Interactions of diuron with dissolved organic matter from organic amendments.

Diuron is frequently detected in some drinking water reservoirs under the Burgundy vineyards, where organic amendments are applied. The environmental effect of these amendments on pesticide transport is ambiguous: on the one hand it could enhance their retention by increasing soil organic carbon content; on the other hand, dissolved organic matter (DOM) could facilitate their transport. Elutions were performed using columns packed with glass beads in order to investigate DOM-diuron interactions, and the possible co-transport of diuron and DOM. Four organic amendments (A, B, C and D) were tested; C and D were sampled at fresh (F) and mature (M) stages. An increase in diuron leaching was observed only for A and D(F) amendments (up to 16% compared to the DOM-free blank samples), suggesting a DOM effect on diuron transport. These results could be explained by the higher DOM leaching for A and D(F) compared to B, C(F), C(M) and D(M) increasing diuron-DOM interactions. These interactions seem to be related to the aromatic and aliphatic content of the DOM, determining formation of hydrogen and non-covalent bonds. The degree of organic matter maturity does not seem to have any effect with amendment C, while a reduction in diuron leaching is observed between D(F) and D(M). After equilibrium dialysis measurement of diuron-DOM complexes, it appeared that less than 3% of the diuron applied corresponded to complexes with a molecular weight >1000 Da. Complexes <1000 Da could also take part in this facilitated transport.

Electron microprobe and synchrotron x-ray fluorescence mapping of the heterogeneous distribution of copper in high-copper vineyard soils.

The response of microorganisms to metal contamination of soils varies significantly from one investigation to another. One explanation is that metals are heterogeneously distributed at spatial scales relevant to microbes and that microoorganisms are able to avoid zones of intense contamination. This article aims to assess the microscale distribution of Cu in a vineyard soil. The spatial distribution of Cu was measured at two resolutions (0.3 mm and 20 microm) in thin sections of the surface 4 cm of undisturbed soil by electron microprobe and synchrotron X-ray microfluo-rescence spectroscopy. Bulk physicochemical analyses of Cu, pH, organic matter, texture, and mineralogy were performed. The results indicate that the Cu distribution is strongly heterogeneous at both scales of observation. Entire regions of the thin sections are virtually devoid of Cu, whereas highly localized "hotspots" have Cu signal intensities thousands of times higher than background. The distribution of Rb, or Al and Si, indicators of clay minerals, or Fe (iron (hydr)oxides), show that Cu is not preferentially associated with these mineral phases. Instead, Cu hotspots are associated with particulate organic matter. These observations suggest modification of current sampling protocols, and design of ecotoxicological experiments involving microorganisms, for contaminated soils.

Influence of 15N enrichment on the net isotopic fractionation factor during the reduction of nitrate to nitrous oxide in soil.

Nitrous oxide, a greenhouse gas, is mainly emitted from soils during the denitrification process. Nitrogen stable-isotope investigations can help to characterise the N(2)O source and N(2)O production mechanisms. The stable-isotope approach is increasingly used with (15)N natural abundance or relatively low (15)N enrichment levels and requires a good knowledge of the isotopic fractionation effect inherent to this biological mechanism. This paper reports the measurement of the net and instantaneous isotopic fractionation factor (alpha(s/p) (i)) during the denitrification of NO(3) (-) to N(2)O over a range of (15)N substrate enrichments (0.37 to 1.00 atom% (15)N). At natural abundance level, the isotopic fractionation effect reported falls well within the range of data previously observed. For (15)N-enriched substrate, the value of alpha(s/p) (i) was not constant and decreased from 1.024 to 1.013, as a direct function of the isotopic enrichment of the labelled nitrate added. However, for enrichment greater than 0.6 atom% (15)N, the value of alpha(s/p) (i) seems to be independent of substrate isotopic enrichment. These results suggest that for isotopic experiments applied to N(2)O emissions, the use of low (15)N-enriched tracers around 1.00 atom% (15)N is valid. At this enrichment level, the isotopic effect appears negligible in comparison with the enrichment of the substrate.

Facilitated transport of diuron and glyphosate in high copper vineyard soils.

