Chemical speciation of trace metals emitted from Indonesian peat fires for health risk assessment

Atmospheric Research 122 (2013) 571–578

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Chemical speciation of trace metals emitted from Indonesian peat fires for health risk assessment Raghu Betha a, Maharani Pradani b, Puji Lestari b, Umid Man Joshi c, Jeffrey S. Reid d, Rajasekhar Balasubramanian a, c,⁎ a b c d

Department of Civil and Environmental Engineering, Faculty of Engineering, National University of Singapore, 1 Engineering Drive 2, E1A-07-03, 117576, Singapore Department of Environmental Engineering, Faculty of Civil and Environmental Engineering, Institute of Technology Bandung, Ganeca 10, Bandung 40132, Indonesia Singapore-Delft Water Alliance, National University of Singapore, 1 Engineering Drive 2, 117576, Singapore Marine Meteorology Division, Naval Research Laboratory, 7 Grace Hopper Ave, Stop 2, Monterey, CA 93943‐5502, USA

a r t i c l e

i n f o

Article history: Received 5 August 2011 Received in revised form 29 May 2012 Accepted 29 May 2012 Keywords: Peat fires Health risk Chemical speciation Trace metals

a b s t r a c t Regional smoke-induced haze in Southeast Asia, caused by uncontrolled forest and peat fires in Indonesia, is of major environmental and health concern. In this study, we estimated carcinogenic and non-carcinogenic health risk due to exposure to fine particles (PM2.5) as emitted from peat fires at Kalimantan, Indonesia. For the health risk analysis, chemical speciation (exchangeable, reducible, oxidizable, and residual fractions) of 12 trace metals (Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Ti, V and Zn) in PM2.5 was studied. Results indicate that Al, Fe and Ti together accounted for a major fraction of total metal concentrations (~ 83%) in PM2.5 emissions in the immediate vicinity of peat fires. Chemical speciation reveals that a major proportion of most of the metals, with the exception of Cr, Mn, Fe, Ni and Cd, was present in the residual fraction. The exchangeable fraction of metals, which represents their bioavailability, could play a major role in inducing human health effects of PM2.5. This fraction contained carcinogenic metals such as Cd (39.2 ng m− 3) and Ni (249.3 ng m − 3) that exceeded their WHO guideline values by several factors. Health risk estimates suggest that exposure to PM2.5 emissions in the vicinity of peat fires poses serious health threats. © 2012 Elsevier B.V. All rights reserved.

1. Introduction Biomass burning is a significant source of airborne particles in many parts of the world, particularly in Southeast Asia (Balasubramanian et al., 1999, 2003; Crutzen and Andreae, 1990; Nichol, 1998; Ristovski et al., 2010; Ryu et al., 2007; See et al., 2006a, 2007a). Smoke-induced haze, caused by uncontrolled forest and peat fires, occurs regularly in Indonesia where tropical rain forests are converted to agricultural lands through heavy logging and slash-and-burn techniques (See et

⁎ Corresponding author at: Department of Civil and Environmental Engineering, Faculty of Engineering, National University of Singapore, 1 Engineering Drive 2, E1A-07-03, 117576, Singapore. Tel.: +65 65165135; fax: +65 67744202. E-mail address: [email protected] (R. Balasubramanian). 0169-8095/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.atmosres.2012.05.024

al., 2006a, 2007a; Siegert et al., 2001). As a result of long-range transboundary transport, biomass emissions can be transformed into a regional haze episode, affecting several countries in Southeast Asia, most notably Singapore, Malaysia and Thailand, and of course, Indonesia itself. The regional haze problem worsens under dry weather conditions, or when it is coupled with extreme droughts brought on by the El-Nino Southern Oscillation (ENSO) phenomenon (Fuller et al., 2004; Nichol, 1998; Odihi, 2003). During the eighties and nineties, thick smoke-induced haze enveloped Southeast Asian region during the months of August–September 1982, September 1983, September 1987, August 1990, August–September 1991, August–October 1994, August–October 1997 and February– May 1998 (Nichol, 1998; Radojevic, 2003). Many less severe smoke-induced haze episodes have been experienced in the other years (Radojevic, 2003). More recent haze events took place in August 2005, October 2006, and September 2009

