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VOC emissions from asphalt pavement and health risks to construction workers
Journal of Cleaner Production xxx (xxxx) xxx
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VOC emissions from asphalt pavement and health risks to construction workers Peng Cui a, b, Gabriella Schito b, Qingbin Cui b, * a b
Southeast University, China University of Maryland, United States
a r t i c l e i n f o
a b s t r a c t
Article history: Received 26 January 2019 Received in revised form 20 September 2019 Accepted 5 October 2019 Available online xxx
Hot Mix Asphalt (HMA) is used in the construction of highway roads, parking lots and other pavement repairs in the US and worldwide. During asphalt pavement installation, a large amount of asphalt fume containing volatile organic compounds (VOCs) is emitted, causing potential health risks to construction workers. The field data investigation in this paper reports the concentration of VOCs around the workers on site using the Photo Ionization Detection (PID) device. Additionally, this paper presents a health risk evaluation model based on the Monte Carlo simulation to assess the carcinogenic and non-carcinogenic risks of workers during pavement construction. More specifically, distribution and sensitivity analyses illustrate the factors that pose the greatest health risks caused by certain VOCs. The study calls for better health risk controls by targeting the emission sources, propagating pathways, and individual receptors of the VOCs to protect workers’ health during pavement construction. This paper contributes to the knowledge of VOCs generated from HMA and the potential health risks to construction workers, as well as suggests the implementation of new requirements for pavement construction codes and safety regulations. © 2019 Elsevier Ltd. All rights reserved.
Handling Editor: Zhen Leng Keywords: VOCs Asphalt pavement Health risk Construction Monte Carlo
1. Introduction Volatile organic compounds (VOCs) are dangerous air pollutants due to their toxic and carcinogenic effects on human health (Lin et al., 2016). They are also of concern in influencing the formation of tropospheric ozone and other oxidants (Yurdakul et al., 2018). Authorities have classified VOCs according to several factors including their compositions, boiling points and ease of emittance (USEPA, 2017). One of the predominant sources of VOC emissions is the natural biological compound, Isoprene, produced by vegetation. However, other significantly harmful VOC emissions come from anthropogenic sources, including but not limited to fuel production, household products, building materials, and furnishings. To control the VOC emissions coming from human activities, countries worldwide have designated regulatory agencies to design testing methods for VOC emissions, including determining emission limits, developing new technologies, and monitoring and controlling measures. In the United States, for example, the Environmental Protection Agency (EPA) regulates both indoor and outdoor VOC
* Corresponding author. E-mail address: [email protected] (Q. Cui).
emissions, and each state establishes its own VOC emission regulations, caps, and source tracking. In China, the Ministry of Environmental Protection has set in place numerous standards, such as integrated emission standards for air pollutants, emission standard of pollutants for the caustic alkali and polyvinyl chloride industries (MEEC, 2016). In Europe, the VOC Solvents Emissions Directive is the main policy instrument to reduce VOC emissions (Liebscher, 2000). The regulation of VOCs in the construction industry is primarily concentrated on the indoor rather than outdoor environment, although pavement construction is a major source of concern. More than 2.5 million miles of pavement in the United States contribute to VOCs, which can be emitted during the production, transportation, construction, and/or maintenance of asphalt. The most commonly used asphalt for pavement construction is hot mix asphalt (HMA), which combines approximately 95% stone, sand, or gravel held together with asphalt cement. The pavement construction process begins, first, with producing HMA in an asphalt plant by heating the binder and drying the aggregate from it prior to mixing. Then, the resulting HMA is loaded into trucks and transported to the paving site, where it is dispensed into hoppers located at the front of paving machines. The HMA is sufficiently re-
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Please cite this article as: Cui, P et al., VOC emissions from asphalt pavement and health risks to construction workers, Journal of Cleaner Production, https://doi.org/10.1016/j.jclepro.2019.118757
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heated to about 150 C in the paver before it is placed, and then compacted using a heavy roller. Traffic is generally permitted on the pavement as soon as the pavement has cooled. Like nicotine in cigarette smoke, VOCs are contained in asphalt fume. As asphalt smoke escapes in the air, it is inhaled by human body or adhered to clothing, skin or eyes through fume condensates, which results in health hazards. Scholars have accumulated many research on asphalt fume, of which the most significant one is the Health Effects of Occupational Exposure to Asphalt (hereafter the Report) conducted by National Institute for Occupational Safety and Health (NIOSH) in 1977 (Butler et al., 2000). Research on pavement asphalt can be divided into three steps: first, sampling on site through three strategies, including total particulate, BenzeneSoluble Particulate fraction, and PAHs; then, analyzing the components of sample in lab; finally, discussing the human health effect through literature review on human and animal experiments. The findings in the Report mainly focused on three toxic and harmful components of pavement asphalt fume, which are polycyclic aromatic hydrocarbons (PAH), polycyclic aromatic compounds (PAC) and VOCs. However, the study of VOCs in the Report has some disadvantages: 1) Due to the timeliness, the negative effects of some pollutants, especially them of VOCs on human health were not verified at that time. 2) The sample collection method used in the Report cannot obtain real-time data. In fact, the VOCs concentration are changing all the time at different location and different moment throughout the paving process, the maximum, minimum and average values of VOCs are unable to measured.3) The Report did not distinguish the sampling location, category of machines, as well as the type of workers, resulting an insufficient precision. 4) The report only measured the total volume of VOCs, but does not analyze the specific components of VOCs in asphalt fume and their impact on human health, respectively. Early studies on VOCs emitted from HMA pavement have focused on the impact that catalytic oxidation technologies, usage of additive products, and new asphalt application have on the amount and characteristics of VOC emissions (Kamal et al., 2016; Wang et al., 2018; Li et al., 2017). Scholars have also compared the VOCs emissions between warm mix asphalt (WMA) and HMA (del Carmen Rubio et al., 2013), in addition to examining major components of VOCs from asphalt pavement (Iwuoha and Udoh, 2016; Lange and Stroup-Gardiner, 2005; Myers et al., 2000). Research efforts have further expanded to establish a nationwide database and a general coefficient method to estimate the total annual VOC emissions from asphalt plants (USEPA, 2000, 2017). All available measurement methods above are selective in what they can measure and quantify accurately, so the challenge remains of measuring all VOCs directly. Two kinds of measurement methods are shown in the previous studies to test the total mixed VOCs and classified VOCs, respectively. Flame Ionization Detection (FID) and Photo Ionization Detection (PID) methods are used to test the total VOCs (Paul Wilford, 2006), while the Gas Chromatograph/Mass Spectrometer (GC/MS) or ambient volatile organic canister sampler (AVOCS) are used to test the classified VOCs (Lange and StroupGardiner, 2005). VOCs usually contain tens or hundreds of components. According to the literature reviews to date, inhalation of VOCs can irritate the eyes, nose and throat, cause difficulty breathing, damage organs, and even contribute to some cancers (Celebi and Vardar, 2008). Previous studies have tried to determine the influence of VOCs on human health from various perspectives, including indoor air quality (Sarigiannis et al., 2011), road markings paint (Burghardt and Pashkevich, 2018), municipal solid waste composting (Nie et al., 2018), and solvents in wooden furniture manufacturing (Tong et al., 2019). Few studies have focused on VOCs generated in asphalt pavement construction and their health
effects on workers (Chong et al., 2014). With regards to HMA pavement construction in the US, workers and operators have little knowledge or pay little attention to the health hazards of VOCs. At the HMA construction site, many VOCs and asphalt fume mixed with VOCs together are volatilized in the air. This can happen during various stages of asphalt, such as dumping, paving, stirring, and compaction, which poses a great risk to the worker’s health. It is customary for the professionals to only wear work clothes and shoes, leaving them exposed to VOCs. Few workers have their own gloves and sunhats, but rarely wear masks, especially the VOC-specific masks. To determine the concentration and pathway of VOCs and their health effects on construction workers, the qualified research team at the University of Maryland, College Park conducted in-situ testing of VOCs from asphalt pavement construction in the Washington Metropolitan area. The team applied the PID method to capture VOCs produced by the machines and materials on the construction site. Following a research framework shown in Fig. 1, this paper presents the health risk exposure of pavement workers to VOC emissions. The paper develops a probability model based on the Monte Carlo simulation and workers’ construction behavior. The results call for better worker protection during pavement construction, as well as improved construction method and materials. 2. Methods 2.1. Detecting VOCs with the PID method The PID method uses an ultraviolet (UV) light source to break down VOCs in the air into positive and negative ions. Then, the charge of the ionized gas is detected or measured as the concentration of VOCs as shown in Fig. 2. The PID device used in this study has a photon energy of 10.6 eV and can detect any VOCs with its photon energy less than 10.6eV. To quantify other air pollutants, it is necessary to calibrate the PID to different compounds using isobutylene by default (RAE Systems, 2014). The calibration is implemented through the mix correction factor CFmix defined in the following equation (1).
X1 X X X CFmix ¼ 1 þ 2 þ 3 þ… i CF1 CF2 CF3 CFi
(1)
Where i represents the major types of VOCs generated from HMA (Myers et al., 2000), Xi is the percentage of VOC i. CFi is the correction factor for VOC i, which can be acquired from the Technical Note TN-106 (RAE Systems, 2014) as shown in Table 1. CFmix is calculated at 0.55. Therefore, a reading of 100 ppm on the device would then correspond to 55 ppm of the total mixture. 2.2. The measurement boundary During the pavement construction process, VOCs are generated from two sources: 1) fugitive emissions from the asphalt itself, such as mixing and storage volatilization, truck loading and transport volatilization, paver loading and paving volatilization, operation and maintenance volatilization, and 2) ducted emissions from the energy consumption of machinery and equipment, including the electricity consumption of mixing equipment, fuel consumption of transportation vehicles, and fuel consumption of paver, roller and other construction equipment. The process of asphalt pavement construction can be divided into three steps: milling, paving and rolling. The milling operation starts with the milling machine smashing the existing pavement, pouring the trash into the truck through a conveyor belt, and then
Please cite this article as: Cui, P et al., VOC emissions from asphalt pavement and health risks to construction workers, Journal of Cleaner Production, https://doi.org/10.1016/j.jclepro.2019.118757
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VOC source identification
VOC concentration measurement Driver
Milling Pavement job decomposition
Emission types
Paving
Operator
Affected groups
Rolling
Laborer
Fugitive emissions
Vapor diffusion
Ducted emissions
Mechanism of health risks
Percentage ISF and RfC
Workers’ health risk evaluation Carcinogenic risk
Health risk model establishment
Non-carcinogenic risk Inhalation risk model Monte Carlo simulation
Method used
Wind, temperature, disturbance effects
Sensitivity analysis
Inhalation intake
On-site measurement
Composition HMA Characteristics
3
Measurement method
Photo Ionization Detection
Interview and investigation
Data collection
Previous reports and studies
Fig. 1. The framework of VOCs health risk evaluation in HMA pavement construction.