The fate of organic herbicides applied to agricultural fields may be affected by other soil amendments, such as copper applied as a fungicide. The effect of copper on the leaching of diuron and glyphosate through a granitic and a calcareous soil was studied in the laboratory using sieved-soil columns. Each soil was enriched with copper sulfate to obtain soil copper concentrations of 125, 250, 500, and 1000 mg kg(-1). Glyphosate leaching was influenced by soil pH and copper concentration, whereas diuron leaching was not. In the calcareous soil, glyphosate leaching decreased as copper levels increased from 17 mg kg(-1) (background) to 500 mg kg(-1). In the granitic soil, glyphosate leaching increased as copper levels increased from 34 mg kg(-1) (background) to 500 mg kg(-1). The shapes of the copper elution curves in presence of glyphosate were similar to shapes of the glyphosate curves, suggesting the formation of Cu-glyphosate complexes that leach through the soil. Soil copper concentration does not influence diuron leaching. In contrast, increasing copper concentrations reduces glyphosate leaching through calcareous soils, and conversely, increases glyphosate leaching through granitic soils. Our findings suggest that the risk of groundwater contamination by glyphosate increases in granitic soils with elevated copper concentrations.

Microbial community structure in soils with decomposing residues from plants with genetic modifications to lignin biosynthesis.

Lignin is a major determinant of the decomposition of plant materials in soils. Advances in transgenic technology have led to the possibility of modifying lignin to improve the pulping properties of plant materials for papermaking. Previous studies have shown that lignin modifications also affect the rate of plant material decay in soil. The aim of this work was to investigate short-term changes in soil microbial community structures when tobacco residues with reduced activity of enzymes in the monolignol pathway decompose. The residues from lignin-modified plants all decomposed faster than unmodified plant materials. The relative proportions of some of the structural groups of microbial phospholipid fatty acids were affected by genetic modifications, especially the proportion of double unsaturated chain fatty acids, indicative of fungi.

C4 plant isotopic composition (delta13C) evidence for urban CO2 pollution in the city of Cotonou, Benin (West Africa).

The carbon isotopic composition (delta13C) of plants can reveal the isotopic carbon content of the atmosphere in which they develop. The delta13C values of air and plants depend on the amount of atmospheric fossil fuel CO2, which is chiefly emitted in urban areas. A new indicator of CO2 pollution is tested using the delta13C variation in a C4 grass: Eleusine indica. A range of about 4 per thousand delta units was observed at different sites in Cotonou, the largest city in the Republic of Benin. The highest delta13C values, from -12 per thousand to -14 per thousand, were found in low traffic zones; low delta13C values, from -14 per thousand to -16 per thousand, were found in high traffic zones. The amount of fossil fuel carbon assimilated by plants represented about 20% of the total plant carbon content. An overall decrease in plant delta13C values was observed over a four-year monitoring period. This decrease was correlated with increasing vehicle traffic. The delta13C dataset and the corresponding geographical database were used to map and define zones of high and low 13C-depleted CO2 emissions in urban and sub-urban areas. The spatial distribution follows dominant wind directions, with the lowest emission zones found in the southwest of Cotonou. High CO2 emissions occurred in the north, the east and the center, providing evidence of intense anthropogenic activity related to industry and transportation.

Leaching of oryzalin and diuron through undisturbed vineyard soil columns under outdoor conditions.

Field studies monitoring herbicide pollution in the vineyards of Burgundy (France) have revealed that drinking water reservoirs are contaminated with several pre-emergence herbicides. An assessment of the leaching of two such herbicides, diuron and oryzalin, was therefore performed using lysimeters, under outdoor conditions, from May 2001 to May 2002. Four vineyard soils from Vosne-Romanée (Burgundy) were chosen along a topolithosequence: a rendosol and three calcosols. After 673 mm of rainfall, greater amounts of diuron than oryzalin were measured in percolates: respectively 0.10-0.84% and 0.02-0.43% of applied herbicide, depending on soils. Measurements for diuron metabolites detected greater amounts of DCPMU than DCPU in the percolates: respectively 0.05-0.13% and 0-0.04% of the applied diuron. At the end of the monitoring period, more residues of diuron than oryzalin were recovered in the soil profiles: respectively 4.6-9% and 1.4-4.4%. The oryzalin residues were found mainly in the upper 10 cm of soil columns, whereas diuron residues were present in the whole core. The mobility of both oryzalin and diuron seems fairly well-related to soil organic carbon content; the mobility of diuron is also related to soil texture (sand and coarse material contents). Under such experimental conditions, this study confirms that diuron leaching, and therefore potential groundwater contamination, is greater than that of oryzalin.

Leaching of glyphosate and AMPA under two soil management practices in Burgundy vineyards (Vosne-Romanée, 21-France).

