urrounding chemical interactions and noted that if theestimated exposure doses for individual contaminants detected at the site are below doses shown tocause adverse effects (No Observed Adverse Effect Level; NOAEL), then ATSDR considers that thecombined effect of multiple chemicals is not expected to result in adverse health effects. It should benoted that typical environmental exposure doses to both carcinogenic and non-carcinogenicchemicals are more than 1,000 times lower than laboratory-induced effect threshold doses. Thisapproach to chemical interactions is based on the results of numerous studies:
- Several animal and human studies [15,16,17,18] have reported thresholds for interactions. Studies have shown that exposure to a mixture of chemicals is unlikely to produce adversehealth effects as long as components of that mixture are detected at levels below the NOAEL for individual compounds [19,20].
- The absence of interactions at doses 10-fold or more below effect thresholds have beendemonstrated [21,22]. Specifically, in two separate subacute toxicity studies in rats [23,24], adverse effects disappeared altogether as the dose was decreased to below the threshold level.
- For carcinogens, the interactions are more difficult to quantify due to the large study size(humans or animals) needed for statistical significance at the low doses observed inenvironmental exposures . In an animal study, Takayama et al. (1989) reported that 40substances tested in combination at 1/50 of their cancer effect level (CEL) resulted in anincrease in cancer . However, Hasegawa et al. (1994) reported no increase in cancerwhen dosing animals at 1/100 of the CEL for 10 compounds .
Estimated maximum hourly and annual nickel concentrations in areas of potential off-site exposuredo not exceed health-based cancer and non-cancer comparison values for either acute or chronicexposures (WKWMA workers and residents; respectively). As the toxicity of other smelted metals islower than nickel and/or the quantity of metals smelted is much lower, estimated airborneconcentrations of the particulates of the other metals are also below levels of public health concern.Past emissions of metal particulates from PGDP smelter operations in building C-746A posed "noapparent health hazard", which means that people may have been exposed to metal particulates butthat such exposure is not expected to cause any adverse health effects.
|Metal||Estimated Amount of Metal Smelted at PGDP (pounds) 1||Health Comparison Value |
|Aluminum||> 11,500,000 pounds over more than 21 years 2||8 hr TWA3- 5000 µg/m3|
|Cobalt||71,500 pounds over 4 years||14-365 day MRL4- 0.03 µg/m3 |
8 hr TWA- 50 µg/m3
|Gold||~5284 pounds over 21 years||Not Available|
|Lead||>1,258,990 pounds (no dates)||8 hr TWA- 50 µg/m3|
|Monel (copper-nickel alloy)||882,440 pounds over 4 years||see Nickel|
|Nickel||~37,000,000 pounds over |
6 ˝ years
|>365 day MRL- 0.2 µg/m3 |
8 hr TWA- 15 µg/m3
|Silver||~9,630 pounds over 8 years||8 hr TWA- 10 µg/m3|
|Steel||22,000 pounds (process terminated after test runs)||8 hr TWA- 5000 µg/m3 (as iron oxide dust/fumes)|
|1 Estimates of total amount of metals smelted are derived from DOE [1,2]. |
2 Internal DOE (or AEC) memos and letters indicate, but do not prove, that aluminum smelting at PGDP began in the 1950's, but that in early years was limited to laboratory and bench testing of methods and processes that were instituted in production scale operations in the 1960's.
3 TWA- is the 8 hour time weighted average occupational exposure limit established by the National Institute of Occupational Safety and Health .
4 MRL- is the minimal risk level for residential exposures established by ATSDR.
Comments and Responses to the Public Release Version of the Health Consultation(November 6, 2001)
The following comments were received by ATSDR in response to the public release version of thehealth consultation dated November 6, 2001, which has been included in the public healthassessment as this Appendix I. These comments elicited several modifications of the originalevaluation. Poten