Table 2 Equipment and labor force needed in each phase. Phase
Equipment
Labor
Milling
Milling machine Trucks (several) Bulldozer Cleaner machine Paver
1 driver 1 driver per 1 driver 1 driver 1 driver, 2 operators, 2-3 Laborer 1 driver per 1 driver per 1 operator
Paving
Rolling
Fig. 2. The working principle of a PID (RAE Systems, 2014).
Table 1 The percentage and correction factor of VOCs generated from HMA. VOCs
Percentage (Xi )
Correction factor (CFi )
Benzene 2-Butanone Cumene Ethylbenzene n-Hexane Toluene m-Xylene p-Xylene o-Xylene
4% 4% 8% 21% 11% 16% 20% 10% 6%
0.47 1 0.54 0.65 4.3 0.45 0.44 0.39 0.45
cleaning the surface with a road sweeper. The paving operation uses a paver as well as loading trucks to lay asphalt concrete. The rolling operation is the final step, wherein compactors roll new pavement several times to make the road firm, hard and smooth. The machine and labor force needed in each phase are shown in Table 2. There were no VOCs from fugitive emissions during the milling
Trucks (several) Rollers (several) Blower
phase. In the rolling phase, the VOC concentration detected was zero, both in the air around the driver and the pavement surface. Given that the detecting range of the PID is 0.1ppme10000 ppm within the temperature range of 20 C to 55 C, a possible explanation for the zero value may be that the concentrations of VOCs nearby above points are less than 0.1 ppm. The VOCs generated from major machines and vehicles used for construction, namely the ducted emissions, were also measured. Due to differences in engine modes, exhaust gas treatment technologies, fuel types and so on, the VOC results from the machinery varied from 0 to 16 ppm. However, the VOC value was zero in the air around drivers and operators of milling machines, trucks, compactors, bulldozers, and cleaner vehicles. For the purposes of this study, the above VOCs that did not directly affect workers’ health were not considered. Therefore, the paving phase was the only operation which was considered in this paper. During this phase, the measured VOCs were mainly generated from two sources: 1) the volatilization of asphalt dumping from the truck into the paver, and 2) the volatilization of asphalt during paving. 2.3. Health risk evaluation There are two methods, deterministic and probabilistic, that are predominantly used for health risk evaluations (Tong et al., 2019). The deterministic method is generally used to evaluate the health effects of a specific pollutant and its concentration. However, under outdoor conditions, the measurement is affected by so many of the influential factors mentioned above that will result in nonuniformity of the results. Due to the uncertainty of inhalation intake, working duration, VOC amount, as well as some other parameters, this paper applies the Monte Carlo simulation for risk evaluation. The Monte Carlo simulation is one of the probabilistic
Please cite this article as: Cui, P et al., VOC emissions from asphalt pavement and health risks to construction workers, Journal of Cleaner Production, https://doi.org/10.1016/j.jclepro.2019.118757
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methods for risk evaluations which uses a probability distribution in statistics to process the input data. After thousands of times of the iteration, the generated results are more realistic and reliable within a certain confidence interval (Yamada et al., 1998). According to the risk impact results, health risks can be divided into either being carcinogenic or non-carcinogenic (Lerner et al., 2012), as shown in Formulas (2) and (3), respectively.
CRi ¼ CDIi ISFi CRi ðWÞ ¼
(2)
X CDIi PSj ISFi
(3)
HQi ¼ Ci =RfCi CDIi ¼
(4)
Ci IR ED EF EL BW AL
(5)
Where CRi denotes the carcinogenic risk of VOC i. CDIi denotes the chronic daily intake of VOC i (mg/kg/day). ISFi is the inhalation slope factor of VOC i (kg$day/mg). CRi ðWÞ denotes the carcinogenic risk of VOC i of a certain worker (kg$day/mg). PSj is the probability of a worker standing straight (j ¼ 1) or bending (j ¼ 2) in the job, namely, the ratio of stay between different WBZs. HQi denotes the hazard quotient, which is the ratio of the concentration of VOC i over a specified period of time to its RfCi derived at the same time. A ratio larger than unity suggests that the concentration of VOC i is high enough to cause chronic non-carcinogenic effects. RfCi is the reference concentration for VOC i (mg/m3). Ci is the concentration of VOC i (mg/m3). IR is the inhalation rate (m3/h). ED is the exposure duration (h/day). EF is the exposure frequency (day/year). EL is the exposure length (year). BW is the body weight (kg). AL is the average lifespan (day). A lifetime of 70 years is typically used in early studies to quantify cancer risk (Li et al., 2009; Yu et al., 2017; Huang et al., 2016; Guo et al., 2004). The ISFi and RfCi of VOCs are shown in Table 3. 3. Case study 3.1. Basic information This study investigated 10 asphalt pavement-resurfacing projects in the Washington D.C. area, performed by Chamberlain contractors Inc. Table 4 summarizes the construction details and conditions. All 10 projects involved the installation of HMA. 3.2. Data collection As detailed previously in Table 2, during the paving phase, 5e6 workers (excluding loading trucks and drivers) were arranged around a paver. Among them, 1 driver was responsible for controlling the forward direction, speed and asphalt dumping of the paver; 2 operators standing behind the paver oversaw controlling the width and thickness of the pavement; and another 2e3 laborers
Table 3 The ISFi and RfCi of VOCs (USEPA, 2010). VOC
CAS Number
ISF (kg$d/mg)
RfC (mg/m3)
Benzene 2-Butanone Cumene Ethylbenzene n-Hexane Toluene m, o, p-Xylene
71432 78933 98828 100414 110543 108883 1330207
0.027 N.A. N.A. N.A. N.A. N.A. N.A.
0.03 5 0.4 1 0.7 5 0.1
who were walking around the paver at the middle and back, were responsible for road surface roughness and roadside mend. Thus, there were seven locations of workers’ breathing zones (WBZs) around the paver that were chosen as the measuring locations including A, B, B0 , C, C0 , D, and D0 , as shown in Fig. 3. The WBZs are defined as the area near the mouth and nose of a worker (Chong et al., 2014). Locations B0 , C0 and D0 were set because the workers often need to bend down to check and clean the mixture. The PID device was placed at the above 7 locations for 10 s each time moving with the workers. To correct for a measurement error, the VOC concentrations during the 5th to 15th second were counted. The maximum, average and standard deviations at each position are recorded in Table 5. The maximum value at each measured location was chosen as the VOC concentration for the health risk analysis. Noting: the measured results are consistent with the values conducted in an authoritative research report (Butler et al., 2000). As seen in Table 5, the concentration of VOCs around the asphalt lay-down ports, namely the WBZ of the laborers are the largest at the C0 and D0 positions where they often need to bend down. In the 10 on-site measurements, a maximum value of 33.86 mg/m3 was recorded at the C0 position, and it was found to be as high as 139.97 mg/m3 at the D0 position. Furthermore, the VOC concentration at position A ranged from 0 to 18.06 mg/m3. The concentration around B varied from 0 to 6.77 mg/m3, and at B0 it varied from 0 to 20.32 mg/m3. 3.3. Influencing factor on site Often, asphalt fume is seen diffusing on the construction site, as shown in Fig. 4. The fume represents the VOCs emitting from asphalt into the air during pavement construction. The fume is also referenced as “vapor” in some studies, which propose that the workers who are exposed to the fumes involved in asphalt paving operations experienced fewer respiratory tract symptoms (e.g., coughing, wheezing, and shortness of breath) and pulmonary function changes (Gamble et al., 1999). Construction workers usually ignore potential health risk from VOCs in the outdoor environment, where many factors, e.g. wind, temperature, and humidity, can affect the inhalation intake. These factors are discussed below. C Wind To investigate the impact of wind on the fume, the following assumptions were made. The angle of a worker exposed to the fume can be determined by the wind direction, construction direction and the relative location of the worker to the fume source in Table 4 and Fig. 3. Assuming that the fume spreads in a fan-shaped manner along the wind direction, then there are five kinds of exposed areas including towards (P1), diagonally towards (P2), aside (P3), backwards (P4) and above (P5) the fume, as shown in Fig. 5. Under the windless condition, assuming the fume or spreads evenly through the diffusion effect, then the direction of exposure is the same as P1. If the wind is directed towards the worker, the VOC concentration of WBZs will become very large, such as that at location C and C0 in Case 5. Conversely, if the wind blows opposite to a worker, the concentration value will significantly reduce, even to zero, such as that at location B in Case 3 and 4, and at location C and C0 in Case 10. Additionally, the asphalt fume gradually dissipates with increasing distance and duration time. Based on the study, the VOC concentration would usually reduce to zero after the fume appeared for several seconds. Therefore, the wind speed was a key factor increasing the speed of the fume dropping to zero. For example, due to the strong wind on site, the fume dissipated faster
Please cite this article as: Cui, P et al., VOC emissions from asphalt pavement and health risks to construction workers, Journal of Cleaner Production, https://doi.org/10.1016/j.jclepro.2019.118757
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Table 4 Project cases summary. Case
Location
Temperature
Wind speed
Wind direction
Paving direction
Humidity
1 2 3 4 5 6 7 8 9 10
Central Park Plaza 1420 silver Parkway Fredericksburg VA Lighthouse 11932 Twinlakes Dr Beltsville MD Brighten 3 West Side Ave Gaithersburg MD 10 Riverview Ct Laurel MD Casino Circle Silver Spring MD Iron Bridge 10611 Iron Bridge Rd Jessup MD Kathrine Thomas 9975 Medical Center Dr Rockville MD Patridge Courts 10376 Failkner Ridge Circle Columbia MD 750 Main Street Reisterstown MD East Village 20302 String Fellow Ct Montgomery Village MD
28 C 21 C 23 C 32 C 26 C 27 C 26 C 22 C 28 C 29 C
2.68 m/s 2.24 m/s 1.79 m/s 3.58 m/s 0.45 m/s 0.89 m/s 4.02 m/s 0 3.13 m/s 2.24 m/s
E SW N W NW W N e SW NW
S NW NE W N N E SE NE NW
63% 97% 93% 57% 72% 71% 46% 63% 56% 69%
Fig. 3. Locations of workers’ breathing zones (WBZs).
Table 5 The VOC concentration at WBZs (mg/m3). Worker title
Position
Case No.
