In this article, we discuss the hazards of asphalt to the workers such as cancer and lung function flaws, and inflammation. The health effects of asphalt and crumb rubber modified asphalt (CRM), which contains used rubber tires, are debatable. Exposures and their effects on lung function, inflammation biomarkers, and airway symptoms in conventional and CRM asphalt road pavers The study included 100 controls, 51 CRM asphalt workers, and 116 conventional asphalt workers. Repeated-measures analysis was performed on 31 workers who used both types of asphalt. Workers' exposure to dust, nitrosamines, benzothiazole and polycyclic aromatic hydrocarbons was assessed (PAH). Spirometry tests were performed before and after work, as well as self-reported symptoms and blood samples. When asphalt paving was not in progress, additional symptoms were collected. Dust, PAHs, and nitrosamine exposure were extremely variable and did not differ between conventional and CRM asphalt workers. CRM asphalt workers had higher levels of benzothiazole (p 0.001). More asphalt workers reported eye symptoms that began while working than controls. Lung function decreased from pre- to post-work in both CRM asphalt workers and controls. CRM asphalt workers had higher pre working interleukin-8 levels than controls, which decreased after 4 days of work. In any of the effects studied, there were no differences between CRM asphalt paving and conventional asphalt paving.
Those who work with asphalt in CRM are more likely to be exposed to benzothiazole. More research is needed to determine the source of nitrosamines in conventional asphalt. Both asphalt and CRM asphalt workers had mildly reduced lung function and work-related eye symptoms. In our study, however, there was little solid evidence that asphalt workers had severe respiratory symptoms or an inflammatory response. The health risks of being exposed to asphalt fumes have long been debated. Asphalt road pavers, according to studies, are more likely to develop eye and upper airway symptoms, have a decline in lung function, mild inflammatory reactions, and develop eye and upper airway symptoms. However, there is a scarcity of data on current exposure conditions for risk assessment, making it difficult to set appropriate occupational exposure limits (OELs). According to a recent assessment by the Swedish Criteria Group for Occupational Standards, there is insufficient data to determine the serious consequences of asphalt fume exposure during road construction.
The debate over the health effects of exposure to crumb rubber modified (CRM) asphalt has also heated up as the use of asphalt containing rubber tire crumbs has increased. However, little research has been conducted on the emissions produced by the paving process, and few studies have specifically examined any potential health risks. The National Institute for Occupational Safety and Health discovered higher levels of mucosal irritant benzothiazole and polycyclic aromatic hydrocarbon (PAH) emissions in CRM asphalt paving, as well as a two to three times higher prevalence of self-reported eye, nasal, and throat irritation in CRM asphalt. workers compared to conventional asphalt workers. However, a review found that the effects of CRM asphalt, if any, were minor. Along with higher particle emissions for CRM than for conventional asphalt, a Swedish report discovered and recently confirmed higher PAH and benzothiazole emissions from CRM asphalt. The goal of this research is to assess asphalt fume exposure and any potential health effects on airway symptoms, lung function, and inflammation response in asphalt workers. It also wants to know if using CRM asphalt for paving results in higher levels of exposure and more negative effects than using conventional asphalt.
Asphalt Workers
From 2012 to 2015, we investigated 116 conventional and 51 CRM asphalt workers at 41 asphalt paving sites. A total of 100 male controls who worked in outdoor gardening and landscaping were also recruited. Only about half of the controls were investigated between January and March due to availability, while all asphalt workers were examined between April and October (during the time that roads are being paved). The participants were examined pre working on Monday morning (06:00-08:00) and post working on Thursday after four consecutive working days (12:00–16:00). Because they worked with both types of asphalt in different years, 31 workers were investigated twice (preworking and post working) when laying conventional asphalt and twice (preworking and postworking) when laying CRM asphalt. The specifics of the investigation and hiring have already been discussed. To participate in the study, all participants provided written informed consent. 25 to 50 asphalt workers were personally sampled on 17 different days for respirable dust, total dust, total airborne PAHs (particle and gas phase), benzothiazole, and nitrosamines (other than the days for medical investigations). In the breathing zone, each employee wore a personal air sampler. Only when it was impossible to place an air sampler personally due to time constraints was a stationary sampling close to the worker performed (mainly for the paving machine drivers).
