Hg Contamnation from New World Gold & Silver Mine Tailings
81
richness ranging from 12 to 15 species m-\ which is higher than that found in
abandoned pasture in the same region (Lane et al. 1988). Many of the plant
species recorded in the area are metal-tolerant species or metal-tolerant
genotypes derived from local populations. All species analyzed in these tailings
presented abnormally high Hg concentrations ranging from 0.2 to 3.5 ~lg g-I
(Lane et al. 1988). All terrestrial plant species studied presented higher Hg
concentrations in roots.
Siegel et al. (1985), studying the vegetation on British Columbia tailings, found
that different concentration factors (enrichment factors) among species occurred
only at low Hg concentrations in soils. When concentrations increased over 0.05
~lg g -I, enrichment factors were relatively constant among taxa, suggesting their
being metal-tolerant genotypes. Although only a few studies were done in Hgcontaminated tailings, it seems that the behavior of the vegetation is similar to
any other vegetation growing on metal-rich tailings.
Many more data, however are needed for a better comprehension of the fate of
Hg in terrestrial vegetation affected by gold mining.
5.2
Aquatic Vegetation
Aquatic macrophytes are more likely to accumulate Hg than terrestrial plants.
The availability of Hg to these plants will be a function of the dissolved Hg in
waters. Under the more acid freshwater conditions typical of tropical systems, Hg
availability should be high, and certainly much higher than in the soil or
sediment solution.
Different habitat of aquatic macrophytes may result in different Hg concentrations. Since the roots may effectively avoid Hg uptake from soils and
sediments, floating and submerged species, with roots in the water column, may
absorb Hg also directly from water through leaves and shoots. This has been
shown both between and within plant genera (Kelly 1988).
Aquatic macrophytes growing on tailings-influenced areas in Canada presented elevated Hg shoot concentrations ranging from 0.18 to 0.55 ~lg g - I dw (Lane
et al. 1988), with root concentrations much higher than in shoots. Lacerda et al.
(1991b), studying Hg concentrations in an emergent macrophyte Potenderia
lanceolata along gold mining tailings drainage in central Brazil, found no
significant correlation between Hg levels in the plant and in bottom sediments.
However, the highest values measured in the plant were generally found
associated with high sediment values. They suggested that the plants preferably
incorporate Hg2+, and since most Hg exported from these tailings was strongly
bound to suspended particles, its availability for plant uptake would vary
according to the environmental conditions of the drainage which would control
Hg release from suspended particles rather than the bulk Hg concentration in
sediments. In a Siberian gold district, little discharged metallic Hg was
assimilated by aquatic plants of local drainages (Tayrayev 1991).
Plants growing on Nova Scotia tailings drainages presented root:shoot ratios
ranging from 1.04 to 11.13 (Lane et al. 1988), and reached 6.17 in the floating
81
richness ranging from 12 to 15 species m-\ which is higher than that found in
abandoned pasture in the same region (Lane et al. 1988). Many of the plant
species recorded in the area are metal-tolerant species or metal-tolerant
genotypes derived from local populations. All species analyzed in these tailings
presented abnormally high Hg concentrations ranging from 0.2 to 3.5 ~lg g-I
(Lane et al. 1988). All terrestrial plant species studied presented higher Hg
concentrations in roots.
Siegel et al. (1985), studying the vegetation on British Columbia tailings, found
that different concentration factors (enrichment factors) among species occurred
only at low Hg concentrations in soils. When concentrations increased over 0.05
~lg g -I, enrichment factors were relatively constant among taxa, suggesting their
being metal-tolerant genotypes. Although only a few studies were done in Hgcontaminated tailings, it seems that the behavior of the vegetation is similar to
any other vegetation growing on metal-rich tailings.
Many more data, however are needed for a better comprehension of the fate of
Hg in terrestrial vegetation affected by gold mining.
5.2
Aquatic Vegetation
Aquatic macrophytes are more likely to accumulate Hg than terrestrial plants.
The availability of Hg to these plants will be a function of the dissolved Hg in
waters. Under the more acid freshwater conditions typical of tropical systems, Hg
availability should be high, and certainly much higher than in the soil or
sediment solution.
Different habitat of aquatic macrophytes may result in different Hg concentrations. Since the roots may effectively avoid Hg uptake from soils and
sediments, floating and submerged species, with roots in the water column, may
absorb Hg also directly from water through leaves and shoots. This has been
shown both between and within plant genera (Kelly 1988).
Aquatic macrophytes growing on tailings-influenced areas in Canada presented elevated Hg shoot concentrations ranging from 0.18 to 0.55 ~lg g - I dw (Lane
et al. 1988), with root concentrations much higher than in shoots. Lacerda et al.
(1991b), studying Hg concentrations in an emergent macrophyte Potenderia
lanceolata along gold mining tailings drainage in central Brazil, found no
significant correlation between Hg levels in the plant and in bottom sediments.
However, the highest values measured in the plant were generally found
associated with high sediment values. They suggested that the plants preferably
incorporate Hg2+, and since most Hg exported from these tailings was strongly
bound to suspended particles, its availability for plant uptake would vary
according to the environmental conditions of the drainage which would control
Hg release from suspended particles rather than the bulk Hg concentration in
sediments. In a Siberian gold district, little discharged metallic Hg was
assimilated by aquatic plants of local drainages (Tayrayev 1991).
Plants growing on Nova Scotia tailings drainages presented root:shoot ratios
ranging from 1.04 to 11.13 (Lane et al. 1988), and reached 6.17 in the floating