Gold Mining in Siberia as a Source of Mercury Contamination of the Environment
371
Previously, with the use of sluice amalgamation, metallic mercury settled down
on the bottom of the reservoir and was buried under the layer of processed
gravels. Thus, a significant amount of metallic mercury may be found under the
layer of bottom sediments and grounds in anaerobic low-temperature conditions
in the areas of mined-out placers, and presents a severe hazard to the
environment in the reworking process of such techno genic deposits.
Low temperatures of waters in natural reservoirs and streams even in summer
and total freezing of some of them in winter reduce the probability of mercury
methylation processes and its emission into the water phase due to the
development of heterotrophic microorganisms in the benthonic water layers and
bottom sediments. The probability of biogenic mercury methylation and its
accumulation in trophic chains of water ecosystems may increase only in shallow
lakes, dredge pits and settling tanks.
The role of vegetation in the biochemical mercury cycle under severe climate
conditions with spreading of permafrost will differ from areas with warm climate,
due to a short vegetation period, lesser growth rates and accumulation of foliage,
nutrition with waters overlying permafrost, which are predominantly formed by
precipitation. Particular distinctions must be observed in the areas of bald peaks,
tundra and mari landscapes, characterized by poor vegetation, chiefly consisting
of mosses, lichens and low forest. The tundra zone is characterized by simple
ecosystems and short trophic chains, therefore mosses and lichens, which can
accumulate mercury and other heavy metals from soils and precipitation, will
prevail in the food of mammalia. Thus, the elevated mercury concentrations in
the meat of wild deer and Manchurian deer 0.039 and 0.035 mg/kg, respectively,
exceeding the MPC for meat products (0.03 mg/kg) have been registered (T.G.
Laperdina, unpub1. data).
The processes of freezing and thawing of rocks, soils, bottom sediments, water
phase of rivers, lakes and industrial water objects are accompanied by a number
of complex chemical, physicochemical and physical processes, leading to the
transformation of mercury forms and their redistribution in the environment.
Thus, it was determined that frozen rocks of the ore gold deposits in Yakutia
(Omelchenko 1985) and some gold placers in Mogocha raion (Laperdina et a1.
1995, 1996) are characterized by a decreased mercury content, resulting from the
possible process of transference and concentration of mobile absorbed mercury
forms on the interface "ice water" during rock freezing. The processes of rock
weathering, which are mostly caused by temperature variations and water
freezing and thawing in rock fractures, are accompanied by the formation of
friable metasomatically altered products, which can be enriched with mercury. It
was determined that in weathering products of rocks the mercury content may
increase tenfold and more in comparison with the original rocks. As a result,
mercury contamination of the environment in Siberia due to technogenic
emission of mercury may be of a more local character in comparison to regions
of warm climate.
Mercury contamination of the environment due to the use of primitive
equipment for gold amalgamation in countries with tropical climate (Brazil,
Tanzania, Indonesia and Vietnam) has reached an enormous extent at present.
Thus, the mercury content in bottom sediments of gold-mining areas accounts
371
Previously, with the use of sluice amalgamation, metallic mercury settled down
on the bottom of the reservoir and was buried under the layer of processed
gravels. Thus, a significant amount of metallic mercury may be found under the
layer of bottom sediments and grounds in anaerobic low-temperature conditions
in the areas of mined-out placers, and presents a severe hazard to the
environment in the reworking process of such techno genic deposits.
Low temperatures of waters in natural reservoirs and streams even in summer
and total freezing of some of them in winter reduce the probability of mercury
methylation processes and its emission into the water phase due to the
development of heterotrophic microorganisms in the benthonic water layers and
bottom sediments. The probability of biogenic mercury methylation and its
accumulation in trophic chains of water ecosystems may increase only in shallow
lakes, dredge pits and settling tanks.
The role of vegetation in the biochemical mercury cycle under severe climate
conditions with spreading of permafrost will differ from areas with warm climate,
due to a short vegetation period, lesser growth rates and accumulation of foliage,
nutrition with waters overlying permafrost, which are predominantly formed by
precipitation. Particular distinctions must be observed in the areas of bald peaks,
tundra and mari landscapes, characterized by poor vegetation, chiefly consisting
of mosses, lichens and low forest. The tundra zone is characterized by simple
ecosystems and short trophic chains, therefore mosses and lichens, which can
accumulate mercury and other heavy metals from soils and precipitation, will
prevail in the food of mammalia. Thus, the elevated mercury concentrations in
the meat of wild deer and Manchurian deer 0.039 and 0.035 mg/kg, respectively,
exceeding the MPC for meat products (0.03 mg/kg) have been registered (T.G.
Laperdina, unpub1. data).
The processes of freezing and thawing of rocks, soils, bottom sediments, water
phase of rivers, lakes and industrial water objects are accompanied by a number
of complex chemical, physicochemical and physical processes, leading to the
transformation of mercury forms and their redistribution in the environment.
Thus, it was determined that frozen rocks of the ore gold deposits in Yakutia
(Omelchenko 1985) and some gold placers in Mogocha raion (Laperdina et a1.
1995, 1996) are characterized by a decreased mercury content, resulting from the
possible process of transference and concentration of mobile absorbed mercury
forms on the interface "ice water" during rock freezing. The processes of rock
weathering, which are mostly caused by temperature variations and water
freezing and thawing in rock fractures, are accompanied by the formation of
friable metasomatically altered products, which can be enriched with mercury. It
was determined that in weathering products of rocks the mercury content may
increase tenfold and more in comparison with the original rocks. As a result,
mercury contamination of the environment in Siberia due to technogenic
emission of mercury may be of a more local character in comparison to regions
of warm climate.
Mercury contamination of the environment due to the use of primitive
equipment for gold amalgamation in countries with tropical climate (Brazil,
Tanzania, Indonesia and Vietnam) has reached an enormous extent at present.
Thus, the mercury content in bottom sediments of gold-mining areas accounts