1
2
3
4
5
6
7
8
9
10
Driver
A
Operator
B
max mean SD max mean SD max mean SD max mean SD max mean SD max mean SD max mean SD
9.03 5.42 2.89 0 0 0 6.77 3.16 1.81 4.52 2.48 1.88 2.26 13.77 9.65 27.09 1.13 1.13 27.09 19.19 5.99
6.77 2.48 2.13 0 0 0 2.26 0.9 1.11 0 0 0 15.8 14.67 7.09 24.83 7.68 4.42 54.18 29.35 17.66
0 0 0 4.52 1.35 1.81 9.03 4.97 3.32 42.89 24.38 11.77 33.86 71.79 22.95 101.59 16.03 10.17 139.97 81.27 38.33
2.26 1.13 1.13 6.77 2.48 2.36 20.32 9.93 8.28 13.55 5.87 3.8 24.83 30.25 16.96 51.92 11.96 6.85 90.3 50.12 26.9
4.52 1.81 1.97 2.26 1.35 1.11 2.26 0.9 1.11 6.77 2.26 2.26 11.29 16.03 8.94 33.86 7.9 4.43 47.41 22.58 15.8
0 0 0 0 0 0 4.52 2.48 1.88 2.26 1.58 1.03 2.26 2.26 2.26 6.77 1.35 1.11 18.06 7.22 4.6
4.52 2.48 1.58 0 0 0 2.26 1.13 1.13 2.26 1.13 1.13 20.32 7.9 3.39 11.29 6.32 7.87 36.12 18.96 8.58
0 0 0 0 0 0 0 0 0 0 0 0 2.26 0 0 0 1.58 1.03 6.77 3.84 1.76
18.06 9.26 4.09 0 0 0 2.26 1.58 1.03 0 0 0 22.58 4.97 3.61 9.03 9.71 8.14 79.01 50.79 22.96
0 0 0 4.52 2.48 1.88 0 0 0 4.52 2.93 1.45 9.03 32.96 13.05 54.18 5.87 2.89 121.91 62.99 29.09
B0
Laborer
C
C0
D
D0
Note: The conversions for VOCs from ppm to mg/m3 in the air are made assuming a pressure of 1 atm and a temperature of 25 C. Convert factor ¼ 0.55 (CFmix ) 0.0409 100.3575 (molecular weight of the mixed VOCs) ¼ 2.258.
Please cite this article as: Cui, P et al., VOC emissions from asphalt pavement and health risks to construction workers, Journal of Cleaner Production, https://doi.org/10.1016/j.jclepro.2019.118757
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P. Cui et al. / Journal of Cleaner Production xxx (xxxx) xxx Table 6 The distribution and parameter set for the factors. Factors Concentration Concentration Concentration Concentration Concentration Concentration Concentration IR ED EF EL BW AL PS $ PS $ Laborer’ PS $ Operator PS $ Operator’
$ $ $ $ $ $ $
A B B0 C C0 D D0
Distributions
Parameters
Normal Normal Normal Normal Normal Normal Normal Triangular Triangular Triangular Normal Normal Constant Uniform Uniform Uniform Uniform
N (5.02, 5.51) N (2.01, 2.48) N (5.52, 5.84) N (8.53, 12.76) N (35.62, 28.45) N (15.8, 10.04) N (68.23, 40.14) T (0.3, 0.84, 1.38) T (3, 4, 5) T (180, 200, 220) N (6, 4) N (77, 8) 70 365 U (0.45, 0.55) U (0.45, 0.55) U (0.65, 0.75) U (0.25, 0.35)
Fig. 4. The asphalt fume emitted during the asphalt pavement job.
C Asphalt fumes in Case 7 than that in other Cases. Conversely, the low speed wind in Case 5 and 6 resulted in the accumulation of the fume. When the fume spread to WBZs, the concentration became larger, which had a great impact on workers’ health. The finding here is consistent with a previous study conducted in Hong Kong (Chong et al., 2014).
When the asphalt is stirred, unloaded from the trucks, crushed, watered, heated or paved, a large amount of asphalt fume will be generated, especially when trucks unload asphalt mixtures into the paver hopper, and when the asphalt is heated and paved on the road by the paver. In these cases, the PID detected a higher value. For example, the concentration at Location A in Case 9 is significantly larger than that in other cases due to the asphalt unloaded from the front truck.
C Asphalt lay-down temperature The lower the temperature of the asphalt, the less VOCs it generates. In theory, the lay-down temperature of asphalt should be consistent for these 10 measurements, because the paver is always set to heat the asphalt to 148.9 C. However, due to restrictions on workers’ operating habits, time control, road conditions, etc., temperature may vary. In Case No. 8, for example, the asphalt had been poured from the truck into the paver hopper, then the workers had a 30-min lunch break, that is, the asphalt remained in the hopper for 30 min. Subsequently, the workers immediately started the machine for road paving, and there was almost no fume on site. Most of the detected values were zero.
3.4. Calculation assumptions Some assumptions were made for the numerical analysis as summarized in Table 6. VOC concentration at each location follows normal distribution with parameters directly from project cases. It should be noted that Case No. 8 was eliminated from the analysis since the workers took several irregular breaks during the construction process. IR was obtained from the EPA, reporting that the average inhalation rate of workers outdoor is 0.84 ± 0.54 m3/h, which follows the triangular distribution (USEPA, 2011). ED came
P3 P2
P4
P5 P1
P4
Wind direction Fume source P2 P4 P3
Fig. 5. The possible areas of the workers standing around the emission source.
Please cite this article as: Cui, P et al., VOC emissions from asphalt pavement and health risks to construction workers, Journal of Cleaner Production, https://doi.org/10.1016/j.jclepro.2019.118757
P. Cui et al. / Journal of Cleaner Production xxx (xxxx) xxx
from an interview with the workers who usually work about 2 h in the morning and 2 h in the afternoon for the asphalt paving job. Thus, the total exposure duration is 4 ± 1 h per day, which follows the triangular distribution. EF was obtained from the interview with the workers. They usually have 15 days of annual leave, and 50 days of winter break. The working rate per week is usually 5 days. Therefore, the total exposure frequency is 200 ± 20 days, which follows the triangular distribution. EL is the length of service of the workers. According to the interview, the average EL was 6 years, which follows the normal distribution. BW was also acquired from the interview with the workers. The average body weight of them is 170lb, which is about 77 kg BW obeys the normal distribution. AL is a constant value of 25550 days. PS was estimated on site during the research, assuming the standing and bending probability for the laborer is 50% each. The probability is 30% standing and 70% bending for the operator. The driver does not need to bend. The PS above obeys the uniform distribution. After the establishment of the evaluation model, the Crystal Ball software was used to simulate. The simulation was set to run 5000 times according to the Monte Carlo sampling with a confidence interval of 95%. The random input, with the probability distribution instead of a single value, makes the evaluation results more scientific and reasonable. 4. Results and implements 4.1. Carcinogenic risk The EPA has classified 2-Butanone, Cumene, Ethylbenzene, nHexane, Toluene, and m-/o-/p-Xylene in Group D, which do not belong to human carcinogenicity. Thus, only the ISF of Benzene is available. This paper analyzed the carcinogenic risks of Benzene to the driver, operators, and the laborers during pavement construction. Benzene has been classified as a known human carcinogen by the EPA. Short-term inhalation exposure to Benzene may cause drowsiness, dizziness, headaches, as well as eye, skin, and
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respiratory tract irritation, and, at high levels, unconsciousness. Long-term exposure to Benzene may cause cancer of the bloodforming organs. According to the EPA estimation, if an individual is exposed continuously to a concentration of Benzene between 1.3 103 and 4.5 103 mg/m3 in the air, then there is a 1/100,000 increased chance of developing cancer (ATSDR, 2007). After 5000 simulations, the normal distribution and the statistics of Benzene carcinogenic risk on the workers are shown in Fig. 6 and Fig. 7. In Fig. 7, the whiskers represent the risk probability of 20% and 90%; the boxes denote the risk probability of 40% and 70%; the solid and dot-dashed lines indicate the median and standard deviation of the probability. Thus, the values in Fig. 7 can be interpreted as follows: for example, the average carcinogenic risk of Benzene on the driver is 0.0007%, and the probability of the risk higher than 0.0034% is 10%. Laborer 2 has the highest risk among the workers affected by Benzene. The average carcinogenic risk is 0.0074%. The probability of the risk higher than 0.0122% is 30%, which is higher than the acceptable cancer risk level (0.01%) in the chemical industry (Li et al., 2007). The risk of Laborer 1 ranked second after Laborer 2. The average carcinogenic risk of Benzene is 0.0038%, followed by the driver and the operator with a probability of 0.0007% and 0.0005%, respectively. The results are in the same order of magnitude as previous studies (Guo et al., 2004; Lerner et al., 2012; Yimrungruang et al., 2008; Li et al., 2009). Aside from Benzene, it is unclear what the carcinogenic mechanisms are for the other VOCs. The actual risk of cancer of all the workers may be greater than what is shown in Fig. 7. Sensitivity analysis was conducted on the cancer risk of the workers, as shown in Fig. 8. The length of work, the concentration of VOCs in WBZs, and inhalation rate were identified to be the three most influential factors. The CR influencing factors of laborers and operators are similar. EL, namely the length of work is the most influential factor, followed by the concentration of VOCs at WBZs. IR and BW also contributed a certain portion of CR, where BW is inversely proportional to CR. Since IR and BW are human attributes,
Fig. 6. Carcinogenic risk of Benzene on the workers.
Please cite this article as: Cui, P et al., VOC emissions from asphalt pavement and health risks to construction workers, Journal of Cleaner Production, https://doi.org/10.1016/j.jclepro.2019.118757
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Laborer 1
Laborer 2
Driver
Operator Carcinogenic risk (10-6)
0
5
10
15
20
40
60
80
120
140
220
Fig. 7. Carcinogenic risk of Benzene to the workers.
