Roofing Asphalt Research Articles

Progressive failure of asphalt shingles under high winds: Assessment via full-field deformation measurements on full-scale roof panels

Failures of roof asphalt shingles under high winds have been reported to occur at wind speeds lower than the shingle performance classification. The understanding of the progressive failure mechanisms of shingles subjected to high-wind pressures has been hindered by difficulty in accurately quantifying uplifts and wind-induced pressures with high spatial resolution, especially for large-scale wind test setups that simulate realistic scenarios. This paper reports on an experimental study to assess the use of three-dimensional digital image correlation (‘StereoDIC’) to accurately measure full-field surface deformations of shingles installed on full-scale roof structures and subjected to realistic high winds. Deformation measurements were acquired on shingles installed on typical wood-frame roof panels and subjected to winds with speed up to 257 km/h (160 mph) using an outdoor wind tunnel. The specimens were designed to study the proposed test setup and StereoDIC measurement method for two different combinations of shingle surface coloration (and thus speckle pattern) and field of view. The experiments produced accurate local and full-field shingle deformation measurements. Different datasets were used to gain new insight into the influence of salient aspects of the wind test setup and deformation measurement method on the understanding of the temporal evolution of shingle uplift and failure mechanisms.

Anthropogenic Secondary Organic Aerosol and Ozone Production from Asphalt-Related Emissions.

Liquid asphalt is a petroleum-derived substance commonly used in construction activities. Recent work has identified lower volatility, reactive organic carbon from asphalt as an overlooked source of secondary organic aerosol (SOA) precursor emissions. Here, we leverage potential emission estimates and usage data to construct a bottom-up inventory of asphalt-related emissions in the United States. In 2018, we estimate that hot-mix, warm-mix, emulsified, cutback, and roofing asphalt generated ~380 Gg (317 Gg - 447 Gg) of organic compound emissions. The impacts of these emissions on anthropogenic SOA and ozone throughout the contiguous United States are estimated using photochemical modeling. In several major cities, asphalt-related emissions can increase modeled summertime SOA, on average, by 0.1 - 0.2 μg m-3 (2-4% of SOA) and may reach up to 0.5 μg m-3 at noontime on select days. The influence of asphalt-related emissions on modeled ozone are generally small (~0.1 ppb). We estimate that asphalt paving-related emissions are half of what they were nearly 50 years ago, largely due to the concerted efforts to reduce emissions from cutback asphalts. If on-road mobile emissions continue their multidecadal decline, contributions of urban SOA from evaporative and non-road mobile sources will continue to grow in relative importance.

Investigation of tribological behavior of Styrene-Butadiene Rubber compound on asphalt-like surfaces

Abstract Tribological behavior of Styrene-Butadiene Rubber (SBR) compound reinforced by silica and carbon-black fillers on two different asphalt-like surfaces is studied using theoretical and experimental approaches. Linear sliding friction and wear tests were performed on two different roofing asphalt papers. The surface roughness power spectra of asphalts and the master curves of the large-strain viscoelastic modulus of SBR compound were used to model the contact area and friction coefficient theoretically. The theoretical results are in good agreement with experiment providing the tribochemical degradation is not the dominant wear mechanism. When the formation of a tribo-modified layer prevails the mechanical abrasion, the wear rate, in terms of mass loss, does not necessarily increase with the increase of frictional work as expected theoretically.

Percutaneous Absorption of Polycyclic Aromatic Compounds from Fume Condensates of Paving and Built Up Roofing Asphalts