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plaguing Singapore and some parts of Malaysia (See et al., 2006a, 2007a; Sundarambal et al., 2010). Among the different types of biomass burned in Indonesia, peat fires are the key source of smoke haze (Page et al., 2002), particularly in El Nino years. Indonesia has the largest area of tropical peat lands in the world, with 27 million hectares scattered around west and central Kalimantan, Merauke and Nabire in Irian Jaya, and along the east coast of Sumatra Island (Wulandari, 2002). Peat fires can smolder deep underground indefinitely, and flare up during dry seasons (Radojevic, 2003). Investigations focusing on the smoke properties of tropical peat fires, however, are scarce. The field studies conducted previously have been restricted to measuring the optical properties of peat smoke particles (e.g., See et al., 2006a) and characterizing the gaseous pollutants, and elemental and organic carbon (EC and OC) in PM2.5 (airborne particulate matter with diameter ≤ 2.5 μm) (Christian et al., 2003; Muraleedharan et al., 2000). A controlled-laboratory experiment was also conducted to study the optical properties of aerosols of peat burning origin (Chand et al., 2005). Our research group conducted a field study in Sumatra to provide information on PM2.5 emissions from peat fires and their associated chemical components (See et al., 2007a). However, no systematic study has been conducted yet to quantify the particulate emissions from peat fires in Kalimantan where the largest tracks of peat lands exist. Particulate pollution associated with biomass burning can result in devastating impacts on human health (Aditama, 2000; Emmanuel, 2005; Karthikeyan et al., 2006a; Kunii et al., 2002; Sastry, 2002; Thurston et al., 1997). A significant increase in hospital admissions due to asthmatic and other respiratory related problems has been reported during regional smoke haze episodes in Southeast Asia (Nichol, 1998; The Straits Times, 2010). PM2.5 emitted from biomass burning is a major contributor for bronchial-related problems (Brunekreef and Holgate, 2002; Dawud, 1998; Karthikeyan et al., 2006a; Kunii et al., 2002). Several epidemiological studies conducted in different parts of the world indicate a strong association between exposure to airborne particulate matter and increased morbidity and mortality (Ackermann-Liebrich et al., 1997; Dockery et al., 1993; Laden et al., 2000; Pope et al., 1999). PM2.5 contains a complex mixture of aggregates of organic and inorganic compounds such as carbonaceous material, polycyclic aromatic hydrocarbons, salts, metals, and endotoxins (See et al., 2007a). Among the chemical components in aerosols, trace metals have attracted great attention due to their potential health effects (Adamson et al., 2000; Betha and Balasubramanian, 2011; Dreher et al., 1997; Dye et al., 2001; Espinosa et al., 2002; Ghio and Devlin, 2001). These metals, when deposited in the lower airways, can lead to acute and chronic effects on the lung (Bradshaw et al., 1998; Sobaszek et al., 2000). Some of the elements contained in PM2.5 such as Cr, Ni, Cd and Co are carcinogenic (IARC, 1980, 1990, 1993) and most other elements are toxic. The mechanisms by which the absorbed metals affect human health are not yet understood completely. However, recent evidence indicates that most of the adverse health effects are derived from oxidative stress initiated by the formation of reactive oxygen species (ROS) within cells (Baulig et al.,

