Wednesday, July 13, 2005

Quantitative Risk Assessment for Coke Oven Emissions

BrooklynDodger was following one line of papers, and was distracted to another. Here's a heavily modeled risk assessment for lung cancer associated with coke oven emissions, based on data in people.

The assessment is based on the two-stage clonal expansion model, which is claimed to be more mechanistically based than the linearized multi-stage model [more arbitrary parameters.] Moolgavkar even has this model named after himself. BrooklynDodger, for the moment, abstains on whether the EPA estimate [6.2, in units to be discussed below], or Moolgavkar's new calculation [1.5] is correct. However, back of the envelope calculations based on the later number instruct, as would a 4-fold multiplier.

The unit risk number is in units of cases per 10,000, cradle to grave exposure at 1 microgram per cubic meter. The OSHA limit is 150 micrograms per cubic meter. People in this environment in the past were exposed far above the OSHA limit, and now are certainly pushing that value.

So, taking a 70 year life span, a 45 year occupational exposure, and multiplying by the OSHA limit, we get 1.4% of exposed workers dying of lung cancer. EPA's less modeled rates predict about 6% mortality at the OSHA limit.

So this paper provides one more example of how high a risk of occupational disease from long term chemical exposure OSHA standards leave behind.

Risk Anal. 1998 Dec;18(6):813-25.

Estimation of unit risk for coke oven emissions.

Moolgavkar SH, Luebeck EG, Anderson EL.

Fred Hutchinson Cancer Research Center, Seattle, Washington 98109-1024, USA.

In 1984, based on epidemiological data on cohorts of coke oven workers, USEPA estimated a unit risk for lung cancer associated with continuous exposure from birth to 1 microgram/m3 of coke oven emissions, of 6.2 x 10(-4). This risk assessment was based on information on the cohorts available through 1966. Follow-up of these cohorts has now been extended to 1982 and, moreover, individual job histories, which were not available in 1984, have been constructed. In this study, lung cancer mortality in these cohorts of coke oven workers with extended follow-up was analyzed using standard techniques of survival analysis and a new approach based on the two stage clonal expansion model of carcinogenesis. The latter approach allows the explicit consideration of detailed patterns of exposure of each individual in the cohort. The analyses used the extended follow-up data through 1982 and the detailed job histories now available. Based on these analyses, the best estimate of unit risk is 1.5 x 10(-4) with 95% confidence interval = 1.2 x 10(-4)-1.8 x 10(-4).

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