Vörös A. szerk.: Fragmenta Mineralogica Et Palaentologica 13. 1987. (Budapest, 1987)
HEGYESSY and KU SLITS (1979) investigated heavy metal pollution of industrial works in the soil. They have recognized that clay minerals fix heavy metals by adsorption and ionic exchange. Adsorption is heavily dependent on the kind of clay mineral, on soil pH and on other ions. The adsorption potential of the humus is higher than those of clay minerals, dependent on pH. Heavy metals form stable complexes with humic acids. HEGYESSY and KUSLITS (1979) have determined that concentration of heavy elements decrease to the average level at ca. 500 m distance from the factory. Concentration of Cd decreases nearest to the plant due to its fixing to the humus. If the ground-water level is high and reaches the polluted level, heavy metals accumulate in the aquifer and spread to great distances by flowing groundwater. A sample taken from 2 m depth 200 m distance from the factory showed higher Zn and Cd concentrations than background values in the upper level. JACKSON and SKIPPEN (1978) have recognized that organic acids increase the solubility of Cu, Zn and Ni in the presence of clay minerals, but the solubility of Pb decreases, mainly in the case of acidic pH, by colloid coagulation with organic complexes. In case of alkaline pH hydrolysis decreases the solubility of Zn and Ni. If carbonate is added to the metal-organic acid-clay mixtures, the solubility of Ni and Zn further decreased. HABLY (1982) investigated soil profiles arranged in increasing distances from a highway, determined trace element concentrations, mainly that of lead in the soil and in plants. Correlation was proved between the pH value of the soils and Pb-rich levels. BRADLEY, RUDEFORTH and WILKINS (1978) investigated soil trace elements in NW Pembrokeshire in an area of 300 sq. km, where subsoil is formed of Lower Palaeozoic sedimentary rocks, magmatic rocks and alluvium. Their methods were applied in the trace element investigations of soil and subsoil of our area. STUDY AREA AND SAMPLING METHODS The investigated area, the surroundings of Mezőnagymihály (Fig. 1) lies at the boundary of the middle course of Tisza river and the Bükk region (Bükkalja). The southern and eastern part is dominated by Holocene fluvial sediments (mainly clay, silt and fine sand). The western and northern part is characterized by Pleistocene diluvial and colluvial clay and silt. The overall picture has been formed by rivers. Due to uneven subsidence of the Great Plain basin, the stream gradient was very variable forming diverse depositional environments frequently interfingering with each other. The ground-water level at rest lies at 1-3 m depth. Six profiles have been dug in the surroundings of Mezőnagymihály (Fig. 1). These were 1.5-2 m deep, reaching ground-water level. Samples were taken at 20 cm intervals. LOCALITIES AND SOIL PROFILES Soil profile 24. Locality: Mezőnagymihály, Libatanya. Humous alluvial soil. The upper part of the profile is dark-brown sandy adobe soil, with a grain size becoming finer downwards, turning into loess-like adobe then into silt. Colour becomes more pale; the lowermost level is whitish-grey (Fig. 2). Soil profile 25. Locality: Mezőnagymihály, Nagyház-tanya. Humous alluvial soil (of sodic character). Not far from the profile (ca. 30-40 m) there is a ditch-like depression filled with water in spring. The upper part of the profile is dark-brown sandy adobe soil. Grain size decreases downwards and colour of the soil turns lighter. The bottom of the profile is clayey silt. Carbonate grains 0.5-1 cm in diameter are characteristic in the whole section (Fig. 3). Soil profile 26. Mezőnagymihály, between Dobozi-tanya and Gulyás-tanya. Meadow soil. The upper part of the profile is dark-brown adobe soil. Downwards the percentage of sand increases. Lowermost level is fine sand (Fig. 4). J°^2_ HL^ÜE. 2.7_- Locality: Mezőnagymihály, Keresztesi gyep, near the well. Humous alluvial soil. The upper part of the profile is black adobe soil, turning into whitish-gray downwards. Downwards sand content increases; the lowermost level is yellowish-white, medium-grained sand (Fig. 5).