2003; Gonzalez-Flecha, 2004). Particulate-bound transition metals are known to generate ROS within cells through Fenton and Haber Weiss reactions (Li et al., 2003; See et al., 2007b). It is often necessary to understand the specific forms of particulate-bound metals, since their bioavailability, solubility and environmental transport largely depend on their chemical forms. In this study, we characterize the chemical speciation of particulate-bound elements in PM2.5 emissions from recent peat fire episodes that occurred in Kalimantan (S 02°20′09″ and E 114°04′38″) during a dry spell in the months of September–October 2009. This speciation scheme consists of four fractions: (1) soluble and exchangeable metals; (2) carbonates, oxides and reducible metals; (3) metals bound to organic matter, oxidizable and sulfidic metals; and (4) residual metals. We also evaluate carcinogenic and non-carcinogenic health risks associated with inhalation exposure to particulatebound elements during peat fires. These results characterize the quantitative health risk associated with PM2.5 emissions from peat fires, and can play an important role in protecting the health of individuals being inadvertently exposed to particulate emissions, for example, plantation workers and wildland fire fighters. 2. Materials and methods 2.1. Description of sampling site PM2.5 samples investigated for this study were collected at a number of sites in and around Pulang Pisau, Kalimantan, Indonesia during peat fires from 19 September to 12 October 2009. A prolonged dry spell was prevalent during the sampling period with temperatures ranging from 30 to 35 °C and winds blowing at a speed of 3.1–5 m/s from the South easterly direction. The sampling location is shown in Fig. 1. The particulate samples were collected in the immediate vicinity (10 to 20 m) of peat fires so that a realistic health risk can be assessed for individuals such as wildland fire fighters who are exposed to concentrated smoke emissions. In addition, background air samples were also collected from the same sampling point in the absence of peat fires. 2.2. Particulate matter sampling Two calibrated MiniVol portable air samplers (Airmetrics, TSI), calibrated with a Gilibrator-2 primary air flow calibrator (Gilian Instrument Corp.) prior to field deployment, were used to collect PM2.5 samples. Air was drawn at a flow rate of 0.005 m 3 min − 1 (5 L min − 1) through size-selective inlets with PM2.5 impactor, and then through a 47 mm Teflon membrane (Polytetrafluoroethylene, PTFE) filter. The sampling time ranged from 6 to 8 h depending on the intensity of peat fires to obtain sufficient mass for chemical analysis. These filters were dried in a desiccator at a constant temperature of 22 °C and a relative humidity of 33% for at least 24 h before and after exposure. The filters were then weighed with an MC5 microbalance (Sartorius AG) accurate to 1 μg. After sampling, the filters were weighed and stored in petri dishes wrapped in aluminum foil and stored at 4 °C until extraction and metal analysis.

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Fig. 1. The sampling site is located at a Taruna Jaya village, Pulau Pisang region (S 02°20′09″ and E 114°04′38″) which is about 35–40 km from Palangkaraya City, the capital city of central Kalimantan.

2.3. Sequential extraction procedure A four-step extraction procedure was applied in this study. Microwave-assisted extraction was used to extract

various fractions of the trace metals. The fractions are identified as follows: exchangeable, reducible, oxidizable and residual metals. The details of the extractants used, extraction conditions and procedures are outlined in Fig. 2.

Fig. 2. Procedure for extraction of various metal fractions in PM2.5 samples collected from peat fires in Kalimantan.

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Experiments were conducted in duplicate, and average mass concentrations of individual metals were quantified (Table 1). Exchangeable, reducible and oxidizable fractions of metals were extracted through a sequential extraction procedure described by Jamali et al. (2009). All four fractions were stored in a refrigerator at 4 °C until ICP-MS analysis could be done to quantify the presence of Al, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Ti, V and Zn. All reagents used in this research were of analytical grade. For fractionation of metals using sequential extraction, acetic acid and hydroxylamine hydrochloride solutions were prepared using ultrapure water (18.2 MΩ) from Maxima Ultra Pure Water system (Elgalabwater, UK). HNO3 (Traceselect for trace analysis, Fluoka, France), H2O2 (Merck), and HF (Merck) were used for the digestion experiments. 2.4. Analysis of metals Working standards were prepared by diluting multielement standard solutions (OC517986, OC285604 and Arsenic standard solution) for the calibration of ICP-MS (Perkin-Elmer Inc. USA). The limits of detection (LODs) for all target analytes were calculated based on three times the standard deviation of the blank. The LODs ranged from 0.01 (Pb) to 1.09 (Fe) μg/L. The precision and accuracy of the extraction procedure were evaluated using standard reference materials (SRM) (NIST SRM 1648, urban particulate matter). The SRM samples in triplicate were processed following the same procedure as that of the samples, and analyzed using ICP-MS. The concentrations in each fraction were added and total concentration was compared with the certified values. The recoveries of total elements were satisfactory and ranged between 84% (Fe) and 109% (Ni). 2.5. Human health risk assessment Human health risk assessment was conducted based on the mean concentrations of carcinogenic and non-carcinogenic metals determined at different locations. This framework is especially useful in understanding the health hazard associated with exposure to emissions from peat fires for fire fighters, plantation workers and people living in nearby locations. The steps involved in the health risk assessment

are described elsewhere (See and Balasubramanian, 2006). Briefly, however, it involves the following four major steps (NRC, 1983): (1) hazard identification — elements with known toxicity values are considered (Al, Cr, and Mn induce non-carcinogenic effects while Cd, Cr, Ni and Co induce carcinogenic health effects); (2) exposure assessment involves estimation of chronic daily intake (CDI) of these elements calculated from the following equation,   −1 −1 CDI mgkg day     Total dose TD; mgm−3  inhalation rate IR; m3 day−1 ¼ Body weight ðBW; kgÞ ð1Þ TD ¼ C  E

