Review of acellular assays of ambient particulate matter oxidative

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Review of acellular assays of ambient particulate matter oxidative potential: methods and relationships with composition, sources, and health effects Josephine Taylor Bates, Ting Fang, Vishal Verma, Linghan Zeng, Rodney J. Weber, Paige E Tolbert, Joseph Abrams, Stefanie Ebelt Sarnat, Mitchel Klein, James A Mulholland, and Armistead G. Russell Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b03430 • Publication Date (Web): 04 Mar 2019 Downloaded from http://pubs.acs.org on March 4, 2019

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Environmental Science & Technology

1

Review of acellular assays of ambient particulate matter oxidative potential: methods and

2

relationships with composition, sources, and health effects

3

Josephine Bates1, Ting Fang2, Vishal Verma3, Linghan Zeng4, Rodney Weber4, Paige Tolbert5,

4

Joseph Abrams6, Stefanie Sarnat5, Mitchel Klein5, James Mulholland1, Armistead Russell1*

5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

1

Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA, USA

[email protected], [email protected], [email protected] 2

Department of Chemistry, University of California Irvine, Irvine, CA

[email protected] 3

Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Champaign, IL, USA

[email protected] 4

Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA

[email protected], [email protected] 5

Rollins School of Public Health, Emory University, Atlanta, GA, USA

[email protected], [email protected], [email protected], 6

Center for Disease Control and Prevention, Atlanta, GA, USA

[email protected]

*corresponding author [email protected] 404.894.3079 311 Ferst Dr NW Ford Environmental Science & Technology Building 3210 Atlanta, GA 30332

ABSTRACT Acellular OP Assays

PM2.5

compositional impacts on OP?

GSH DTT AA ESR HPLC

oxidative stress-related health impacts?

Asthma COPD IHD

29 30

Oxidative stress is a potential mechanism of action for particulate matter (PM) toxicity and

31

can occur when the body’s antioxidant capacity cannot counteract or detoxify harmful effects of

32

reactive oxygen species (ROS) due to an excess presence of ROS. ROS are introduced to the

ACS Paragon Plus Environment


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body via inhalation of PM with these species present on and/or within the particles (particle-

34

bound ROS) and/or through catalytic generation of ROS in vivo after inhaling redox-active PM

35

species (oxidative potential, OP). The recent development of acellular OP measurement

36

techniques has led to a surge in research across the globe. In this review, particle-bound ROS

37

techniques are discussed briefly while OP measurements are the focus due to an increasing

38

number of epidemiologic studies using OP measurements showing associations with adverse

39

health effects in some studies. The most common OP measurement techniques, including the

40

dithiothreitol assay, glutathione assay, and ascorbic acid assay, are discussed along with

41

evidence for utility of OP measurements in epidemiologic studies and PM characteristics that

42

drive different responses between assay types (such as species composition, emission source, and

43

photochemistry). Overall, most OP assays respond to metals like copper than can be found in

44

emission sources like vehicles. Some OP assays respond to organics, especially photochemically

45

aged organics, from sources like biomass burning. Select OP measurements have significant

46

associations with certain cardiorespiratory endpoints, such as asthma, congestive heart disease,

47

and lung cancer. In fact, multiple studies have found that exposure to OP measured using the

48

dithiothreitol and glutathione assays drives higher risk ratios for certain cardiorespiratory

49

outcomes than PM mass, suggesting OP measurements may be integrating the health-relevant

50

fraction of PM and will be useful tools for future health analyses. The compositional impacts,

51

including species and emission sources, on OP could have serious implications for health-

52

relevant PM exposure. Though more work is needed, OP assays show promise for health studies

53

as they integrate the impacts of PM species and properties on catalytic redox reactions into one

54

measurement, and current work highlights the importance of metals, organic carbon, vehicles,

55

and biomass burning emissions to PM exposures that could impact health.

56

1. Introduction

57

Extensive literature supports the association between airborne particulate matter (PM)

58

and adverse human health effects, especially cardiorespiratory endpoints 1-7. However, the

59

mechanisms of action for PM-related health effects are not completely understood. Growing

60

evidence in DNA methylation observations, animal models, and human biomarker studies shows

61

that PM exposure can induce oxidative stress in the body, offering one potential mechanism of

62

PM toxicity 5, 6, 8-16. Oxidative stress occurs when the concentration of reactive oxygen species

63

(ROS) are in excess of the body’s antioxidant capacity, leading to a redox state change in cells


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that, in turn, can initiate or exacerbate inflammation in the respiratory tract and cardiovascular

65

systems, chemically alter DNA, proteins, and lipids, and lead to cell and tissue damage or death

66

5, 6, 8, 13.

