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Occupational Exposure to Polycyclic Aromatic Hydrocarbon of Wildland Firefighters at Prescribed and Wildland Fires Kathleen Navarro, Ricardo Cisneros, Elizabeth Noth, John R. Balmes, and S. Katharine Hammond Environ. Sci. Technol., Just Accepted Manuscript • Publication Date (Web): 12 May 2017 Downloaded from http://pubs.acs.org on May 13, 2017

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Environmental Science & Technology

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Occupational Exposure to Polycyclic Aromatic

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Hydrocarbon of Wildland Firefighters at Prescribed

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and Wildland Fires

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Kathleen M. Navarro1,*, Ricardo Cisneros2, Elizabeth M. Noth1, John R. Balmes1, S. Katharine

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Hammond1

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1. Division of Environmental Health Sciences, School of Public Health, University of California,

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Berkeley, Berkeley, CA

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2. School of Social Sciences, Humanities and Arts, University of California, Merced, Merced,

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CA

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Corresponding Author: Kathleen Navarro School of Social Sciences, Humanities & Arts 5200 N. Lake Road SSM 361A Merced, CA 95343 E-mail: [email protected] Phone: 408-644-0186

TOC Abstract Art

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ACS Paragon Plus Environment


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Abstract

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Wildland firefighters suppressing wildland fires or conducting prescribed fires work long shifts

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during which they are exposed to high levels of wood smoke with no respiratory protection.

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Polycyclic aromatic hydrocarbons (PAHs) are hazardous air pollutants formed during incomplete

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combustion. Exposure to PAHs was measured for 21 wildland firefighters suppressing two

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wildland fires and 4 wildland firefighters conducting prescribed burns in California. Personal air

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samples were actively collected using XAD4-coated quartz fiber filters and XAD2 sorbent tubes.

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Samples were analyzed for 17 individual PAHs through extraction with dichloromethane and gas

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chromatograph-mass spectrometer analysis. Naphthalene, retene, and phenanthrene were

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consistently the highest measured PAHs. PAH concentrations were higher at wildland fires

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compared to prescribed fires and were highest for firefighters during job tasks that involve the

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most direct contact with smoke near an actively burning wildland fire. Although concentrations

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did not exceed current occupational exposure limits, wildland firefighters are exposed to PAHs

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not only on the fire line at wildland fires, but also while working prescribed burns and while off-

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duty. Characterization of occupational exposures from wildland firefighting is important to

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understand better any potential long-term health effects.

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Introduction

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Over the past 10 years approximately 63 million hectares in the United States have been burned

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by wildland fires. In 2015 27,000 wildland firefighters employed by the federal government

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worked to suppress wildland fires over 4 million hectares, the highest amount of forested land

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burned in the last decade.1,2 Prescribed fires are intentionally ignited, low-intensity fires used for

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land management and ecological benefit and can reduce risks of future wildland fires.3 Annually

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in the United States, roughly 900,000 hectares are treated with prescribed fire.1 Wildland

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firefighters suppressing wildland fires or conducting prescribed burns often work long hours, are

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exposed to high levels of wood smoke. 4,5

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Wildland fires emit large amounts of air pollutants known to cause adverse health effects.

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Previous studies of wildland firefighters have shown that wood smoke exposure is associated

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with increases in airway responsiveness, decreases in lung function, and a significant cross-shift

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difference in circulating cytokine levels.5,6 Gaughan et al. reported that some wildland

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firefighters had acute lung function decline after exposure to fine smoke particles.7 Past exposure

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assessments of wildland fires have measured levels of fine and respirable particulate matter

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(PM2.5, PM4), acrolein, benzene, carbon dioxide, carbon monoxide, formaldehyde, crystalline

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silica, total particulates, and polycyclic aromatic hydrocarbons (PAHs).4,8 Currently in the United

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States, wildland firefighters do not wear respiratory protection, as is not currently practical given

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the physically demanding nature of wildland firefighting.4,5 De Vos et al. 2009, evaluated the

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use of the negative pressure half face air purifying respirators with organic vapor and

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formaldehyde filters and reported that they were effective in reducing exposures and provided

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protection for firefighter’s airway. However, these firefighters only wore respiratory protection

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for 2 hours, not representative of a full shift (12-16 hours), did not perform any firefighting tasks,

