Research Needs

The research identified below represents the many facets of information needed to assess completely the health risks associated with dermal and respiratory exposures to asphalt and asphalt fumes and aerosols. The principal goal of the proposed research should be to answer the following questions. (1) What health effects are associated with exposure to asphalt? (2) What constituent(s) of asphalt fumes is responsible for acute and possibly chronic adverse health effects? (3) What constituent(s) of asphalt fumes should be used as the metric for monitoring workplace exposures? (4) What types of control technology (e.g., engineering, work-practice controls) are feasible to prevent worker exposure to asphalt? (5) What is an appropriate "health-based" exposure concentration of asphalt fumes (or its constituents) that will prevent acute and possibly chronic adverse health effects?

8.1 Human Studies

8.1.1 Cancer Studies

Determine the availability of U.S. worker cohorts suitable for evaluating cancer risk from exposure to asphalt fumes during paving and roofing operations; the manufacture of asphalt products; and the use of asphalt-based paints, cutback asphalts, and asphalt emulsions. This study should be coordinated with the IARC study to facilitate comparison of results and perhaps integrate U.S. data with IARC data in a pooled analysis.

If suitable populations and methods of study are found, design and conduct epidemiologic studies that include—

• Careful characterization of past and current worker exposures
• Consideration of potential confounders, such as smoking, diet, medication, coal tar, and diesel exhaust
• Use of suitable biological monitoring methods

Perform quantitative risk estimates for any identified cancers.

Conduct biomarker studies (see section 8.3).

Conduct studies in which representative samples of exposure levels are evaluated in workers exposed to asphalt products, such as roofers, applicators, etc.

8.1.2 Noncancer Studies

Using a population of U.S. workers exposed to asphalt during paving and roofing operations; the manufacture of asphalt products; and the use of asphalt-based paints, cutback asphalts, and asphalt emulsions—

• Test for the occurrence of acute effects
• Characterize the nature of the exposures, and if possible
• Establish exposure-response relationships

Develop and validate biomarkers of acute effects.

Conduct a morbidity study of U.S. workers.

8.2 Animal Studies

Generate asphalt fumes that are chemically representative of roofing and paving fumes in the field and test their carcinogenic potential with lifetime inhalation bioassays in rodents.

Use these fumes to conduct limited skinpainting studies to determine tumorigenicity.

Use these fumes in range-finding toxicity studies to characterize acute and subchronic effects and to develop novel techniques for biological monitoring and biomarkers.

Use toxicity testing to determine doseresponse relationships for both acute and chronic endpoints.

8.3 Biomarker Studies

Study biomarkers associated with cancer risk as surrogates for cancer mortality or morbidity. Also study biomarkers that in-dicate exposure to known carcinogens (e.g., DNA adducts) and genotoxins.

Develop an alternative to urinary 1-hy-droxypyrene, which seems only weakly useful as a biomarker of exposure to as-phalt fumes. Urinary biomarkers derived from these more abundant compounds, such as methylnaphthalenes, naphthalene, C3-alkylbenzothiophenes, C2-alkyl-benzothiophenes, and methylphenan-threnes or methylanthracenes, might better represent exposure to asphalt fumes than urinary 1-hydroxypyrene.

Develop biomarker methods that allow PAH exposure from asphalt to be dif-ferentiated from other sources of PAH exposure, such as coal tar, tobacco smoke, and ambient pollution.

8.4 Fume Characterization, Sampling, and Analytical Methods

Conduct studies to identify and evaluate properties of crude source, asphalt type and use, and manufacturing processes that contribute to the qualitative and quantitative chemical composition of asphalt fumes and vapors.

Continue to assess the differences be-tween laboratory-generated and field-generated fumes and continue the search for the constituents of asphalt fumes that correlate closely with health effects. Once relevant compounds or compound classes are identified, develop analytical sampling and analysis methods.

One approach to identifying a marker chemical or chemical class for carcinogeni-city is to determine which components of the fumes used by Sivak et al. [1989, 1997] caused cancer in mouse skin-painting models. Continue research to identify these chemicals or to measure them without iden-tification. Once they are identified, use these marker compounds to determine how the positive animal studies relate to the risks posed by workplace fumes.

Develop or improve analytical sampling and analysis methods.

Develop a method for determining the total three-ring and higher PAC content, since asphalt fumes contain many alkylated PACs.

Develop an analysis method for determining individual PACs or other chemical analytes so that correlations can be made between air concentrations and biomarkers.

Conduct additional studies of the genotoxicity and mutagenicity of fumes collected during paving, roofing, and manufacturing using modified Ames assays, SCE assays, and DNA adduct assays.

Characterize the molecular weight distribution of the chemical classes and different chemical functional groups in the vapors and fumes to which workers are exposed. Collect vapors and fumes from worksites where paving asphalt, roofing asphalt, cutback asphalts, asphalt emulsions, or asphalt-based paints are being used. Use increasingly sophisticated techniques to characterize further the chemistry of these exposures.

Develop and validate a dermal method for assessing asphalt fume exposure, because exposure to asphalt fumes may also occur by dermal contact.

Characterize particle sizes of fumes. Because the hazard potential of chemicals present in inhaled air depends both on particle size and concentration, additional research is needed to define the size fractions present in asphalt fumes more clearly. This research would help determine the most effective sampling devices (inhalable, thoracic, or respirable) to use when evaluating asphalt fume exposures.

Determine the effect of modifiers on asphalt fume composition.

8.5 Control Technology

8.5.1 Paving Operations

Evaluate new formulations (e.g., introduction of additional polymers) to determine whether the constituents and amount of fumes generated change.

Evaluate the effectiveness of the engineering controls recently incorporated into highway-class pavers. Identify the type and frequency of maintenance required to maintain optimum effectiveness of these controls.

Determine the feasibility of engineering controls on commercial-class pavers (smaller than 16,000 pounds) to reduce asphalt fume exposures.

Investigate the feasibility of incorporating engineering controls on nonpaver equipment used in laying hot-mix asphalt during road construction and repair. Such equipment includes surface grinders, materials-transfer vehicles, windrow machines, truck-mounted patching pavers, and crack sealers.

Evaluate the design and use of receiving hoppers operated in conjunction with materials-transfer vehicles to determine whether changes can be made to reduce worker exposure to asphalt fumes.

8.5.2 Roofing Operations

Continue to evaluate the various types of asphalt kettles and determine what types of engineering controls and design configurations provide optimal reductions in asphalt fume exposure. Investigate alternative methods for feeding asphalt into the kettle that will reduce the need for and frequency of lifting the kettle lid. The efficacy of new "low-fuming" asphalts should be evaluated.

Investigate all sources of asphalt fume exposure during the application of hot asphalt to roofs and determine what types of engineering control methods and work practice changes can be instituted to reduce such exposures.

Evaluate procedures and equipment used during roof tear-off to determine the most effective means of reducing worker exposures.

8.5.3 Waterproofing Operations

Investigate methods (e.g., engineering controls, work practices) that are effective in minimizing airborne and dermal exposures during the application of asphalt waterproofing materials.

8.6 Training and Education Effectiveness

Ascertain the effectiveness of current training and educational efforts to inform workers of the potential hazards associated with working with asphalt. Develop intervention strategies where warranted.