from the testing done.
ATSDR Response: The Commentor is correct that radionuclide concentrations in the nickelbuttons underestimate the total radionuclide concentration of the feed material due tosegregation in the slag and nickel ingots. However, as stated in the above response to item 1,radionuclide stack emissions were also directly measured. Annual emissions from the C-746A stack are reported for the calender year 1985 . As these values are all at least fiveorders of magnitude lower than the emissions from other previously evaluated sources forearlier years (1956-59), they do not comprise a significant additional source of radionuclideemissions (see Table E-1 in Apendix E for uranium values evaluated for specific releaseyears).
ATSDR Response: The section containing the cited paragraph is entitled "Evaluation ofModeled Concentrations of Airborne Metals Particulates." While this clearly indicates thatthe data in question are model results, we will add the term "modeled" or "estimated" to thecited sentences. The comment is not correct in stating that "better data" are available whichshould be demanded from DOE. As historic off-site airborne nickel concentrations were notcollected for the express purpose of quantifying potential off-site exposures, any additionaldata will be subject to inherent uncertainty which limits its utility for exposure assessment.The best response to such uncertainty is to seek consistency from different types of data.Because our modeled off-site concentrations are based on measured stack concentrations andare consistent with measured soil concentrations, we are confident that the results of theevaluation are protective of public health.
ATSDR Response: The suggested revision has been incorporated into the healthconsultation. It is important to note the distinction between emissions from primary andsecondary (such as PGDP) nickel smelting operations. More than 90% of emissions fromsecondary smelters are in an oxide form . Refinery dust (primarily nickel subsulfide) ismore typically produced 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