o potential cancer risk(4). Similarly, the maximum short term nickel concentration of 1.1 µg/m3 (at 500 m from source; maximum one hour average) is more than 10 times lower than the worker exposure limit of 15 µg/m3 (which includes consideration of potential occupational cancer risk). The estimated maximum hourly, daily, and annual nickel air concentrations from PGDP smelter operations, with potential contributions from the PGDP steam plant and TVA facility, are below levels of health concern.
These estimated off-site nickel concentrations in air include potential contributions from the PGDPnickel smelter emissions, the PGDP steam plant nickel emissions, and the TVA Shawnee coal plantnickel emissions. Modeled emission rates from the PGDP steam plant were based on healthprotective assumptions concerning fuel usage, operating schedules, and emission factors. Actualemission rates are probably lower than modeled rates. All estimated nickel air concentrations,calculated using health protective model assumptions, in areas of potential off-site exposure aremore than 10 times lower than relevant health comparison values.
|500 m||1000 m||1500 m|
|1989 Annual Average||0.018||0.003||0.001|
|1990 Annual Average||0.022||0.004||0.002|
|1991 Annual Average||0.018||0.003||0.001|
|1989 1 hour maximum||1.0||0.12||0.05|
|1990 1 hour maximum||1.0||0.15||0.07|
|1991 1 hour maximum||1.1||0.17||0.06|
|1989 8 hour maximum||0.25||0.05||0.02|
|1990 8 hour maximum||0.23||0.05||0.02|
|1991 8 hour maximum||0.25||0.05||0.02|
Table I-2 lists the metals smelted at PGDP along with the estimated total amount of each metal andthe relevant inhalation health comparison values for each metal. The health comparison values forresidential and occupational exposure are a measure of the toxicity of each metal. The most toxicmetals have the lowest health comparison values because it takes a lower amount of the substance tocause sickness or adverse health effects. This evaluation focuses on nickel because it is relativelytoxic and very large quantities of the metal were smelted resulting in the highest potential off-site airconcentrations.
As the smelting of other metals will release particulates in proportion to the total amount of materialsmelted and the dispersion of those metals will follow the same dispersion patterns as nickel, itfollows that the off-site concentrations of other metal particulates will be proportional to the amountof metal smelted. Based on the relative toxicities of the various metals and the amounts of eachmetal smelted, off-site concentrations of all metals smelted at PGDP are below levels of healthconcern.
ATSDR considered interactive effects (cumulative, additive, synergistic, and antagonistic) ofsubstances following exposure to multiple substances to the extent of scientific knowledge in thisarea.
- Cumulative effects (the effects associated with concurrent exposure by all relevant pathwaysand routes of exposure to a group of substances that share a common mechanism of toxicity) were addressed on pages 91 and 92 and in Table 24 of the PHA.
- Additive effects (the combined effects of two substances is equal to the sum of the effects ofeach agent given alone) were considered for exposure to radioactive materials on pages 117through 119 in the PHA. Of the metals evaluated in this appendix only nickel and monel areconsidered to have additive effects (because monel is a nickel alloy). However, the amountof monel smelted and emitted is insignificant with regard to the amount of nickel smelted.
- Existing information is inconclusive with regard to potential synergistic effects (when thecombined effect of two substances is much greater than the sum of the effect of each agent given alone) for the metals evaluated in this appendix.
- Antagonistic effects (when a substance reduces the toxicity or uptake of another substance)were not considered in this appendix in order to maintain a health-protective screeningscenario even though concurrent exposures to magnesium or zinc reduce the toxicity ofnickel.
ATSDR has reviewed the scientific literature s