67

making them highly reactive, and include species like hydrogen peroxide (H2O2), superoxide

68

radical (O2-), and hydroxyl radical (•OH). These species can be introduced to the body via

69

particulate matter inhalation with ROS directly bound to the particles (particle-bound ROS)

70

and/or by catalytic generation of ROS in vivo via cellular redox reactions stimulated by specific

71

inhaled PM components 10, 17. The catalytic generation of ROS by such inhaled components with

72

simultaneous depletion of antioxidants is defined in this paper as “oxidative potential” (OP).

73

The recent development of acellular assays for OP has led to a rapid rise in OP

ROS are any oxygen-containing molecules that have one or more unpaired electrons,

74

measurements worldwide using varying methods with differing results. Acellular assays are

75

currently faster and less resource intensive than cellular assays, allowing more rapid

76

development of reasonably large data sets in different locations for use in source apportionment

77

and health analyses. Common acellular OP assays include electron spin (or paramagnetic)

78

resonance (OPESR), dithiothreitol assay (OPDTT), ascorbic acid assay (OPAA), and glutathione

79

assay (OPGSH). OPESR measures the generation of hydroxyl radicals via electron spin resonance

80

while OPDTT, OPAA, and OPGSH measure the depletion rate of chemical proxies for cellular

81

reductants (DTT) or antioxidants (AA, GSH) which is proportional to the generation rate of

82

ROS. Particle-bound ROS measurements use fluorescent-based techniques to measure

83

concentrations of specific ROS, usually the hydroxyl radical or hydrogen peroxide, on and/or

84

within a PM sample. The development of particle-bound ROS measurements precedes the

85

development of acellular OP assays, but recent literature has shown the relevance of OP to

86

health. Studies using cellular assays or focusing on the impact of persistent free radicals (PFR)

87

are outside the scope of this review and can provide additional information on the relationship

88

between PM exposure and health not discussed here, especially with regards to biological

89

mechanisms.

90

Epidemiologic analyses using acellular assays have found that exposure to PM with high

91

OP affects cardiorespiratory health 18-21. In fact, OP was more strongly associated with acute

92

cardiac and respiratory endpoints than fine PM concentration in multiple studies, suggesting that

93

OP may be a more relevant health metric than PM mass for certain outcomes of interest 18, 19, 22.

94

OP measurements integrate multiple aspects of PM, including species composition, synergistic



95

interactions between chemical species and emission source impacts, redox cycling by complex

96

organics, and oxidative stress delivered by surfaces, making it a potentially advantageous health

97

metric with shown associations with acute cardiorespiratory health.

98 99

Species and source composition, photochemical aging, volatility, and pH affect OP and size distribution of OP measurements. Organic compounds can generate oxidative stress through

100

redox cycling of quinone-based radicals and metals can directly support electron transport to

101

generate ROS while diminishing antioxidant levels 23. In general, all OP methods are responsive

102

to metals, though the types of metals that drive responses and the degrees of those responses vary

103

by assay. For example, OPAA is more sensitive to iron and copper and OPDTT to copper and

104

manganese. OPDTT is also sensitive to organic species, especially highly oxidized organics.

105

Literature shows that PM related to vehicle emissions drives responses in all OP assays, most

106

likely due to the high copper content in brake and tire wear, and biomass burning PM

107

significantly contributes to OPDTT due to its large oxidized aromatic (e.g., quinone) fraction. Size

108

distribution is a current topic of interest due to the ability of different size fractions to reach

109

different parts of the lung, and OP size distribution can vary by OP assay. Understanding the

110

current state of knowledge on acellular OP assays, along with their relationship to composition,

111

sources, and PM physical properties, could guide future research investigating the epidemiologic

112

relevance of OP assays and further our understanding on the relationship between PM and

113

health.

114

This review summarizes the current state of knowledge on the relationship between

115

health endpoints and OP of ambient PM along with the sensitivities of various acellular OP

116

assays to PM composition, emission sources, and size. Particle-bound ROS measurements are

117

described in brief, but the focus is on OP measurement techniques due to the growing body of

118

literature linking these assays to adverse health outcomes. Limited work is available assessing

119

utility of particle-bound ROS measurements in health studies, so future work is needed before

120

conclusions about the relevance or lack thereof of particle-bound ROS to health can be made;

121

although one may expect the large levels of antioxidants in the lung lining fluid would minimize

122

the effect of particle-bound ROS.