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and were not protected against carbon monoxide exposure.9

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PAHs are a class of compounds consisting of two or more fused benzene rings.10 They are

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hazardous air pollutants formed during incomplete combustion and are known mutagens and

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carcinogens. The International Agency for Research on Cancer has listed benzo[a]pyrene as a

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human carcinogen, benz[a]anthracene and dibenzo[a,h]anthracene as probable human

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carcinogens and benzo[b]fluoranthene, benzo[j]fluoranthene, benzo[k]fluoranthene, chrysene,

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and naphthalene as possible human carcinogens.11–13 Exposure to PAHs has also been associated

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with cardiopulmonary mortality and decreased immune function.14,15 Past occupational health

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studies found that exposure to PAHs was associated with a higher risk of lung and bladder cancer

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and skin cancer from dermal exposure to PAHs.16,17

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Lower molecular weight PAHs exist in the environment in the gas phase or partitioned between

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the gas and particle phases, while higher molecular weight PAHs exist in the particle phase.8 Past

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studies have demonstrated that open-air burning of wood generates more gas-phase than particle-

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phase PAHs.18–20 Only a few studies have characterized personal exposures to PAHs during

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wildland fires. Materna et al. measured PAH concentrations in northern California during three

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wildfire seasons (1986-1989) and reported highest mean concentrations for pyrene, phenanthrene

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and fluoranthene. A National Institute for Occupational Safety and Health (NIOSH) Health

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Hazard Evaluation Report completed in 1994, detected acenaphthene, anthracene, and

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naphthalene in the gaseous phase and acenaphthene, anthracene, benzo[b]fluoranthene, and

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fluoranthene in the particulate phase in the breathing zone of wildland firefighters in Yosemite

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National Park.21 During prescribed burning of wood piles, Robinson et al. detected only gas-

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phase naphthalene, phenanthrene, and fluorene in personal air samples.22

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The objective of our study was to characterize exposures to PAHs of wildland firefighters

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suppressing wildland fires and conducting prescribed fires.

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Methods

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Study Participants and Location. The study population consisted of members of an

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Interagency Hotshot Crew (IHC), a Wildland Fire Engine Crew, and participants of a prescribed

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fire training event. Prescribed fire samples were collected in October 2014 and 2015 at two

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annual trainings hosted by the Mid-Klamath Watershed Council and The Nature Conservancy in

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the Klamath River region of northern California. All prescribed burns conducted were broadcast

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burns, where fire was applied directly to a predetermined area and is confined to that space.

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Wildland fire samples were collected at two fires, during day shifts of the Willow Fire from July

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26, 2015 - August 1, 2015 and during night shifts at the Rough Fire from September 1 - 5, 2015.

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The Willow Fire burned 2,307 ha (5,702 ac) in the Sierra National Forest.23 The Rough Fire

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burned over 61,000 ha (151,623 ac) in Kings Canyon National Park, Sequoia National Forest,

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Sierra National Forest, and adjoining state and private lands.24

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Wildland firefighters perform a variety of job tasks to suppress fires; these include operating a

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fire engine, fire line construction, holding, patrol, staging, mop-up, and firing operations. Engine

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operators work as a part of an engine crew and operate the diesel pumps that provide water to

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crews working near the fire. Fire line construction involves clearing vegetation and digging or

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scrapping down to mineral soil with hand tools to create a break in fuels to stop the spread of a

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fire. Crew members engaged in holding walk along the active fire and check that it has not

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crossed the fire line; if it has, suppression tactics are used to control the fire, while patrol

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involves inspecting an inactive fire perimeter. Often crews will wait at a location near the fire to

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hear where they have been assigned (staging). After the fire has been controlled, crews will

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extinguish any burning material by digging out the burning material or applying water to stop

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any smoldering material that may re-ignite a fire (mop-up). Ignition of fuels with torches filled

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with a 3:2 diesel/unleaded gasoline mixture is used at prescribed fires, and often in wildland fire

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suppression (firing). Additionally, when working on a large wildland fire, firefighters will sleep

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and eat at a base camp that provides logistical support (incident command base) and is situated

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close to the fire. Firefighters working at the Willow Fire performed the following job tasks:

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engine operator, fire line construction, holding, mop-up and firing. At the Rough Fire,

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firefighters performed the following job tasks: engine operator, holding, patrol, and staging.