Paving and roofing workers can be exposed to low levels of polycyclic aromatic compounds (PACs) while working with asphalt at elevated temperatures via both the inhalation and dermal routes. Inhalation exposure date are readily available. However, dermal information is more complicated and not as well-studied. Here we evaluate condensed fumes from four paving and four BURA asphalts for percutaneous absorption through human skin using in vitro studies. Test materials included eight asphalt (bitumen) fume condensates (AFCs) collected from the headspace above four paving and four Type III built up roofing asphalt (BURA) tanks, each proven to match worker breathing zone exposures. Sections of human cadaver skin were sliced with a dermatome to a thickness of 250–350 μm, one-inch circular pieces were mounted in Franz diffusion cells epidermis side up. Receptor fluids were sampled at intervals over 48 hr and the aliquots analyzed for PACs using HPLC with fluorescence detection to determine the dermal flux rates of anthracene, fluoranthene/pyrene, and total 3-6 ring PACs.For paving/BURA AFCs, respectively, the average (N = 4) concentrations (μg/g) were: anthracene, 50.6 (SD = 14)/27.2 (SD = 28); fluoranthene/pyrene, 66.5 (SD = 47)/83.2 (SD = 100); Ʃ3-6 ring PACs, 833 (SD = 302)/2191 (SD = 240). Dermal flux rates (ng/cm2/hr) were: anthracene, 4.4 (SD = 1.1)/1.9 (SD = 2.0); fluoranthene/pyrene, 3.8 (SD = 2.8)/3.6 (SD = 5.0); Ʃ3-6 ring PAC, 35 (SD = 14)/21 (SD = 15). The estimated dermal flux of benzo[a]pyrene B[a]P in paving AFCs ranged from 0.0006 to 0.007 ng/cm2/hr and for BURA AFCs from 0.016 to 0.19 ng/cm2/hr. The averaged experimentally determined permeability coefficient (Kp) for anthracene for all eight samples was 0.90 ± 0.13 × 10−4 cm/hr (95% CI). Results show limited absorption of PACs across the skin in AFCs under the most conservative conditions (occluded/infinite dose). Dermal flux results can be used to support dermal exposure and risk assessments for asphalt emissions.

3D Analysis and Modelling of Thermal Stress Restrained Specimen Test (TSRST) on Asphalt Mixes with RAP and Roofing Shingles

The thermo-mechanical behavior of asphalt mixes, with Recycled Asphalt Pavement (RAP) and manufacturing waste roofing asphalt shingles (RAS), is investigated. The cracking behavior at low temperature is studied using the Thermal Stress Restrained Specimen Test (TSRST). The experimental device has been improved with a radial strains measurement system during the performed TSRST. Tri-dimensional behavior could thus be investigated. Studied mixes are made with different RAP contents (up to 25%) and RAS contents (up to 10%). First, the influence of the content of RAP and RAS is analyzed and a ranking of the different mixes is proposed based on the classical TSRST results (stress and temperature at failure). Then, in order to simulate TSRST, a three dimensional modelling is performed with the visco-elasto-plastic DBN model. The calibration steps in the small domain (linear visco-elasticity) and in the large strain domain (non-linearity and visco-plastic flow) are presented. The comparison between experimental and simulated results obtained using the DBN model has shown the potential of the DBN model to simulate the low temperature cracking behavior of asphalt mixes.

Investigation of two Warm Mix Asphalt additives

In order to address pertinent issues in relation to the use of Warm Mix Asphalt (WMA) in pavement construction, it is imperative to understand the effects that such additives have on rheological and failure properties in service. In this study, two commercial WMA additives, a proprietary siloxane-based compound and an oxidized polyethylene wax, were added to a soft Roofing Asphalt Flux (RAF), a soft Recycled Engine Oil Bottom (REOB) tainted binder, and a somewhat harder binder containing 20% oxidized asphalt derived from Recycled Asphalt Pavement (RAP). Binders were aged according to standard Rolling Thin Film Oven (RTFO) and Pressure Aging Vessel (PAV) protocols. Selected compositions were subjected to a period of extended PAV aging for 40h. Standard and advanced rheological and failure tests were used to predict the performance of these binders in service. Dynamic Shear Rheometer (DSR) and Bending Beam Rheometer (BBR) tests according to Superpave™ protocols were done to determine performance grades. Extended BBR (EBBR) and Double-Edge-Notched Tension (DENT) tests were done to provide further insights into durability and strain tolerance, properties of utmost importance to assure long term pavement performance. The findings of this study show that the addition of the oxidized polyethylene wax WMA additive to REOB and/or RAP tainted systems can provide binders that are unstable and likely prone to premature and excessive low temperature failure in service. In contrast, the siloxane-based WMA additive appears to be a better choice to avoid premature low temperature and fatigue cracking distress.

