 such as soil, water, and sediment. The rationale for conducting this healthconsultation (this appendix) is that we did not include metal particulates released fromsmelting operations in assessing airborne contaminant distributions. The form of nickelevaluated in the Public Comment Release of the Public Health Assessment for the groundwater, surface water, soil and sediment, and biota pathways is total nickel. For the airpathway in this consultation (this appendix), the chemical form is, as referenced, nickeloxide(s); however, the nickel health comparison values used are applicable to elemental ormetallic nickel, and both soluble and insoluble forms.
With regard to the chemical form of nickel compounds, only the nickel carbonyl form has asignificantly higher toxicity than other forms (and only via inhalation). As nickel carbonyl isnot thermodynamically stable in soil, air, or water, it will be converted to other morethermodynamically stable forms, such as nickel hydrates in water and nickel ferrite in soil. Nickel also tends to strongly adsorb onto larger particles in both soil sediment whichlimits its subsequent mobility . Although in some cases, it may be important to assess thepotential distribution and concentrations of the most toxic chemical forms, the limitedchemical stability of nickel carbonyl precludes significant off-site transport and exposure.For the determination of the off-site contaminants of concern at PGDP, if the totalenvironmental nickel concentrations are below levels of health concern, it is not necessary todelineate the specific sources of the nickel.
With regard to the total nickel distribution in the environment surrounding PGDP, there area number of potential sources including naturally occurring background levels in all media(nickel is the 24th most common element in the earth's crust) . In addition to the PGDPsmelter and steam plant and the TVA facility, minor sources include forest fires, volcanoes,fuel oil combustion, and other manufacturing processes. Any measurement of nickel in anyenvironmental media will include contributions from all sources. Neither the public healthassessment nor the health consultation attempted to discern the specific source of nickel inany media. The objective in these contaminant evaluations is to determine if the totalexposures result in doses of public health concern. If the doses are at concentrations of publichealth concern, it may become necessary to determine the specific sources in order toimplement a dose reduction strategy.
The annual smelter nickel emissions for the years 1983 to 1986 is estimated to be about 794pounds per year (based on an instantaneous emission rate of 0.05 g/sec for 8 hours per dayand 250 days per year). This operating schedule is in agreement with estimates of annualsmelter production of 6.7 million pounds per year (for the radiologically contaminatednickel). Using an average smelter loading rate of 3350 pounds per hour for 8 hours day, 250days per year equals a smelter output of 6.7 million pounds per year which is very close tothe average annual nickel production. It is assumed that releases of non-contaminated andcontaminated nickel are similar even though the maximum amount of non-contaminatednickel produced was stated to be just over 5 million pounds per year.
Although ATSDR was aware that metal smelting operations had taken place at PGDP, wehad not included such emissions in the Public Comment Release of the Public HealthAssessment. This consultation (this appendix) is a response to comments received.
ATSDR Response: Nickel stripping operations in C-400-C consisted primarily in use oforganic solvents (either trichloroethylene or trichloroethane) to remove surfacecontamination from nickel components. This process will not result in the release ofsignificant quantities of nickel. Emissions of and potential exposures to the organic solventswere evaluated in the PHA.
ATSDR Response: Any such health data is confidential information. ATSDR has no accessto such data unless provided by the individual in question and cannot review or ev