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The study protocol was approved by the UC Berkeley Committee for Protection of Human

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Subjects and informed consent was obtained from each study participant.

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Exposure Assessment. Gas-phase and particle-bound PAH samples were collected using a

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XAD2 sorbent tube and a 37mm closed face cassette (SKC, Inc. Eighty Four, PA) with two

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quartz fiber filters (PallFlex Tissuquartz) in series impregnated with XAD4, respectively.25–27 Air

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was drawn through the cassettes using SKC Airchek 52 sampling pumps (SKC, Inc. Eighty Four,

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PA) at 1.5 – 2 L/min and the XAD2 sorbent tubes using PAS-500 Micro Air Samplers (Spectrex,

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Redwood City, Ca) sampled at 0.2 L/min. To verify flow rates, pumps were calibrated before

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and after each sampling event with representative sampling media using a Defender 510 DryCal

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(Mesa Labs, Inc. Butler, NJ).

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Sampling pumps were placed inside the pack and cassettes and XAD2 sorbent tubes were placed

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as close to the breathing zone as possible, on the shoulder straps of each firefighter’s gear pack,

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to prevent interference with work tasks. These packs contain emergency fire shelters, food, and

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water and are required to be worn while firefighters are working on an active fire. Depending on

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work schedule and location, pumps were started when crews left the incident command base

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(ICB) or when they arrived to their work location for the day on the wildland or prescribed fire.

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At the end of each shift, participants self-reported the job duty they performed during the

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majority of their work shift and rated the smoke conditions they experienced (none, mild,

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moderate, severe).7 Participants were also asked if they used a chainsaw during the work shift,

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which could potentially add to their PAH exposure.

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Laboratory Analysis and Quality Control. Prior to coating with XAD4, filters were baked at

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800 °C for three hours to remove contaminants. Coated filters were stored in baked amber jars

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until sampling. Filters were extracted by sonication in dichloromethane followed by filtration

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under vacuum. XAD2 sorbent tubes were extracted by shaking in dichloromethane (2 mL) for

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one hour. All analyses were performed on a gas chromatograph (Hewlett Packard model 6890)

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equipped with a 30 m (50%-Phenyl) methylpolysiloxane-fused silica capillary column and a

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5972 Mass Selective Detector operated in selected ion-monitoring mode. XAD2 sorbent tubes

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were analyzed for naphthalene (NAP). Filters were analyzed for 17 PAHs: acenaphthylene

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(ACY), acenaphthene (ACE), fluorene (FLU), phenanthrene (PHE), anthracene (ANT),

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fluoranthene (FLT), pyrene (PYR), and retene (RET), benz[a]anthracene (BAA), chrysene

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(CHR), benzo[b]fluoranthene (BBF), benzo[k]fluoranthene (BKF), benzo[a]pyrene (BAP),

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indeno[1,2,3-cd]pyrene (ICP), dibenz[a,h]anthracene (DBA), and benzo[ghi]perylene (BGP).

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Sorbent tubes and filters were tested for adequate recoveries with spiked samples for the full

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extraction and analysis procedure. The spiked recovery of naphthalene on sorbent tube was

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114%. The mean spiked recovery for the 17 PAH measured by filter was 96%, with individual

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PAH recoveries ranging from 78% to 127%. PAH concentrations of individual PAHs measured

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by sorbent tubes and filters were summed for statistical analysis. However, some personal

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samples consisted of only a filter sample and were not paired with a sorbent tube, so NAP

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concentrations were not measured.

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During the first analyses of a set of samples, selected XAD sorbent tubes and filters were

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checked for breakthrough. If there was evidence of breakthrough, the front and back sections of

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all filters or tubes from that sampling event were analyzed separately and the amount of

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breakthrough was quantified. We determined breakthrough by whether the amount of each

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analyte in the back filter or tube was greater than 25% of the total amount of analyte detected in

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both the front and back filters or sections of sorbent tubes. Field blanks for filter cassettes (n=2-

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4) and XAD sorbent tubes (n=2-4) were collected at each sampling event to examine

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contamination of sampling media in the field or during transport. All samples were adjusted for

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blank concentrations by media type and event. Blank correction for the 16 PAHs on the filters

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was generally low with all blank mass less than 16 ng, except for fluorene at the Rough Fire. The

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blank correction for fluorene on filters at the Rough Fire was high – 37 ng – but the

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concentrations at the Rough Fire were, on average, a magnitude higher. The blank correction

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for naphthalene collected by sorbent tubes was 7 to 18 ng. The LQ was determined for each PAH

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and day of laboratory analysis. The average LQ was 2.6 ng (typically 3.7 ng m-3) with a range of

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1.0 – 5.3 ng (1.71 – 7.14 ng m3). To perform statistical analyses, samples that were less than the

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LQ were assigned the LQ divided by 2.