Airborne Exposures to Polycyclic Aromatic Compounds Among Workers in Asphalt Roofing Manufacturing Facilities

We studied exposure of 151 workers to polycyclic aromatic compounds and asphalt emissions during the manufacturing of asphalt roofing products—including 64 workers from 10 asphalt plants producing oxidized, straight-run, cutback, and wax- or polymer-modified asphalts, and 87 workers from 11 roofing plants producing asphalt shingles and granulated roll roofing. The facilities were located throughout the United States and used asphalt from many refiners and crude oils. This article helps fill a gap in exposure data for asphalt roofing manufacturing workers by using a fluorescence technique that targets biologically active 4–6 ring polycyclic aromatic compounds and is strongly correlated with carcinogenic activity in animal studies. Worker exposures to polycyclic aromatic compounds were compared between manufacturing plants, at different temperatures and using different raw materials, and to important external benchmarks. High levels of fine limestone particulate in the plant air during roofing manufacturing increased polycyclic aromatic compound exposure, resulting in the hypothesis that the particulate brought adsorbed polycyclic aromatic compounds to the worker breathing zone. Elevated asphalt temperatures increased exposures during the pouring of asphalt. Co-exposures in these workplaces which act as confounders for both the measurement of total organic matter and fluorescence were detected and their influence discussed. Exposures to polycyclic aromatic compounds in asphalt roofing manufacturing facilities were lower than or similar to those reported in hot-mix paving application studies, and much below those reported in studies of hot application of built-up roofing asphalt. These relatively low exposures in manufacturing are primarily attributed to air emission controls in the facilities, and the relatively moderate temperatures, compared to built-up roofing, used in these facilities for oxidized asphalt. The exposure to polycyclic aromatic compounds was a very small part of the overall worker exposure to asphalt fume, on average less than 0.07% of the benzene-soluble fraction. Measurements of benzene-soluble fraction were uniformly below the American Conference of Governmental Industrial Hygienists' Threshold Limit Value for asphalt fume.

Quantification of Residential Energy Consumption Reduction Using Glass-Modified Asphalt Shingle

AbstractThe urban heat island (UHI) phenomenon is defined as the differences in temperatures between urban and rural areas caused by the thermal properties of urban materials, urban geometry, and air pollution. Rooftops are playing a vital role in urban sustainability efforts and mitigating the UHI effect. Continuing these efforts, a study was conducted to evaluate the effectiveness of using recycled broken and waste glass cullet in the production of asphalt shingles to mitigate heat island effects and reduce building energy consumption by increasing the reflectivity of the roof asphalt shingles. To achieve this objective, shingle samples were prepared with and without glass cullet and the Solar Reflectance Index (SRI) of the specimens was measured based on ASTM E1980-11. The SRI of the asphalt shingles prepared with glass cullet and a white pigment powder was found to be 30, whereas it was 0 for the asphalt shingles without glass cullet. A three-dimensional transient finite-element (FE) model was formula...

Calorimetric and heat transfer studies of the spontaneous combustion of two low carbon fuels

The self-heating and heat transfer characteristics of creosote-treated wooden railway tie dust and roofing asphalt shingle particles, which are considered as low carbon fuels, are investigated. Self-heating was measured with isothermal calorimetry and thermal conductivity was measured using a guarded hot plate. The self-heating of petroleum coke and poplar wood pellets were also measured as reference materials. Self-heating models and heat transfer parameters were then defined assuming constant moisture content. The self-heating of petroleum coke was found to be similar to coal, while both poplar pellets and railway tie dust were found to be more reactive compared to oven test results of similar materials. As both poplar pellets and railway ties both had significant water content, the higher reactivity was attributed to the effect of moisture. Furthermore, critical conditions for spontaneous combustion were evaluated with the Frank–Kamenetskii parameter, assuming an ambient temperature of 40 °C. It was found that cubic volumes of railway tie dust and asphalt particles, 1.6 m and 58 m to a side, respectively, would spontaneously combust; however, compaction effects associated with asphalt softening may invalidate the assumptions of the Frank–Kamenetskii spontaneous combustion theory.