Fig. 8. Sensitivity analysis of Benzene carcinogenic risk of workers.
it is difficult to optimize them. The workers’ standing to bending ratio, as well as the working time per day cannot be ignored. For the driver, the most influential factor is the concentration of Benzene at location A, followed by EL, IR, EF, ED, and BW. It is worth mentioning that the concentration of VOCs at location D will also affect the CR. 4.2. Chronic non-carcinogenic risk In this paper, the HQ is used to indicate the harm of noncarcinogenic VOCs to the human body. The calculation for chronic non-carcinogenic risk only relates to the concentration of BWZs, and the value of a location is compared to 1 as mentioned in the Methods section. The value within (0, 1] marked in green means
harmless; (1, 10] marked with yellow represents moderate hazard; the value greater than 10 expressed in red represents serious hazard. Table 7 shows the intermediate value of HQi as normally distributed. Most of the VOCs at location D0 exceed the health standard that makes D0 the most harmful location; the concentrations of m-/o-/p-Xylene in the above seven locations all exceed 1 and even reached 244.79 at location D0 , which is extremely harmful to the human body. Relatively, location A and location B are the two least harmful locations, but individual VOCs such as Benzene and m-/o-/p-Xylene caused adverse effect on the human body. In summary, the laborers near the asphalt dump have the highest chronic health risks, especially taking the superimposed effects of the various pollutants into account. The air near the WBZs of the
Please cite this article as: Cui, P et al., VOC emissions from asphalt pavement and health risks to construction workers, Journal of Cleaner Production, https://doi.org/10.1016/j.jclepro.2019.118757
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Table 7 The Median value of the HQ at seven locations
HQ HQ1 HQ2 HQ3 HQ4 HQ5 HQ6 HQ7 Good
A 6.64
B 2.76
B' 7.50
C 11.20
C' 46.34
0.04 1.00
0.02 0.41
0.04 1.12
0.07 1.68
1.05
0.44
1.18
0.78 0.16
0.33 0.07
0.88 0.18
17.93
7.46
20.24 Moderate
operators is relatively clean, but still half of the VOC concentrations exceeded the safety standard. Only two pollutants in the driver’s concentration exceeded the standard, however, they are high enough to cause health risks to the human body. The EPA has classified these non-carcinogenic VOCs in Group D, not classifiable as to human carcinogenicity (USEPA, 2005). The general introduction of the non-carcinogenic VOCs escaping from asphalt pavement construction is summarized as follows (ATSDR, 2007): Cumene is a skin and eye irritant with depressant action on the central nervous system (CNS). Short-term inhalation exposure to Cumene may cause headaches, dizziness, drowsiness, slight incoordination, and unconsciousness in humans. Ethylbenzene mainly affects the hearing system. Short-term exposure to Ethylbenzene leads to respiratory and neurological system disease, as well as eyes problems. Long-term exposure to Ethylbenzene by inhalation in humans may harm the blood system, liver and kidney. 2-Butanone is also called the Methyl ethyl ketone. Short-term or acute inhalation exposure to 2-Butanone results in irritation to the eyes, nose, and throat. The long-term impact on humans remains unknown. Some serious health effects in animals have seen only at very high levels. m-/o-/p-Xylene are found to have very similar effects on health. Short-term inhalation exposure to Xylenes results in irritation of the eyes, nose, throat, and stomach. Long-term inhalation exposure results primarily in CNS effects, such as headache, dizziness, fatigue, and incoordination. Cardiovascular and kidney diseases have also been reported. Toluene may cause CNS disease under both short-term and long-term exposures with symptoms of fatigue, sleepiness, headaches, and nausea. Studies have reported that short-term inhalation exposure to Toluene may cause CNS dysfunction, attention deficits, and minor craniofacial and limb anomalies in children of pregnant women. Chronic inhalation exposure to Toluene also causes irritation of the upper respiratory tract, eyes, and throat, resulting in dizziness, and headache. n-Hexane influences neurotoxicity. Short-term inhalation exposure of humans to high levels of Hexane may cause dizziness, slight nausea, and headache. Chronic exposure to Hexane could lead to numbness in the extremities, muscular weakness, blurred vision, headache or fatigue.
4.3. Possible implements The analysis suggests an undeniable health risk to pavement construction workers. Such health risks can be reduced through the
D 20.58
D' 90.66
0.28 6.95
0.12 3.09
0.54 13.60
1.76
7.30
3.24
14.28
1.32 0.27
5.46 1.11
2.43 0.49
10.69 2.18
30.23
125.13
55.58
244.79 Serious
implementation of the following measures that target the emission sources, propagating pathways, and individual receptors of the VOCs. C Reducing the asphalt lay-down temperature. Based on the investigation, the asphalt lay-down temperature has a significant impact on the VOC emissions. If the asphalt is left in the truck or hopper for a while, the fume containing VOCs can be effectively reduced. Additionally, WMA, foam asphalt, and other recycled asphalt are installed under much lower temperatures and therefore reduce VOC emissions. For example, WMA can be mixed and paved at a temperature of 90e120 C (Aliha et al., 2017), which is 30e60 C lower than the HMA. C Reducing the asphalt disturbances. Minimizing the chance of mixing and dumping the asphalt, as well as unloading from the truck can prevent the volatilization of fume with VOCs. During the observation, it was found that sometimes the truck unloaded the asphalt on the road directly and the asphalt was transferred to the hopper by a forklift. This process would increase fugitive emissions of VOCs, and thus should be avoided as much as possible C Suppressing the fume propagation. Appropriate water spray can effectively cool down the paved asphalt and suppress the fume. However, if a large amount of water is poured directly onto the hot asphalt, on one hand, it will reduce asphalt strength and viscosity, but on the other hand, much fume will escape and cause the workers to be exposed acutely to VOCs. Therefore, water should be sprayed with high pressure towards the fume. C Changing the fume propagation direction. If possible, choosing a paving direction that is the same as the wind direction will decrease the chance of workers exposed to VOCs. Moreover, setting up a blower next to the paver to blow the asphalt fume containing VOCs away from the workers would be a good way to reduce the health risk. As mentioned above, the concentration of VOCs will gradually decrease over distance and time. C Wearable protection. Based on the investigation, after an individual is exposed to the fume with VOCs, many oil substances will stick to the skin, clothes, eyes, glasses and so on. Given that VOCs not only harm the human bodies by inhalation, but also irritate the skin and eyes, workers are highly encouraged to wear a mask, long clothing, gloves and glasses to protect themselves. C Behavioral approach. The driver, operators, and especially the laborers should exchange their jobs every once in a while, to
Please cite this article as: Cui, P et al., VOC emissions from asphalt pavement and health risks to construction workers, Journal of Cleaner Production, https://doi.org/10.1016/j.jclepro.2019.118757
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avoid long time exposure in the high-concentration VOCs for a certain worker. The above method requires workers to be proficient in each operation of the entire construction process. To reduce the tendency of bending over to contact highconcentration VOCs, workers should use long equipment or new methods to reduce the bending frequency. Construction companies are also obliged to provide their workers with protective measures and training on VOC hazards. 5. Conclusions VOCs are recognized as mixed harmful gases that can place both people and the environment in jeopardy. A considerable number of VOCs are generated during asphalt pavement construction, and present negative effects on workers’ health. Only rarely have there been studies on the carcinogenic and non-carcinogenic risks on these workers, making the health of asphalt workers unprotected by laws or codes. This paper studied the concentration of VOCs obtained by on-site measurements, as well as analyzed the carcinogenic risk and other health effects of different types of VOCs on workers, and made suggestions for improvements going forward. The findings were: 1) During the pavement construction process, VOC emissions generated from the paving job have the greatest impact on the workers’ health; 2) The VOCs escape with the asphalt fume from the asphalt to the air. The fume is influenced by many factors, such as wind speed and direction, asphalt fume, temperature and so on; 3) The concentration of VOCs around the workers varies from 0 to 139.97 mg/m3. The workers who are responsible for the cleaning job of pavement surface beside the paver suffer the biggest risk of cancer, followed by the paver driver and operators. 4) The VOC concentration at workers’ breathing zones, length of work, working postures, and body weight are all key factors to the carcinogenic risk; 5) The results of noncarcinogenic risk show that n-Xylene and Benzene have the highest hazard quotient, and the laborers are affected most during the job; 6) Mitigation measures will help reduce the health risk for the workers including reducing the asphalt temperature and disturbance, controlling the concentration and direction of the fume, and protecting the workers themselves. As the outdoor environment is complex, many factors could potential affect the VOC emissions from pavement construction. These factors include wind, temperature, and humidity, as well as workers’ behavior in construction, e.g. standing position, bending frequency, and inhalation rate. While this paper presents potential health risks of pavement construction due to VOC emissions, more studies are necessary to better understand the actual health impacts. Detailed data should be collected and put in the evaluation model to make more accurate and reliable predictions. The composition and percentage of VOCs generated from asphalt obtained from early studies by the EPA need to be re-examined to fit the construction context. Finally, the VOCs are only a kind of harmful substances in asphalt fume. However, the negative effect of asphalt fume to human health, especially long-term carcinogenic risks, need to take all the harmful substances into account and to take a multi-factor superimposed risk assessment. References Agency for Toxic Substances and Disease Registry, 2007. Toxicological Profile for Benzene (Atlanta, GA). Aliha, M.R.M., Razmi, A., Razavi, M., Mansourian, A., 2017. The influence of natural and synthetic fibers on low temperature mixed mode IþII fracture behavior of warm mix asphalt (WMA) materials. Eng. Fract. Mech. 182, 322e336. https:// doi.org/10.1016/j.engfracmech.2017.06.003. Burghardt, T.E., Pashkevich, A., 2018. Emissions of volatile organic compounds from road marking paints. Atmos. Environ. 193, 153e157. https://doi.org/10.1016/ j.atmosenv.2018.08.065.
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Emission characteristics and health risk assessment of volatile organic compounds produced during municipal solid waste composting. Waste Manag. 79, 188e195. https://doi.org/ 10.1016/j.wasman.2018.07.024. Paul Wilford, 2006. VOC Detection and Measurement Techniques. AWE International. Weymouth, England. RAE Systems, 2014. Technical Note TN-106 (Washington D.C). Sarigiannis, D.A., Karakitsios, S.P., Gotti, A., Liakos, I.L., Katsoyiannis, A., 2011. Exposure to major volatile organic compounds and carbonyls in European indoor environments and associated health risk. Environ. Int. 37, 743e765. https://doi.org/10.1016/j.envint.2011.01.005. Tong, R., Zhang, L., Yang, X., Liu, J., Zhou, P., Li, J., 2019. Emission characteristics and probabilistic health risk of volatile organic compounds from solvents in wooden furniture manufacturing. J. Clean. Prod. 208, 1096e1108. United States Environmental Protection Agency, 2017. 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P. Cui et al. / Journal of Cleaner Production xxx (xxxx) xxx Boltzmann solver vs. Monte Carlo method. Astron. Astrophys. 9, 1e19. Yimrungruang, D., Cheevaporn, V., Boonphakdee, T., Watchalayann, P., Helander, H.F., 2008. Characterization and health risk assessment of volatile organic compounds in gas service station workers. Environ. Asia 2, 21e29. Yu, G., Wei, Y., Cheng, J., Jiang, T., Ling, C., Xu, B., 2017. Health risk assessment and personal exposure to Volatile Organic Compounds (VOCs) in metro carriages d a case study in Shanghai, China. Sci. Total Environ. 574, 1432e1438. https:// doi.org/10.1016/j.scitotenv.2016.08.072. € Dog an, G., Pekey, H., Tuncel, G., 2018. Temporal Yurdakul, S., Civan, M., Kuntasal, O., variations of VOC concentrations in Bursa atmosphere. Atmos. Pollut. Res. 9, 189e206. https://doi.org/10.1016/j.apr.2017.09.004.