Respirable dust was collected using 37 mm mixed cellulose ester (MCE) membrane filters with 0.8 m pore sizes (Millipore AAWP03700) mounted on cyclones (BGI4L, BGI, USA). Total dust and airborne particulate PAHs were collected simultaneously on 37 mm polytetrafluoroethylene (PTFE) membrane filters (Pall Life Sciences, USA) mounted in conductive filter cassettes. Following the total dust filters, benzothiazole and gaseous PAH components were collected using adsorption tubes (XAD-2, SKC, USA). Nitrosamines were collected using a special sampler (Thermosorb/N adsorption tubes). The flow rates for total airborne PAHs, nitrosamines, and total dust were 1.5 L/min and 2.2 L/min, respectively, for respirable dust. As measured by particle mass in the field, our study revealed a highly variable (up to two orders of magnitude) exposure to dust, which was comparable to when CRM and traditional asphalt were used for paving. In an experimental setting, however, the particle number emission of CRM was greater than that of conventional asphalt. There was no discernible difference in airway symptoms, lung function, or inflammation biomarker changes among 14 CRM asphalt workers who were exposed to benzothiazole at higher levels than conventional asphalt workers. The unexpected discovery of nitrosamines in conventional asphalt paving indicates that there may be a source other than the recycled rubber tires added to the asphalt. In terms of health effects, it was discovered that CRM asphalt workers' lung function had moderately declined after 4 days of paving. Furthermore, there was a marginally higher prevalence of lower airway symptoms during the working season compared to the off-season among traditional asphalt workers.
These findings could point to the effects of exposure on the lower airways. Furthermore, an increase in the number of reports of eye symptoms in asphalt workers that appeared after starting the current job could indicate occupational irritation. This study has several advantages. We conducted a 4-day exposure study rather than a 1-day exposure study to simulate a typical working cycle in the Swedish asphalt industry and to reduce day-to-day variation. We obtained complete occupational and exposure histories in order to control for potential confounders such as potential exposure to other chemical agents. Through repeated examinations of each participant, acute changes in both objective (changes in lung function and inflammatory cytokines) and subjective (symptoms) measures during the work week could be evaluated. The repeated-measures analysis has the advantage of allowing workers to act as their own controls. Nonetheless, despite adequate sample sizes for controls and conventional asphalt workers, the small sample size and lack of CRM asphalt workers in the repeated-measures analysis made identifying significant differences difficult. Furthermore, because of the similar working conditions (outdoors, manual labor, and potential exposure to diesel exhaust), we chose lawn and garden maintenance workers as the control group rather than construction workers, as in previous studies. Unfortunately, among the controls, we overestimated the potential consequences of organic dust exposure during mowing, which has similar effects on the airways. Furthermore, a higher prevalence of mite allergies among controls could indicate some difficult-to-measure potential home exposures. These may help to prevent a significant difference between asphalt workers and controls.