Life cycle assessment of a single-family residential building in Canada: A case study

The present study quantified the significant environmental impacts of a two-story residential building located in Vancouver, Canada, with a projected 60-year life span: (i) an inventory of all the construction materials was analyzed, covering the building structure and exterior and interior envelopes as well as the energy consumption; (ii) four types of functional units were defined; (iii) the five top building materials were examined, and a sensitivity analysis was conducted to investigate the impact associated with the choice of building materials. Two life cycle phases, manufacturing and operation, were more significant in all of the impact categories, and two building assemblies, the walls and the roof, bore most of the environmental loads. In terms of the sensitivity analysis, the roofing asphalt had the largest impact, dominating three of the seven selected impact categories. Despite different definitions of functional units, the function of the dwelling buildings is always the same, to provide protection and housing for their habitants. Additionally, to improve the performance of an existing building, several strategies were proposed for the building renovation and maintenance, including alternative replacement materials regarding the building components with high environmental burdens, good patterns of the occupants’ consumption behaviors as well as considerations of the financial and environmental cost. Finally, limitations and challenges are discussed to explore better design decisions in future studies.

Sulfur extended heavy oil fly ash and cement waste asphalt mastic for roofing and waterproofing

Waste materials recycling has been the logical and widely accepted means of conserving the diminishing global natural resources. This comes as a result of increased scarcity of raw industrial materials, coupled with environmental hazard of most of the waste products. In this paper, the effect of different waste material fillers, namely heavy oil fly ash (HOFA), coal fly ash, limestone dust, and cement kiln dust, and sulfur on the physical properties and performance of roofing and waterproofing asphalt has been examined. Conventional asphalt consistency tests in addition to a new bond strength test were conducted on the modified asphalt mastic. The results were analyzed statistically and assessed in accordance with ASTM D 332 and ASTM D 449 specifications. HOFA proved to be a superior filler additive compared to the other three additives. The sulfur mixes were found to be short on flash point values, but in spite of this, results show a promising potential alternative and cost effective material composite having the least amount of asphalt content.

Temperature-Dependent Emission Concentrations of Polycyclic Aromatic Hydrocarbons in Paving and Built-Up Roofing Asphalts