Abbreviation List AL: Average Lifespan AVOCS: Ambient Volatile Organic Canister Sampler BW: Body Weight C: Concentration CAS: Chemical Abstracts Service
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CDI: Chronic Daily Intake CF: Correction Factor CR: Carcinogenic Risk ED: Exposure Duration EF: Exposure Frequency EL: Exposure Length EPA: Environmental Protection Agency FID: Flame Ionization Detection GC/MS: Gas Chromatograph/Mass Spectrometer HMA: Hot Mixed Asphalt HQ: Hazard Quotient IR: Inhalation Rate ISF: Inhalation Slope Factor PID: Photo Ionization Detection PS: Probability of Standing Position RfC: Reference Concentration UV: Ultraviolet VOCs: Volatile Organic Compounds WBZs: Workers’ Breathing Zones WMA: Warm Mix Asphalt
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Contents lists available at ScienceDirect
Journal of Cleaner Production journal homepage: www.elsevier.com/locate/jclepro
VOC emissions from asphalt pavement and health risks to construction workers Peng Cui a, b, Gabriella Schito b, Qingbin Cui b, * a b
Southeast University, China University of Maryland, United States
a r t i c l e i n f o
a b s t r a c t
Article history: Received 26 January 2019 Received in revised form 20 September 2019 Accepted 5 October 2019 Available online xxx
Hot Mix Asphalt (HMA) is used in the construction of highway roads, parking lots and other pavement repairs in the US and worldwide. During asphalt pavement installation, a large amount of asphalt fume containing volatile organic compounds (VOCs) is emitted, causing potential health risks to construction workers. The field data investigation in this paper reports the concentration of VOCs around the workers on site using the Photo Ionization Detection (PID) device. Additionally, this paper presents a health risk evaluation model based on the Monte Carlo simulation to assess the carcinogenic and non-carcinogenic risks of workers during pavement construction. More specifically, distribution and sensitivity analyses illustrate the factors that pose the greatest health risks caused by certain VOCs. The study calls for better health risk controls by targeting the emission sources, propagating pathways, and individual receptors of the VOCs to protect workers’ health during pavement construction. This paper contributes to the knowledge of VOCs generated from HMA and the potential health risks to construction workers, as well as suggests the implementation of new requirements for pavement construction codes and safety regulations. © 2019 Elsevier Ltd. All rights reserved.
Handling Editor: Zhen Leng Keywords: VOCs Asphalt pavement Health risk Construction Monte Carlo
1. Introduction Volatile organic compounds (VOCs) are dangerous air pollutants due to their toxic and carcinogenic effects on human health (Lin et al., 2016). They are also of concern in influencing the formation of tropospheric ozone and other oxidants (Yurdakul et al., 2018). Authorities have classified VOCs according to several factors including their compositions, boiling points and ease of emittance (USEPA, 2017). One of the predominant sources of VOC emissions is the natural biological compound, Isoprene, produced by vegetation. However, other significantly harmful VOC emissions come from anthropogenic sources, including but not limited to fuel production, household products, building materials, and furnishings. To control the VOC emissions coming from human activities, countries worldwide have designated regulatory agencies to design testing methods for VOC emissions, including determining emission limits, developing new technologies, and monitoring and controlling measures. In the United States, for example, the Environmental Protection Agency (EPA) regulates both indoor and outdoor VOC
* Corresponding author. E-mail address: [email protected] (Q. Cui).
emissions, and each state establishes its own VOC emission regulations, caps, and source tracking. In China, the Ministry of Environmental Protection has set in place numerous standards, such as integrated emission standards for air pollutants, emission standard of pollutants for the caustic alkali and polyvinyl chloride industries (MEEC, 2016). In Europe, the VOC Solvents Emissions Directive is the main policy instrument to reduce VOC emissions (Liebscher, 2000). The regulation of VOCs in the construction industry is primarily concentrated on the indoor rather than outdoor environment, although pavement construction is a major source of concern. More than 2.5 million miles of pavement in the United States contribute to VOCs, which can be emitted during the production, transportation, construction, and/or maintenance of asphalt. The most commonly used asphalt for pavement construction is hot mix asphalt (HMA), which combines approximately 95% stone, sand, or gravel held together with asphalt cement. The pavement construction process begins, first, with producing HMA in an asphalt plant by heating the binder and drying the aggregate from it prior to mixing. Then, the resulting HMA is loaded into trucks and transported to the paving site, where it is dispensed into hoppers located at the front of paving machines. The HMA is sufficiently re-
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Please cite this article as: Cui, P et al., VOC emissions from asphalt pavement and health risks to construction workers, Journal of Cleaner Production, https://doi.org/10.1016/j.jclepro.2019.118757
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heated to about 150 C in the paver before it is placed, and then compacted using a heavy roller. Traffic is generally permitted on the pavement as soon as the pavement has cooled. Like nicotine in cigarette smoke, VOCs are contained in asphalt fume. As asphalt smoke escapes in the air, it is inhaled by human body or adhered to clothing, skin or eyes through fume condensates, which results in health hazards. Scholars have accumulated many research on asphalt fume, of which the most significant one is the Health Effects of Occupational Exposure to Asphalt (hereafter the Report) conducted by National Institute for Occupational Safety and Health (NIOSH) in 1977 (Butler et al., 2000). Research on pavement asphalt can be divided into three steps: first, sampling on site through three strategies, including total particulate, BenzeneSoluble Particulate fraction, and PAHs; then, analyzing the components of sample in lab; finally, discussing the human health effect through literature review on human and animal experiments. The findings in the Report mainly focused on three toxic and harmful components of pavement asphalt fume, which are polycyclic aromatic hydrocarbons (PAH), polycyclic aromatic compounds (PAC) and VOCs. However, the study of VOCs in the Report has some disadvantages: 1) Due to the timeliness, the negative effects of some pollutants, especially them of VOCs on human health were not verified at that time. 2) The sample collection method used in the Report cannot obtain real-time data. In fact, the VOCs concentration are changing all the time at different location and different moment throughout the paving process, the maximum, minimum and average values of VOCs are unable to measured.3) The Report did not distinguish the sampling location, category of machines, as well as the type of workers, resulting an insufficient precision. 4) The report only measured the total volume of VOCs, but does not analyze the specific components of VOCs in asphalt fume and their impact on human health, respectively. Early studies on VOCs emitted from HMA pavement have focused on the impact that catalytic oxidation technologies, usage of additive products, and new asphalt application have on the amount and characteristics of VOC emissions (Kamal et al., 2016; Wang et al., 2018; Li et al., 2017). Scholars have also compared the VOCs emissions between warm mix asphalt (WMA) and HMA (del Carmen Rubio et al., 2013), in addition to examining major components of VOCs from asphalt pavement (Iwuoha and Udoh, 2016; Lange and Stroup-Gardiner, 2005; Myers et al., 2000). Research efforts have further expanded to establish a nationwide database and a general coefficient method to estimate the total annual VOC emissions from asphalt plants (USEPA, 2000, 2017). All available measurement methods above are selective in what they can measure and quantify accurately, so the challenge remains of measuring all VOCs directly. Two kinds of measurement methods are shown in the previous studies to test the total mixed VOCs and classified VOCs, respectively. Flame Ionization Detection (FID) and Photo Ionization Detection (PID) methods are used to test the total VOCs (Paul Wilford, 2006), while the Gas Chromatograph/Mass Spectrometer (GC/MS) or ambient volatile organic canister sampler (AVOCS) are used to test the classified VOCs (Lange and StroupGardiner, 2005). VOCs usually contain tens or hundreds of components. According to the literature reviews to date, inhalation of VOCs can irritate the eyes, nose and throat, cause difficulty breathing, damage organs, and even contribute to some cancers (Celebi and Vardar, 2008). Previous studies have tried to determine the influence of VOCs on human health from various perspectives, including indoor air quality (Sarigiannis et al., 2011), road markings paint (Burghardt and Pashkevich, 2018), municipal solid waste composting (Nie et al., 2018), and solvents in wooden furniture manufacturing (Tong et al., 2019). Few studies have focused on VOCs generated in asphalt pavement construction and their health
effects on workers (Chong et al., 2014). With regards to HMA pavement construction in the US, workers and operators have little knowledge or pay little attention to the health hazards of VOCs. At the HMA construction site, many VOCs and asphalt fume mixed with VOCs together are volatilized in the air. This can happen during various stages of asphalt, such as dumping, paving, stirring, and compaction, which poses a great risk to the worker’s health. It is customary for the professionals to only wear work clothes and shoes, leaving them exposed to VOCs. Few workers have their own gloves and sunhats, but rarely wear masks, especially the VOC-specific masks. To determine the concentration and pathway of VOCs and their health effects on construction workers, the qualified research team at the University of Maryland, College Park conducted in-situ testing of VOCs from asphalt pavement construction in the Washington Metropolitan area. The team applied the PID method to capture VOCs produced by the machines and materials on the construction site. Following a research framework shown in Fig. 1, this paper presents the health risk exposure of pavement workers to VOC emissions. The paper develops a probability model based on the Monte Carlo simulation and workers’ construction behavior. The results call for better worker protection during pavement construction, as well as improved construction method and materials. 2. Methods 2.1. Detecting VOCs with the PID method The PID method uses an ultraviolet (UV) light source to break down VOCs in the air into positive and negative ions. Then, the charge of the ionized gas is detected or measured as the concentration of VOCs as shown in Fig. 2. The PID device used in this study has a photon energy of 10.6 eV and can detect any VOCs with its photon energy less than 10.6eV. To quantify other air pollutants, it is necessary to calibrate the PID to different compounds using isobutylene by default (RAE Systems, 2014). The calibration is implemented through the mix correction factor CFmix defined in the following equation (1).