ð2Þ

where C is the concentration of pollutant and E is the deposition fraction of particles by size given by (Volckens and Leith, 2003) E ¼ −0:081 þ 0:23lnðDpÞ2 þ 0:23 √ðDpÞ

ð3Þ

where Dp is the diameter of particles. In this study, PM2.5 was used (i.e. Dp is 2.5 μm). Healthy adults were considered for risk assessment. IR is typically assumed to be 20 m 3 day − 1 and BW to be 70 kg for adults; (3) dose–response assessment: it reflects the probability of health effects based on the dose of inhaled air pollutants. Assuming only inhalation as exposure route, the reference dose (RfD, mg kg − 1, day − 1) for metals that are non-carcinogenic was calculated from reference concentrations (RfC, mg/m 3) provided by the United States Environmental Protection Agency (USEPA). Likewise, for carcinogenic metals the inhalation slope factor (SF, mg − 1 kg day) was calculated from inhalation unit risk values (IUR, mg − 1 m 3) provided by USEPA. Finally, (4) risk characterization or estimation of health risk was calculated based on the exposure and dose–response assessments. For non-carcinogenic metals, it is indicated by hazard quotient (HQ) = CDI / RfD. For carcinogenic metals, total carcinogenic risk is estimated in terms of excess life time cancer risk given by (ELCR) = CDI × SF (United Stated Department of Energy, US DOE, 1999). 3. Results and discussion 3.1. Mass concentrations

Table 1 Concentrations of trace metals in PM2.5. Metals (ng/m3)

Background (n = 2)

Smoke haze (n = 11)

Al Ti V Cr Mn Fe Co Ni Cu Zn Cd Pb

2156 ± 203 953 ± 183 129.1 ± 12 217 ± 16 112 ± 20 1381 ± 156 22 ± 9 279 ± 133 872 ± 293 247 ± 86 7±2 260 ± 164

19,881 ± 10,802 8209 ± 1006 653 ± 288 1333 ± 718 826 ± 103 13,565 ± 1204 237 ± 98 3103 ± 304 2465 ± 794 1788 ± 126 106 ± 70 460 ± 238

n = number of PM2.5 samples.

The mass concentration of PM2.5 emissions in the immediate vicinity of peat fires in Kalimantan ranged from 235 to 7817 μg m− 3 during the months of September and October 2009. A major peat fire episode that occurred on 1 October 2009 resulted in the highest concentration of PM2.5 emissions (7817 μg m− 3) measured during the smoldering phase, which lasted for several hours. This concentration decreased to 2742 μg m− 3 over a period of 48 h and eventually to background levels (~55 μg m− 3) after nearly a month. In our previous study on peat fire emissions in Sumatra, Indonesia (See et al., 2007a), the highest concentration of PM2.5 measured was 1600 μg m− 3. However, the PM2.5 increase observed in this study on 1 October 2009 was much higher. The main reason for

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such a large increase in PM2.5 concentration in Kalimantan is that the particulate samples were collected in the immediate vicinity of peat fires (within 10 m from the site) while the PM2.5 sampling was conducted in Sumatra about 100 m away from peat fires. In addition, there could be a significant difference in the intensity of peat fires between the two episodes. PM2.5 measured in both Kalimantan and Sumatra exceeded the 24-hour PM2.5 standard set by the USEPA (35 μg m − 3) on several occasions. The exceedance of the 24hour PM2.5 standard is of particular health concern as fine particles can bypass the normal body defense mechanism and penetrate deep into alveoli region of the lungs (Infante and Acosta, 1991; Oberdörster et al., 2005). The epidemiological study conducted by Pope et al. (1999) reported that every 10 μg m − 3 increase in fine particles would increase the risk for death from lung cancer by 8%. The annual average concentration of PM2.5 in the peat fire-affected site is likely to be much higher than background levels of recurring peak smoke episodes with high intensity. Thus, the exposure of the residents living in areas affected by peat fires to fine particles poses a health risk.