To characterize temperature-dependent emissions from paving and built-up roofing asphalt (BURA) and to quantify differences in temperature-related concentrations and composition. Using headspace gas chromatography, 18 polycyclic aromatic hydrocarbon (PAH) emission concentrations were quantified over eight temperatures (120-315°C) for paving asphalt (n = 20) and Types II, III, and IV BURA (n = 5) and were summarized by geometric means (GMs) and geometric standard deviations (GSDs) at each temperature. The relationships between temperature and concentration were evaluated for PAH analytes using mixed-effects regression models. Temperature was categorized into regimes: Regime 1 (120-150°C) representing temperatures typical of paving asphalt application, Regime 2 (180-230°C) representing temperatures typical of BURA application, and Regime 3 (260-315°C) which were high temperatures outside typical application temperatures. An interaction term was used to evaluate differential effects of temperature on paving asphalt versus BURA. In the paving regime (120-150°C), paving asphalt emission concentrations were highest for 2- and 3-ring PAHs [GM (GSD) at 150°C of 4.51 (2.07), 3.77 (1.63), 2.26 (1.53), and 1.80 (1.66) μg m(-3) for 2-methyl naphthalene, naphthalene, phenanthrene, and acenaphthene, respectively], with all the 4- and 5- to 6-ring individual PAHs mean concentrations below the detection limit, with the exception of benz[a]anthracene. In the BURA regime (180-230°C), BURA emission concentrations were highest for 2- and 3-ring PAHs [GM (GSD) at 205°C of 121.3 (1.37), 99.5 (1.31), 69.5 (1.32), and 68.1 (1.37) μg m(-3) for acenaphthene, anthracene, 2-methyl naphthalene, and phenanthrene, respectively], with lower but detectable concentrations for 4- and 5- to 6-ring PAHs. For both paving asphalt and BURA, concentrations increased log linearly with temperature. At a given temperature, the highest concentrations were observed for 2-ring PAHs with lower and decreasing concentrations observed with increased ring size. Temperature was a statistically significant (P < 0.01) predictor of concentration for each analyte. Furthermore, the categorical temperature regime variable explained a large percent of the variability in concentrations accounting for 74-92% of the total variability in PAH concentration. In both paving asphalt and BURA, the relationship between temperature and concentration was non-linear. There was a statistically significant difference between paving asphalt and BURA in the temperature-concentration relationship for the each analyte. Temperature alone did not account for differences in paving asphalt and BURA concentrations in 5- to 6-ring PAHs. Emission concentrations are driven by temperature for both paving asphalt and BURA samples under studied experimental conditions. There are differences in paving asphalt and BURA emission concentrations that are not explained by temperature alone; concentrations were higher and consisted of larger ring (4 and 5 to 6) PAHs for BURA as compared to paving asphalt at the respective application temperature ranges.

Application of Rheological Models to Modified Roofing Asphalts

Abstract The increased understanding of material behavior with rheology has existed for approximately 80 years as a science and has been applied to roofing products for over 50 years. With asphalt binders, several techniques exist for understanding rheology via the use of models. One of the best recognized models for the evaluation of the rheology of unmodified asphalt binders is the Christensen-Anderson model, and various developments of that model have occurred, enabling its use with filled systems such as those used in roofing applications. In addition to this model, the Rowe-Baumgardner-Sharrock model (developed by the authors) is introduced as an alternate method for defining the properties of roofing products that exhibit visco-elastic solid properties. When rheological data are fitted to master curve functional forms, changes in the model parameters can be rapidly visualized. The performance of various products can be assessed using this technique and can be related to the rheological parameters developed from this model (for example, the rheological index, crossover frequency, etc.). An analysis of the data is presented that includes testing using various rheometers over a wide range of temperatures. These data have been combined into a single master curve and plotted in various formats. The data show how the rheological index and the crossover frequency of the materials change over time, particularly with aging. Performance products can then be assessed and evaluated from both the historical data and models that enable the prediction of cracking and deformation. Adiscussion of the key parameters and a trend analysis are shown. Furthermore, the analysis is applied toward understanding the effectiveness of polymer networks in the roofing materials. As materials age, their properties change, and this can be observed, allowing the study of the effects of polymer network degradation with aging. This paper offers some further understanding of how key rheological parameters change.

Asphalt fume dermal carcinogenicity potential: II. Initiation–promotion assay of Type III built-up roofing asphalt

Clark et al. (accepted for publication) reported that a sample of field-matched fume condensate from a Type III built-up roofing asphalt (BURA) resulted in a carcinogenic response in a mouse skin bioassay, with relatively few tumor-bearing animals, long tumor latency and chronic skin irritation. This mouse skin initiation/promotion study was conducted to assess possible mechanisms, i.e., genotoxic initiation vs. tumor promotion subsequent to repeated skin injury and repair. The same Type III BURA fume condensate sample was evaluated in groups of 30 male Crl:CD1® mice by skin application twice per week (total dose of 50 mg/week) for 2 weeks during the initiation phase and for 26 weeks during the promotion phase. Positive control substances were 7,12-dimethylbenz(a)anthracene (DMBA, 50 μg applied once) as an initiator and 12-O-tetradecanoyl-13-acetate (TPA, 5 μg, applied twice weekly) during the promotion phase. During the 6 months of study with the asphalt fume condensate, eight skin masses were observed when tested for initiation, five of which were confirmed microscopically to be benign squamous cell papillomas. Only two papillomas were observed when tested for promotion. There was no apparent relationship between skin irritation and tumor development in this study. These results are more indicative of genotoxicity rather than a non-genotoxic mode of action.