123

2. Overview of Measurement Methods

124 125

ROS associated with PM can exist on and/or within the particle itself or can be generated in vivo by constituents in the inhaled particles chemically interacting with fluids and cells in the


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body. There are various methods to measure these two different phenomena. Approaches that

127

measure ROS that exist on and/or within particles, or “particle-bound ROS” techniques, typically

128

report levels in units of concentration (e.g. nmol H2O2 equivalents m-3air). Techniques that

129

quantify the catalytic generation of ROS under simulated biological conditions, or “OP”

130

measurement techniques, use units of time rate-of-change of volume-based concentration (nmol

131

or % depletion per min per m3 of air) or mass-based concentration (nmol or % depletion per min

132

per μg of PM; sometimes referred to as intrinsic OP), depending on the assay. If particle-bound

133

ROS are present on samples during the OP analyses, they will drive a response in the OP assay.

134

However, significant sample storage times and short lifetimes of particle-bound ROS often limit

135

their impact in OP assays. Volume-based concentration rates of OP are relevant for

136

epidemiologic studies while mass-based concentration rates of OP are useful for comparing

137

between OP observational studies. Both methods can provide information on the capacity of PM

138

species and sources to potentially drive catalytic redox reactions in the body, which is

139

hypothesized to lead to health impacts related to oxidative stress; however, the difference in

140

measurement methods can make comparisons across studies difficult.

141

2.1.1. Measuring Particle Bound ROS

142

Measurements of ROS present within and/or on PM are typically measured using various

143

fluorescence techniques adapted from intracellular ROS measurement techniques. These particle-

144

bound ROS methods suspend particles in a reagent and measure the spectra of specific oxidation

145

byproducts. Dichlorofluorescin (DCFH) is the most common probe used when quantifying

146

particle-bound ROS 24, 25. This chemical is a non-fluorescent reagent that becomes fluorescent

147

(DCF) when oxidized in the presence of ROS. DCFH is mixed with Horseradish Peroxidase

148

(HRP) in a sodium phosphate buffer prior to analysis to catalyze reactions. Then the DCFH-HRP

149

reagent is added to each sample filter. The solution is sonicated to extract ROS in the particles,

150

and fluorogenic intensity of DCF is measured. Fluorescent intensity is converted to H2O2

151

concentration using least squares regression with a H2O2 calibration assay to obtain the final

152

particle-bound ROS measurement 24. Other particle-bound ROS methods can vary by reagent

153

type and concentration, mixing time and method, and fluorescence measurement technology.

154

Other common reagents include the 9-(1,1,3,3,tetramethylisoindolin-2-yloxyl-5-ethynyl)-10-

155

(phenylethynyl)anthracene (BPEAnit) probe, aminophenyl fluorescamine (APF) probe, and the

156

10-acetyl-3,7-dihydroxyphenoxazine (Amplex Red) probe 26-28.



157

Molecular probes vary in their sensitivities to species. In general, the DCFH probe is the

158

least specific method, reacting similarly with multiple ROS, including hydroxyl radical (•OH),

159

H2O2, peroxyl radicals, and peroxynitrite. This is largely due to the ease of abstraction of the

160

hydrogen atom located at the 9’ position of the DCFH molecule 27. APF reacts with •OH but not

161

peroxynitrite, unlike the DCFH and Amplex Red probes, making it potentially useful for specific

162

hydroxyl radical measurements 28.

163

Artifacts can occur using these techniques during sonication. Increased sonication of

164

BPEAnit in dimethyl sulfoxide (DMSO) and of DCFH-HRP in 10/90 ethanol/water are

165

correlated with an increase in fluorescence, implying sonication results in the formation of ROS

166

29.

167

higher than the values obtained for PM samples using the same probe 29. Particle-bound ROS

168

measurements are also sensitive to pH, reagent concentration, and extraction method but not

169

incubation temperature 30. According to Huang et al., 30 optimized performance in stability,

170

reliability, and operability for offline particle-bound ROS measurements occurs at a pH of a

171

phosphate buffer at 7.2 with the DCFH-HRP reagent at a concentration of 10M DCFH + 0.5

172

unit/ml HRP. Care should be taken in the laboratory setup and methods when using molecular

173

probe techniques to measure particle-bound ROS.

