the chloromethylfluoranthenes were estimated from electronic structure calculations using the MNDO and the PM3 semi-empirical methods. The bromomethylfluoranthenes showed the smallest differences between the heats of formation of the carbocations and the heats of formation of the parent bromomethyl derivatives. Therefore, the bromomethylfluoranthenes were estimated to be the most reactive of the halomethylfluoranthenes studied. The compound that showed the largest change in heat of formation (the most stable halomethylfluoranthene) going from the halomethylfluoranthene to the carbocation was 2-chloromethylfluoranthene. However, neither the most reactive nor the most stable halomethylfluoranthenes were the most mutagenic in either strain of bacteria. These results are interpreted to suggest that the reactivity of the parent halomethylfluoranthene is not a critical factor in the mechanism by which these compounds are mutagenic, but some other factor, perhaps intercalation, must be a critical step in the mechanism of mutagenesis of these compounds.