80
L.D. Lacerda and W. Salomons
et al. 1988). Nriagu et al. (1992), studying Hg partitioning between dissolved and
particulate forms in the Madeira River waters, also showed that dissolved
mercury concentrations are independent of its concentrations in suspended
sediments. Mudroch and Clair (1986) found the same Hg distribution pattern in
waters draining tailings in Canada. They have also suggested that contamination
of sediments was due to transport and deposition of suspended particles brought
into the drainage by erosion of mining wastes. Similar behavior was reported by
Lechler and Miller (1993) for tailings in the Carson River Valley, USA, and by
Nelson et al. (1977) for mineralized areas in Alaska.
Most studies have found no significant changes in dissolved mercury
concentrations, even during strong storm events. Apparently, only small
amounts of Hg are remobilized into solution and Hg concentrations in water
appear to be independent of Hg content in sediments. Thus, controlling waste
erosion and suspended particle transport by means of dams and impermeabilization and other protecting devices to tailings should be quite efficient
in preventing Hg contamination in areas surrounding tailing. Among the many
techniques available to stabilize tailings deposits is revegetation (Archer et al.
1988; Ernst 1988; von Michaelis 1988). However, few data exist which are
applicable to Hg-rich gold and silver mine tailings.
5
Impact on Biota
5.1
Terrestrial Vegetation
Terrestrial vegetation interacts with both soil and the atmosphere in the
acquisition of Hg (Siegel et al. 1987). We have shown (Lacerda and Salomons
1998) the importance of the atmospheric Hg in the geochemical cycles in gold
mining areas. Terrestrial plants can takeup Hg from the atmosphere directly
through gas exchange at the stomatal level or through membrane exchange with
wet and dry precipitation (Browne and Fang 1978). These processes are likely to
be enhanced in tropical vegetation, due to the efficient mechanisms of chemical
elements acquisition from the atmosphere mediated by epiphyllic organisms, in
particular algae and lichens (Jordan et al. 1980) at the crown leaflevel, and those
mediated by the high diversity and biomass of ephiphytes typical of most tropical
ecosystems (Benzing 1981; Nadkarni 1984). Therefore, tropical terrestrial
vegetation may provide rapid plant colonization with a self-sustaining plant
community able to efficiently decrease Hg mobilization from tailings to the
atmosphere. On the other hand, since Hg export from tailings to adjacent
drainages is particularly enhanced by erosion, terrestrial vegetation is a key
factor in protecting the tailings deposit integrity.
Some studies have been done on the vegetation cover of old mining tailings. At
the Oldham tailings, Nova Scotia, vegetation coverage exceeds 100%, with species
L.D. Lacerda and W. Salomons
et al. 1988). Nriagu et al. (1992), studying Hg partitioning between dissolved and
particulate forms in the Madeira River waters, also showed that dissolved
mercury concentrations are independent of its concentrations in suspended
sediments. Mudroch and Clair (1986) found the same Hg distribution pattern in
waters draining tailings in Canada. They have also suggested that contamination
of sediments was due to transport and deposition of suspended particles brought
into the drainage by erosion of mining wastes. Similar behavior was reported by
Lechler and Miller (1993) for tailings in the Carson River Valley, USA, and by
Nelson et al. (1977) for mineralized areas in Alaska.
Most studies have found no significant changes in dissolved mercury
concentrations, even during strong storm events. Apparently, only small
amounts of Hg are remobilized into solution and Hg concentrations in water
appear to be independent of Hg content in sediments. Thus, controlling waste
erosion and suspended particle transport by means of dams and impermeabilization and other protecting devices to tailings should be quite efficient
in preventing Hg contamination in areas surrounding tailing. Among the many
techniques available to stabilize tailings deposits is revegetation (Archer et al.
1988; Ernst 1988; von Michaelis 1988). However, few data exist which are
applicable to Hg-rich gold and silver mine tailings.
5
Impact on Biota
5.1
Terrestrial Vegetation
Terrestrial vegetation interacts with both soil and the atmosphere in the
acquisition of Hg (Siegel et al. 1987). We have shown (Lacerda and Salomons
1998) the importance of the atmospheric Hg in the geochemical cycles in gold
mining areas. Terrestrial plants can takeup Hg from the atmosphere directly
through gas exchange at the stomatal level or through membrane exchange with
wet and dry precipitation (Browne and Fang 1978). These processes are likely to
be enhanced in tropical vegetation, due to the efficient mechanisms of chemical
elements acquisition from the atmosphere mediated by epiphyllic organisms, in
particular algae and lichens (Jordan et al. 1980) at the crown leaflevel, and those
mediated by the high diversity and biomass of ephiphytes typical of most tropical
ecosystems (Benzing 1981; Nadkarni 1984). Therefore, tropical terrestrial
vegetation may provide rapid plant colonization with a self-sustaining plant
community able to efficiently decrease Hg mobilization from tailings to the
atmosphere. On the other hand, since Hg export from tailings to adjacent
drainages is particularly enhanced by erosion, terrestrial vegetation is a key
factor in protecting the tailings deposit integrity.
Some studies have been done on the vegetation cover of old mining tailings. At
the Oldham tailings, Nova Scotia, vegetation coverage exceeds 100%, with species