M. Sánchez-Camazano

Lead and cadmium in soils and vegetables from urban gardens of Salamanca (Spain)

The Pb and Cd contents of soils and vegetables from 16 urban gardens of Salamanca (Spain) have been determined. The metals were found to occur at concentrations in the ranges 20.1-96.2 and 0.20-0.95 microgram/g for Pb and Cd, respectively. The mean Pb concentration found was 2.60 times higher than that in natural soils of the Salamanca province, whereas that of Cd exceeded its mean concentration in natural and cultivated soils by a factor of 2.73 and 2.04, respectively. The Pb and Cd contents of the vegetables (branches) ranged between 4.17 and The Pb and Cd contents of the vegetables (branches) ranged between 4.17 and 52.7 micrograms/g, and between 0.35 and 3.05 micrograms/g, respectively. According to these results, Pb and Cd occur at pollution levels in the surveyed gardens. The total and soluble Pb (extractable with 1 N ammonium acetate) levels were found to be related to the traffic density. On the other hand, the Cd levels appear to be more closely related to the distance from roadways, as well as to the age of the garden and the flow of visitors.

Hydrotalcites and organo‐hydrotalcites as sorbents for removing pesticides from water

This paper reports on the adsorption of different organic pesticides by hydrotalcite, hydrotalcite heated to 500 degrees C and organo-hydrotalcite in aqueous medium by employing adsorption isotherms, and using X-ray diffraction and infrared spectroscopy techniques. The results suggest that the adsorption capacity of the different materials depends on their nature as well as on the structure, polarity and hydrophobic or anionic nature of the pesticides. The results also show that hydrotalcite, both natural and after calcination at 500 degrees C, is not a good sorbent of hydrophobic pesticides. The data demonstrated that both types of hydrotalcite, however, are very good sorbents of glyphosphate. Furthermore, the organo-hydrotalcites may be as good sorbents as organo-montmorillonites for hydrophobic pesticides.

Pesticide adsorption in a soii-water system in the presence of surfactants

In the present work changes in the adsorption of four 14C-labelled pesticides -diazinon, acephate, atrazine and ethofumesate- on a sandy loam soil, induced by application of anionic, cationic and nonionic surfactants - tetradecyltrimethylammonium bromide (TDTMA), sodium dodecyl sulphate (SDS) and polyoxyethylene sorbitanmonooleate (Tween 80)-, were determined using a batch equilibrium method. Three concentrations of each surfactant were used: lower, equal to or higher than the critical micellar concentration. The increases or decreases in the values of the Freundlich constant K for adsorption of the different pesticides by soil in the experiments revealed that the behaviour of pesticides in soil-water systems with micelle-forming surfactants mainly depends on the degree of hydrophobicity of the pesticide and the type of surfactant, as well as on the concentration of surfactant in the system.

Significance of soil properties for content and distribution of cadmium and lead in natural calcareous soils

The total content of Cd and Pb in 30 natural (uncultivated and unpolluted) calcareous soils from the province of Valladolid (Spain) were determined. The ranges of total Cd and Pb were 0.05–0.43 μg g−1 and 4.44–50.34 μg g−1, respectively. Significant correlations were found between total Cd and carbonate contents (P<0.05), between total Pb and organic matter (P<0.01) and between total Pb and clay contents (P<0.01). The mean contents of both elements were higher in the less developed soils (leptosols, regosols, fluvisols, solonchaks) than in the more developed ones (acrisols, cambisols, luvisols, solonetzs). This distribution is parallel to that of soil components for the accumulation of Cd and Pb in the soils studied. In the distribution of both metals and the other soil components in the soil profiles only there were similarities between the distribution patterns of Pb and clay.

Effect of different surfactants on the mobility of selected non-ionic pesticides in soil

The influence of the surfactants tetradecyltrimethylammonium bromide (cationic), lauryl sulphate (anionic) and twee 80 (non-ionic) on the leaching of pesticides diazinon, atrazine, metolachlor and acephate in soil was studied by using soil thin layer chromatography, 14C-labelled pesticides and a linear analyser for measuring the mobdity parameter Rf. The results obtained are quite interesting in that they support the use of surfactants for solving soil pollution problems caused by pesticides. The increase or decrease of pesticide mobility in soil was found to depend on the chemical nature of the surfactant, its concentration in the soil or in the leaching water and the pesticide hydrophobicity. Consequent)y, the surfactant of choice and its concentration will be dictated in each case by the nature of the pesticide ulmvolved and the. specific problem faced (pesticide immobilization or leaching).

Sodium dodecyl sulphate-enhanced desorption of atrazine: effect of surfactant concentration and of organic matter content of soils.

A study was made of the adsorption-desorption of atrazine in aqueous medium in five soils with organic matter (OM) contents in the range 1.4-10.3% and also of the desorption of the herbicide in aqueous solutions of the anionic surfactant sodium dodecyl sulphate (SDS) at critical micelle concentrations (cmc) of 0.75, 1.50, 5 and 10. The adsorption and desorption isotherms in water together with the desorption isotherms in SDS solutions with concentrations of 0.75 and 1.50 cmc fit the Freundlich adsorption equation. All the desorption isotherms displayed hysteresis. The increase or reduction in hysteresis of the desorption isotherms in SDS solutions with respect to those of desorption in water depend on the SDS concentration and on the OM content of the soils. Below the cmc, SDS only increases the desorption of atrazine in the soil with the highest OM content (10.3%). However, above the cmc (5 and 10 cmc) the desorption of atrazine increases in all soils, the efficiency of desorption increasing with the OM content of the soils.

