Environmental Engineering Reference
In-Depth Information
photogeology, thermal analysis, geochemistry and satellite imaging. Thus
geobotanical methods of mineral exploration, concerned with the detection
of subsurface mineralisation by an interpretation of its vegetative cover or
'indicator plants' (Brooks
1998
) are rarely reported in the literature of the
Region. Two of the few geobotanical surveys published in the Region are
those of Viladevall et al. (
1994
) in Bolivia and Fern´ndez-Turiel et al. (
1994
)in
Argentina. Viladevall et al.(
1994
) suggested that Baccharis incarum (Asteraceae)
and Fabiana densa (Solanaceae) are good shrubs or 'tholas' to be used as regional
metal indicator plants in geobotanical surveys for Au, As, Sb and other metals
in the altiplanic areas of Bolivia, as their leaves are indicators of the metal
contents in the subsoil. In the Puna belt of Argentina, however, these species
grow on many soil types (Bonaventura et al.
1995
). Although these plants cannot
be classified as hyperaccumulator plants as they only reached a maximum of
540mg kg
1
Sb in their leaves, a value below the criteria of
1000mg kg
1
for
Sb-hyperaccumulating plants, they may have metallophyte status. Fern´ndez-
Turiel et al.(
1994
) suggested that Prosopis alba (Mimosaceae) and Larrea divaricata
(Caesalpiniaceae) growing near an old smelter in the Sierra Pampeanas in
Argentina had two to six times more Sr, Cd, Bi, Zn, Ni, Li and Cu than the same
plants growing on unpolluted soils. They reported that all the shrubs studied
had the same pattern of metal accumulation in above-ground structures as
metal levels increased in soils, with the exception of P. alba and P. nigra which
accumulated more Zn than the other plants growing in the same soils (700 vs.
200mg kg
1
Zn in ash), a characteristic of metallophytes. Furthermore, with the
exception of serpentine floras described in Cuba and Brazil, there are no reports
of unusual locations where metallophytes dominate.
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Information from artesanal small-scale miners
Small-scale mining activities reveal additional, albeit unconfirmed, data on
metal ore indicating plants, as artesanal miners searched for metal ores using
simple biogeochemical methods of exploration based on rock colouration and
the associated plants. For example, when the Chilean endemic shrub Gymno-
phyton robustum (Apiaceae) grows on green-coloured rocks, miners are sure that
a copper ore is present in the subsoil. Although this information has not been
gathered extensively and reported formally in the literature, it may represent
an important source of information to commence a search for further metal-
lophytes, as artesanal mining is common in the Region.
Environmental threats from metal mining in Latin America
A lack of environmental regulations in most countries of the Region until
recent decades has allowed metal mining to result in serious and diverse
environmental problems threatening local vegetation in general and metallo-
phytes in particular. Although the situation has changed more recently due to