174

The amount of ROS generated upon sonication can be approximately two orders of magnitude

One limitation of off-line particle-bound ROS measurements is the very short lifetime of

175

ROS, ranging from only a few minutes to a day or longer, so off-line measurement techniques

176

with delays of hours to days may severely underestimate true particle-bound ROS concentrations

177

31.

178

On-line measurement technologies have been developed to measure particle-bound ROS, in

179

particular, three using DCFH 31, 35-37. The main difference between the three on-line

180

measurement techniques available is the particle collection method. One instrument collects PM

181

in an aqueous HRP solution on a paper filter that then flows through Teflon tubing immersed in a

182

water bath for 15 minutes 31. This instrument was further developed to be portable (Online

183

Particle-bound ROS Instrument, OPROSI) for automated continuous field deployment over

184

many hours or days 35. Another method uses a particle into liquid sampler (PILS), which allows

185

particle collection at a high flow rate 27. The final method uses a mist chamber to collect particles

186

for online particle-bound ROS measurement 36. Nevertheless, the growing epidemiologic

Specifically, H2O2 bound to particles has been shown to significantly decrease over time 32-34.


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evidence suggests OP measurement techniques are potentially more relevant than particle-bound

188

ROS measurements, pushing future research towards OP measurements.

189

2.1.2. Measuring Oxidative Potential (OP)

190

OP is most commonly measured as the capacity of PM to oxidize target molecules over

191

time. Common methods include OPDTT, OPAA, and OPGSH. Assays using antioxidants, including

192

OPAA and OPGSH, can be performed in a chemical assay or in surrogate lung fluid (SLF).

193

Currently, all OPGSH studies have been performed with SLF, but OPAA has been measured in

194

chemical and SLF environments. To differentiate if AA depletion was measured in SLF or not,

195

subscripts will be used throughout this review (e.g., OPAA versus OPAA SLF). Two other techniques

196

measure the actual generation of ROS over time rather than the depletion of target molecules

197

using electron spin resonance (OPESR) or high-performance liquid chromatography (HPLC) with

198

fluorescent probes. Different OP assays capture different redox reactions that lead to the

199

generation of different ROS species. For example, OPESR and HPLC techniques measure the

200

production rate of specific ROS, including •OH and H2O2, while antioxidant depletion assays

201

(OPAA and OPGSH) have not been shown to be correlated with the generation of any specific

202

ROS. OPDTT is most correlated with O2- and H2O2 formation and is not correlated with •OH

203

generation 38.

204

OPESR measures the ability of PM to induce •OH formation in the presence of H2O2 by

205

measuring the electron paramagnetic resonance signals of the spin trap 5,5-dimethyl-1-pyrroline-

206

N-oxide byproduct DMPO-OH quartet as the average of total amplitudes expressed in arbitrary

207

units (A.U.) 39, 40. HPLC techniques measure the concentration of reduced byproducts of

208

chemicals reacting with •OH or H2O2, such as 2,3 dihydroxygenzoic acid (2,3 DHBA)—the

209

hydroxyl radical adduct of salicylic acid, p-hydroxybenzoate (p-HBA)—forming from the

210

reaction of •OH with benzoate, and parahydroxylphenyl acetic acid (POPHAA) dimer—a result

211

of the oxidation of POPHAA by H2O2 41-43. Other techniques measure the fluorescence of probes,

212

such as disodium terephthalate (TPT)—which reacts with •OH to form 2-hydroxyterephthalic

213

acid (2 OHTA), over time 38, 44. Sample measurements are taken over time in order to determine

214

a time-rate of change in •OH or H2O2 concentration. One limitation of the benzoate (BA) probe is

215

that it binds with manganese, but •OH production from manganese is negligible so results should

216

not be affected significantly 45.



217

Other OP assays, including OPDTT and OPAA, measure the depletion of biologically

218

relevant chemicals due to oxidation. OPDTT is a commonly used chemical assay that has been

219

used in epidemiologic analyses 46. DTT is a surrogate for the cellular oxidant NADPH, which

220

reduces oxygen to the superoxide anion (O2-). Overall, the rate of O2- generation by a PM sample

221

is measured by the rate at which DTT is consumed, which is proportional to the concentration of

222

redox-active species in the PM sample. Specifically, solvent-extracted (e.g., in water or

223

methanol) PM samples are incubated with DTT and a potassium phosphate buffer for times

224

varying from 15 – 90 minutes. Some studies add metal chelators, often Chelex 100 or in some

225

studies, EDTA, to the mixture to eliminate certain effects of metals. A small aliquot is removed

226

from the mixture at designated times and mixed with 1% w/v Trichloraoacetic acid (TCA) to