X1 X X X CFmix ¼ 1 þ 2 þ 3 þ… i CF1 CF2 CF3 CFi
(1)
Where i represents the major types of VOCs generated from HMA (Myers et al., 2000), Xi is the percentage of VOC i. CFi is the correction factor for VOC i, which can be acquired from the Technical Note TN-106 (RAE Systems, 2014) as shown in Table 1. CFmix is calculated at 0.55. Therefore, a reading of 100 ppm on the device would then correspond to 55 ppm of the total mixture. 2.2. The measurement boundary During the pavement construction process, VOCs are generated from two sources: 1) fugitive emissions from the asphalt itself, such as mixing and storage volatilization, truck loading and transport volatilization, paver loading and paving volatilization, operation and maintenance volatilization, and 2) ducted emissions from the energy consumption of machinery and equipment, including the electricity consumption of mixing equipment, fuel consumption of transportation vehicles, and fuel consumption of paver, roller and other construction equipment. The process of asphalt pavement construction can be divided into three steps: milling, paving and rolling. The milling operation starts with the milling machine smashing the existing pavement, pouring the trash into the truck through a conveyor belt, and then
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VOC source identification
VOC concentration measurement Driver
Milling Pavement job decomposition
Emission types
Paving
Operator
Affected groups
Rolling
Laborer
Fugitive emissions
Vapor diffusion
Ducted emissions
Mechanism of health risks
Percentage ISF and RfC
Workers’ health risk evaluation Carcinogenic risk
Health risk model establishment
Non-carcinogenic risk Inhalation risk model Monte Carlo simulation
Method used
Wind, temperature, disturbance effects
Sensitivity analysis
Inhalation intake
On-site measurement
Composition HMA Characteristics
3
Measurement method
Photo Ionization Detection
Interview and investigation
Data collection
Previous reports and studies
Fig. 1. The framework of VOCs health risk evaluation in HMA pavement construction.
Table 2 Equipment and labor force needed in each phase. Phase
Equipment
Labor
Milling
Milling machine Trucks (several) Bulldozer Cleaner machine Paver
1 driver 1 driver per 1 driver 1 driver 1 driver, 2 operators, 2-3 Laborer 1 driver per 1 driver per 1 operator
Paving
Rolling
Fig. 2. The working principle of a PID (RAE Systems, 2014).
Table 1 The percentage and correction factor of VOCs generated from HMA. VOCs
Percentage (Xi )
Correction factor (CFi )
Benzene 2-Butanone Cumene Ethylbenzene n-Hexane Toluene m-Xylene p-Xylene o-Xylene
4% 4% 8% 21% 11% 16% 20% 10% 6%
0.47 1 0.54 0.65 4.3 0.45 0.44 0.39 0.45
cleaning the surface with a road sweeper. The paving operation uses a paver as well as loading trucks to lay asphalt concrete. The rolling operation is the final step, wherein compactors roll new pavement several times to make the road firm, hard and smooth. The machine and labor force needed in each phase are shown in Table 2. There were no VOCs from fugitive emissions during the milling
Trucks (several) Rollers (several) Blower
phase. In the rolling phase, the VOC concentration detected was zero, both in the air around the driver and the pavement surface. Given that the detecting range of the PID is 0.1ppme10000 ppm within the temperature range of 20 C to 55 C, a possible explanation for the zero value may be that the concentrations of VOCs nearby above points are less than 0.1 ppm. The VOCs generated from major machines and vehicles used for construction, namely the ducted emissions, were also measured. Due to differences in engine modes, exhaust gas treatment technologies, fuel types and so on, the VOC results from the machinery varied from 0 to 16 ppm. However, the VOC value was zero in the air around drivers and operators of milling machines, trucks, compactors, bulldozers, and cleaner vehicles. For the purposes of this study, the above VOCs that did not directly affect workers’ health were not considered. Therefore, the paving phase was the only operation which was considered in this paper. During this phase, the measured VOCs were mainly generated from two sources: 1) the volatilization of asphalt dumping from the truck into the paver, and 2) the volatilization of asphalt during paving. 2.3. Health risk evaluation There are two methods, deterministic and probabilistic, that are predominantly used for health risk evaluations (Tong et al., 2019). The deterministic method is generally used to evaluate the health effects of a specific pollutant and its concentration. However, under outdoor conditions, the measurement is affected by so many of the influential factors mentioned above that will result in nonuniformity of the results. Due to the uncertainty of inhalation intake, working duration, VOC amount, as well as some other parameters, this paper applies the Monte Carlo simulation for risk evaluation. The Monte Carlo simulation is one of the probabilistic
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methods for risk evaluations which uses a probability distribution in statistics to process the input data. After thousands of times of the iteration, the generated results are more realistic and reliable within a certain confidence interval (Yamada et al., 1998). According to the risk impact results, health risks can be divided into either being carcinogenic or non-carcinogenic (Lerner et al., 2012), as shown in Formulas (2) and (3), respectively.
CRi ¼ CDIi ISFi CRi ðWÞ ¼
(2)
X CDIi PSj ISFi
(3)
HQi ¼ Ci =RfCi CDIi ¼
(4)
Ci IR ED EF EL BW AL
(5)
Where CRi denotes the carcinogenic risk of VOC i. CDIi denotes the chronic daily intake of VOC i (mg/kg/day). ISFi is the inhalation slope factor of VOC i (kg$day/mg). CRi ðWÞ denotes the carcinogenic risk of VOC i of a certain worker (kg$day/mg). PSj is the probability of a worker standing straight (j ¼ 1) or bending (j ¼ 2) in the job, namely, the ratio of stay between different WBZs. HQi denotes the hazard quotient, which is the ratio of the concentration of VOC i over a specified period of time to its RfCi derived at the same time. A ratio larger than unity suggests that the concentration of VOC i is high enough to cause chronic non-carcinogenic effects. RfCi is the reference concentration for VOC i (mg/m3). Ci is the concentration of VOC i (mg/m3). IR is the inhalation rate (m3/h). ED is the exposure duration (h/day). EF is the exposure frequency (day/year). EL is the exposure length (year). BW is the body weight (kg). AL is the average lifespan (day). A lifetime of 70 years is typically used in early studies to quantify cancer risk (Li et al., 2009; Yu et al., 2017; Huang et al., 2016; Guo et al., 2004). The ISFi and RfCi of VOCs are shown in Table 3. 3. Case study 3.1. Basic information This study investigated 10 asphalt pavement-resurfacing projects in the Washington D.C. area, performed by Chamberlain contractors Inc. Table 4 summarizes the construction details and conditions. All 10 projects involved the installation of HMA. 3.2. Data collection As detailed previously in Table 2, during the paving phase, 5e6 workers (excluding loading trucks and drivers) were arranged around a paver. Among them, 1 driver was responsible for controlling the forward direction, speed and asphalt dumping of the paver; 2 operators standing behind the paver oversaw controlling the width and thickness of the pavement; and another 2e3 laborers
Table 3 The ISFi and RfCi of VOCs (USEPA, 2010). VOC
CAS Number
ISF (kg$d/mg)
RfC (mg/m3)
Benzene 2-Butanone Cumene Ethylbenzene n-Hexane Toluene m, o, p-Xylene
71432 78933 98828 100414 110543 108883 1330207
0.027 N.A. N.A. N.A. N.A. N.A. N.A.
0.03 5 0.4 1 0.7 5 0.1
who were walking around the paver at the middle and back, were responsible for road surface roughness and roadside mend. Thus, there were seven locations of workers’ breathing zones (WBZs) around the paver that were chosen as the measuring locations including A, B, B0 , C, C0 , D, and D0 , as shown in Fig. 3. The WBZs are defined as the area near the mouth and nose of a worker (Chong et al., 2014). Locations B0 , C0 and D0 were set because the workers often need to bend down to check and clean the mixture. The PID device was placed at the above 7 locations for 10 s each time moving with the workers. To correct for a measurement error, the VOC concentrations during the 5th to 15th second were counted. The maximum, average and standard deviations at each position are recorded in Table 5. The maximum value at each measured location was chosen as the VOC concentration for the health risk analysis. Noting: the measured results are consistent with the values conducted in an authoritative research report (Butler et al., 2000). As seen in Table 5, the concentration of VOCs around the asphalt lay-down ports, namely the WBZ of the laborers are the largest at the C0 and D0 positions where they often need to bend down. In the 10 on-site measurements, a maximum value of 33.86 mg/m3 was recorded at the C0 position, and it was found to be as high as 139.97 mg/m3 at the D0 position. Furthermore, the VOC concentration at position A ranged from 0 to 18.06 mg/m3. The concentration around B varied from 0 to 6.77 mg/m3, and at B0 it varied from 0 to 20.32 mg/m3. 3.3. Influencing factor on site Often, asphalt fume is seen diffusing on the construction site, as shown in Fig. 4. The fume represents the VOCs emitting from asphalt into the air during pavement construction. The fume is also referenced as “vapor” in some studies, which propose that the workers who are exposed to the fumes involved in asphalt paving operations experienced fewer respiratory tract symptoms (e.g., coughing, wheezing, and shortness of breath) and pulmonary function changes (Gamble et al., 1999). Construction workers usually ignore potential health risk from VOCs in the outdoor environment, where many factors, e.g. wind, temperature, and humidity, can affect the inhalation intake. These factors are discussed below. C Wind To investigate the impact of wind on the fume, the following assumptions were made. The angle of a worker exposed to the fume can be determined by the wind direction, construction direction and the relative location of the worker to the fume source in Table 4 and Fig. 3. Assuming that the fume spreads in a fan-shaped manner along the wind direction, then there are five kinds of exposed areas including towards (P1), diagonally towards (P2), aside (P3), backwards (P4) and above (P5) the fume, as shown in Fig. 5. Under the windless condition, assuming the fume or spreads evenly through the diffusion effect, then the direction of exposure is the same as P1. If the wind is directed towards the worker, the VOC concentration of WBZs will become very large, such as that at location C and C0 in Case 5. Conversely, if the wind blows opposite to a worker, the concentration value will significantly reduce, even to zero, such as that at location B in Case 3 and 4, and at location C and C0 in Case 10. Additionally, the asphalt fume gradually dissipates with increasing distance and duration time. Based on the study, the VOC concentration would usually reduce to zero after the fume appeared for several seconds. Therefore, the wind speed was a key factor increasing the speed of the fume dropping to zero. For example, due to the strong wind on site, the fume dissipated faster
Please cite this article as: Cui, P et al., VOC emissions from asphalt pavement and health risks to construction workers, Journal of Cleaner Production, https://doi.org/10.1016/j.jclepro.2019.118757
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Table 4 Project cases summary. Case
Location
Temperature
Wind speed
Wind direction
Paving direction
Humidity
1 2 3 4 5 6 7 8 9 10
Central Park Plaza 1420 silver Parkway Fredericksburg VA Lighthouse 11932 Twinlakes Dr Beltsville MD Brighten 3 West Side Ave Gaithersburg MD 10 Riverview Ct Laurel MD Casino Circle Silver Spring MD Iron Bridge 10611 Iron Bridge Rd Jessup MD Kathrine Thomas 9975 Medical Center Dr Rockville MD Patridge Courts 10376 Failkner Ridge Circle Columbia MD 750 Main Street Reisterstown MD East Village 20302 String Fellow Ct Montgomery Village MD
28 C 21 C 23 C 32 C 26 C 27 C 26 C 22 C 28 C 29 C
2.68 m/s 2.24 m/s 1.79 m/s 3.58 m/s 0.45 m/s 0.89 m/s 4.02 m/s 0 3.13 m/s 2.24 m/s
E SW N W NW W N e SW NW
S NW NE W N N E SE NE NW
63% 97% 93% 57% 72% 71% 46% 63% 56% 69%
Fig. 3. Locations of workers’ breathing zones (WBZs).
