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Comment on "cancer risk from incidental ingestion exposures to PAHs associated with coal-tar-sealed pavement".

PAHs Associated with Coal-Tar-Sealed Pavement” M sources of human exposures to polycyclic aromatic hydrocarbons (PAHs) have been identified in food (deposition onto farms, cooking food, smoking of food), air (cigarettes, power plant emissions, vehicle emissions, fireplaces, wood burning stoves, industrial emissions, and all combustion sources) and consumer products (shampoos, ointments, medications, paints, coatings, fuels, and lubricating oils). Diet has been recognized as the greatest source of exposure to PAHs for the general nonsmoking population. In comparison, exposure to PAHs in soil and dust are less significant. Estimates of PAH intake from food vary widely, ranging from a few nanograms to a few micrograms per person per day. For patients treated with coal tar for psoriasis, atopic dermatitis and other skin disorders, the intake of PAHs from coal tar pharmaceuticals is estimated to be greater than dietary, air and smoking exposures combined. Intakes from exposures to PAHs in soil or dust are expected to be lower than dietary intakes and significantly lower than patients applying coal tar directly to their skin. There is no evidence that coal-tar-based sealants increase cancer risks. In fact, there is good evidence from robust epidemiological studies on the use of coal tar pharmaceuticals that coal tar does not increase the risk of cancer in that highly exposed population. There has been concern that coal-tar-based sealant use on parking lots are a source of PAH exposures to adults and children. Insufficient data exist on PAH concentrations in soil or settled house dust attributable to coal-tar-based sealants and as such, a risk assessment cannot be performed. A recent screening level regulatory risk assessment attempted to link the presence of PAHs in coal-tar-based sealants to significant health risk. Given the many safety factors used, regulatory risk assessments do not predict actual risks to people nor do they find associations between chemicals in the environment and health outcomes. The authors assert that the presence of coal-tar-based pavement sealants is associated with significant increases in estimated cancer risks for residents living adjacent to coal-tarsealed paved surfaces. We are unaware that any association has been established between residents living adjacent to coal-tarsealed paved surfaces and health risks, and our evaluation finds that no increases in estimated cancer risks above regulatory levels of concern have been established by the screening level risk assessment. The authors acknowledge a limited data set was used: 7 out of 11 soil samples collected adjacent to coal-tar-sealed parking lots, and 3 out of 7 soil samples collected adjacent to unsealed surfaces. The authors do not explain the selective use of data. Soil samples were collected from the edges of two parking lots in Illinois and one parking lot in New Hampshire. Soil samples collected in New Hampshire cannot be reliably identified as affected/unaffected by coal-tar-sealant because sealed and unsealed parking lots are adjacent to each other. Sample locations overlap with snow plow disposal areas for abutting parking lots, and snow mixing from multiple adjacent lots makes it impossible to link surface soil results to one parking lot. Furthermore, in terms of potential exposure points, children routinely play in residential yards, not at the edge of commercial parking lots. A separate USGS study found that PAH concentrations are much lower in residential yards and directly adjacent to residential driveways than adjacent to commercial parking lots. Samples from edges of commercial parking lots are not relevant for residential risk assessment. Should additional studies be performed to collect data from actual exposure areas that can isolate the effect of coal-tar-based sealant use, the risk assessment undertaken at that time could use standard U.S. Environmental Protection Agency (EPA) risk assessment assumptions to evaluate “reasonable maximum” exposures. The authors used a soil ingestion rate of 400 mg per day (mg/day), double what EPA recommends for the reasonable maximum exposure case (200 mg/day). The EPA rate accounts for both soil and dust ingestion. The authors calculated intake for dust separately and added this to soil intake, in effect increasing the soil/dust ingestion rate for children to 500 mg/day and inappropriately increasing the resulting risk estimates by a factor of 2.5. An additional nonstandard increase in the soil ingestion rate was done by assuming 7−13 year olds ingest soil at the same rate as children age 0−6 years. Risks for this subgroup are inappropriately increased by a factor of 4 with use of a soil ingestion rate four times greater than the 100 mg/day rate recommended by EPA for this age group. Another factor to consider in a future risk assessment of coaltar-based sealants is bioavailability. PAHs are bound to soil and other matrices (pieces of asphalt pavement) and are not 100% absorbed into the systemic circulation. While this is true for all PAHs in soil, it is particularly important if coal-tar-sealed pavement is the source. USGS and UNHSC have reported that large pieces of sealant or sealant adhered to pavement enter soil by surface water runoff or the action of snowplows. Sample photographs 16 identify particles far larger than the 250μm size cutoff that EPA considers relevant for human risk assessment, and bioavailability would be far lower than the bioavailability of smaller particles. Risks to people living near coal-tar-sealed pavement from PAHs in soil have not been estimated by the authors. Soil exposures to coal tar constituents in areas near sealed pavement where people might actually be exposed have not been characterized. The risk estimates presented by the authors cannot be used to make decisions about the risk of coal-tarbased sealants. Since the risk associated with coal-tar-based sealants has not been characterized due to insufficient data, it is not justifiable to pursue policies to ban the use of coal-tar-based sealants. Risk management decisions should not be made on the basis of screening level risk assessments, particularly those