The characterization of pig sludge liquid fraction (PSLF) was conducted to achieve a better understanding of its chemical and physical chemical characteristics. Total dissolved organic carbon (TDOC) from pig sludge was separated into two fractions: acid insoluble dissolved organic carbon (AIDOC) and acid soluble dissolved organic carbon (ASDOC). Elemental analysis, acidic functional group determination, E4/E6 ratio, Gel‐Filtration Cromatography and FTIR Spectroscopy of ASDOC and AIDOC showed a similarity with humic and fulvic acids, isolated from soils and organic wastes. Phosphorus‐31 Nuclear Magnetic Resonance spectra demonstrated that the organic P in PSLF was present as P‐monoester. The complexing capacity of DOC vs. trace metals was demonstrated by Gel Filtration Chromatography and FTIR Spectroscopy. The interactions of DOC, Cu, and Zn, present in PSLF, with a calcareous soil were evaluated by adsorption isotherms that indicated that Zn was completely adsorbed by the soil, while Cu followed the same behavior as DOC, with only partial adsorption. Therefore, both Cu and DOC should be taken into consideration as a possible groundwater pollution hazard after pig sludge application to calcareous soil.

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Experiments were carried out on three Italian farms to assess the degree of spatial variation of pesticide field concentration during treatment and during dissipation trials. Test pesticides were chloridazon and metamitron (both sugar‐beet herbicides) applied as a tank mix. The classical statistical technique and geostatistics were used to summarize and evaluate variable spatial data. The results show that the actual values of pesticide concentration for application rate and initial concentration in all three areas are lower than expected, thus indicating that under field conditions only a part of the pesticide reaches the soil during the distribution. The actual values for both herbicides in all three areas expressed as percentage of expected values ranged from 44·1% to 64·2% for application rate and from 40·5% to 99·5% for initial concentration. The coefficient of variation was similar for both pesticides and ranged from 23·8 to 74·1 for application rate, 24·1 and 58·8 for initial concentration and 11·1 and 110·0 for dissipation half‐lives. The high variability in application rate and initial concentration could be ascribed to an uneven herbicide distribution, and in dissipation studies to variation in half‐lives for the rate of herbicide loss from soil in different parts of the field. Geostatistic analysis indicated little spatial correlation, probably because the sampling sites were widely spaced on the field. In all cases, the data were not sufficient to estimate the range of influence, probably because of the size of the experimental fields and the sampling strategy. © 1997 SCI.

The aim of this research is to corroborate the results obtained with Pb (II) sorption and desorption macroscopic equilibrium studies on some soil minerals (montmorillonite, illite, kaolinite and goethite) using microscopic techniques. The sorption isotherms demonstrate that the adsorption capability of the substrates varies in the following sequence: illite > montmorillonite > kaolinite > goethite, and the desorption isotherms demonstrate the irreversibility of the bonds formed. pH adsorption edges on montmorillonite show that at a pH lower than the hydrolysis point the sorption edge is primarily due to ion exchange, while at a pH higher than the hydrolysis point, it is a combination of both ion exchange and precipitation. The EDS semi-quantitative analysis performed by SEM demonstrates that in the clays Pb replaced almost exclusively Ca ions. In the montmorillonite this replacement may also include the Ca ions in the interlayer space, and in the illite also, the replacement of protonated OH groups and the K ions situated at the edge of interlattice sites. Goethite shows an adsorption capability of the same magnitude as kaolinite. lead / clays / goethite / sorption-desorption / microscopic techniques Résumé-Mécanismes d'absorption et de désorption du Pb (II) à l'interface entre solution aqueuse et certaines argiles et la goethite. L'objectif de cette recherche est d'étayer, au moyen de techniques microscopiques, les résultats obtenus par le biais d'études macroscopiques d'équilibre sur l'absorption et la désorption du Pb (II) sur certains composants minéraux du sol (montmorillonite, illite, kaolinite et goethite). Les isothermes d'absorption ont montré que la capacité d'adsorption des substrats variait de la façon suivante : illite > montmorillonite > kaolinite > goethite, et les isothermes de désorption ont démontré l'irréversibilité des liens formés. La variation du pourcentage de Pb adsorbé par la montmorillonite en fonction du pH montrait que, lorsque l'on a une valeur de pH inférieure au point d'hydrolyse, l'absorption est principalement due à une réaction d'échange ionique alors que, lorsque l'on a une valeur de pH supérieure au point d'hydrolyse, l'absorption est due à une combinaison de réactions d'échange ionique et précipitation. Les analyses semi-quantitatives effectuées au microscope électronique à balayage (MEB) couplé à la micro-analyse aux rayons X par dispersion d'énergie (EDS) ont démontré que, dans les argiles, le Pb remplaçait exclusivement les ions Ca. Dans la montmorillonite, cette substitution pourrait intéresser aussi les ions Ca de l'espace interlamellaire et, dans l'illite, il pourrait également y avoir substitution de groupes OH protonés et d'ions K situés au bord des sites interstrates. La goethite a montré une capacité d'adsorption équivalente à celle de la kaolinite. plomb / argiles / goethite / absorption-désorption / techniques microscopiques