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Statistical Methods. Characteristics of participants and samples collected from participants are

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presented in Table 1. PAHs were summed to create summary measures by the number of fused

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benzene rings. We created summary metrics for low molecular weight PAHs (Σ3 ring PAH),

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medium molecular weight PAHs (Σ4 ring PAH), high molecular weight PAHs (Σ5-6 ring PAH),

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and a total PAH metric of 3 through six ring PAHs, composed of 15 PAHs (Σ15 PAH). These

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summary measures did not include naphthalene or retene. The geometric mean (GM) and

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geometric standard distribution (GSD) were calculated for each PAH analyte and summary PAH

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metrics. We used SAS 9.4 (SAS Institute Inc. Cary, NC) and R v. 3.1.0 (R Foundation, Vienna,

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Austria) for all data cleaning, calculations, and graphical processing.

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Results

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Twenty-five wildland firefighters participated in personal air sampling; 15 were members of an

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IHC, 6 were members of an engine crew and 4 were members of a prescribed burn crew (Table

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1). Participants working at wildland fires were primarily males (85%) and worked the day shift

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(71%), while approximately half of the participants working at prescribed fires were male. Only

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three participants (10%) at wildland fires used a chainsaw while working. All participants were

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non-smokers. When asked to rate their smoke exposure, participants at wildland fire and

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prescribed fires mostly rated their smoke exposure during their work shift as mild and moderate.

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A small subset of wildland fire participants (14%) rated their smoke exposure as severe.

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The summary metrics of the PAH concentrations are reported in Table 2. Arithmetic mean and

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standard deviation for each sampling event can be found in the Supplemental Information (Table

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S.2). Table S.1 presents the sampling time and number of samples collected for each of personal

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exposure sampling events. Distribution of each PAH analyte and Σ15 PAH exposures by job

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tasks performed at prescribed fire and wildland fires are presented in Figures 1 and 2,

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respectively

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Prescribed Fire. Participants at prescribed fires reported performing firing, holding, and mop-up

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tasks (N=3 for each task) and also twice performing a combination firing and holding tasks.

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Personal job task samples had mean sampling times that ranged from 340 to 439 minutes (Table

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S.2).

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The PAH analyses of samples collected at prescribed fires revealed that lower molecular weight

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PAHs were detected more frequently and at higher concentrations compared to higher molecular

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weight PAHs. With the exception of anthracene, all 2 and 3-ring PAHs were detected in at least

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73% of all the samples. Detection of 4, 5, and 6-ring PAHs ranged from 33% to 73% of all

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samples collected. The GM for Σ3 ring PAH was 135 ng m-3 and contributed the most to the Σ15

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PAH GM of 265 ng m-3 compared to the GM for Σ4 ring PAH (54 ng m-3) and Σ5-6 ring PAH

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(25 ng m-3). The GMs of the highest concentration of PAHs measured were 669 ng m-3, 76 ng m-

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, and 50 ng m-3 for NAP, RET, and PHE, respectively. NAP concentrations ranged from less

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than 4 ng m-3 to 5073 ng m-3 and NAP was consistently was the highest measured PAH. NAP

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GM concentration was 2.5 times higher than the Σ15 PAH GM.

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PAH exposures measured at prescribed fires were found to vary by job task (Figure 1).

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Firefighters performing firing and holding during the same shift at prescribed fires were

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consistently exposed to significantly higher levels of PAHs compared to those doing a single task

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-- firing, holding, or mop-up. Firing had higher concentrations of ACY, ACE, and FLT

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compared to holding or mop-up. Firefighters performing mop-up had higher distributions of

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PHE, FLU, and RET concentrations. Across all job categories, naphthalene was the highest

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measured PAH with a median ranging from 304 ng m-3 for holding to 2918 ng m-3 for

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firing/holding. When comparing Σ15 PAH across job task, firing/holding had the highest

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median, followed by firing, holding, and mop-up.