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condensation and coagulation, the release of incompletely combusted plant tissues and ash and suspension of soil particles (Gaudichet et al., 1995; Karthikeyan et al., 2006a,b). Al was found to have the highest concentration compared to all other metals in most of the samples, followed by Fe and Ti. Al, Fe and Ti together constituted 67 and 83% of the total metal concentration in the background and peat fire samples, respectively. 3.3. Fractionation of metals in PM2.5 Sequential extraction was used to fractionate metal species in PM2.5 measurements. The different fractions investigated in this study were (i) exchangeable, (ii) reducible, (iii) oxidizable, and (iv) residual fractions (Espinosa et al., 2002; Marika and Markku, 2003). Average concentrations of the different fractions of metals found in PM2.5 emissions sampled from peat fires as well as in background air are presented in Table 3, with the respective concentration ranges. The relative distribution of metals in different fractions is shown in Fig. 3. For the peat fire samples, Al (90%), Pb (72%), Ti (69%), V (64%) and Cu (54%) were present mainly in the residual fraction compared to other three fractions. Cr (52%), Mn (56%), and Fe (43%), were mainly found in the reducible fraction while Co (28%), Cd (38%) and Ni (46%) were predominantly found in the oxidizable fraction. Cd (37%) was also found in the exchangeable fraction. A similar metal speciation was observed for back-ground PM2.5 samples as well. Al (93%), Pb (80%), Ti (74%), V (84%) and Cu (89%) were mainly found in the residual fraction while Cr (62%), Mn (70%), and Fe (50.0%) were present in the reducible fraction. Ni (50%) and Co (22%) existed in the oxidizable fraction while Cd was present in both oxidizable and exchangeable fractions (40% and 36%, respectively). Among the four fractions investigated in this study, the exchangeable fraction had the highest potential to cause adverse health effects, as it can easily go into the dissolved fraction and enter blood stream from lung fluids (Espinosa et al., 2002). Within the exchangeable fraction of PM2.5, the lowest concentration was observed for Pb (33 ng m − 3) followed by Cd (39 ng m − 3) and Co (39 ng m − 3) and the highest concentration for Fe (2305 ng m − 3). It can be seen

3.2. Total concentration of metals The total concentration of metals was determined by adding together the four fractions (Section 3.4) analyzed in this study, and a summary of the concentration data is presented in Table 2. Overall, the metals analyzed constituted 1 to 12% of the total mass concentration of PM2.5. A higher concentration of total metals with an average of 30% was reported during a previous peat fire episode in Sumatra, Indonesia (See et al., 2007a). The percentage of particulatebound metals is dependent on the amount of other chemical constituents present in PM2.5, especially carbonaceous matter. Comparing individual metal concentrations, it can be seen that the concentration of most of the metals increased significantly by factors ranging from ~ 2 and 16 during the peat fire episodes compared to background. A maximum increase was observed in carcinogenic metals such as Co, Ni, and Cd (11, 11 and 16% respectively) compared to other metals. Most of these metals are generated from various sources during biomass burning, including fine-mode

Table 2 Concentration of trace metals in the background air and during peat fires in Kalimantan, Indonesia. Emissions from peat fires 3

Metals (ng/m )

Al Ti V Cr Mn Fe Co Ni Cu Zn Cd Pb

Background air

Exchangeable

Reducible

Oxidizable

Residual

Exc

Red

Oxi

Res

Mean

Min–max

Mean

Min–max

Mean

Min–max

Mean

Min–max

77 146 4 27 9 253 3 31 50 62 3 21

60 36 7 134 78 566 2 58 17 37 0 38

8 70 4 37 9 250 5 140 30 12 3 3

2011 702 106 18 15 312 12 50 775 136 1 209

1024 1269 47 243 91 2305 39 249 400 398 39 33

128–2107 179–3289 24–84 32–562 11–190 301–5759 6–73 42–609 81–994 153–881 6–74 25,508

875 429 119 689 465 5780 26 614 497 572 7 80

122–1874 73–1037 25–195 202–1405 53–987 856–14,200 10–53 94–1544 82–1260 194–978 5–9 33–142

123 838 70 233 129 2102 66 1420 213 115 46 17

38–291 140–1710 28–92 54–400 81–170 318–5322 18–156 242–3937 100–287 64–245 35,400.00 44,470

17,860 5674 416 169 141 3378 107 819 1355 704 13 331

6788–32,065 980–10,717 161–731 25–427 57–345 501–7794 14.4–292 146–2425 454–2701 115–1740 13,912.00 120–616

Exc: Exchangeable; Red: Reducible; Oxi: Oxidizable; Res: Residual.

