| الوصف: |
Hydrophobic symmetric triazine herbicides and their less hydrophobic degradation products, as well as hydrophobic but ionisable chlorophenols are widely distributed environmental pollutants. A series of experiments was carried out in which three differently substituted triazine herbicides: atrazine, ametryn, and atratone, two atrazine degradation products: hydroxyatrazine and didealkylated atrazine, and three chlorophenols: 2, 4, 6-trichlorophenol, 2, 3, 4, 6-tetrachlorophenol, and pentachlorophenol, were sorbed in three moderately organic natural soils (native and after removal of organic phase) and in four mineral sorbents. Two surface soils and one subsurface aquifer sediment were collected at a depth of 0.1-0.2 m and 14.1 m, respectively. The surface soils were of sandy gravel and silty sand type with quartz, calcite and dolomite as the main minerals whereas the aquifer sediment was of clayey silt type with montmorilonite as the most abundant mineral. Mineral sorbents were quartz, calcite and two clay minerals: kaolinite and montmorillonite. Sorption isoterms were determined using a batch equilibration procedure. The equilibrium concentrations of triazine compounds in aqueous phase were determined by high performance liquid chromatography with diode-array detection. Chlorophenols were accumulated from the aqueous phase by C18 solid-phase extraction and analysed as acetyl derivatives by gas chromatography with electron capture detection. The results of sorption experiments were evaluated in terms of Freundlich isotherm. Freundlich sorption coefficients Kf and 1/n were calculated and compared with respect to the chemicophysical properties of sorbates and sorbents. Sorption intensities (Kf coefficients) of all triazine compounds, save didealkylated atrazine in one and atrazine in both surface soils, were higher in organic-free than in native soils containing from 7.7 to 12.2 % of organic matter. In all organic-free soils and in native subsurface soil with higher content of clay minerals the highest sorption coefficients were calculated for hydroxyatrazine followed by atratone and/or ametryn. Sorption of triazines in mineral sorbents was most intensive in acidic montmorillonite, a clay mineral characterized by a very large specific surface area and a high cation exchange capacity. The Kf values decreased in sequence atratone>ametryn>atrazine≈ hydroxyatrazine>didealkylated atrazine. In all sorbents, save in native surface soils and quartz, chlorophenols were sorbed less intensively than triazines. In two native surface soils the chlorophenol Kf values were the highest and comparable to those of triazines, but the intensity of sorption interaction drastically decreased as the organic phase was removed [1]. Contrary to surface soils the sorption intensity of all chlorophenols in organic-free aquifer sediment was significantly higher than in the native sorbent indicating a stronger interaction with the mineral surface than with the organic phase. Their sorption in organic-free aquifer sediment was comparable to sorption intensities in mineral sorbents, especially in montmorillonite. Sorption intensity of chlorophenols is highly dependent on the sorbent acidity and upon the degree of the sorbate dissociation in the water phase [2]. Ionized forms of chlorophenols dominated in almost all sorption experiments. Penta- and tetrachlorophenol were ionized partially (≈ 50 %) and trichlorophenol was predominantly in the neutral form (88 %) only in the acidic aqueous suspension of montmorillonite. The decrease of Kf values with the increase of pH in organic-free soil was noticed for all three chlorophenols indicating that sorption of chlorophenolate anions was lower than sorption of their neutral form. Significant deviation of sorption isotherms from linearity (1/n ≠ 1) was observed for both triazine and chlorophenol compounds in almost all sorbents pointing at limited sorption capacity. Differences in Gibbs energy values also emphasised considerable differences in sorption mechanisms between two groups of compounds. 1. Fröbe, Z. ; Fingler, S. ; Drevenkar, V. ; Juračić, M. Sci.Total Environ. 1994, 155, 199. 2. DiVincenzo J.P., Sparks, D.L. ; Arch. Environ. Contam. Toxicol. 2001, 40, 445. |