MUTAGENICITY OF DIESEL EXHAUST PARTICLES FROM AN ENGINE WITH

DIFFERING EXHAUST AFTER TREATMENTS

X.-C. Shi1, M. J. Keane1, T. Ong1, S-Q. Li1,

1U.S. Department of Health and Human Services, Public Health Service, Centers for Disease

Control and Prevention, National Institute for Occupational Safety and Health, Health Effects

Laboratory Division, Morgantown, West Virginia

A. B. Bugarski2

2U.S. Department of Health and Human Services, Public Health Service, Centers for Disease

Control and Prevention, National Institute for Occupational Safety and Health, Pittsburgh

Research Laboratory, 626 Cochrans Mill Road, Pittsburgh, Pennsylvania, USA

The findings and conclusions in this article are those of the authors and do not necessarily represent the views of the National

Institute for Occupational Safety and Health (NIOSH). The mention of any company names or products does not imply an endorsement

by NIOSH or the Centers for Disease Control and Prevention, nor does it imply that alternative products are unavailable, or unable to

be substituted after appropriate evaluation. We acknowledge support from the NIOSH Pittsburgh Research Laboratory Diesel Team and

Lake Lynn Laboratory personnel for their help and assistance in the experimental phase of this study.

Address correspondence to M. J. Keane, Chemical Engineer, U.S. Department of Health and Human Services, Public Health Service,

Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, Health Effects Laboratory Division,

1095 Willowdale Road, Morgantown, WV 26505, USA. E-mail: MKeane@cdc.gov

This study was conducted to investigate the effects of engine operating conditions and exhaust

aftertreatments on the mutagenicity of diesel particulate matter (DPM) collected directly in

an underground mine environment. A number of after-treatment devices are currently used

on diesel engines in mines, but it is critical to determine whether reductions in DPM concentrations result in a corresponding decrease in adverse health effects. An eddy-current

dynamometer was used to operate naturally aspirated mechanically controlled engine at several steady-state conditions. The samples were collected when the engine was equipped with

a standard muffler, a diesel oxidation catalytic converter, two types of uncatalyzed diesel

particulate filter systems, and three types of disposable diesel particulate filter elements.

Bacterial gene mutation activity of DPM was tested on acetone extracts using the Ames

Salmonella assay. The results indicated strong correlation between engine operating conditions and mutagenic activity of DPM. When the engine was fitted with muffler, the mutagenic

activity was observed for the samples collected from light-load, but not heavy-load operating

conditions. When the engine was equipped with a diesel oxidation catalyst, the samples did

not exhibit mutagenic activity for any of four engine operating conditions. Mutagenic activity

was observed for the samples collected when the engine was retrofitted with three types of

disposable filters and sintered metal diesel particulate filter and operated at light load conditions. However, those filtration systems substantially reduced the concentration-normalized

mutagenic activity from the levels observed for the muffler.

It has been estimated that approximately 1.35 million workers are occupationally exposed to combustion products

of diesel fuel in about 80,000 workplaces

across the United States (NIOSH, 1988).

Occupational exposure is common among

transportation workers, among operators of

diesel-powered equipment, and among miners

operating diesel-powered equipment underground. Diesel exhaust consists of both gaseous

and particulate fractions. Diesel particulate

matter (DPM), composed mostly of carbon formed through the incomplete combustion of fuel, contains chemicals such as
polycyclic aromatic hydrocarbons (PAH), nitroPAH, oxygenated PAH, aliphatic hydrocarbons,

ketones and aldehydes (McClellan, 1987;

Lowenthal et al., 1994, Hammerle, et al.,

1995, McDonald et al., 2002). According to

the National Institute for Occupational Safety

and Health (NIOSH, 1988), the International

Agency for Research on Cancer (IARC, 1989),

and the U.S. Environmental Protection Agency

(U.S. EPA, 2002), DPM was declared a potential or probable human carcinogen. Therefore,

DPM poses potential carcinogenic and other

health hazards to workers where diesel engines

are used.

In January 2001, the Mining Safety

and Health Administration (MSHA) promulgated two rules (Mine Safety and Health

Administration, 2001, 2006) limiting the exposure of metal and nonmetal underground miners and coal miners to DPM. As of May 20,

2008, the exposure of metal and nonmetal

miners is limited to 160 μg 3 /m total carbon.