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Table 3 Health risk assessment of trace metals in PM2.5. Metals Non carcinogenic metals Al Cr Mn Carcinogenic metals Cr Co Ni Cd

CDI (mg kg− 1 day− 1)

RfD (mg kg− 1 day− 1)

HQ

2.0 × 10− 4 4.9 × 10− 5 1.8 × 10− 5

1.4 × 10− 3 2.9 × 10− 5 1.4 × 10− 5

1.4 × 10− 1 1.7 1.3

3.7 × 10− 4 4.0 × 10− 5 5.0 × 10− 5 1.7 × 10− 5 Σ = 3.1 × 10°

from Table 3 that the concentration of trace metals such as Pb (33 ng m − 3) and V (47 ng m − 3) in the exchangeable fraction was well below the WHO (World Health Organization) guideline values of 500 and 1000 ng m − 3, respectively while that of cadmium (39 ng m − 3) and nickel (249 ng m− 3) exceeded the WHO guideline values by several factors (WHO, 2000). Since these chemicals are highly carcinogenic, they represent a serious health threat. The other three fractions (reducible, oxidizable and residual) are not very relevant in terms of health risk associated with inhalation of PM2.5 emissions. However, the

SF (mg− 1 kg day)

ELCR

4.2 3.2 × 101 8.4 × 101 6.3

2.0 × 10− 4 2.5 × 10− 4 4.2 × 10− 3 5.0 × 10− 5 Σ = 4.7 × 10− 3

reducible fraction of metals can pose a threat to human health when they become bioavailable under certain conditions. Metals in the reducible fraction of PM2.5 can be bioavailable or soluble only under very low pH conditions (Espinosa et al., 2002). These conditions could occur naturally during acidic rain and these metals can penetrate into water bodies through wet deposition, causing environmental and health related problems. Oxidizable and residual fractions are not easily bioavailable since these fractions of metals in airborne particulate matter are relatively stable (Espinosa et al., 2002). These two fractions represent 70% of

Fig. 3. Average percentage of different fractions of trace metals extracted from PM2.5 collected in Kalimantan, Indonesia. (a) Background air, (b) during peat fires.

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the total metal concentration, and do not possess a major risk to human health. The health risk analysis associated with other exposure pathways, such as ingestion of contaminated water, is beyond the scope of this paper. In this study, only the health risk due to inhalation of PM2.5 was considered. Therefore, the exchangeable, or the soluble fraction of metals is useful in estimating the health risk. From Fig. 3, it can be seen that Cd and Zn exhibited higher exchangeable fractions for both background air and peat fires in Kalimantan followed by Fe, Ti, Cr, and Ni. However, as the absolute concentration of these metals during peat fires was much greater than that of background air, the possible adverse effect on human health could also be proportionally higher. The concentrations of Cd, Zn, Fe, Ti, Cr, and Ni were 2, 61.5, 253.4, 145.8, 27.4, and 31.4 ng m − 3 in the background air, and were 39, 398, 2305, 1269, 243, and 249 ng m − 3 during intense peat fires, respectively. The concentrations of these metals in the exchangeable fraction increased by factors ranging from 1 to 16 during peat fires relative to those in the background samples. Carcinogenic metals (Cd, Cr, Ni, and Co) increased by a factor of 16, 9, 8, and 13, respectively compared to their background levels. These results suggest that the amount of particulate-bound carcinogenic metals that are potentially bioavailable increased drastically during episodes of peat fires. 3.4. Health risk estimates The human health risk assessment was carried out as described in Section 2.5. The risk analysis revealed that about 70% of PM2.5 could be deposited within the body due to inhalation exposure. The pertinent information of the TD and RfD, HQ, inhalation SF and ELCR for the different metals is given in Table 3. The levels of non-carcinogenic (total HQ) and carcinogenic risk (total ELCR) were estimated to be 3.1 and 4.7 × 10− 3, respectively. These results indicate that 4 or 5 individuals out of 1000 can be affected by cancer after exposure to the carcinogenic metals in PM2.5 emitted from peat fires. The total HQ was higher than the acceptable value (i.e. 1). In the case of ELCR, the estimate risk was much higher than the acceptable level (1 in a million i.e. 1 × 10 − 6). Overall, the estimated health risk suggests that the inhalation exposure to particulate-bound carcinogenic and non-carcinogenic metals of peat fire origin by plantation workers, fire fighters who try to extinguish peat fires, and people living nearby the affected areas could lead to adverse health outcomes. In addition to health risk associated with carcinogenic and non-carcinogenic metal emissions, polycyclic aromatic hydrocarbons (PAHs), nitrated PAHs emitted during peat fires could pose additional adverse health impacts (Hsiao et al., 2000). 4. Conclusions Regional smoke-induced haze episodes resulting from peat fires in Sumatra and Kalimantan, Indonesia have severe implications on human health, especially for people living in the vicinity of forest fires and for fire fighters due to exposure to very high PM2.5 emissions. Peat fires make a substantial contribution to PM2.5 emissions during the smoldering phase than those collected under other combustion conditions. In this study, inhalation health risk associated with trace

