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Technogenic Associations of River Sediments in a City-Industrial Environment [Electronic resource] // Engineering geology for Developing Countries: 9 th Congress of the International Association for Engineering geology and the Environment. (Durban, South Africa. 16-20 Sept. 2002). – Electronic optical disks (CD-ROM). – P. 1216-1221.

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The scale and form of technogenic influence on the city environment are increasing enormously. Around the cities big territories are polluted by organic and unorganic compounds. All parts of city environment are exposed by technogenic pressure.

As to river ecosystems in cities they are very sensitive to pollution. The rivers and creaks wash huge squares of city territories and collect different technogenic materials from sources of pollution.

The process of river sediment pollution is typical for city-industrial areas (McCrone, 1967; Kozak, Janku and Jehlicka, 1995; Maximovich, Menshikova and Osovetskiy, 2000). They result in the formation of technogenic-alluvial units. Tecnogenic-alluvial sediments are composed of grains of natural minerals (mostly quartz, feldspar, mica, rock fragments, etc.) and particles of technogenic origin (slag, metallic wastes, brick, industrial dust and so on). Some aggregates, including fine natural grains, are cemented by technogenic organic or inorganic material (natural-technogenic aggregates). The correlation between technogenic and natural grains in alluvium depends on sorting processes and their migration capacity.

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 originated from industrial sources. Near metallurgical plants river sediments are enriched in metallurgical slag particles, technogenic spherules, fragments of metals, etc. Surrounding with chemical plants enrich river sediments with different compounds depending on their profile. Variable composition of specific technogenic fragments is especially found around mines.

The rivers are transporting technogenic particles over long distances from city-industrial areas together with natural grains. 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.

The technogenic assemblage of hard particles in river sediments is connected with definite geochemical association of rare elements. The main rare chemical elements of technogenic genesis in river sediments are zinc, lead and copper. They are usual for every industrial centers. But sometimes there are abnormal concentrations of such rare elements as cadmium, bismuth, selenium, arsenic, nickel, cobalt and so on.

Technogenic geochemical association is usually investigating in comparison with natural one. The last consist of different combination of such main rare elements as titanium, manganese, chromium, barium, zirconium, phosphorus.

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, Chusovoi, Nizhniy Tagil), chemical industry (Perm, Ufa, Gubakha), machinery (Ekatherinburg, Perm) and mining activity (Solikamsk, Berezniki, Kizel, etc.). The common technogenic particles are slag, coal, magnetic and glass spherules, brick, glass, metallic fragments, etc. Sometimes natural silt and clay particles coated with technogenic compounds enriched heavy metals are met.

The detailed investigations were fulfilled on the territories of Perm city-industrial agglomeration and Kizel Coal Basin with a lot of adjacent towns and countries (Maximovich, Gorbunova, 1990; Maximovich, Blinov and Menshikova, 1995; Maximovich, 1997). As to the territory of Perm City there are typical technogenic products in small river sediments such as industrial dust, spherules, metallic particles, brick and other fragments of construction materials (Osovetskiy, Menshikova, 1997). Technogenic geochemical rare element association in suspended load besides manganese and chromium include zinc, copper, lead, tin, nickel (table 1).

Table 1. Element percentage in silt of small rivers on the polluted territory of Perm City, ppm
River Part Mn Cr Zn Ni Cu Pb Sn N*
Muljanka Suburb 650 150 45 60 65 7,5 2,5 3
City 940 250 130 77 100 17 6 10
Egoshikha Suburb 600 500 200 400 90 30 6 2
City 860 520 220 460 110 32 7,4 4
Danilikha Suburb 550 230 85 85 100 18 2,5 2
City 1260 420 250 180 120 50 12 9
* — a number of samples.

A great number of technogenic products supplied by the Perm plants is transporting in bottom load of small rivers. Among them metallic shaving and fragments of metals are prevailed. They concentrate in heavy fractions of alluvial sediments. Its chemical composition is enriched in one or several metals according to the industrial specialization. For instance, lead content in heavy fraction of the Danilikha River sandy-gravel alluvium reaches 0,15%, that is in 30 times more than in polluted silt.

Territory of Kizel Coal Basin (the Western Urals) is polluted due to intensive coal mining during long period prevailing 120 years. Nowadays mining of coal is practically stopped. But river sediments at the territory contain a lot of technogenic products including fragments of rock with coal, slag, magnetic spherules, aggregates of natural grains with ferroxides, etc. Some technogenic compounds are creating now in consequence of specific reactions between superficial waters and coal rock wastes. A great mass of technogenic material is composed by amorphic ferroxides and alumogel. Sometimes crystal technogenic minerals are formed there (for instance, goethite, lepidocrocite, jarosite).

Composition of natural-technogenic sediments of Kizel Coal Basin territory roughly differ from that of natural ones. They contain a lot of water-soluble compounds (5-25 g/kg in comparison with 0,3-0,6 g/kg for natural sediments). The water extract giving idea about migration forms of elements has got sulphate-ferrous composition (figure 1).

