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Ecotoxicology and Human Environmental Health
Particle size distributions of oxidative potential of lung-deposited particles – assessing contributions from quinones and water-soluble metals Yan Lyu, Huibin Guo, Tiantao Cheng, and Xiang Li Environ. Sci. Technol., Just Accepted Manuscript • Publication Date (Web): 02 May 2018 Downloaded from http://pubs.acs.org on May 2, 2018
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Particle size distributions of oxidative potential of lung-deposited
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particles – assessing contributions from quinones and water-soluble
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metals
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Yan Lyu1, Huibin Guo1, Tiantao Cheng1 and Xiang Li*, 1, 2
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1
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P.R. China
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2
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Department of Environmental Science & Engineering, Fudan University, Shanghai 200438,
Shanghai Institute of Pollution Control and Ecological Security, Shanghai 200092, P.R.
China
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Correspondence to: Xiang Li (
[email protected])
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*Corresponding author.
14 15
ABSTRACT
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Redox-active species in ambient particulate matter (PM) cause adverse health effects through
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the production of reactive oxygen species (ROS) in the human respiratory tract. However,
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respiratory deposition of these species and their relative contributions to oxidative potential
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(OP) have not been described. Size-segregated aerosols were collected during haze and non-
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haze periods using a MOUDI sampler at an urban site in Shanghai to address this issue.
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Samples were analyzed for redox-active species content and PM OP. The average
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dithiothereiol (DTT) activity of haze samples was approximately 2.4-fold higher than that of
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non-haze samples and significantly correlated with quinone and water-soluble metal
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concentrations. The size-specific distribution data revealed that both water-soluble OP DTT v
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(volume-normalized OP quantified by DTT assay) and OPDTT (mass-normalized OP) were m
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unimodal, peaking in 0.56–1 µm and 0.1–0.32 µm, respectively, due to contributions from
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accumulation-mode quinones and water-soluble metals. We further estimated that transition
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metals (mainly copper and manganese) contributed 55±13% of the DTT activity, while
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quinones accounted for only 8±3%. Multiple-path particle dosimetry (MPPD) calculations
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estimated that OP deposition in the pulmonary region was mainly from accumulation-mode
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transition metals despite quinones having the highest DTT activity. This behavior is primarily
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attributed to the deposition efficiency of transition metals in the pulmonary region being
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approximately 1.2-fold greater than that of quinones. These results reveal that accumulation-
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mode transition metals are significant contributors to the OP of deposited water-soluble
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particles in the pulmonary region of the lung.
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INTRODUCTION
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Many epidemiologic studies have shown the link between exposure to particulate matter (PM)
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and increases in adverse respiratory1-3 and cardiovascular outcomes.4-6 Recently, mounting
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evidence indicates that the deposition of PM in the human respiratory tract (RT) can cause
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adverse health effects via oxidative stress through the overproduction of reactive oxygen
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species (ROS).7-9 These ROS could be either carried by the PM themselves10 or generated via
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interactions between particle-bound redox-active components and antioxidants (i.e., ascorbate,
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reduced glutathione, uric acid, and vitamin E) in lung lining fluid.11
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The dithiothreitol (DTT) assay is a widely used cell-free approach for the measurement of
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ROS generation capacity, the so-called oxidative potential (OP).12 In the DTT assay, redox-
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active species oxidize DTT to its disulfide form and then transfer an electron to dissolved
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oxygen, generating superoxide radical (O2·-) that can then form other ROS (i.e., ·OH). Many
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chemical species in particles are considered redox-active, including transition metals,13
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quinones,12, 14 humic-like substances (HULIS),15 soot or black carbon,16, 17 environmentally
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persistent free radicals (EPFRs)18, 19 and secondary organic aerosols (SOAs) from biogenic
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precursors.20 Chamber studies suggested that many compounds in PM other than the
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quinones that were identified and measured in ambient atmosphere drive its OP.21 Previous
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studies on the contributions of chemical species to the OP of ambient particles are rather
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limited. Charrier and Anastasio13 reported that as much as 80% of DTT activity could be
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ascribed to transition metals (especially Cu and Mn) based on hypothetical PM2.5 and data
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from the literature. The major redox-active components of water-soluble PM were found to
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be HULIS, which contained compounds such as quinones.15 Verma et al.14 showed that
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quinones only accounted for ~10% of water-soluble DTT activity of PM2.5 in Atlanta, USA.
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The varying of redox-active components with particle size indicates that the OP of PM is
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size-dependent. Particle size partly affects deposition in the human RT. Small particles, along
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with various chemicals, can penetrate the lower (deeper) regions of the human RT (i.e., the
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pulmonary region), and they are very harmful due to the difficulties in clearing them and
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their easy access to blood.22 Ultrafine particles are particularly difficult to clear because they 2
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avoid phagocytosis by alveolar macrophages and thus enter the pulmonary interstitial sites,
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inducing pulmonary inflammation. 23 In contrast, coarse particles are probably inhibited by
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rhinothrix via impaction processes and are more likely to deposit in upper regions of the RT
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(nasal area). Some researchers have shown that metals in particles deposited in the nasal
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region could cross synapses in the olfactory bulb and migrate via secondary olfactory neurons
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to the distant nuclei of the brain, 24 causing olfactory deficits25 and brain lesions. 26
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There is a wide array of studies on the size-depend OP all over the world,27-30 but such
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information is lacked to an extent in China. In this study, size-resolved ambient PM was
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collected during haze and non-haze periods using a Micro-Orifice Uniform Deposit Impactor
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(MOUDI) sampler at an urban site in Shanghai, China. We systematically examined the
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contributions of quinones and water-soluble metals to the size-dependent water-soluble OP of
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ambient PM in combination with measurements of the OP of pure quinones and metals.
