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

seven there is no consumption restriction, except for East Mill Creek where children
under the age of seven should not eat more than four 4-ounce meals per month of
Yellowstone Cutthroat and Brook trout. This recommendation is just for caution, since
fish from the East Mill Creek are very limited and subsistence consumption of fish from
East Mill Creek is highly unlikely. Therefore, the selenium contamination in fish from
Blackfoot watershed is unlikely to result in any adverse health effects to adults and
children, including subsistence populations.
To conduct the Area Wide Human Health and Ecological Risk Assessment, TtEMI and
IDEQ personnel collected more fish tissue samples (TtEMI 2001) in July 2001. In total,
samples of fish tissue were collected from six areas located in both impacted and
unimpacted reaches of the streams (TtEMI 2002). Based on the data in TtEMI (2002), the
area-weight average concentrations (AWAC) of the contaminants in fish tissue are
summarized in Table C-6 (Appendix C).
BCEH found that the concentration of selenium in the Blackfoot watershed was higher
than the concentrations in the Salt and Georgetown watersheds (Appendix C, Table C-6).
Therefore, it is unlikely the selenium in fish tissue from the Salt and Georgetown
watersheds will result in any adverse health effects to adults and children, including
subsistence populations.
In the 2003 health consultation (BCEH 2003), only the selenium contamination was
evaluated. To evaluate the cadmium and chromium contamination in the fish, BCEH
calculated estimated daily exposure doses for all the contaminants. According to EPA’s
exposure factors handbook (EPA 1997), the estimated mean and 95 th percentile fish
consumption rates for recreational freshwater anglers are 8 grams per day (g/day) and 25
g/day respectively, while the recommended mean fish consumption rate for Native
American subsistence population is 70 g/day. It should be emphasized that 70 g/day
refers only to the Native American subsistence fishing population, not the Native
American general population. Several studies (West et al., 1989; Ebert et al., 1993) show
that the consumption rate of recreationally caught fish among Native Americans with
state fishing licenses are somewhat higher than consumption rates among other anglers,
but far lower than the rate (70 g/day) for the Native American subsistence population.
To be conservative and more protective of the population, BCEH used the Native
American mean fish consumption rate of 70 g/day and the adult body weight of 75
kilograms (kg) (165 lbs) (BVRHS 2001) to calculate the estimated daily exposure. The
estimated daily exposure doses (Appendix C, Table C-6) for cadmium and chromium are
at least 10 times lower than ATSDR’s chronic oral minimal risk level (MRL) and EPA’s
chronic oral reference dose (RfD) (Appendix C, Table C-7). The estimated exposure dose
for selenium (Appendix C, Table C-6) is also lower than both the MRL and RfD for
selenium (Appendix C, Table C-7). RfDs and the chronic MRLs are estimates of daily
human exposure to a contaminant that is unlikely to result in adverse non-cancer health
effects over a lifetime. Since these exposures are below both the MRL and RfD, the
exposure to cadmium, chromium, and selenium from eating fish from the Resource Area
is unlikely to result in any non-cancer adverse health effects to the general public, as well
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