227

quench DTT reactions. The aliquot is mixed with 0.5 mL 5,5-dithiobis-(2-nitrobenzoic acid)

228

(DTNB) to form 2-nitro-5-mercaptobenzoic acid (TNB) by reacting with the residual DTT,

229

which is then measured using a spectrometer. The DTT consumption rate, otherwise known as

230

DTT activity, is determined from the linear slope of DTT consumption and is used as a measure

231

of OP 46, 47. Work has been done to alter the DTT assay protocol for personal monitoring use, but

232

most current studies focus on ambient or chamber PM samples 48. The chemical OPAA protocol is

233

very similar to the OPDTT protocol 49. Semi-automated OPDTT and OPAA assays have been

234

developed to reduce labor intensity 47, 50. Online systems for OPDTT have also been developed to

235

avoid filter sampling of PM that may lose reactive species before analysis and provide better

236

temporal resolution (between 3 minutes and 3 hours) 51, 52. One system couples a PILS with

237

microfluidic-electrochemical detection of reduced DTT using a cobalt(II) phthalocyanine

238

(CoPC) electrode 52, 53, while another uses a Liquid Spot Sampler 51. Nevertheless, offline

239

systems have been more commonly used because online technoloogy is still relativley new.

240

The chemiluminescent reductive acridinium triggering (CRAT) assay measures the

241

interaction of reductants, such as DTT or GSH, and oxidants. These chemicals act as reducing

242

agents leading to the formation of H2O2, which in turn reacts with acridinium ester after addition

243

of a buffer and emits light that can be used to quantify rates of H2O2 production 54. CRAT is a

244

relatively new technique that, to the best knowledge of the authors, has not yet been used in

245

ambient PM studies.

246 247

GSH OPAA SLF and OP SLF measure % depletion of antioxidants in SLF exposed to PM rather than

directly from PM samples exposed only to the depletion chemical of interest. SLF is composed


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248

of multiple antioxidants, which is more indicative of realistic lung conditions. However, the

249

composition of SLF varies by study and affects OP measurements, with AA being the most

250

critical component in SLF for reactions with metals, making comparison across studies difficult

251

45.

252

monitoring absorbance over time, and/or a DTNB-enzyme recycling assay to obtain %

253

antioxidant depletion per unit time 20, 55-57.

The concentration of antioxidants in SLF is quantified at specific time intervals using HPLC,

254

There are many OP assays, and even within each assay, protocols can vary, making

255

results across studies difficult to compare. Differences in methods that can affect magnitudes of

256

measurements within an OP assay include choices of PM extraction solvents, PM filter types,

257

incubation times, and metal chelators. For example, OPAA, OPDTT, OPESR, and OPCRAT are lower

258

for PM measured on quartz filters than Teflon filters 58. Further, the fraction of PM extracted

259

(water-soluble or water-insoluble) can affect OP results. Methanol can extract hydrophilic

260

species and hydrophobic organic species, resulting in higher OPDTT than water-soluble extracts

261

58-60.

262

type, etc.), it is critical examine which OP assays are relevant for epidemiologic analyses in order

263

to focus research on optimizing methods for these assays and to further the understanding of the

264

association between PM and health.

265

3. OP Measurements in Epidemiologic Analyses

Due to the differences in methods (use of SLF or not, choice of extraction method, filter

266

Health studies focusing on OP have used OP measurement data and modeling

267

approaches, such as land-use regression (LUR) and source impact regressions, to extend OP

268

estimates where and when measurements are not available 18, 20, 49. Some studies use oxidative

269

burden (OB), which is calculated by multiplying PM2.5 concentration from multiple locations or

270

times by measured mass-based OP at one location and one time, assuming the mass-based OP

271

does not vary significantly in time or space in the study area during the study period; [(µgPM_other

272

sites

273

to be associated with cardiorespiratory outcomes (Table 1). In some cases, those associations

274

have been stronger than the associations between the same health outcome and PM mass,

275

supporting the hypothesis that oxidative stress is a mechanism of PM toxicity (Table 1). Based

276

on current literature, OPDTT and OBGSH SLF are the OP assays most relevant to health.

