ced during primary nickel smelting operations (i.e., during theproduction of nickel metal from nickel ore). Nickel operations at PGDP may have producedlimited quantities of the non-oxide forms. However, from a quantitative perspective, mostPGDP emissions were in an oxide form.
ATSDR Response: Information supporting and clarifying this statement has been added tothe consultation. The toxicity of all of the metals smelted was assessed using healthcomparison values and quantities of smelted metals. These comparison values are stated interms of a dose or contaminant mass per unit body weight per unit time (mg/kg/day). Themore toxic metals have lower comparison values, i.e., it takes less of the metal to causeillness. As nickel was by far the most toxic metal that was smelted in quantity, it was used asa benchmark for assessing levels of significant exposure. Cobalt was the only smelted metalwith a higher toxicity than nickel. Based on ATSDR and EPA health comparison values,cobalt is approximately 10 times more toxic than nickel. However, only about 38,000pounds of cobalt were smelted which is about 1700 times lower than the 6.7 million poundsof annual nickel production. Because smelting operations of relatively toxic nickel did notproduce off-site concentrations at levels of health concern, smelting of much smallerquantities of other toxic metals will also be below levels of health concern.
ATSDR Response: ATSDR considered cumulative, additive, synergistic, and antagonisticeffects of exposure to the extent of scientific knowledge in this area. Information andreferences related to ATSDR's process of evaluation have been added to the consultation.
ATSDR Response: See above for response to assessing interactive effects to differentcontaminants. The PGDP Public Health Assessment does assess potential cumulative dosesand health effects to community members that may be exposed to contaminants throughmultiple pathways. Potential exposure doses to nickel (and other metals) were estimatedfrom ground water, surface water, soil, 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 plan