The current regulations are established on feasibility of implementing diesel emissions control technologies and strategies rather than on

firm understanding of the health risks associated with exposure to DPM. Extensive use

of diesel-powered equipment makes reduction of underground miner exposure to particulate matter and gaseous emissions from

diesel-powered equipment a major challenge

for the mining industry in the United States

and worldwide. Aforementioned MSHA regulations spurred implementation of advanced

diesel engine and exhaust after-treatment technology and alternative fuels in underground

mines. Diesel exhaust after-treatment technologies can dramatically change the physical and chemical properties of DPM (Maricq

et al., 2002; Kittelson et al., 2005; Bugarski

et al., 2006a) and potentially change their associated health effects (Bugarski et al., 2009).

While use of a diesel particulate filter (DPF)

systems was reported to reduce total mass

concentration of emitted aerosols from 80

to 95% (Schnakenberg & Bugarski, 2002;

Bugarski et al., 2006a, 2009), several investigators reported high concentrations of nucleation

mode aerosols when DPF systems were used.

Organic solvents, such as acetone, have

been used to extract PAH and other chemicals

from DPM for toxicological studies (U.S. EPA,

2002). While methylene chloride was used in

many studies, acetone was found to extract

more mutagenic activity from airborne particulates than dichloromethane or other solvents

(Krishna et al., 1983). Acetone has been used

in recent motor vehicle exhaust mutagenicity

studies (Seagrave et al. (2002), and in chemical characterization studies (McDonald et al.,

2004), and has the advantage of low toxicity to

tester cells and no mutagenic properties, unlike

methylene chloride.

Solvent extracts of DPM are known to be

genotoxic to bacteria and mammalian cells

(Wallace et al., 1987; Liu et al., 2005). Liu

et al. (2005) found that exhaust emissions of

diesel and gasoline engine vehicles operated on

a unified driving cycle induce gene mutations

in bacteria and induce micronucleus (MN) formation as well as DNA damage in cultured V79

cells (Chinese hamster lung fibroblasts). It was

also shown that the mutagenic activity of DPM

solvent extracts in bacteria varied with fuel type

and engine speed (McMillian et al., 2002).

The objective of this study was to investigate the effects of engine operating conditions,

a muffler, a diesel oxidation catalyst (DOC),

two types of DPF systems, and three types of

filtration systems with high-temperature disposable filter elements (DFE) on the mutagenicity

of diesel aerosol solvent extracts in Salmonella

typhimurium. The samples analyzed in this

study were collected directly in an underground mining environment at the NIOSH Lake

Lynn Experimental Mine, Fairchance, PA, using

the in-mine NIOSH Diesel Laboratory.

METHODOLOGY

Experimental Setup

A schematic of the laboratory layout for the

sample collection is shown in Figure 1. The

D-drift is approximately 530 m long, 6 m wide,

and 2 m high. The major components of the

laboratory are an engine/dynamometer system, three sampling and measurement stations,
and a ventilation measurement and control

system.

FIGURE 1. NIOSH Diesel Laboratory in D-drift of Lake Lynn Experimental Mine (not to scale).

The Isuzu C240, one of the most commonly used light-duty engines in U.S. underground coal mines (MSHA 2009), was operated

at four steady-state engine operating modes

(Table 1).

TABLE 1. Engine Operating Modes

Engine

speed Torque Power

Mode Description (rpm) (Nm) (kW)

R50 Rated speed, light load 2950 55.6 17.2

(50% load)

R100 Rated speed, heavy 2950 111.2 34.3

load (100% load)

I50 Intermediate speed, 2100 69.1 14.9

light load (50% load)

I100 Intermediate speed, 2100 136.9 30.6

heavy load (100%

load)

The modes were selected to cover

a wide range of engine operating parameters

such as exhaust temperatures and emission

rates. The R50 and I50 are considered to be

representative of light load conditions, and

R100 and I100 are considered to be representative of heavy load conditions. Fresh air was

supplied to the underground facility via a ventilation shaft located in the E-drift (Figure 1).

A series 1000 model 23017–3450 Axivane fan

(Joy Technologies, New Philadelphia, OH) and

a subsonic Venturi meter (Primary Flow Signal,

Inc., Tulsa, OK) were used to maintain and

measure constant flow of fresh air through the

drift throughout the tests. The measurements

showed an average volumetric flow rate of

5.69 ± 0.05 m3/s. The low test-to-test variability in flow rate (0.86%) eliminated the need

for normalization of the data with respect to

it. The average exhaust dilution ratios for R50,

R100, I50, and I100 engine operating modes

were calculated to be 148, 149, 186, and

188, respectively. The average ambient temperatures upstream of the engine were between

10.5 and 18.7◦C. The corresponding average

ambient temperatures at the downstream measurement station ranged between 14.7 and

22.3◦C.