Table 5 The VOC concentration at WBZs (mg/m3). Worker title
Position
Case No.
1
2
3
4
5
6
7
8
9
10
Driver
A
Operator
B
max mean SD max mean SD max mean SD max mean SD max mean SD max mean SD max mean SD
9.03 5.42 2.89 0 0 0 6.77 3.16 1.81 4.52 2.48 1.88 2.26 13.77 9.65 27.09 1.13 1.13 27.09 19.19 5.99
6.77 2.48 2.13 0 0 0 2.26 0.9 1.11 0 0 0 15.8 14.67 7.09 24.83 7.68 4.42 54.18 29.35 17.66
0 0 0 4.52 1.35 1.81 9.03 4.97 3.32 42.89 24.38 11.77 33.86 71.79 22.95 101.59 16.03 10.17 139.97 81.27 38.33
2.26 1.13 1.13 6.77 2.48 2.36 20.32 9.93 8.28 13.55 5.87 3.8 24.83 30.25 16.96 51.92 11.96 6.85 90.3 50.12 26.9
4.52 1.81 1.97 2.26 1.35 1.11 2.26 0.9 1.11 6.77 2.26 2.26 11.29 16.03 8.94 33.86 7.9 4.43 47.41 22.58 15.8
0 0 0 0 0 0 4.52 2.48 1.88 2.26 1.58 1.03 2.26 2.26 2.26 6.77 1.35 1.11 18.06 7.22 4.6
4.52 2.48 1.58 0 0 0 2.26 1.13 1.13 2.26 1.13 1.13 20.32 7.9 3.39 11.29 6.32 7.87 36.12 18.96 8.58
0 0 0 0 0 0 0 0 0 0 0 0 2.26 0 0 0 1.58 1.03 6.77 3.84 1.76
18.06 9.26 4.09 0 0 0 2.26 1.58 1.03 0 0 0 22.58 4.97 3.61 9.03 9.71 8.14 79.01 50.79 22.96
0 0 0 4.52 2.48 1.88 0 0 0 4.52 2.93 1.45 9.03 32.96 13.05 54.18 5.87 2.89 121.91 62.99 29.09
B0
Laborer
C
C0
D
D0
Note: The conversions for VOCs from ppm to mg/m3 in the air are made assuming a pressure of 1 atm and a temperature of 25 C. Convert factor ¼ 0.55 (CFmix ) 0.0409 100.3575 (molecular weight of the mixed VOCs) ¼ 2.258.
Please cite this article as: Cui, P et al., VOC emissions from asphalt pavement and health risks to construction workers, Journal of Cleaner Production, https://doi.org/10.1016/j.jclepro.2019.118757
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P. Cui et al. / Journal of Cleaner Production xxx (xxxx) xxx Table 6 The distribution and parameter set for the factors. Factors Concentration Concentration Concentration Concentration Concentration Concentration Concentration IR ED EF EL BW AL PS $ PS $ Laborer’ PS $ Operator PS $ Operator’
$ $ $ $ $ $ $
A B B0 C C0 D D0
Distributions
Parameters
Normal Normal Normal Normal Normal Normal Normal Triangular Triangular Triangular Normal Normal Constant Uniform Uniform Uniform Uniform
N (5.02, 5.51) N (2.01, 2.48) N (5.52, 5.84) N (8.53, 12.76) N (35.62, 28.45) N (15.8, 10.04) N (68.23, 40.14) T (0.3, 0.84, 1.38) T (3, 4, 5) T (180, 200, 220) N (6, 4) N (77, 8) 70 365 U (0.45, 0.55) U (0.45, 0.55) U (0.65, 0.75) U (0.25, 0.35)
Fig. 4. The asphalt fume emitted during the asphalt pavement job.
C Asphalt fumes in Case 7 than that in other Cases. Conversely, the low speed wind in Case 5 and 6 resulted in the accumulation of the fume. When the fume spread to WBZs, the concentration became larger, which had a great impact on workers’ health. The finding here is consistent with a previous study conducted in Hong Kong (Chong et al., 2014).
When the asphalt is stirred, unloaded from the trucks, crushed, watered, heated or paved, a large amount of asphalt fume will be generated, especially when trucks unload asphalt mixtures into the paver hopper, and when the asphalt is heated and paved on the road by the paver. In these cases, the PID detected a higher value. For example, the concentration at Location A in Case 9 is significantly larger than that in other cases due to the asphalt unloaded from the front truck.
C Asphalt lay-down temperature The lower the temperature of the asphalt, the less VOCs it generates. In theory, the lay-down temperature of asphalt should be consistent for these 10 measurements, because the paver is always set to heat the asphalt to 148.9 C. However, due to restrictions on workers’ operating habits, time control, road conditions, etc., temperature may vary. In Case No. 8, for example, the asphalt had been poured from the truck into the paver hopper, then the workers had a 30-min lunch break, that is, the asphalt remained in the hopper for 30 min. Subsequently, the workers immediately started the machine for road paving, and there was almost no fume on site. Most of the detected values were zero.
3.4. Calculation assumptions Some assumptions were made for the numerical analysis as summarized in Table 6. VOC concentration at each location follows normal distribution with parameters directly from project cases. It should be noted that Case No. 8 was eliminated from the analysis since the workers took several irregular breaks during the construction process. IR was obtained from the EPA, reporting that the average inhalation rate of workers outdoor is 0.84 ± 0.54 m3/h, which follows the triangular distribution (USEPA, 2011). ED came
P3 P2
P4
P5 P1
P4
Wind direction Fume source P2 P4 P3
Fig. 5. The possible areas of the workers standing around the emission source.
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from an interview with the workers who usually work about 2 h in the morning and 2 h in the afternoon for the asphalt paving job. Thus, the total exposure duration is 4 ± 1 h per day, which follows the triangular distribution. EF was obtained from the interview with the workers. They usually have 15 days of annual leave, and 50 days of winter break. The working rate per week is usually 5 days. Therefore, the total exposure frequency is 200 ± 20 days, which follows the triangular distribution. EL is the length of service of the workers. According to the interview, the average EL was 6 years, which follows the normal distribution. BW was also acquired from the interview with the workers. The average body weight of them is 170lb, which is about 77 kg BW obeys the normal distribution. AL is a constant value of 25550 days. PS was estimated on site during the research, assuming the standing and bending probability for the laborer is 50% each. The probability is 30% standing and 70% bending for the operator. The driver does not need to bend. The PS above obeys the uniform distribution. After the establishment of the evaluation model, the Crystal Ball software was used to simulate. The simulation was set to run 5000 times according to the Monte Carlo sampling with a confidence interval of 95%. The random input, with the probability distribution instead of a single value, makes the evaluation results more scientific and reasonable. 4. Results and implements 4.1. Carcinogenic risk The EPA has classified 2-Butanone, Cumene, Ethylbenzene, nHexane, Toluene, and m-/o-/p-Xylene in Group D, which do not belong to human carcinogenicity. Thus, only the ISF of Benzene is available. This paper analyzed the carcinogenic risks of Benzene to the driver, operators, and the laborers during pavement construction. Benzene has been classified as a known human carcinogen by the EPA. Short-term inhalation exposure to Benzene may cause drowsiness, dizziness, headaches, as well as eye, skin, and
7
respiratory tract irritation, and, at high levels, unconsciousness. Long-term exposure to Benzene may cause cancer of the bloodforming organs. According to the EPA estimation, if an individual is exposed continuously to a concentration of Benzene between 1.3 103 and 4.5 103 mg/m3 in the air, then there is a 1/100,000 increased chance of developing cancer (ATSDR, 2007). After 5000 simulations, the normal distribution and the statistics of Benzene carcinogenic risk on the workers are shown in Fig. 6 and Fig. 7. In Fig. 7, the whiskers represent the risk probability of 20% and 90%; the boxes denote the risk probability of 40% and 70%; the solid and dot-dashed lines indicate the median and standard deviation of the probability. Thus, the values in Fig. 7 can be interpreted as follows: for example, the average carcinogenic risk of Benzene on the driver is 0.0007%, and the probability of the risk higher than 0.0034% is 10%. Laborer 2 has the highest risk among the workers affected by Benzene. The average carcinogenic risk is 0.0074%. The probability of the risk higher than 0.0122% is 30%, which is higher than the acceptable cancer risk level (0.01%) in the chemical industry (Li et al., 2007). The risk of Laborer 1 ranked second after Laborer 2. The average carcinogenic risk of Benzene is 0.0038%, followed by the driver and the operator with a probability of 0.0007% and 0.0005%, respectively. The results are in the same order of magnitude as previous studies (Guo et al., 2004; Lerner et al., 2012; Yimrungruang et al., 2008; Li et al., 2009). Aside from Benzene, it is unclear what the carcinogenic mechanisms are for the other VOCs. The actual risk of cancer of all the workers may be greater than what is shown in Fig. 7. Sensitivity analysis was conducted on the cancer risk of the workers, as shown in Fig. 8. The length of work, the concentration of VOCs in WBZs, and inhalation rate were identified to be the three most influential factors. The CR influencing factors of laborers and operators are similar. EL, namely the length of work is the most influential factor, followed by the concentration of VOCs at WBZs. IR and BW also contributed a certain portion of CR, where BW is inversely proportional to CR. Since IR and BW are human attributes,
Fig. 6. Carcinogenic risk of Benzene on the workers.
Please cite this article as: Cui, P et al., VOC emissions from asphalt pavement and health risks to construction workers, Journal of Cleaner Production, https://doi.org/10.1016/j.jclepro.2019.118757
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P. Cui et al. / Journal of Cleaner Production xxx (xxxx) xxx
Laborer 1
Laborer 2
Driver
Operator Carcinogenic risk (10-6)
0
5
10
15
20
40
60
80
120
140
220
Fig. 7. Carcinogenic risk of Benzene to the workers.
