M.J. Sánchez-Martín

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.

Field-scale dissipation of tebuconazole in a vineyard soil amended with spent mushroom substrate and its potential environmental impact

The persistence, mobility and degradation of tebuconazole were assessed under field conditions in a sandy clay loam soil amended with spent mushroom substrate (SMS) at two rates. The aim was to evaluate the environmental impact of the simultaneous application of SMS and fungicide in a vineyard soil. SMS is the pasteurized and composted organic material remaining after a crop of mushroom is produced. SMS is generated in increasing amounts in La Rioja region (Spain), and could be used as soil amendment in vineyard soils, where fungicides are also applied in large amounts. The study was carried out in 18 experimental plots (6 treatments and 3 replicates per treatment) over one year. Laboratory experiments were also conducted to verify the changes over time in the adsorption of fungicide by soils and in soil dehydrogenase activity caused by the fungicide and/or SMS. Tebuconazole dissipation followed biphasic kinetics with a rapid dissipation phase, followed by a slow dissipation phase. Half-life (DT50) values ranged from 8.2 to 12.4 days, with lower DT50 for amended soils when compared to the non-amended controls. The distribution of tebuconazole through the soil profile (0-50 cm) determined at 124, 209 and 355 days after its application indicated the higher mobility of fungicide to deeper soil layers in amended soils revealing the influence of solid and dissolved organic matter from SMS in this process. Tebuconazole might be available for biodegradation although over time only chemical or photochemical degradation was evident in surface soils. The results obtained highlight the interest of field and laboratory data to design rational applications of SMS and fungicide when they are jointly applied to prevent the possible risk of water contamination.

Significance of the long-chain organic cation structure in the sorption of the penconazole and metalaxyl fungicides by organo clays

Sorption-desorption of two different hydrophobic fungicides, penconazole and metalaxyl, by a series of clay minerals layered and non-layered (montmorillonite, illite, kaolinite, muscovite, sepiolite and palygorskite) modified with the two-chain cationic surfactant, dihexadecyldimetylammonium (DHDDMA) was studied by first time in this work. DHDDMA-clays showed a good capacity to sorb both fungicides from water. Freundlich sorption constants (K(f)) increased 22-268-fold for penconazole and 4-112-fold for metalaxyl in relation to natural clays. High sorption irreversibility was observed for penconazole for all modified clays, while for metalaxyl this occurred only for some of the modified clays. Additionally, a comparative study of the sorption of the fungicides by clay minerals modified with organic cations of different structure was carried out by a statistical approach. Non-layered and layered clay minerals modified with the two-chain alkylammonium organic cation DHDDMA, and with single-chain organic cations octadecyltrimethylammonium (ODTMA) and hexadecylpyridinium (HDPY) were used as sorbents. The study indicated a significant linear regression between the distribution coefficients K(d) of fungicides and the organic carbon (OC) content of the organo clays (r(2)>or=0.80, p<0.001). According to this sorption of fungicides by partition between the aqueous solution and the organic medium created by the alkyl chains of the exchanged ammonium cations regardless of the type and structure of these cations is suggested. However, linear relationships between K(d) values of each pesticide by the different organo clays and their relative OC contents revealed higher increase in sorption for HDPY-clays (penconazole) and for ODTMA-clays (metalaxyl) pointing out different effectiveness of the OC provided by each organic cation. These effects were also supported by the values of K(d) relative to OC, K(d)(oc). The results evidenced the different relative weight of alkyl cations to make organo clays effective barriers to prevent the mobility of pesticides from a point source of pollution.

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).

Effect of Spent Mushroom Substrate Amendment of Vineyard Soils on the Behavior of Fungicides: 1. Adsorption−Desorption of Penconazole and Metalaxyl by Soils and Subsoils

The effect of the addition of fresh and composted spent mushroom substrates (F-SMS and C-SMS) to vineyard soils on the adsorption-desorption of penconazole and metalaxyl was studied under laboratory conditions. SMS is a promising agricultural residue as an amendment to increase the soil organic matter (OM) content. It may also modify the behavior of fungicides applied to vineyards. Freundlich Kf adsorption constants of both fungicides by soils and subsoils from three experimental plots unamended and amended in the field ranged between 2.78 and 13.4 (penconazole) and 0.14 and 0.67 (metalaxyl) with scant differences for unamended soil and subsoil. However, Kf values of amended soils were higher than those corresponding to subsoils and generally higher than those of unamended soils (up to 2.3 times for penconazole and 1.3 times for metalaxyl). The influence of SMS treatment (fresh or composted) was observed in the adsorption of the most hydrophobic fungicide penconazole. Simple and multiple correlations between soil and subsoil properties and adsorption constants indicated the influence of the OM on the adsorption of both fungicides, together with the clay, silt, and CaCO(3) content for metalaxyl and the pH for penconazole. The results revealed changes in the adsorption-desorption processes of these fungicides, which could give rise to a decrease in the mobility of metalaxyl (highly water-soluble) and an increase in the retention of penconazole (more hydrophobic). These effects could have an impact on surface and/or groundwater contamination.

Organo-clays as adsorbents for azinphosmethyl and dichlorvos in aqueous medium

Using adsorption isotherms, a study was performed of the adsorption of two organophosphorus pesticides, azinphosmethyl (sparingly soluble in water) and dichlorvos (moderately soluble in water), by montmorillonites saturated with the cations hexadecyltrimethylammonium (HDTMA+), dodecyltrimethylammonium (DDTMA+) and tetramethylammonium (TMA+) in aqueous media. The results were compared with those obtained for the adsorption of these pesticides by natural montmorillonite, humic acid and by the soil organic matter and with the octanol-water partition coefficient (Kow) of the compounds. Results indicated that regarding the capacity to remove azinphosmethyl from water the organic matter derived from the organic cations HDTMA+ and DDTMA+ is 5–10 times more effective than humic acid; 10–20 times more effective than the organic matter from the soil and 20–50 times more efficient than octanol. However, both organic phases, that derived from the organic matter of the soil and that of the organic cations, have similar effectiveness for removing dichlorvos from water, in turn, their efficiency is 50 times higher than that of octanol. These findings may find application in the removal of azinphosmethyl or other sparingly water soluble organophosphorus pesticides from aquifers.

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.