Exhaust Treatment Technologies and Fuel

The DPM samples were collected downstream of the engine operated with DPF and

DFE systems and DOC representative of the

devices currently available to the underground

mining industry to curtail emissions from dieselpowered equipment. The scope of the project

limited collection to the particulate fraction

of the diesel emissions only; no vapor-phase

fractions were collected

The DPF systems evaluated in this study

were:

1. A DPF system manufactured by Catalytic

Exhaust Products (CEP), Toronto, ON,

model 912-SXT with uncatalyzed Corning

EX-80 Cordierite element (31 cells/cm2 and

0.3 mm wall thickness) (C DPF).

2. A	 DPF system manufactured by

Mann+Hummel GMBH, Speyer, Germany,

Model SMF-AR with an uncatalyzed sintered metal element (10 μm mean pore
size, 45% porosity, and 0.38 mm wall thickness) used with Satacen 3, an iron-based

fuel additive (SM DPF).

Both DPF systems were installed at an identical location in the exhaust system for their

respective tests.

Three types of high-temperature DFE with

synthetic filtration media were tested using

a filtration system consisting of custom filter housing and an air-to-air heat exchanger

designed and built by Mac’s Mining Repair

Service (Huntington, UT). The heat exchanger

was installed between the engine and the DFE

housing to cool exhaust below 343◦C. The

following DFEs were evaluated:

1. A	 DFE manufactured by Donaldson

Company, Minneapolis, MN, model

P604516 (DFE-A).

2. A laundered DFE, identical to DFE-A, but

laundered by Mac’s Mining Repair Service,

Huntington, UT, following their internal

standard procedure (LDFE-A).

3. A	 DFE manufactured by FST Systems

Corporation, Price, UT, model FST-115-26

(DFE-B).

The laundering process is used by some

coal mine operators to extend the life cycle of

the high-temperature DFE. The laundered version of DFE-A (LDFE-A) tested in this study was

laundered only once. After installation, the two

brand new elements (DFE-A and DFE-B) and

the laundered element (LDFE-A) were conditioned prior to the 4-mode tests by running the

engine for 13 h at the R50 mode.

A DOC used in this study was manufactured by Engine Control Systems Ltd.,

Newmarket, ON (model A16-0130) with a

Cordierite substrate and a proprietary catalyst

formulation. A generic muffler installed in place

of the DPF system and the DOC was used

as a baseline or control when the effects of

aftertreatment devices were examined. Singleconsignment ultra-low-sulfur diesel fuel (11

ppm S by weight) supplied by Guttman Oil

(Belle Vernon, PA) was used for all tests in this

study; synthetic 5W40 oil was used for engine

lubrication.

Sample Collection

A custom sampling method was used

to collect integrated DPM samples from

the centrally located sampling point at the

downstream sampling stations (Figure 1). Two

sampling trains were used concurrently to

collect the sample onto two pairs of seriesconnected 90-mm Teflon-coated glass fiber

filters (TX40HI20-WW, Pall Corporation, Ann

Arbor, MI). A URG cyclone was used at

the inlet to each of the sampling streams to

remove aerosols with aerodynamic diameter

larger than 1 μm. A model SV25 rotary vane

pump from Oerlikon Leybold Vacuum was

used to draw sample at 90 L/min through

each of the trains. The total mass flow rate

through each of the trains was maintained

using Sierra Instruments (Monterey, CA) mass

flow controllers (model C100M).

The gravimetric analysis was performed

using an ultra-microbalance (model UMX2,

Mettler-Toledo, Columbus, OH), equipped

with a special 110-mm-diameter weighing pan.

The filters were conditioned and weighed

in a climate-controlled room (20–22◦C and

47–50% relative humidity [RH]). Thirteen samples were collected for the analysis. Table 2

shows the information on the exhaust configuration and engine operating mode pertinent

to each of the samples.

Sample Preparation

Each of the concurrently collected filter

pairs was treated as a single sample. The gravimetric analysis showed that the mass of the

DPM collected on all of the secondary filters was negligible. Therefore, the secondary

filters were not used in the further analysis.

