Southeast Idaho Phosphate Mining Resource Area - Agency for ...

y request so that the agency could determine if the meat was fit for human consumption and
therefore donated to the Idaho Food Bank (Talcott et. al. 2000a). Ultimately, the meat was not
donated. Preliminary results from the Depuration Study were also reported in the Draft Interim
Investigation Data Report in April 2000. Study protocols can be found in that report (MW 2000).
More details about the grazing/depuration study are presented in Attachment B.
Initially, 45 steers were pastured for nine weeks on reclaimed overburden dumps at the Henry
Mine that were reclaimed approximately 20 years ago (MW 2000). Initially, the average
selenium content in the muscle at the time of slaughter B defined as Atypically five months
following removal from reclaimed land B one month on lowland pasture and four months in
feedlot@ B was estimated using correlations between blood and muscle. The 30 days on
nonselineferous forage and 4 months in the feed lot was said to be Atypical of normal cattle
handling practices in the area, in which, cattle are grazed on lowland pasture prior to shipment to
a feedlot.@(MW 2000). Selenium concentrations in muscle and other tissues were measured after
the animals were slaughtered at the end of the study. None of the steers exhibited symptoms of
selenium toxicosis during the duration of the study. Although this is a useful study for depuration
and can be used to estimate exposure of people eating beef from steers subject to 150 days off
seleniferous pasture, it is not very helpful for estimating exposure for the rancher, owner of a
steer or someone illegally killing a steer while it is still on the seleniferous pasture, then
consuming it or selling it for consumption.
b).
Sheep
Bollar (2000) believes that several herds of sheep, approximately 3,000 animals, are grazed for
30 B 60 days on pasture in the area under USFS permits during the summer months. Exactly
what happens to most of the sheep after they are taken off these lands is unclear. Some of the
lambs may go directly to slaughter. Many of the lambs may go onto feedlots. Most of the ewes
are likely grazed on other pasture. Many of these sheep may be sent to California for the winter
(Bollar 2000; Talcott 2000). It is unknown how many are consumed and when, in relation to
their time on the reclaimed mine pasture.
The deaths of several groups of sheep have been rumored to have been caused by selenium, but
evidence is not well documented. A diagnosis of acute myocardial necrosis and degeneration was
determined from several sheep samples analyzed by the University of Idaho. This condition is
associated with selenium exposure, but may also be caused by exposure to plant toxins,
rodenticides and other substances. Selenium levels in the tissues were high and selenium
toxicosis was thought to be the most likely diagnosis. Acute exposure to a selenium source was
suspected (Talcott 2000). Water and plants near the area where animals had died were collected
but a definite source for acute exposure was not identified. Samples have not been taken from all
of the sheep reported to have died. It is unclear how selenium exposure contributed to the death
of these sheep, how they were exposed to selenium, and where the exposure occurred. There are
many questions about the as-yet unexplained finding of another group of dead sheep at the
Wooley Valley Mine Overburden dump. It appears that selenium=s contribution to the death of
those sheep is still not understood.
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