Comparison of Pesticide Sorption by Physicochemically Modified Soils with Natural Soils as a Function of Soil Properties and Pesticide Hydrophobicity

The objectives of this paper were to determine the efficiency of physicochemically modified soils with a surfactant in the sorption of pesticides, the stability against washing of the pesticides sorbed, and the effective sorption capacity of surfactant adsorbed by soils as a function of pesticide hydrophobicity and soil characteristics. Five soils of different characteristics and five pesticides (penconazole, linuron, alachlor, atrazine and metalaxyl) with different Kow values were selected and octadecyltrimethylammonium bromide (ODTMA) was chosen as model of cationic surfactants. Sorption-desorption isotherms were obtained and constants Kf and Kfd for natural soils (from Freundlich equation) and K and Kd for ODTMA-soils (from linear equation) were determined. Sorption on ODTMA-soils was higher than on natural soils. K increased 27–165 times for penconazole, 22–77 times for linuron, 7–14 times for alachlor, 9–23 times for atrazine, and 21–333 times for metalaxyl in relation to Kf. Sorption coefficients normalized to 100% of total organic matter (TOM) from organo soils KOM (K 100/%TOM), were always higher than those from natural soils KfOM (Kf 100/%OM), indicating that the organic matter (OM) derived from the ODTMA (OMODTMA) had a greater sorption capacity than the OM of the natural soil. KOM values were also higher than the Kow (octanol/water distribution coefficient) value for each pesticide. The similarity of the high KOM values for the sorption of each pesticide by the five soils and the linearity of isotherms point to a partitioning of the pesticides between surfactant and water. The use in this work of different soils and various pesticides, unusual in this type of investigation, allowed us to obtain equations to know the sorbed amount of a given pesticide by the surfactant-modified soils as a function of the OM content derived from the cation and the Kow of the pesticide. The results obtained are of interest when it becomes necessary to increase the sorption capacity of soils with low OM contents with a view to delaying pesticide mobility in soils from pollution point sources (high concentration in small area), and preventing the pollution of waters.

City refuse compost and sodium dodecyl sulphate as modifiers of diazinon leaching in soil

Abstract The effect of a city refuse compost (CRC) and of an anionic surfactant (sodium dodecyl sulphate (SDS) on the leaching of diazinon (0,0-diethyl 0-2-isopropyl-6-methylpyrimidin-4-yl-phosphorothioate) in the soil was studied using packed soil columns. Breakthrough curves showed the existence of various regimes of pesticide adsorption related to the pesticide and organic material nature and the soil properties. Leaching rate and mass transfer of diazinon decrease following the addition of CRC to the soil and increase after the addition of SDS. The degree of increase or decrease was found to depend strongly on the amendment dose added, especially in the case of SDS. The results afford basic data on which to base the possible use of the organic amendments studied in physicochemical methods designed to prevent the pollution of water by hydrophobic pesticides (immobilization) or to restore soils contaminated by these compounds (leaching).

GLYPHOSATE-HYDROTALCITE INTERACTION AS INFLUENCED BY pH

Adsorption and the mechanism of adsorption of the herbicide glyphosate [N-(phosphonomethyl) glycine] by hydrotalcite (HT) and by hydrotalcite calcined at 500°C (HT500) was studied. The values of the Freundlich K constant of the adsorption isotherms and the distribution coefficients, Kd, depend on the pH of the adsorption system and vary between 55.54–9603 (K) and 36.82–6252 (Kd) for HT and between 10,106–23,242 (K) and 17,801–26,558 (Kd) for HT500. X-ray diffraction and infrared spectroscopy studies showed that glyphosate is not adsorbed into the interlayer of HT. The adsorption mechanisms are (1) electrostatic attraction between the surface of HT, charged positively below pH 12 according to its point of zero charge and the glyphosate anion, and (2) ligand exchange between the P-OH and/or C=O groups of the herbicide and the Al and Mg atoms of the HT surface. The occurrence of one or both mechanisms depends on the pH of the adsorption system. These adsorption mechanisms and the amphoteric nature of glyphosate account for the variation in K and Kd values with respect to pH. Previous studies on adsorption of different organic anions by HT have only considered the mechanism of anion exchange as important.

Study of the desorption of linuron from soils to water enhanced by the addition of an anionic surfactant to soil–water system

The influence of the addition of the anionic surfactant sodium dodecyl sulphate (SDS) to the soil-water-linuron system in the herbicide desorption from soils with different organic matter (OM) content to water have been studied. SDS was used at critical micelle concentrations (cmc) of 0.75, 1.50, 5 and 10. The adsorption-desorption isotherms of linuron in aqueous medium and in SDS solutions at concentration of 0.75 cmc fitted the Freundlich adsorption equation for all the soils studied. When the SDS concentration was 1.50 cmc only the desorption isotherms for the soils with OM content < or = 5.40% fit this equation and was not fulfilled by any of the soils when the SDS concentration was 5 or 10 cmc. All the desorption isotherms displayed hysteresis, the hysteresis coefficients of the desorption isotherms in SDS solutions always being lower than those of the desorption isotherms in water. The efficiency coefficients, defined as the relationship between the percentages of linuron desorbed in SDS solution and the percentages of linuron desorbed in water, range from 1.02 to 2.41 in the soil with the lowest OM content, and from 1.91 to 17.1 in the soil with the highest OM content. The results obtained indicate the enhancement of linuron desorption by the addition of SDS surfactant to soil-water system. The efficiency of SDS is seen as from surfactant concentrations below the cmc and varies with the surfactant concentration and with the soil OM content.