The DPM was extracted simultaneously from

both primary filters using acetone and sonication for 2 h. The extract was reduced to less

than 40 ml by evaporation under N2, transferred to a 40-ml sterile glass centrifuge tube,

and centrifuged at 6000 × g for 40 min. The

supernatant was removed and filtered through
25-mm sterile PTFE filters. Removal of particles

is essential since the particles often fluoresce

and interfere with electronic colony counting.

The filtrate was transferred to a tared 40-ml

sterile brown bottle and evaporated to dryness under N2. Twelve milligrams DPM extract

per milliliter dimethyl sulfoxide (DMSO) solutions was made as stock solution. Samples

were diluted further with DMSO to obtain the

required concentrations.

TABLE 2. DPM Samples Collected With Pertinent Information

on Engine Operating Conditions Configurations and Engine

Operating Conditions

Engine

Sample operating

number Exhaust after-treatment conditions

1 Muffler R50

2 Muffler R100

3 Muffler I50

4 Muffler I100

5 Diesel oxidation catalyst (DOC) R50

6 Diesel oxidation catalyst (DOC) R100

7 Diesel oxidation catalyst (DOC) I50

8 Diesel oxidation catalyst (DOC) I100

9 Disposable filter element (DFE-A) R50

10 Laundered disposable filter R50

element (LDFE-A)

11 Disposable filter element (DFE-B) R50

12 Sintered metal diesel particulate R50

filter (SM DPF)

13 Cordierite diesel particulate filter I100

(C DPF)

Ames Salmonella Assay

The mutagenicity of the extracted DPM

samples was determined using the preincubation variant of the Ames Salmonella assay

system (Maron & Ames, 1983; Kado et al.,

1983). Overall results from previous studies

indicate that TA98 and YG1024 gave better

mutagenic responses than TA100 and YG1029

to DPM tested, and that S9 was not necessary

for mutagenic activity of DPM (Liu et al., 2005;

McMillian, 2002; Shi et al., 2009). Since only

limited amounts of sample were available, only

Salmonella typhimurium TA 98 without S9 was

used in this study.

The cell suspensions of Salmonella

typhimurium TA98 were prepared by overnight

incubation of a small piece of frozen culture

in 50 ml nutrient broth. Subsequently, 25 μl

of that TA 98 overnight culture broth along

with 10 μl of DPM-extracted sample solution

and 65 μl physiological saline were added

and preincubated at 37◦C for 30 min on a

rotary shaker. Two tubes were prepared for

four different concentrations of each sample

tested. The concentrations previously used in

DPM mutagenicity studies (Shi et al., 2009)

of 13.3, 40, 120, or 180 μg per treatment

were adopted for this study. The control was

established using DMSO in place of sample

solution. After incubation, 2.5 ml of molten

top agar was added to each tube, and the

contents were mixed and poured onto a

plate. All plates were incubated at 37◦C for

48 h prior to counting. The conditions of the

bacterial background lawn were examined

during every experiment in order to know

whether cytotoxicity appeared in any of

the samples. Three readings of the revertant

colonies per plate were scored by an automatic

colony counter (Accucount 1000, Biologics,

Inc., Gainsville, VA). The average number of

revertant colonies and corresponding standard

deviation from both plates were calculated for

each concentration. A repeat experiment was

performed to confirm the results obtained from

the original experiment.

Statistical Treatment

Samples were considered to be mutagenic

if a positive concentration-response relationship was observed and for at least one concentration the sample number of revertants

was twice that of the respective solvent control (Ames et al., 1975). A concentration was

considered to be cytotoxic if it produced a thin

lawn and reduced the number of revertants per

plate.

RESULTS

The results of the Salmonella gene mutation tests are shown in Table 3, with notations

of concentrations that were positive for mutagenicity and any samples that were cytotoxic to

the tester strain.
TABLE 3. Revertants Induced by DPM Samples

Revertants/platea (μg/plate)

