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Maximovich N. G., Menshikova E. A., Osovetsky B. M. Technogenic Associations of River Sediments in a City-Industrial Environment // Engineering geology for Developing Countries : 9 th Congress of the International Association for Engineering geology and the Environment :Keynote Lectures and Extended Abstracts, a 16-20 Sept. 2002,Durban, South Africa. Saieg; Pretoria, 2002. P. 263.


Nikolay G. Maximovich , Elena A. Menshikova and Boris M. Osovetskiy

The scale and form of technogenic influence on the city environment are increasing enormously. The river ecosystems in cities are very sensitive to pollution. The process of river sediment pollution is typical for city-industrial areas that result in the formation of technogenic-alluvial units. Technogenic-alluvial sediments are composed of grains of natural minerals (mostly quartz, feldspar, mica, rock fragments, ets.) and particles of technogenic origin. Some aggregates, including fine natural grains, are cemented by organic or unorganic material.
The main sources of technogenic components in river sediments are industries located in river valleys. Alluvial sediments from a city include specific technogenic associations of hard components that are originate from industrial sources. Near metallurgical plants river sediments are enriched in slag particles, technogenic spherules, fragments of metals, etc. Surroundings with chemical plants enrich river sediments with different compounds depending on their profile. Variable composition is especially found around mines.
The rivers are transporting technogenic particles over long distances from city-industrial areas. A part migrates as bottom load, others are included in suspension and finally also dispersed as silt and clay sediments along river valleys which result in soil pollution. Migration capacity of technogenic particles depends on their specific gravity, size and form. As a common indicator of migration capacity settling velocity of particle normalized to its size can be used.
Negative influence of hard technogenic components that are concentrated by fine-grained alluvium may be explained by solution and absorption processes connected with health-threatening elements (nickel, cadmium, copper, lead, etc.). Clay particles may concentrate such elements as selenium, arsenic, molybdenum, bismuth, etc.
Technogenic-alluvial sediments were investigated by ecologists of the Perm University in the main city-industrial areas of the Urals. There are centers of metallurgy (Magnitogorsk, Lysva, Chusovay, Nizniy Tagil), chemical industry (Ufa, Perm, Gubakha), machinery (Ekatherinburg, Perm) and mining activity (Solicamsk, Berezniki). The common technogenic particles are slag, coal, magnetic and glass spherules, brick, glass, metallic fragments, amorphous ferriferous hydroxides, etc. There are also natural silt and clay particles coated with technogenic enriched heavy metals. The correlation between technogenic and natural grains in alluvium depends on sorting processes and their migration capacity. Every city-industrial center has specifical assemblages of technical components that is connected with its industrial specialization. For example, the small rivers in the vicinity of Perm City are enriched with industrial dust, spherules, metallic particles, and so on. In the Gornozavodsk Region there are coal particles and amorphic ferroxides in the alluvium.
According to our investigations the morphological, physical and chemical properties of hard technogenic components are rather changeable and variable. The technogenic assemblage of hard particles in river sediments is related to definite geochemical associations. The main chemical elements of technogenic genesis of river sediments are zinc, led and copper. Sometimes there are abnormal concentrations of rare elements such as cadmium, bismuth, selenium, arsenic, nikel, cobalt, etc.
Sediment pollution is especially expanding in ponds and river reservoirs of industrial territories that accumulate huge masses of technogenic components. Cumulative effect of technogenic sedimentation in such ecosystems is hazardous to the future of mankind.