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elements present in PM2.5 emissions during peat fires was estimated. PM2.5 samples were collected on Teflon and quartz filters in Pulang Pisau, Kalimantan, Indonesia, during peat fire episodes using portable mini-vol samplers. Trace metals which contribute to human health effects were quantified and characterized from the samples collected during peat fire episodes in four major fractions (soluble and exchangeable, oxidizable, reducible and residual fractions). The bioavailable fraction, as indicated by the exchangeable or soluble metals, plays an important role in health impacts. Results obtained in this study revealed that major carcinogenic metals such as Cr, Ni, and Cd were present in a significant proportion in the exchangeable fraction of metals, exceeding WHO guideline values. Health risks associated with the inhalation of PM2.5 emissions were estimated. The risk analysis indicates that 4 or 5 individuals out of 1000 exposed to smoke haze can be affected by cancer after prolonged exposure to high concentrations of carcinogenic metals in PM2.5 emitted from peat fires. Non-carcinogenic risk associated was found to greater than the acceptable limit. People such as plantation workers and wildland fire fighters who could be present in the immediate vicinity of peat fires are likely to experience severe health problems from exposure to these carcinogenic and non-carcinogenic metals in high concentrations present in peat fire smoke. Apart from metals, there are other chemical constituents of major health concern such as PAHs and nitrated-PAHs which were not quantified in this study. These organic compounds are likely to be released in significant amounts during peat fire episodes. Therefore, the actual health risk due to inhalation exposure to PM2.5 emissions is likely higher than what was estimated in this study. Acknowledgment This field study was conducted in Indonesia as part of the 7 SEAS program. We are thankful to the National University of Singapore for providing the financial support to carry out the PM2.5 characterization study. References Ackermann-Liebrich, U., Leuenberger, P., Schwartz, J., Schindler, C., Monn, C., Bolognini, G., Bongard, J.P., Brandli, O., Domenighetti, G., Elsasser, S., Grize, L., Karrer, W., Keller, R., Keller-Wossidlo, H., Kunzli, N., Martin, B.W., Medici, T.C., Perruchoud, A.P., Schoni, M.H., Tschopp, J.M., Villiger, B., Wuthrich, B., Zellweger, J.P., Zemp, E., 1997. Lung function and long term exposure to air pollutants in Switzerland. Study on air pollution and lung diseases in adults (SAPALDIA) team. Am. J. Respir. Crit. Care. 155, 122–129. Adamson, I.Y.R., Prieditis, H., Hedgecock, C., Vincent, R., 2000. Zinc is the toxic factor in the lung response to an atmospheric particulate sample. Toxicol. Appl. Pharmacol. 166, 111–119. Aditama, T.Y., 2000. Impact of haze from forest fires to respiratory health: Indonesia experience. Respirology 5, 169–174. Balasubramanian, R., Victor, T., Begum, R., 1999. Impact of biomass burning on rainwater acidity and composition in Singapore. J. Geophys. Res. 104, 881–890. Balasubramanian, R., Qian, W.B., Decesari, S., Facchini, M.C., Fuzzi, S., 2003. Comprehensive characterization of PM2.5 aerosols in Singapore. J. Geophys. Res. 108, 4523. Baulig, A., Garlatti, M., Bonvallot, V., Marchand, A., Barouki, R., Marano, F., Baeza-Squiban, A., 2003. Involvement of reactive oxygen species in the metabolic pathways triggered by diesel exhaust particles in human airway epithelial cells. Am. J. Physiol. Lung Cell 2853, 671–679.

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