Acid Rock Drainage - Mining and the Environment: From Ore to Metal - page 691

may be impaired. Once the pH falls below 4, most biota will die, although some benthic
organisms may survive. At very low pH values, only specialized bacteria and algae may
occur, but these will have little, if any, value in terms of the overall ecology.
In practice, the scenario described above is an over-simplii cation. Factors such as pH
and the concentrations of cations and anions are commonly subject to considerable vari-
ation, with changes in discharge volumes in response to seasonal and specii c events, such
as the previously mentioned pulses which follow rainfall events. As a result, the ecosystem
may be in a constant state of change, both spatially and temporally, with periodic episodes
where organisms are killed, followed by partial or complete recovery, and with different
parts of the ecosystem affected to different degrees at different times. Of course, for rapid
recovery to occur, part of the ecosystem must remain unaffected so that it can provide
supplies of organisms to re-colonize affected areas. Another signii cant factor is that the
capacity of some environmental attributes that act to ameliorate the effects of ARD, may
eventually be exceeded, so that the situation could suddenly deteriorate as, for example,
when the buffering capacity of a receiving water body is overcome.
ARD discharges to the sea have been relatively rare. For many years, pyritic tailings from
the large Toquepala and Cuajone Copper Mines, operated by Southern Peru Copper, accu-
mulated along the shoreline of the Pacii c Ocean. While the resulting ARD produced an
unsightly scene, monitoring indicated little or no effect on the marine environment except
within and immediately adjacent to the tailings deposition area which extended for a dis-
tance of 10 km along the Pacii c Ocean coast. This is to be expected given the large buffering
capacity of sea-water and the open ocean situation in which water is constantly circulating.
Large quantities of tailings also accumulated within Macquarie Harbour on the west
coast of Tasmania, during many decades of mining at the Mt Lyell Copper Mine (see Case
17.1 ) in the Queenstown area. While ARD has occurred on exposed areas of tailings, the
effects have been highly localized and Macquarie Harbour supports a productive i shery.
Far more severe effects have occurred along the Queen and King Rivers, along which tail-
ings l owed before entering the sea.

Social and Community Effects
ARD may affect surface waters or groundwater supplies used for drinking and bathing.
In extreme cases, water supplies contaminated by ARD may become toxic, due to the pres-
ence of heavy metals such as arsenic at toxic concentrations. More commonly, acidic water
will have an unpleasant taste, leading to its abandonment as a source of potable water.
The ecological effects of ARD are also likely to be detrimental to local communities,
particularly in developing countries where aquatic resources such as i sh, shelli sh and
crustaceans contribute to subsistence. Again, adverse effects are more likely to result from
the disappearance of organisms used for food, rather than from consumption of contami-
nated organisms, although the latter is possible, particularly in the event of mercury con-
tamination (see discussion on Artisanal Mining in Chapter Five). Allegations of surface
water contamination from mining and mineral processing have been made in several
countries including Indonesia and the Philippines, with claims of rashes and other skin
disorders ascribed to the alleged contamination. In most, if not all such cases, consequent
investigations have revealed that such symptoms have not been related to ARD.
Finally, ARD commonly causes adverse visual effects such as red or brown staining
of the river bed and adjacent rocks or the accumulation of unsightly gelatinous sludge
(hydrated ferric hydroxides) where acidic seepage emerges or mixes with receiving waters.
While such adverse aesthetic effects may not, in themselves, cause damage, they certainly
draw attention to ARD and potentially contribute to community concerns which may or
may not be justii ed in terms of the real risks. There is no doubt that community concern
and community outrage are aggravated by visible signs of pollution.

Acidic water will have an
unpleasant taste, leading to its
abandonment as a source of
potable water.

ARD commonly causes adverse
visual effects such as red or
brown staining of the river bed
and adjacent rocks.