Effects of Toxic Chemicals and Other Pollutants on Aquatic Ecosystems - Freshwater Ecology: Concepts and Environmental Applications - page 285

TABLE 14.4 Effects on Aquatic Environment Related to Various
Mining Activities a

Type of mining Potential impacts

Coal High water demand; high sediment load in runoff; acid

runoff from high sulfur deposits; high concentrations of
iron, manganese, and other metals

Gold and silver Same as sulfur ores; possible mercury, cyanide, or arsenic

contamination

Iron Heavy water demand; runoff of sediments; toxic metals

Salt Salinization of wastewater

Sulfide ores (copper, nickel, Acidification by sulfuric acid; possible arsenic contamination,

lead, and zinc) sediments

Uranium Acid tailing drainage; runoff of radioactive materials, toxic

metals, sediments, and organic compounds

a Adapted from Ripley et al. (1996).

and Wildlife Service has phased out use of lead shot in favor of steel shot
(Laws, 1993). Lead fishing weights are still in use and have been implicated
in wildlife deaths. In addition, atmospheric lead deposition increases lead con-
centration in lakes throughout the world. Analysis of peat bog sediments in
Switzerland indicated that anthropogenic inputs increased lead contamination
starting 3000 years ago, and that in 1979 deposition rates were 1570 times
the natural background values found prior to 1000 BC (Shotyk et al., 1998).
Mercury contamination of fish is a problem that has beset many areas.
Methylmercury can be assimilated and concentrated by organisms in aquatic
food webs. It enters aquatic systems mostly from atmospheric fallout from
coal burning, trash incineration, and industrial emissions. Mercury accu-
mulation in a Spanish peat bog increased about 2500 years ago, at a time
when mercury mining began in the region (Martínez-Cortizas et al., 1999).
In some countries, mercury is used indiscriminately to extract gold in min-
ing operations and can heavily contaminate freshwater systems (Cursino
et al., 1999). Periphyton mats appear to be an important site of mercury
methylation and its entry into the food web (Cleckner et al., 1999). Bio-
magnification has resulted in levels of mercury in fish high enough to war-
rant consumption advisories. Such restriction on consumption may be prob-
lematic for people that utilize fish as a large component of their diet (Egeland
and Middaugh, 1997). Eutrophic systems can have less severe problems
with production and concentration of methylmercury in the food web
(Gilmour et al., 1998), but generalizations may be difficult since the rela-
tionships between organic C and methylmercury concentrations are com-
plex (Hurly et al., 1998). The problem has been studied in the Everglades,
where fish consumption advisories have been issued because methylmercury
concentrations in fish tissues exceed 30 ng g 1 (Cleckner et al., 1998).
Selenium has caused severe problems in some wetlands. Irrigation mo-
bilizes selenium naturally found in soils and concentrates the selenium as
the water evaporates. In Kesterson Reservoir, a National Wildlife Refuge
in central California, selenium contamination caused congenital deformi-
ties and mass mortality of waterfowl. Although selenium is a required nu-
trient in trace levels, it bioaccumulates and becomes toxic at higher con-