Among heavy metals in natural-technogenic sediments of the Kizel Coal Basin are typical manganese, zinc, nickel, cobalt, lead, copper. Besides, they include such toxic elements as bismuth, cadmium, beryllium.

City-industrial centers create big zones of polluted territories around them. In connection with that it is very prominent to appreciate a migration capacity of technogenic particles.

Firstly, migration capacity of technogenic grains depends on their size, specific gravity, form and grain surface. As an integrative indicator of grain migration capacity taking into opinion all previous properties settling velocity of grain can be used. The correlation between particle settling velocity and stream velocity controls the manner of grain transporting namely migration as bottom or suspended load. The more a settling velocity of particle the less a distance of migration (Osovetskiy, Menshikova, 1996).

Secondly, migration capacity of particle depends on stability to grinding that is abrasive durability. The more such stability the more a distance of shift.

Hence migration capacity of particle in bottom load may be approximately appreciate by formula (Osovetskiy, 1992):

formula 1   (1)
where H — stability of technogenic particle to grinding, in balls;

W — settling velocity of particle, in cm/sec.
Figure 1

Figure 1. Chemical composition of water extraction for polluted bottom load of the Kizel Coal Basin rivers: a — the Kosva River, b — the Vilva River

Physical sense of migration capacity meaning (in sec/cm) consists in a time (sec) of particle settling in alluvial sediment at a depth of 1 cm. The more a time of such settling the more a distance of particle migration along river valley.

Settling velocities of definite technogenic particles were experimentally defined. The group of 22-80 grains presenting every technogenic product was chosen for experiments. They presented all range of particle sizes. The size of every grain was previously measured under microscope. Settling velocity was measured in glass cylinder with water by means of settling time determination at the depth of 30 cm (figure 2).

According to the experiment results there are essential differences in settling velocities of grains that belong to the same group (figure 2). Though the main factor controlling meaning of settling velocity is the particle size nevertheless the influence of other factors (individual form, specific gravity, etc.) is marked. It is one of the reasons why their migration capacity is rather changeable.

The common formula was used for approximation of experiment results:

 (2)
where D — grain average diameter, mm.

Using formula (2) it is possible to appreciate a role of grain size in varying of settling velocities for every group of technogenic products (table 2).

Table 2. The results of experiments on settling velocity determination
Group of technogenic product k b Numder
of grains
Coal «light» 1,35 1,35 43
» «heavy» 3 1,0 39
Slag metallic non-magnetic 3,35 1,1 31
» glassy 7,87 0,78 80
» magnetic 9,52 0,715 54
Brick 8,09 0,927 36
Spherules glassy 12,5 0,844 23
» «red» 6,18 1,08 22
» magnetic 17,2 0,853 42
Figure 2 Figure 2. The relation between settling velocity and size for technogenic particles in alluvial sediments of the Urals: a — «light» coal, b — «heavy» coal, c — magnetic slag, d — non-magnetis slag, e — glassy slag, f — brick, g — magnetic spherules, h — glassy spherules, j — «red» spherules
The next experiments were fulfilled for the purpose of abrasive stability measurement for every group of technogenic products. The hardness of grain was adopted as an indicator of stability to grinding. But problem was in the fact that hardness is unknown for technogenic products yet.

The hardness was experimentally defined with usage minerals of Moos scale. The grains of 1-2 mm in size were chosen for it. Five determinations were done for every group of technogenic products and average meaning was calculated.

The settling velocity of grain 1 mm in size calculated using formula (2) was adopted for migration capacity estimation on the basis of formula (1). The data of migration capacity were rather variable (table 3).

Table 3. Migration capacity of technogenic particles in bottom load
Group of technogenic products W,
cm/sec		 H L,
sec/cm
Spherules «red» 6,18 1 0,16
» magnetic 17,2 4,6 0,27
» glassy 12,5 5 0,40
Brick 8,09 4 0,49
Slag magnetic 9,52 5 0,53
» glassy 7,87 4,5 0,57
» non-magnetic 3,35 4,6 1,37
Coal «heavy» 3,0 2,6 0,87
» «light» 1,35 2 1,48
Three groups of technogenic components may be detached for the Urals territory:

  1. High migration capacity (L more 1 sec/cm),
  2. Middle migration capacity (L from 1 to 0,3 sec/cm),
  3. Low migration capacity (L less 0,3 sec/cm).
The special investigations have shown the first group migrates in bottom load at the distance more than 75 km from the source of pollution. As to the third group the distance of particle migration do not exceed 10 km.

Migration in suspended load is the main way of technogenic grain moving. It is typical one for silt and clay particles. The distance of their transporting is more larger than that of traction way and may reach several hundreds kilometers.

Negative influence of hard technogenic components that are concentrated by fine-grained alluvial sediments may be explained by solution and absorption processes connected with concentration of health-threatening elements (nickel, cadmium, copper, lead, etc.). According our investigations clay alluvial sediments in the Urals contain selenium, arsenic, molybdenum, bismuth at some places.

Sediment pollution is especially expanding in pond and river reservoirs of industrial territories that accumulate huge masses of technogenic components. Cumulative effect of technogenic sedimentation is hazardous to the future of mankind.

References
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