Despite wide variation in personal exposure levels to respirable dust, total dust, and total airborne PAHs (up to two orders of magnitude), most measurements were within the parameters of previous studies involving open-area paving workers. The levels were also lower than the American Conference of Governmental Industrial Hygienists (ACGIH) PAH threshold limit value (200 g/m3) and Sweden's current OELs (5 mg/m3 for respirable dust and 10 mg/m3 for inhalable dust). Despite our observed levels of PAHs, which are non-threshold carcinogens, we may still be at risk. Because the emitted particles are typically small (1 m14), they produce a large surface area per unit of mass, and the low effect levels reported for combustion products may be more relevant. Despite our expectations, two nitrosamines (N-nitroso-piperidine and N-nitroso-phenylamine) were detected in conventional and CRM asphalt workers regardless of asphalt type or paving temperature. In our study, we discovered two nitrosamines, which may indicate that the source was not only the reused rubber tires added to the asphalt mixture but also other additives. The most common nitrosamines found in the rubber industry, including tire manufacturing, are N-nitroso-dimethylamine and N-nitroso-morpholine. Given that nitrosamines are suspected of being carcinogenic to humans and have powerful carcinogenic effects in animal studies, it is critical to identify and, if possible, eliminate the source of nitrosamines in asphalt paving. Similar to other studies, our findings that CRM asphalt workers were exposed to benzothiazole at levels nearly six times higher than conventional asphalt workers suggest that this substance may be a useful indicator of CRM asphalt fume exposure.
Lung Function Inflammation
There is, however, no OEL for benzothiazole. Despite finding a higher benzothiazole exposure during CRM asphalt paving, we found no differences in airway symptoms, lung function, or inflammation response between conventional and CRM asphalt paving. However, when paving in unfavorable conditions, it may still irritate the airways. The complex outdoor working environment resulted in highly variable exposure levels among the groups of conventional asphalt and CRM asphalt workers in our study. Furthermore, it was likely to increase the variability of potential exposure-related symptoms, making systematic differences between groups less likely. According to our findings, there may be a link between work-related airway irritation caused by asphalt fumes and lower airway symptoms in conventional asphalt workers during the paving season compared to off-season, as well as more reports of eye symptoms that began after starting the current job in asphalt workers compared to controls. Although the controls reported similar symptoms of airway irritation throughout the workweek, the causes were different, as indicated by the open-ended question on the questionnaire: the asphalt workers reported hot asphalt fumes, whereas the controls reported mowing grass or weeds (organic dust), which may have similar irritative effects. The phenomenon of the healthy worker effect may be responsible for the overall higher lung function in asphalt workers compared to controls, as well as the weak but positive associations between years of employment and lung volumes among asphalt workers. We observed declines in lung function in asphalt workers after 4 days of paving. Given the lack of a diurnal improvement in lung function, the decreased lung function could be related to asphalt paving (i.e., lung function is typically higher between 12:00 and 16:00 than in the early morning, between 06:00 and 08:00). However, the controls experienced a comparable decline, so no distinction could be drawn between the three groups. It is unknown what caused the decline in lung function in the controls. One possible explanation is that exposure to grass pollen has been linked to decreased lung function34 in one study.
Another reason that could exist is potential coexposure to diesel exhaust. However, we believe it is less likely. In chamber studies with diesel exhaust, transient airway irritation and lung function decline were observed at exposure levels of around 300 g/m3. That level of diesel exhaust exposure among study participants is unlikely, especially in open areas. Because CRM asphalt workers' pre working IL-8 levels were higher than the controls, it's possible that earlier exposure had a carryover effect. The decreases in IL-8 levels observed in asphalt workers after four days could indicate a shift in the site of inflammation from the blood to the mucous membranes. More research on these immune reactions is needed to learn how exposure to asphalt fumes can harm one's health. Asphalt workers are exposed to moderate levels of particles, airborne PAHs, and nitrosamines, which vary greatly. It is necessary to determine the source of the nitrosamines found in conventional asphalt. Despite the absence of acute airway irritation, there was a decline in lung function after 4 days of paving. Furthermore, asphalt workers have been linked to mild work-related symptoms (particularly in the eyes). However, because the controls showed comparable changes in some effects, these results should be interpreted with caution. When CRM asphalt paving was used, benzothiazole exposure was found to be higher. The lack of evidence that adverse health effects from CRM asphalt paving are more severe than those from conventional asphalt paving may be due to the smaller sample size in the repeated-measures analysis.