Gold [Au, 79]
133
In sea- and river-bottom sediments, Au may be present in cationic species, of
different oxidation states such as Au°, Au + , and Au 3+ . Gold occurs in several types
of deposits such as lode (metalliferous ores), residual, alluvial, bench, ancient rivers,
and flood layers. A lode deposit is the original source of its deposits, mainly as pieces
of ore. Pieces of Au ore are also likely to be deposited in cracks or crevices in the
rocks, at the bottom of streams and rivers.
Some aquatic biota (e.g., brown algae) may accumulate considerable amounts
of Au, especially near the mining and smelting areas. Mackerel (Pneumatophorus
japonicus) and common mussel (Mytilus edulis) may concentrate Au up to 12 μg/kg
and up to 38 μg/kg, respectively.
18.4 AIR
Gold concentrations in air of remote areas do not exceed 1.5 pg/m 3 , whereas it may be
up to 300 pg/m 3 in industrial regions (Table 18.1). Its wet deposition in Sweden was
estimated at 0.07 g/ha/yr, and in the United Kingdom between the range of <0.07
and <0.2 g/ha/yr (Cawse, Eriksson vide Kabata-Pendias and Mukherjee 2007).
Gold particulates in the atmosphere are mainly from volcanic emissions in both
gaseous and aerosol forms. It has been calculated that Mt. Etna, Italy, emitted 880 kg
Au during the eruption, and Mt. St. Helen, United States, emitted 1100 kg of Au
(Reimann and de Caritat 1998).
Gold content in lichens nearby Au mines accumulated from 0.22 to 1.45 mg Au/kg,
whereas the background values for Au in this area is 0.12 mg/kg (Limbong et al. 2003).
18.5 PLANTS
Gold is easily phytoavailable, and when it enters the root vascular systems, it is easily transported to the tops. In reducing media, however, Au precipitates on a cell
surface, and thus inhibits membrane permeability. Therefore, in most plants, its content in roots is higher than in above-ground parts. Ability of microorganisms to
mobilize elemental Au has been often observed. Especially microorganisms in the
plant rhizosphere are responsible for the Au mobility and availability (Eisler 2004).
The background Au contents of plants growing in uncontaminated soils is within
the range of <0.001–<0.005 mg/kg (Girling, Greger vide Kabata-Pendias 2011).
Plants from Au-contaminated sites contain Au commonly within the range of
0.007–0.17 mg/kg. Several Au-accumulator plants (e.g., Artemisia persia, Prangos
popularia, and Pinus laricio) may contain Au at level of 0.1–100  mg/kg. In most
plants, Au concentration in seeds is higher than in leaves and stems. Forest mushroom (Boletus edulis) from uncontaminated site accumulates Au up to 0.235 mg/kg
(Falandysz et al. 2012).
Gold concentration in plants and shrubs has been extensively used for the biogeochemical survey for Au-mineralized areas, and some plants (e.g., Sedum aceotatum,
Phacelia sericea, and Artemisia sp.) have been successfully used. Various plants
collected from the mineralized areas of British Columbia (Canada) contained Au
within the range of 0.7–6.5 mg/kg. Several plants are relatively resistant to higher