Evaluation of reproductive/developmental and repeated dose (subchronic) toxicity and cytogenetic effects in rats of a roofing asphalt fume condensate by nose-only inhalation

A Type III Built-up Roofing Asphalt (BURA) fume condensate was evaluated for subchronic systemic toxicity and reproductive/developmental toxicity screening in Wistar rats, by OECD protocol 422 and OECD cytogenetic protocol 474. Animals were exposed by nose-only inhalation to target concentrations of 30, 100 and 300mg/m3 total hydrocarbons (actual concentrations, 30.0, 100.1 and 297.3mg/m3). The study was performed to assess potential hazards from asphalt fumes to which humans could be exposed during application. No adverse effects were seen for spermology, reproductive or developmental parameters or early postnatal development of offspring from day 1 to 4 postpartum. BURA fume condensate did not induce any significant increases in micronucleus frequency in polychromatic erythrocytes of rat bone marrow nor was neurobehavioral toxicity observed at any dose. Systemic effects were slight and seen at doses above those measured at work sites. The systemic NOAEC of 100mg/m3 for males was based on decreased body weight gain, food consumption and increased absolute and relative lung wet weight correlated with slight histological changes in the lung, primarily adaptive in nature at 300mg/m3. The female NOAEC of 30mg/m3 was based on a statistically significant increase in relative wet lung weight at higher doses, correlated with slight histopathologic effects in the lungs at the highest dose. However, no increase in relative lung weight was seen in breeding females at 100mg/m3.

Specifications for Roofing and Industrial Asphalts Using Dynamic Shear Rheometry (DSR)

Abstract Asphalt specifications in the U.S., Europe, and elsewhere in the world are increasingly dependent upon basic principles of rheology, in particular dynamic shear rheology (DSR). The roofing industry would be benefited by a revised ASTM specification featuring DSR measurements as opposed to the current ASTM Standard Specification D 312 in which softening point is the primary distinguishing characteristic of roofing asphalts. Rheological performance is the critical determinant of satisfactory roofing asphalt quality in that it must possess sufficient stiffness at higher temperatures to resist slippage on slopes and also be flexible enough at lower temperatures to resist cracking and debonding. This paper demonstrates the use of rheological parameters to replace the current softening point parameters, as well as introduces high and low temperature rheological parameters for climatic consideration. The proposed change incorporates climatic performance grades with high and low temperature limits which are based on DSR testing for the basic types of roofing asphalt.

A case control study of lung cancer and non-malignant respiratory disease among employees in asphalt roofing manufacturing and asphalt production.

Two case control studies, one for lung cancer and one for non-malignant respiratory disease excluding influenza and pneumonia, of workers engaged in asphalt roofing manufacturing and asphalt production were performed to determine whether there was an increased risk associated with exposure to asphalt fumes or respirable crystalline silica in these industries. Industrial hygiene data for these roofing and asphalt plants do not exist before 1977. Pre-1977 exposure scenarios were constructed to estimate historic exposures for asphalt fumes and respirable crystalline silica. The only statistically significant elevated ORs were for cigarette smoking in both the lung cancer and the non-malignant disease analyses. The lack of an apparent dose-response relationship with exposure to asphalt fumes argues against an association between exposure to asphalt fumes at levels present in the industries reported on here and lung cancer and non-malignant respiratory disease, excluding influenza and pneumonia risk.

DNA strand breaks, oxidative damage, and 1-OH pyrene in roofers with coal-tar pitch dust and/or asphalt fume exposure.

