Sources and Impacts of Selenium Contamination
9
from surface residuals by natural rainfall/snowmelt is not as great as it
would be in regions of high precipitation. For many years, these conditions prevented major selenium runoff from occurring. However, the
immense size of mine tailings piles (up to 50 million m3) has changed
subsurface hydrology in such a way that groundwater has risen within
the tailing piles and created miniature aquifers that seep laterally and
exit the mine spoils as streams of selenium-laden leachwater containing up to 1500 Jlg SelL (Desborough et al. 1999; Herring et al. 1999).
Local fish, wildlife, and livestock have been contaminated, and a major recreational fishery is threatened (Lemly 1999). Although there
are presently no other well-documented cases of this type of selenium
pollution, natural resource managers around the world should understand that phosphate mining has the potential to impact aquatic life
wherever the practice occurs. It is also important to recognize that
local climate and hydrology will determine the rate and type of selenium leaching that takes place from surface residuals.
Metal Smelting
Metal ores contain some amount of selenium, and the physical/chemical
treatment of this ore to extract the desired metal releases selenium
and other constituents into the process water or solid waste that is left.
These wastes often contaminate local aquatic habitats (Lemly 1994a).
However, some ores are also heated (smelted) in order to mobilize and
separate the desired metal, in particular, copper, nickel, and zinc. When
heating occurs, selenium is readily volatilized and can be emitted into
the air as a vapor. Once released, this selenium cools and can coalesce
or adhere to atmospheric dust particles (some of which are produced
by the smelters themselves), subsequently reaching terrestrial and
aquatic systems by either dry or wet deposition (Germani et al. 1981;
Small et al. 1981). In some situations, these processes can be a substantial factor in the cycling of selenium near smelting facilities. One
such example occurred near Sudbury, Ontario, Canada (Table 1.2, Fig.
l.1). Selenium is quite common in copper ore and may actually be
more concentrated in copper ore than in coal (20-82 Jlg Se/g for copper ore versus 0.4-24 Jlg Se/g for coal) (Table l.1) (Nriagu and Wong
1983). On a total-mass basis, the Sudbury ore deposits north of Lake
Huron in Canada are the largest source of selenium in North America
(Shamberger 1981). Large-scale copper smelting at Sudbury began in
the early 1900s, and sampling conducted in the late 1970s showed that
selenium discharges had contaminated freshwater lakes for a distance
of at least 30 km downwind of the smelter (Nriagu and Wong 1983).
The aerial plume was also implicated as the primary cause of elevated
concentrations of selenium in fish and other biota of Georgian Bay in
9
from surface residuals by natural rainfall/snowmelt is not as great as it
would be in regions of high precipitation. For many years, these conditions prevented major selenium runoff from occurring. However, the
immense size of mine tailings piles (up to 50 million m3) has changed
subsurface hydrology in such a way that groundwater has risen within
the tailing piles and created miniature aquifers that seep laterally and
exit the mine spoils as streams of selenium-laden leachwater containing up to 1500 Jlg SelL (Desborough et al. 1999; Herring et al. 1999).
Local fish, wildlife, and livestock have been contaminated, and a major recreational fishery is threatened (Lemly 1999). Although there
are presently no other well-documented cases of this type of selenium
pollution, natural resource managers around the world should understand that phosphate mining has the potential to impact aquatic life
wherever the practice occurs. It is also important to recognize that
local climate and hydrology will determine the rate and type of selenium leaching that takes place from surface residuals.
Metal Smelting
Metal ores contain some amount of selenium, and the physical/chemical
treatment of this ore to extract the desired metal releases selenium
and other constituents into the process water or solid waste that is left.
These wastes often contaminate local aquatic habitats (Lemly 1994a).
However, some ores are also heated (smelted) in order to mobilize and
separate the desired metal, in particular, copper, nickel, and zinc. When
heating occurs, selenium is readily volatilized and can be emitted into
the air as a vapor. Once released, this selenium cools and can coalesce
or adhere to atmospheric dust particles (some of which are produced
by the smelters themselves), subsequently reaching terrestrial and
aquatic systems by either dry or wet deposition (Germani et al. 1981;
Small et al. 1981). In some situations, these processes can be a substantial factor in the cycling of selenium near smelting facilities. One
such example occurred near Sudbury, Ontario, Canada (Table 1.2, Fig.
l.1). Selenium is quite common in copper ore and may actually be
more concentrated in copper ore than in coal (20-82 Jlg Se/g for copper ore versus 0.4-24 Jlg Se/g for coal) (Table l.1) (Nriagu and Wong
1983). On a total-mass basis, the Sudbury ore deposits north of Lake
Huron in Canada are the largest source of selenium in North America
(Shamberger 1981). Large-scale copper smelting at Sudbury began in
the early 1900s, and sampling conducted in the late 1970s showed that
selenium discharges had contaminated freshwater lakes for a distance
of at least 30 km downwind of the smelter (Nriagu and Wong 1983).
The aerial plume was also implicated as the primary cause of elevated
concentrations of selenium in fish and other biota of Georgian Bay in