Bioavailability of Red Dog Mine Lead Ore
Assessment of Battelle Study, "Evaluation of Lead Ore in Fischer 344 Rats"
Scott Arnold, Ph.D.
July 16, 2001
Lead sulfide, galena (PbS), is the chemical form of lead in the ore from Red Dog Mine. It is well known lead sulfide is very insoluble and has low bioavailability.
In response to the discovery of high concentrations of lead in Skagway, AK from transportation of lead ore concentrate from mining operations in Canada in the late 1980s, the Section of Epidemiology, Alaska Division of Public Health (ADPH) conducted an extensive investigation in collaboration with the National Centers for Disease Control and Prevention. As part of the investigation, lead ore concentrate from the Curraugh mine in Canada was tested for bioavailability in animal feeding studies by the National Toxicology Program (NTP), National Institute of Environmental Health Sciences (NIEHS).
In the early 1990s, the ADPH conducted studies of lead exposure related to the Red Dog Mine, including measuring blood lead levels of all residents of Noatak and Kivalina. Blood lead levels of the residents of Noatak and Kivalina were very low. Because of the potential for future possible exposure to the ore concentrate derived from Red Dog Mine, the ADPH suggested in 1991 that the lead ore concentrate from the Red Dog Mine undergo bioavailability studies by the NTP.
The bioavailability of lead in both ores was evaluated by the NTP. In 1993, the NTP published a study evaluating the bioavailability of the Skagway lead ore concentrate in a rat model. The results of the Skagway study, published by the NTP 1993 in the Journal of Toxicology and Environmental Health, documented the low bioavailability of the lead from the Skagway ore. Also in 1993, the NTP conducted a similar study of lead ore concentrate from Red Dog Mine. The study of the Red Dog Mine ore was completed by the NTP contractor; however, the results have not been analyzed and officially evaluated by NTP. At the request of the ADPS, the NTP provided the contractor’s report to the ADPH. The Section of Epidemiology has reviewed NTP contractor’s report, and the results of the study are directly comparable to the Skagway ore concentrate bioavailability study. The results of our analysis are outlined below.
Comparison of the bioavailability of lead ore concentrate from Skagway, Alaska and Red Dog Mine.
The bioavailability studies performed using the Red Dog Mine and Skagway ore concentrate were very similar. Both studies were designed and carried out using standard NTP protocols. Both studies used six to eight-week old male Fisher 344 rats, similar animal housing, animal handling, dosing schedule, and feed. Ten rats were sacrificed for each analysis. The analytical procedures used in measuring lead tissue concentrations were similar.
Although the lead concentrations in the two ore concentrates were slightly different (Skagway 57.9 percent; Red Dog Mine 45.2 percent), feed was prepared in a similar manner resulting in dosing levels of 0, 10, 30, and 100 ppm lead. Both studies amended the feed with sieved lead ore concentrate of similar particle size (< 38 m m), which is very important since particle size will have a large effect on the absorption of the lead.
In the Skagway study, rats were fed for 30 days with feed amended with lead acetate, lead oxide, lead sulfide, or lead ore concentrate at the doses mentioned above. Lead acetate, lead oxide and lead sulfide were used as a relative comparison in determining the bioavailability of lead in the ore concentrate. Lead acetate is known to be the most bioavailable form, and lead sulfide is the least bioavailable form.
In the Red Dog Mine study, rats were fed for 30, 60, and 90 days with feed amended with lead sulfide, Red Dog Mine ore concentrate, and the concentrate of two other mines at dosing levels of 0, 10, 30, 100 ppm lead.
A variety of assays (e.g., blood, bone, kidney, liver, and brain lead concentrations, and the levels of enzymes and intermediates involved with heme synthesis) were performed in each study to determine the bioavailability of lead in the rat model. Determination of blood and bone lead concentrations were the two endpoints that are directly comparable from the two studies.
Table 1 presents the blood lead concentrations for the Red Dog Mine and Skagway ore 30 day feeding studies. Blood lead concentrations for the Red Dog Mine ore (11.5 m g/dL) and Skagway ore (8.5 m g /dL) were relatively the same at the highest administered lead dose (100 ppm). These concentrations were only 10 to 14 percent of the blood lead concentrations found in the rats fed lead acetate (84.8 m g/dL) at 100 ppm, indicating a significantly reduced bioavailability.
Table 2 presents the bone lead concentrations for the Red Dog Mine and Skagway ore 30 day feeding studies. Similar to the blood lead concentrations, the bone lead concentrations for Red Dog Mine ore (11.2 mg/kg) and Skagway ore (13.8 mg/kg) were relatively similar at the highest administered lead dose (100 ppm). The lead bone concentration in animals fed 100 ppm lead acetate was 260 mg/kg. Again, this indicates a significant reduction in the bioavailability of the lead contained in the Red Dog Mine ore concentrate and Skagway ore concentrate.
It is apparent from these results the Red Dog Mine lead ore concentrate has a similar bioavailability to the Skagway lead ore concentrate, and the lead contained in these ores (lead sulfide) has a much lower bioavailability compared to lead acetate. Because the Red Dog Mine study has not been officially released by the NTP, the Section of Epidemiology has requested the NTP to review our analysis and evaluate the contractor's report.
The results of NTP’s Skagway lead ore bioavailability study support the findings of the ADPH health hazard and risk assessment activities evaluating lead exposure in Skagway, AK in 1989. Although the lead concentrations in the Skagway community were present above regulatory clean up levels for many years, there were no clinical signs of lead toxicity present in any children, adults, or animals tested in Skagway. In addition, the mean blood levels of children and adults were similar to those found in pristine, rural communities and below national averages. These results indicated, although environmental exposure to lead ore was potentially very high for extended periods of time, the actual biological exposure was minimal because of the low bioavailability of the lead contained in the ore concentrate. The rat bioavailability study performed by the NTP confirmed these conclusions.
Concerning the Red Dog Mine haul road situation, the ADPH preliminary evaluation of the data indicate:
Red Dog Mine employees receive routine blood lead testing under requirements of the Mine Safety and Health Administration (MSHA). Results of these blood tests document that the lead ore concentrate is partially bioavailable and that lead can be absorbed by workers who are heavily exposed to lead ore concentrate. Continued blood lead monitoring of occupationally exposed workers is essential to protect worker health and safety.
TABLE 1. Blood Lead (mg/dL) in Male F344 Rats Fed Compounds as Lead in Diets for 30 days
aMeans ± standard error; n = 10, except where indicated in parentheses; these are values above detection limit.
bBDL, below detection limits of 0.3 mg/dL.
cMeans ± standard deviation; n = 10, except where indicated in parentheses; these are values above detection limit.
dMeans ± standard error; n = 5, the first set of numbers were used to compare to the 100 ppm group while the second set was used for comparisons with the 10 and 30 ppm groups.
TABLE 2. Bone Lead Concentration (mg/kg) in Male F344 Rats Fed Compounds as Lead in Diets for 30 days
aValues are interpreted from graph presented in Dieter et al. 1993; n = 10; mean ± standard error.
bValues are mean ± standard error; n = 10.
cMeans ± standard error; n = 5, the first set of numbers were used to compare to the 100 ppm group while the second set was used for comparisons with the 10 and 30 ppm groups.