To determine the potential for asphalt fume exposure to increase DNA damage, we conducted a cross-sectional study of roofers involved in the application of roofing asphalt. DNA strand breaks and the ratio of 8-hydroxydeoxyguanosine (8-OHdG) to 2-deoxyguanosine (dG) were measured in peripheral blood leukocytes of roofers. In addition, urinary excretion of 8-OHdG and 8-epi-prostaglandin F2alpha (8-epi-PGF) was also measured. The study population consisted of 26 roofers exposed to roofing asphalt and 15 construction workers not exposed to asphalt during the past 5 years. A subset of asphalt roofers (n = 19) was exposed to coal-tar pitch dust (coal tar) during removal of existing roofs prior to applying hot asphalt. Personal air monitoring was performed for one work-week to measure exposure to total particulates, benzene-soluble fraction of total particulates, and polycyclic aromatic compounds (PACs). Urinary 1-OH-pyrene levels were measured as an internal biomarker of PAC exposure. Full-shift breathing zone measurements for total particulates, benzene-solubles and PACs were significantly higher for coal-tar exposed workers than for roofers not exposed to coal tar. Similarly, urinary 1-OH-pyrene levels were higher in coal-tar exposed roofers than roofers not exposed to coal tar. Total particulates or benzene-soluble fractions were not associated with urinary 1-OH-pyrene, but PAC exposure was highly correlated with urinary 1-OH-pyrene. When stratified by 1-OH-pyrene excretion, DNA strand breaks increased in a dose-dependent manner, and leukocyte 8-OHdG/dG decreased in a dose-dependent manner. Significant changes in DNA damage appeared to be linked to PACs from coal-tar exposure, although asphalt fume alone was associated with a small but significant increase in urinary 1-OH-pyrene and DNA strand breaks. Results are consistent with previous reports that asphalt or coal-tar exposure can cause DNA damage. Urinary 8-epi-PGF remained relatively constant during the week for virtually all subjects, regardless of exposure indicating that neither asphalt nor coal-tar exposure induces an overt oxidative stress. A small, but statistically significant increase in 8OHdG was evident in end-of-week urine samples compared with start-of-week urine samples in roofers exposed to coal-tar. The increase in urinary 8OHdG coupled with the decrease in leukocyte 8-OHdG/dG, suggests that coal-tar exposure induces protective or repair mechanisms that result in reduced levels of steady-state oxidative-DNA damage.

Bio-Directed Fractionation of Laboratory-Generated Asphalt Fumes: Relationship Between Composition and Carcinogenicity

In the 1980's the National Institute of Occupational Safety and Health (NIOSH) sponsored mouse skin-painting bioassays of roofing asphalt fume condensates laboratory generated at 316°C. Five HPLC subfractions (designated A-E) were skin-painted individually and in various combinations. The whole fume condensates and two of the five fractions (B and C) were shown to be carcinogenic. The present study repeated the fume generation and fractionation phases of the NIOSH study using the same asphalt (bitumen), fume generation apparatus, and HPLC method. The carcinogenic fractions, B and C, were then subfractionated by cyanopropyl and silica gel column chromatography. Biological activity was tracked using the Modified Ames Assay, while relative PAC content was monitored using a newly developed fluorescence method. The results were consistent with the hypothesis that relatively high molecular weight PACs were largely responsible for the carcinogenic activity of the NIOSH fumes.

Effects of Mode of Generation on the Composition of Asphalt Fumes

Asphalt is used as the binder (cement) in road paving, and in the manufacture and application of roofing materials. At the elevated temperatures used in these industries, asphalt emits fumes. Concerns about the possible presence of carcinogenic PACs in asphalt fumes prompted the National Institute of Occupational Safety and Health (NIOSH) to sponsor two mouse skin-painting bioassays[1,2] of roofing asphalt fumes laboratory generated at 232° and 316°C. The studies showed that the whole fume condensates and two of five HPLC subfractions of the higher temperature fume were carcinogenic. The present investigation was designed to determine the extent to which NIOSH's mode of fume generation affected their composition, and hence biological activity. The results show that minor changes in generation mode produce marked differences in fume composition. Relative to field fumes, the laboratory-generated fumes were significantly enriched in higher molecular weight PACs associated with carcinogenicity in animal studies.