277 278

m-3 )* (% depletion µgPM_one site-1min-1)]. Both modelled and measured OP have been found

Fractional exhaled nitric oxide (FeNO), used as a measure of airway inflammation, has been used in the most OP epidemiologic studies and studied with the most OP assays (OPESR,



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279

DTT, OBGSH) with mixed results (Table 1). A human exposure study in the OPAA, OPAA SLF, OP SLF

280

Netherlands found a significant association between OPESR, OPAA, and OPDTT and FeNO after 5

281

hours of exposure (to our knowledge, this is the only study to find an association between OPAA

282

and health effects) 21. Interestingly, in two-pollutant models using two different OP

283

measurements, effects of OPDTT remained after adjustment for OPESR and OPAA and vice versa,

284

suggesting that the PM component drivers of OPDTT and OPESR or OPAA may have independent

285

effects on FeNO. The same was not true for OPESR and OPAA as they were too correlated to

286

disentangle their effects. A longer follow-up study in the Netherlands using OP estimates from a

287

LUR model did not find an association between FeNO and OPESR but did find an association

288

between FeNO and OPDTT 20. OPDTT has also been associated with FeNO in healthy adults after 2

289

hours of exposure and in schoolchildren with persistent asthma in southern California (FeNO

290

increased 8.7-9.9% per Interquartile Range (IQR): 0.43 nmol min-1 m-3) with exposures lagged

291

one and two days 21, 61. The association of FeNO with OPDTT in the schoolchildren study was

292

nearly twice as strong as with other measures (macrophage ROS and traffic-related markers) per

293

AA IQR 61. OBGSH SLF was also shown to have an effect on FeNO up to 3 days after exposure, but OB SLF

294

was not 62. OPAA has been found to have no association with other adverse health endpoints in

295

multiple studies, including epidemiologic analyses on all-cause, respiratory, and cardiovascular

296

mortalities, cardiorespiratory emergency department visits, myocardial infarction, and lung

297

cancer mortality 22, 49, 63, 64, suggesting that OPAA may have limited utility in future epidemiologic

298

studies. OPESR has had mixed results in limited health studies, and more work is needed before a

299

conclusion of epidemiologic relevance is reached.

300 301

Table 1. Reported results of tested associations between OP assays and health endpoints.

302

Associations that were reported to be stronger for OP than PM concentration in at least one study

303

are marked with an *. No significant negative (protective) associations were reported by any study. Health Endpoint Respiratory Health

Assays with Positive Associations

Assays with Null Associations

(confidence interval does not include null)

(confidence interval does include null)

Assay

Reference

General

DTT*

19 20, 21, 61

FeNO

DTT * ESR * GSHSLF

21, 65 62


Assay

Reference

AASLF ESR GSHSLF

9, 62 20 9

Page 11 of 40


AA *

Asthma/Wheeze

DTT *

Lung Cancer Mortality

GSHSLF *

All-cause Mortality

-

21

18, 19, 49

22

AA AASLF UASLF GSHSLF

49

AASLF

22

AASLF GSHSLF

64

66 66 66

64

Cardiovascular Health Microvascular Function

DTT

67

Myocardial Infarction

GSHSLF

63

AASLF

63

Congestive Heart Failure

DTT *

18, 49

AA

49

Ischemic Heart Disease

DTT *

19

AASLF UASLF GSHSLF AASLF GSHSLF

66

Chronic Obstructive Pulmonary Disease All-cause Mortality

-

66 66 64 64

304 305 306

OPDTT has been linked with various acute cardiorespiratory endpoints in multiple studies

307

(Table 1). Markers of respiratory health, including forced expiratory volume, asthma, and

308

rhinitis, were more associated with LUR-estimated OPDTT than PM2.5 concentrations in a 14-year

309

study in the Netherlands 20. Another study utilized a 10-year data set of modelled OPDTT in

310

Atlanta, GA estimated via a regression with emission source impacts and found an association

311

between OPDTT exposure and asthma/wheeze and congestive heart failure emergency department

312

(ED) visits. In fact, OPDTT remained associated with ED visits in both one- and two-pollutant

313

models while the PM2.5 association became null in the two-pollutant model, suggesting that

314

OPDTT can explain much of the PM impact on these two health endpoints 18. A similar, shorter

315

term (196 days), epidemiologic study was conducted on OPDTT measurements in Atlanta, GA

316

rather than modelled concentrations, and this study showed a similarly significant association

317

between OPDTT exposure and asthma/wheezing and ischemic heart disease ED visits despite the

318

small sample size 19. Finally, particle size may play a role in determining health effects

319

associated with OPDTT exposure as a study in Los Angeles showed an inverse relationship



320

between microvascular function in elderly adults and 5-day average OPDTT of PM

Review of acellular assays of ambient particulate matter oxidative

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