Sample number Exhaust after-treatment Engine mode Control 13.3 40 120 180

1 Muffler R50 13 ± 1.1 26 ± 1.1 37 ± 5.5b 61 ± 1.6b 46 ± 6.0b,c

2 Muffler R100 13 ± 1.1 13 ± 0.6 22 ± 1.6 22 ± 1.6 16 ± 0.6c

3 Muffler I50 24 ± 3.8 29 ± 2.2 41 ± 2.7 61 ± 5.0 70 ± 1.6b

4 Muffler I100 13 ± 1.1 13 ± 2.2 18 ± 3.3 13 ± 0.6 16 ± 1.1c

5 DOC R50 14 ± 1 18 ± 1.6 20 ± 3.3 31 ± 5.9 15 ± 1.1

6 DOC R100 14 ± 1 17 ± 1 18 ± 0.5 24 ± 2.3 24 ± 1.2

7 DOC I50 14 ± 1 14 ± 1.6 17 ± 1.5 22 ± 4 19 ± 0.4

8 DOC I100 10 ± 1.1 18 ± 6.9 18 ± 6.8 23 ± 1.2 10 ± 2.4c

9 DFE-A R50 13 ± 1.1 15 ± 0.6 36 ± 3.8c 44 ± 2.2d 41 ± 8.8b,c

10 LDFE-A R50 13 ± 1.2 29 ± 3.3 51 ± 2.7b 108 ± 16.6b 56 ± 4.4b,c

11 DFE-B R50 13 ± 1.1 21 ± 0.8 47 ± 1.1b 93 ± 5.5b 99 ± 14.2b,c

12 SM DPF R50 13 ± 1.2 20 ± 0.8 41 ± 1.8b 90 ± 12.3b 70 ± 10.6b,c

13 C DPF I100 15 ± 2.1 14 ± 1.4 20 ± 7.9 31 ± 3.9 23 ± 3.8

aMean value of two plates ± standard deviation.
 

bPositive response (the observation average exceeds twice the respective negative control).
 cCytotoxicity.
 

The effects of the four engine operating

conditions were examined using the results of

the analysis performed on the samples collected for the engine equipped with the muffler; the mutagenic activity was found to be

positive for the samples collected for the R50

and I50 conditions, but the samples collected

at the I100 and R100 conditions were not

mutagenic (Figure 2).

The effects of the DOC were compared

with those of the muffler for all four test conditions. Figure 3 shows that for the R50 and

I50 conditions the muffler samples showed a

positive mutagenicity while the DOC samples

exhibited a negative response. For the R100

and I100 conditions, the mutagenic activity

was negative and did not measurably differ

between the DOC and muffler samples.

The effects of the muffler, three types of

DFE, and SM DPF were compared using the

results obtained for the cases when the engine

was equipped with those devices and operated at R50 conditions (Figure 4). The results

showed positive mutagenic activity for DFE-A,

LDFE-A, DFE-B, and SM DPF samples.

A comparison of normalized mutagenic activities based on the number of

revertants m3 / of air for Muffler, DFE-A,

LDFE-A, DFE-B, and SM DPF for mode R50

are shown in Table 4. DFE-A, LDFE-A, DFE-B,

and SM DPF samples showed a 71, 34, 30 and

62% reduction respectively in the number of

mass-normalized revertants from the muffler

samples.

DISCUSSION

This study demonstrates that DPM emitted by a naturally aspirated, indirectly injected

engine in a realistically simulated mining workplace environment was mutagenic for some

steady-state operating conditions. The results

indicate that the engine operating condition

is one of the dominant parameters affecting

the mutagenic activity of DPM. For the engine

equipped with the muffler, the DPM samples

collected at light-load engine operating modes

(R50 and I50) were mutagenic. No mutagenic

activity was found for samples collected at

heavy-load engine operating modes (R100 and

I100). While the study used only four speed

and load conditions, the dependence of mutagenicity on operating conditions is similar to a

systematic study of an engine evaluated over

a full range of operating variables (McMillian

et al., 2002). In the limiting case of high speed

and high loading, the mutagenicity of the DPM

in that study was not eliminated, as in this study,

but did become minimal. The maximum in the
graph of mutagenicity versus load also peaked

near 50% load in that study. The potential

interpretation is that the combustion at partial

loads is less complete than that at higher loads,

resulting in the higher emissions of organic

compounds that exhibit higher mutagenicity. A

detailed explanation of this effect is outside the

scope of this study and should be addressed in

combustion chemistry studies.

0.0 

10.0 

20.0 

30.0 

40.0 

50.0 

60.0 

70.0 

80.0 

0.0 

R50 

R100 

I50 

I100 

Muffler * 

* 

* 

* 

Positive response 

13.3 40.0 120.0 

FIGURE 2. Mutagenic activity of DPM samples collected for the engine equipped with the muffler and at four engine operating

conditions. Positive response was when the observation exceeded twice the respective negative control.

