, and food items. None of these other pathwaysresulted in nickel exposure doses of public health concern. It is also important to note thathow the nickel is taken into your body affects the toxicity. Inhaled nickel, via airborneparticulates, is much more toxic than the same amount of nickel ingested with food or water.Also, nickel particles larger than 5 microns are not considered respirable  and are routedthrough the gastro-intestinal system rather than the lungs. As the estimated inhaled nickeldose is below a level of public health concern, adding a minor amount of less toxic ingestednickel will not significantly increase the total estimated nickel dose.
I thank you for the opportunity to comment on the Health Consultation, "Exposure Assessment of Airborne Nickel and other Metal Particulates from Historic Smelter Operations at the Paducah Gaseous Diffusion Plant" (Public Comment Release- November 6, 2001). I am pleased that the investigation found no cause for public concern. I have the following comments on the report.
It would be helpful to have a statement of no public concern near the beginning of the report. I suggest adding to the first paragraph- "Concentrations of concern were not found and no recommendations are warranted."
The rationale for not including metal particulates from the TVA Shawnee Steam Plant is not clear. While the emissions of the steam plant and smelter stacks will not be additive during any short period, the annual average concentrations would be additive. The lack of any significant contribution from the steam plant may be deduced from the results of the soil sampling. The 12 ppm nickel found in off-site soils probably represents deposition from steam plant effluents during its nearly 50 years of operation, during many of which the stack heights were only about 60 meters. The significantly higher soil concentrations on the PGDP site is evidence that the contribution, however small, of the nickel smelter to airborne concentrations was significantly higher than that from the steam plant and that from the steam plant may be ignored.
ATSDR Response: A summary has been added to the revised document (to the healthconsultation; not in this appendix). We have also reconfigured the ISC air dispersion modelto include potential contributions from both PGDP steam plant and the TVA facility. Basedon 1998 and 1999 Toxic Release Inventory data for the TVA facility , the instantaneousnickel air emissions average ~0.0025 g/sec. Assuming that those later years are similar tothe years of PGDP nickel smelter emissions, the instantaneous TVA release is about 20times lower than the PGDP smelter release (0.05 g/sec) and is dispersed from an 800+ footstack. Similarly, using standard emission factors for coal and oil combustion and annual fuelusage rates, instantaneous nickel emissions from the PGDP steam plant averaged 0.00009g/sec, which is 500 times lower than the smelter emissions (dispersed from two adjacent 110foot stacks). The results of the revised air dispersion models indicate no differences in theshort term or annual distributions of nickel. All estimated concentrations are still well below levels of health concern.
- Kentucky Environmental Oversight: List of Hazardous Waste and RadionuclideParameters Currently Analyzed and Monitored by the Commonwealth of Kentuckyat the Paducah Gaseous Diffusion Plant (Name Redacted) includes nickel, nickelcompounds, nickel carbonyl, and nickel cyanide. What PGDP operation(s) producesthis waste stream? Did this Health Consultation and/or the Public Health Assessmentfor PGDP include this source of nickel? Is this nickel monitored in air, soil, or water?
- Phase II Independent Investigation of the Paducah Gaseous DiffusionPlant...February 2000, section 3.2.5 smelting, refers to scrap metal recovery recordsbeing "...removed by another DOE team investigating scrap metal recovery at theplant." Has ATSDR reviewed those records? Additionally, the same section of PhaseII refers to "a 1972 study of radionuclides in scrap..."; did ATSDR review that study?Further, a chart on page 7