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Furthermore, the relative importance of quinones and metals to the respiratory deposition of
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aerosol water-soluble OP is illustrated using a multiple-path particle dosimetry (MPPD)
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model in this study.
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MATERIALS AND METHODS
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Sample Collection. Size-resolved particle samples were collected in urban Shanghai, China,
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during haze and non-haze periods using a MOUDI (110R, MSP Corp., Shoreview, MN). The
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impactor was placed on the rooftop of teaching building No. 4 at the Handan Campus of
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Fudan University (31.30 °N, 121.50 °E) with a flow rate of 30 L/min from January to May,
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2016. Details on the sampling site can be found in Lyu et al. 31 The MOUDI fractionates
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particles at the aerodynamic cutoff sizes of 0.056, 0.1, 0.18, 0.32, 0.56, 1.0, 1.8, 3.2, 5.6, 10,
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and 18 µm. Particles were collected on prebaked (under 500 °C for 4 h) quartz fiber filter
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(QFF, 47 mm, Whatman QMA) for a continuous 24 and 48 h during haze and non-haze
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periods, respectively, both beginning at 9 a.m. Four MOUDI sample batches were collected
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during haze periods (January 15 and 18, March 5 and 18, 2016), and the other four batches
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were collected during non-haze periods (April 22 and May 3, 12 and 22, 2016). Three field
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blanks were included. The particle mass loadings were determined by the difference in the
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filter weight before and after the sampling and ranged from 0.30 to 1.26 mg. All data were
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later blank corrected with the combined average of the three field blanks. The loaded filters
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were immediately sealed in Petri dishes and stored in a freezer (−24 °C) until further analysis.
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The samples were analyzed for the content of quinones and water-soluble metals and water-
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soluble DTT activity (Figure S1). 3
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Chemical analysis. One-half of the quartz filter was used for quinone determination using
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GC-MS/MS (7890A-7000B, Agilent Technologies, Wilmington, DE). These quinones
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included
1,2-naphthoquinone (2H-14NQ),
(12NQ),
1,4-naphthoquinone
(14NQ),
5-hydroxy-1,4-naphthoquinone
2-hydroxy-1,4-
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naphthoquinone
(5H-14NQ),
9,10-
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anthracenequinone (AQ), 9,10-phenanthraquinone (PQ) and benz(a)anthracene-7,12-quinone
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(BAQ). Briefly, one-half of each filter was cut into pieces and extracted twice (ultrasonicated
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each time for 30 min) using 4 mL of dichloromethane (DCM) as solvent. The combined
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extracts were filtered using pore syringe filters (PTFE, 0.45 µm) and subsequently rinsed
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with 2 mL of DCM. To enhance the sensitivity and stability of GC-MS/MS measurements,
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the target quinones were converted to their diacetyl derivatives using the method used by
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Delgado-Saborit et al. 32 The results showed that major quinones (12NQ, 14NQ, PQ, AQ, and
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BAQ) can be successfully derivatized at low concentrations (those expected in ambient air).
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The detailed derivatization method and GC-MS/MS conditions for analyzing acetylated
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derivatives are included in supporting information (SI). In addition, a recovery test was
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conducted after each sample batch using freshly baked QFF spiked with 1 mL of a quinone
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stock solution. The average recovery of the derivatized quinones was 103±14%. The reported
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concentrations were all corrected by the blank and recovery values.
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For determining water-soluble metals, we cut one-quarter of the filter and sonicated it in 2
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mL of DI water for 1 h with an ultrasonic cleanser. After sonication, the extracts were filtered
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using PTFE 0.45-µm pore syringe filters. HNO3 (4%) was then added to produce a final
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volume of 10 mL. Here, we focus on Cu, Mn, and Fe as they are common transition metals
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linked to aerosol toxicity.
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potential ship emissions may influence the environment. 35 Vanadium has been suggested to
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indicate ship traffic emission in Shanghai36 and is thus also quantified in this study. The
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signal response of a series of standard metal solutions (0.1-100 ppb) was recorded by 7900
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ICP-MS (Agilent Technologies, Wilmington, DE). The determination coefficient (R2) of the
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standard calibration curves ranged from 0.9991 to 0.9997 (N = 6) for the target metals. The
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background equivalent concentration (BEC) values (4% HNO3 blank) for Cu, Mn, Fe and V
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were 0.034, 0.0032, 0.31 and 0.0008 ppb, respectively. A 20-ppb internal standard of
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scandium (Sc) and germanium (Ge) was added to all samples and standards to monitor
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analytical drift. The recoveries of the target metals ranged from 82 to 117%. Target metals
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were found in blank filter extracts (Cu: 0.25 ppb, Mn: 0.32 ppb, Fe: 10.8 ppb, and V: 0.03
33, 34
In addition, Shanghai has the largest port worldwide, and
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ppb). The reported concentrations for ambient PM samples were all blank- and recovery-
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corrected.
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Oxidative potential. The remaining one-quarter of the filter was used for the OP
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measurement. The loaded filters were cut and sonicated in DI water for 1 h, which was then
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filtered with 0.45-µm syringe filters. The dithiothreitol (DTT) assay adopted in this study
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mainly follows that the procedure used in Cho et al. 37 We measured DTT consumption rates
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of both samples and pure quinones and metal solutions. The details can be found in SI. Light
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in the work space was excluded as much as possible (e.g., experiments were performed with
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the lights off, and vials were covered with aluminum foil when not in use) because both DTT
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and DTNB are sensitive to light. 38. Blank tests showed that a negligible amount of DTT was
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consumed in buffer solutions (