0.0 

10.0 

20.0 

30.0 

40.0 

50.0 

60.0 

70.0 

80.0 

Muffler

DOC

R50 R100 I50 I100

* 

* * 

* 

Positive response 

0.0

13.340.0

120.0

0.0

13.340.0

120.0

0.0

13.340.0

120.0

0.0

13.340.0

120.0 

FIGURE 3. Comparison of the mutagenic activity between DOC and muffler samples for all four engine operating conditions. Positive

response was when the observation exceeded twice the respective negative control.

The DFE systems and SM DPF system

reduced the concentration of DPM in the

sampled aerosol, ranging from 51 to 71%. The
reductions in mutagenicity did not always parallel the reductions in DPM concentrations

in the exhausts. In one case, the laundered

DFE lowered the concentration of DPM more

than the unused DFE, but the mutagenicity

increased. When the DOC was used, the samples showed no marked mutagenic activity,

although the reduction in DPM concentration

was comparable to the other devices. Those

results can be explained by catalytic oxidation

of the organic fraction of particulate matter by

DOC (Pataky et al., 1994). The results of this

study suggest that despite only moderate effects

on mass concentrations (Bugarski et al., 2009),

the DOC might play important role in reducing

potential adverse health effects associated with

exposure to diesel aerosols.

0.0 

20.0 

40.0 

60.0 

80.0 

100.0 

120.0 

140.0 

Muffler 

DFE-A 

LDFE-A 

DFE-B 

SM DPF 

R50

* Positive response 

* * 

* 

* 

* 

* * 

* 

* * 

0.0 13.3 40.0 120.0 

FIGURE 4. Effects of muffler, DFE-A, LDFE-A, DFE-B, and SM DPF on the mutagenicity of samples collected for R50 engine operating

condition. Positive response was when the observation exceeded twice the respective negative control.

TABLE 4. Reductions in Mass-Normalized Ames Salmonella/Microsomal Assay Mutagenic Activity for R50 Test Conditions

Exhaust

system

Average

concentrations

(μg/m3)

Mutagenic activity Reduction in

concentration (%)

Reduction

mutagenic

in

(Revertants/μg) (Revertants/m activity (%) 3)

Muffler 239 0.5 117.1 N/A N/A
 

DFE-A 107.9 0.3 34.5 54.9 71.
 

LDFE-A 89.5 0.9 76.9 62.6 34.3
 

DFE-B 117.9 0.7 82.5 50.7 29.5
 

SM DPF 69.4 0.7 45.1 71.0 61.5
 

When compared with DFE systems and

DPF systems, the DOC exerted minor effects

on aerosol mass and number concentrations

(Bugarski et al., 2009). However, the DOC

were found to be effective in reducing soluble organic fraction (SOF)/organic carbon (OC)

fractions of diesel particulate matter (DPM)

and vapor-phase organics (XOC)/gaseousphase hydrocarbons emitted by heavy-duty

(Bagley et al., 1998; Shah et al., 2007) and

light-duty diesel engines (Klein et al., 1998).

The DOC lowered concentrations of PAH associated with SOF fraction and OC (Pataky et al.,

1994; Khair & McKinnon, 1999). The effectiveness of the DOC control was dependent

on the fraction of OC present in the engine

exhaust, with total PM reduction efficiency
increasing with increasing OC content (Shah

et al., 2007). Previous studies (Pataky et al.,

1994; Bagley et al., 1998) showed that use

of DOC reduced both particle- and vaporphase-associated mutagenic activity by 50%

or more. The DOC was found to generally

increase the mutagenic activity per mass of the

SOF and XOC; however, the rise was offset

by the decrease in the SOF and XOC levels

(Pataky et al., 1994). The 50% or more of the

detected mutagenic activity was attributed to

XOC (Pataky et al., 1994).

The DFE and DPF systems were found

to be effective in reducing mass emissions of

DPM (Shah et al., 2007) and consequently

can be effectively used to lower concentrations of DPM in mine air (Bugarski et al.

2009). This control technology was effective in

reducing both the elemental carbon (EC; 97%)

and organic carbon (OC; 92%) fraction (Shah

et al., 2007). The mutagenic activity of the

DPM samples collected for DFE and the uncatalyzed SM DPF was primarily associated with

hydrocarbon-rich aerosols that passed through

DFE and DPF in a vapor phase and nucleate after leaving tailpipe. Those aerosols are

semivolatile in nature (Bugarski et al., 2009).

Further research is needed to investigate the

effects of DOC and DPF systems and to extend

these findings to other engine types and potential alternative diesel fuels.

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