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Wildland Fire. A total of 28 XAD4-coated filters and 21 XAD-2 sorbent tubes were collected as

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personal samples at wildland fires. Participants sampled at wildland fires mostly constructed fire

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line (8) and performed mop-up (8) and holding (5). Personal job task samples had mean

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sampling times that ranged from 186 to 778 minutes (Table S.1). PAHs with 2, 3 or 4 fused

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benzene rings were consistently detected above the LQ, with the percent detected ranging from

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75% to 100%. PAHs with 5 or 6 fused benzene rings were detected in only 29% to 75% of

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samples collected. Breakthrough on filters was detected for ACY, ACE, FLU, PHE, ANT, FLT,

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(all 3-ring PAHs) and PYR (a 4-ring PAH), which indicates that those samples could have been

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an underestimate of the true concentration.

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During wildland firefighting, Σ15 PAH mean concentration was 586 ng m-3 and ranged from 88

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ng m-3 to 7925 ng m-3. When comparing GM concentration by molecular weight, NAP was

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highest 3189 ng m-3 followed by Σ3 ring PAHs (429 ng m-3), Σ4 ring PAH (90 ng m-3) and Σ5-6

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ring PAH (38 ng m-3) molecular weight PAHs. NAP and RET had the highest GM concentration

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of all PAHs detected, 3189 ng m-3 and 3,641 ng m-3, respectively. RET was the highest single

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measured PAH (24,562 ng m-3). PHE was also detected at elevated concentrations (GM = 210 ng

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m-3) followed by FLU (GM = 77 ng m-3) and ACY (GM = 72 ng m-3).

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Firefighters were exposed to different concentrations of PAHs based on their job task (Figure 2).

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Firefighters performing holding, patrol, and staging tasks often had higher measured

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concentrations of PAHs compared to firefighters performing fire line construction, firing, and

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mop-up tasks. NAP was consistently the highest measured PAH across all job tasks, and had a

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median concentration of 8358 ng m-3 and 3946 ng m-3 for holding and patrol tasks respectively

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and a measured concentration of 6258 ng m-3 staging. Firefighters performing holding and patrol

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tasks were exposed to elevated levels of benzo[a]pyrene compared to other job tasks. When

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compared by job task, holding had the highest median for Σ15 PAH of 322 ng m-3, ranging from

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182 to 7935 ng m-3 . Not including NAP and RET concentrations, firefighters performing engine

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operator, holding, mop-up, patrol, and staging duties were predominantly exposed to PHE.

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Firefighters performing firing operations were predominately exposed to FLU when compared to

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the other 15 PAHs. Across all job tasks, the 3-ring PAHs had higher concentrations compared to

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the 4-ring and 5-6 ring PAHs.

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Discussion

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Our study objectives were to quantify personal exposures to PAHs of firefighters exposed to

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smoke at wildland and prescribed fires as well as off-duty at base camps (“staging”). Generally,

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firefighters working at both wildland and prescribed fires categorized their smoke exposure as

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mild to moderate. We detected measurable concentrations of 17 PAHs in personal samples on

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firefighters at prescribed and wildland fires. NAP, RET, and PHE were consistently the highest

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measured PAHs at all sampling scenarios. Lower molecular weight PAHs (Σ3ring PAH) were

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2.5 to 11 times higher compared to Σ4 and Σ5-6 ring PAHs and contributed the most mass to the

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Σ15 PAH metric at wildland and prescribed fires.

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Our measured concentrations of PAHs were consistent with those reported by Materna et al. for

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12 particle-phase PAHs (4 – 257 ng m-3).18,28 However, the PAH concentrations measured by

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Reh et al. in Yosemite National Park (range 600 – 35,900 ng m-3) were higher than our measured

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GMs and were closer to our measured maximum concentrations. Participants in that study were

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from two Type 1 crews (N=5) and performed firing, holding, and mop-up tasks. Robinson et al.

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evaluated PAH exposure at prescribed burning of piles, where debris is piled together and

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burned, and were able to detect only NAP, FLU, and PHE concentrations between

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