Zs. P. Komáromy szerk.: Studia Botanica Hungarica 16. 1982 (Budapest, 1982)
Hably, Lilla: The relation between Pb-pollution along mainroads and the trace element-composition in soil and vegetation (Examination of section rectangular to M3 mainroad)
2. Organic material, clay mineral and carbonate in the soils (The results of derivatographic examinations) Our derivatogramms made it possible to distinguish four major curve stages, resulting from the presence of water, organic material, clay mineral and carbonate. The first endotermic peak and the accompanying loss of weight results from the loss of water in the organic material built into the colloid fraction adsorbtively . After that the DTG curve reaches its balance at about 200-240°C. This is the interval where the line can be drawn between the loss of water and the burnout domain of the organic material. Following this all the graphs show a great exotherm peadk of the organic material. In the DTA curve this peak shows between 200-240 and 500°C, thus is hides several phenomena within this domain. Of these the most significant one is the invisibility of the endothermic peaks of ferri-oxi-hydroxids and of the siliceous colloids. These latter ones do not indicate loss of weight, thus all the losses of weight in this domain were calculated for the organic material. When the organic material was not humus, i.e. a relatively homogenious fraction, but contained also undecomposed, fragments or organs, the DTA peak of the organic material spread wider. In certain cases this can effect the clay mineral interval, the reason for which is that the decomposition temperature of the inhomogenious organic fraction (root, chitin armour etc.) is different in each. In this case the exothermic peak of the burnout of the organic material and the endothermic DTA-peak of the clay mineral partly neutralize each other, in the interval around 500°C. In such cases the limit of the weight losses arising from these reactions has been determined at 540°C. The weight per cent of the organic material was calculated on the basis of the weight loss of the interval mentioned. The exothermic DTA-peak of the organic material shows three smaller peaks in most cases. First we supposed it to be pyrite, later it turned out to be the result of the inhomogenity of the organic material. The fact that our soil samples did not contain pyrite was proved by the following experiment: HCl was added to the soils, than the opening of the test tube was covered with filter paper soaked in Pb-acetate. If pyrite were present, HCl would release H2S. This, reacting to Pb-acetate would yield black PbS precipitation. The smallest quantity of pyrite demonstrable by this reaction is 10" 12 g and this can be regarded as highly sensitive (ERDE Y 1970). None of our samples yielded this reaction, so the presence of pyrite can be excluded. The third interval of the graphs is between 500 and 600°C, with variabilities. The exothermic peak produced by the organic material continues in the endothermic peak of the clay minerals. In almost all cases even this becomes flat and almost asymmetrical, which indicates that the Illite is not clean, but mixed with Montmorillonite, i.e. there is a transition of IlliteMontmorillonite. This is proved also by the break at the endothermic peak of the sorptive water, which is characteristic of smectites; water is released in two stages: between 120 and 140°C, and 140 and 280°C. This is also proved by data from literature according to which Montmorillonite crystallizes looser in the soil and thus its endothermic peak appears at 600°C (NEMECZ 1973). On closer observation of the DTA curve it can be seen that at about 900°C usually the exothermic peak is low, which also indicates Montmorillonite. All these indicate that our soil samples contain Illite and Montmorillonite together or mixed structures. A more precise solution of the problem requires closer examinations. The fourth important section of the DTA curve is determined by the character of the carbonates. The endothermic peak of the carbonates contains an indefinite section with low temperature on one hand and a well-marked section with higher temperature on the other. This can be observed on the DTG curve as well: after 600°C a sloping flat "peak" can be observed, and only after that does the curve fall more markedly. As a result of a more intensive treatment of the samples with acid the mildly sloping peak preceding the strong endothermic peak disappeared, which proves its relation to carbonate minerals. This allows for the supposition that above 600°C carbonates of mild crystallization which, occasionally may from a colloid film begin to leave. This can be assumed to be the cause of the mild sloping at the carbonate peak. The characteristic carbonate peak around 800°C is already the result of crystallized carbonate grains. In a few cases around 700-750°C we find a smaller endothermic peak preceding the high endothermic peak of Calcite. This arises from a higher MgC0 3 content, and, occasionally shows such marked presence as indicating Dolomite in addition to Calcite. The isolation of these carbonate varies would demand changes in methodology, so quantitative data here were calculated as CaC0 3 .