Fig. 8. Sensitivity analysis of Benzene carcinogenic risk of workers.
it is difficult to optimize them. The workers’ standing to bending ratio, as well as the working time per day cannot be ignored. For the driver, the most influential factor is the concentration of Benzene at location A, followed by EL, IR, EF, ED, and BW. It is worth mentioning that the concentration of VOCs at location D will also affect the CR. 4.2. Chronic non-carcinogenic risk In this paper, the HQ is used to indicate the harm of noncarcinogenic VOCs to the human body. The calculation for chronic non-carcinogenic risk only relates to the concentration of BWZs, and the value of a location is compared to 1 as mentioned in the Methods section. The value within (0, 1] marked in green means
harmless; (1, 10] marked with yellow represents moderate hazard; the value greater than 10 expressed in red represents serious hazard. Table 7 shows the intermediate value of HQi as normally distributed. Most of the VOCs at location D0 exceed the health standard that makes D0 the most harmful location; the concentrations of m-/o-/p-Xylene in the above seven locations all exceed 1 and even reached 244.79 at location D0 , which is extremely harmful to the human body. Relatively, location A and location B are the two least harmful locations, but individual VOCs such as Benzene and m-/o-/p-Xylene caused adverse effect on the human body. In summary, the laborers near the asphalt dump have the highest chronic health risks, especially taking the superimposed effects of the various pollutants into account. The air near the WBZs of the
Please cite this article as: Cui, P et al., VOC emissions from asphalt pavement and health risks to construction workers, Journal of Cleaner Production, https://doi.org/10.1016/j.jclepro.2019.118757
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Table 7 The Median value of the HQ at seven locations
HQ HQ1 HQ2 HQ3 HQ4 HQ5 HQ6 HQ7 Good
A 6.64
B 2.76
B' 7.50
C 11.20
C' 46.34
0.04 1.00
0.02 0.41
0.04 1.12
0.07 1.68
1.05
0.44
1.18
0.78 0.16
0.33 0.07
0.88 0.18
17.93
7.46
20.24 Moderate
operators is relatively clean, but still half of the VOC concentrations exceeded the safety standard. Only two pollutants in the driver’s concentration exceeded the standard, however, they are high enough to cause health risks to the human body. The EPA has classified these non-carcinogenic VOCs in Group D, not classifiable as to human carcinogenicity (USEPA, 2005). The general introduction of the non-carcinogenic VOCs escaping from asphalt pavement construction is summarized as follows (ATSDR, 2007): Cumene is a skin and eye irritant with depressant action on the central nervous system (CNS). Short-term inhalation exposure to Cumene may cause headaches, dizziness, drowsiness, slight incoordination, and unconsciousness in humans. Ethylbenzene mainly affects the hearing system. Short-term exposure to Ethylbenzene leads to respiratory and neurological system disease, as well as eyes problems. Long-term exposure to Ethylbenzene by inhalation in humans may harm the blood system, liver and kidney. 2-Butanone is also called the Methyl ethyl ketone. Short-term or acute inhalation exposure to 2-Butanone results in irritation to the eyes, nose, and throat. The long-term impact on humans remains unknown. Some serious health effects in animals have seen only at very high levels. m-/o-/p-Xylene are found to have very similar effects on health. Short-term inhalation exposure to Xylenes results in irritation of the eyes, nose, throat, and stomach. Long-term inhalation exposure results primarily in CNS effects, such as headache, dizziness, fatigue, and incoordination. Cardiovascular and kidney diseases have also been reported. Toluene may cause CNS disease under both short-term and long-term exposures with symptoms of fatigue, sleepiness, headaches, and nausea. Studies have reported that short-term inhalation exposure to Toluene may cause CNS dysfunction, attention deficits, and minor craniofacial and limb anomalies in children of pregnant women. Chronic inhalation exposure to Toluene also causes irritation of the upper respiratory tract, eyes, and throat, resulting in dizziness, and headache. n-Hexane influences neurotoxicity. Short-term inhalation exposure of humans to high levels of Hexane may cause dizziness, slight nausea, and headache. Chronic exposure to Hexane could lead to numbness in the extremities, muscular weakness, blurred vision, headache or fatigue.
4.3. Possible implements The analysis suggests an undeniable health risk to pavement construction workers. Such health risks can be reduced through the
D 20.58
D' 90.66
0.28 6.95
0.12 3.09
0.54 13.60
1.76
7.30
3.24
14.28
1.32 0.27
5.46 1.11
2.43 0.49
10.69 2.18
30.23
125.13
55.58
244.79 Serious
implementation of the following measures that target the emission sources, propagating pathways, and individual receptors of the VOCs. C Reducing the asphalt lay-down temperature. Based on the investigation, the asphalt lay-down temperature has a significant impact on the VOC emissions. If the asphalt is left in the truck or hopper for a while, the fume containing VOCs can be effectively reduced. Additionally, WMA, foam asphalt, and other recycled asphalt are installed under much lower temperatures and therefore reduce VOC emissions. For example, WMA can be mixed and paved at a temperature of 90e120 C (Aliha et al., 2017), which is 30e60 C lower than the HMA. C Reducing the asphalt disturbances. Minimizing the chance of mixing and dumping the asphalt, as well as unloading from the truck can prevent the volatilization of fume with VOCs. During the observation, it was found that sometimes the truck unloaded the asphalt on the road directly and the asphalt was transferred to the hopper by a forklift. This process would increase fugitive emissions of VOCs, and thus should be avoided as much as possible C Suppressing the fume propagation. Appropriate water spray can effectively cool down the paved asphalt and suppress the fume. However, if a large amount of water is poured directly onto the hot asphalt, on one hand, it will reduce asphalt strength and viscosity, but on the other hand, much fume will escape and cause the workers to be exposed acutely to VOCs. Therefore, water should be sprayed with high pressure towards the fume. C Changing the fume propagation direction. If possible, choosing a paving direction that is the same as the wind direction will decrease the chance of workers exposed to VOCs. Moreover, setting up a blower next to the paver to blow the asphalt fume containing VOCs away from the workers would be a good way to reduce the health risk. As mentioned above, the concentration of VOCs will gradually decrease over distance and time. C Wearable protection. Based on the investigation, after an individual is exposed to the fume with VOCs, many oil substances will stick to the skin, clothes, eyes, glasses and so on. Given that VOCs not only harm the human bodies by inhalation, but also irritate the skin and eyes, workers are highly encouraged to wear a mask, long clothing, gloves and glasses to protect themselves. C Behavioral approach. The driver, operators, and especially the laborers should exchange their jobs every once in a while, to
Please cite this article as: Cui, P et al., VOC emissions from asphalt pavement and health risks to construction workers, Journal of Cleaner Production, https://doi.org/10.1016/j.jclepro.2019.118757
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avoid long time exposure in the high-concentration VOCs for a certain worker. The above method requires workers to be proficient in each operation of the entire construction process. To reduce the tendency of bending over to contact highconcentration VOCs, workers should use long equipment or new methods to reduce the bending frequency. Construction companies are also obliged to provide their workers with protective measures and training on VOC hazards. 5. Conclusions VOCs are recognized as mixed harmful gases that can place both people and the environment in jeopardy. A considerable number of VOCs are generated during asphalt pavement construction, and present negative effects on workers’ health. Only rarely have there been studies on the carcinogenic and non-carcinogenic risks on these workers, making the health of asphalt workers unprotected by laws or codes. This paper studied the concentration of VOCs obtained by on-site measurements, as well as analyzed the carcinogenic risk and other health effects of different types of VOCs on workers, and made suggestions for improvements going forward. The findings were: 1) During the pavement construction process, VOC emissions generated from the paving job have the greatest impact on the workers’ health; 2) The VOCs escape with the asphalt fume from the asphalt to the air. The fume is influenced by many factors, such as wind speed and direction, asphalt fume, temperature and so on; 3) The concentration of VOCs around the workers varies from 0 to 139.97 mg/m3. The workers who are responsible for the cleaning job of pavement surface beside the paver suffer the biggest risk of cancer, followed by the paver driver and operators. 4) The VOC concentration at workers’ breathing zones, length of work, working postures, and body weight are all key factors to the carcinogenic risk; 5) The results of noncarcinogenic risk show that n-Xylene and Benzene have the highest hazard quotient, and the laborers are affected most during the job; 6) Mitigation measures will help reduce the health risk for the workers including reducing the asphalt temperature and disturbance, controlling the concentration and direction of the fume, and protecting the workers themselves. As the outdoor environment is complex, many factors could potential affect the VOC emissions from pavement construction. These factors include wind, temperature, and humidity, as well as workers’ behavior in construction, e.g. standing position, bending frequency, and inhalation rate. While this paper presents potential health risks of pavement construction due to VOC emissions, more studies are necessary to better understand the actual health impacts. Detailed data should be collected and put in the evaluation model to make more accurate and reliable predictions. The composition and percentage of VOCs generated from asphalt obtained from early studies by the EPA need to be re-examined to fit the construction context. Finally, the VOCs are only a kind of harmful substances in asphalt fume. However, the negative effect of asphalt fume to human health, especially long-term carcinogenic risks, need to take all the harmful substances into account and to take a multi-factor superimposed risk assessment. References Agency for Toxic Substances and Disease Registry, 2007. Toxicological Profile for Benzene (Atlanta, GA). Aliha, M.R.M., Razmi, A., Razavi, M., Mansourian, A., 2017. The influence of natural and synthetic fibers on low temperature mixed mode IþII fracture behavior of warm mix asphalt (WMA) materials. Eng. Fract. Mech. 182, 322e336. https:// doi.org/10.1016/j.engfracmech.2017.06.003. Burghardt, T.E., Pashkevich, A., 2018. Emissions of volatile organic compounds from road marking paints. Atmos. Environ. 193, 153e157. https://doi.org/10.1016/ j.atmosenv.2018.08.065.
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Abbreviation List AL: Average Lifespan AVOCS: Ambient Volatile Organic Canister Sampler BW: Body Weight C: Concentration CAS: Chemical Abstracts Service
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CDI: Chronic Daily Intake CF: Correction Factor CR: Carcinogenic Risk ED: Exposure Duration EF: Exposure Frequency EL: Exposure Length EPA: Environmental Protection Agency FID: Flame Ionization Detection GC/MS: Gas Chromatograph/Mass Spectrometer HMA: Hot Mixed Asphalt HQ: Hazard Quotient IR: Inhalation Rate ISF: Inhalation Slope Factor PID: Photo Ionization Detection PS: Probability of Standing Position RfC: Reference Concentration UV: Ultraviolet VOCs: Volatile Organic Compounds WBZs: Workers’ Breathing Zones WMA: Warm Mix Asphalt
Please cite this article as: Cui, P et al., VOC emissions from asphalt pavement and health risks to construction workers, Journal of Cleaner Production, https://doi.org/10.1016/j.jclepro.2019.118757