Some drinking water reservoirs under the vineyards of Burgundy are contaminated with herbicides. Thus the effectiveness of alternative soil management practices, such as grass cover, for reducing the leaching of glyphosate and its metabolite, AMPA, through soils was studied. The leaching of both molecules was studied in structured soil columns under outdoor conditions for 1 year. The soil was managed under two vineyard soil practices: a chemically treated bare calcosol, and a vegetated calcosol. After 680 mm of rainfall, the vegetated calcosol leachates contained lower amounts of glyphosate and AMPA (0.02% and 0.03%, respectively) than the bare calcosol leachates (0.06% and 0.15%, respectively). No glyphosate and only low amounts of AMPA (<0.01%) were extracted from the soil. Glyphosate, and to a greater extent, AMPA, leach through the soils; thus, both molecules may be potential contaminants of groundwater. However, the alternative soil management practice of grass cover could reduce groundwater contamination by the pesticide.

Diuron mobility through vineyard soils contaminated with copper.

The herbicide diuron is frequently applied to vineyard soils in Burgundy, along with repeated treatments with Bordeaux mixture (a blend of copper sulfate and calcium hydroxide) that result in elevated copper concentrations. Cu could in principle affect the fate and transport of diuron or its metabolites in the soil either directly by complexation or indirectly by altering the populations or activity of microbes involved in their degradation. To assess the effect of high Cu concentrations on diuron transport, an experiment was designed with ten undisturbed columns of calcareous and acidic soils contaminated with 17--509 mg kg(-1) total Cu (field-applied). Grass was planted on three columns. Diuron was applied to the soils in early May and in-ground lysimeters were exposed to outdoor conditions until November. Less than 1.2% of the diuron applied was found in the leachates as diuron or its metabolites. Higher concentrations were found in the effluents from the grass-covered columns (0.1--0.45%) than from the bare-soil columns (0.02--0.14%), and they were correlated with increases in dissolved organic carbon. The highest amounts of herbicide were measured in acidic-soil column leachates (0.98--1.14%) due to the low clay and organic matter contents of these soils. Cu also leached more readily through the acidic soils (32.8--1042 microg) than in the calcareous soils (9.5--63.4 microg). Unlike in the leachates, the amount of diuron remaining in the soils at the end of the experiment was weakly related to the Cu concentrations in the soils.

Laboratory leaching studies of oryzalin and diuron through three undisturbed vineyard soil columns.

The leaching of diuron and oryzalin through undisturbed soil columns was studied in the laboratory using three vineyard soils from Vosne-Romanée (Burgundy): a rendosol, a calcosol and a vegetated calcosol. After 845 mm of simulated rainfall in 15 days, soil leachates contained higher amounts of diuron (3.2%, 11.8% and 18.8% of applied diuron, respectively) than oryzalin (0.2%, 4.9%, 3.7%, respectively). A greater proportion of soil extractable residues was obtained for diuron (42.5%, 26.8% and 32.2%, respectively) than for oryzalin (14.7%, 12% and 15.5%, respectively). The greater mobility of diuron might be related to its higher water solubility (36.4 mgl(-1) compared with 2.6 mgl(-1) for oryzalin) and smaller adsorption coefficient (400 lkg(-1), compared with 700-1100 lkg(-1) for oryzalin). The mobility of the two herbicides was greater in the two calcosols than in the rendosol, not only due to different organic carbon contents but also different soil textures and structures.

Comparison of three sequential extraction procedures used to study trace metal distribution in an acidic sandy soil.

On an acid sandy soil contaminated with trace metals (Fe, Mn, Cu, Pb and Zn), three sequential extraction procedures were compared to determine the efficiency of the reagents used and the effects of the step order on the fractionation of metal species. In all cases, a magnesium nitrate solution (MgNIT) was previously used to extract exchangeable forms. In the first procedure (I), the next extraction step was performed with sodium acetate buffer (NaOAc), as used on calcareous soils, to dissolve active calcium carbonate. Then trace metals bound to different forms of oxi-hydroxides (NH(2)OH, TAMOx and TAMAs fractions) were extracted before organic matter/sulfide oxidation with hydrogen peroxide at pH 2.0 in nitric acid medium (OMHyd). Finally, residual bound metals (RESID) in each procedure were extracted with a nitric-hydrofluoric-perchloric acid mixture. The second procedure (II) was the same as I, but without the NaOAc step, because of the absence of carbonate in the study soil. In procedure III, the NaOAc step was omitted and the oxidizable organic/sulfide fraction was extracted with sodium hypochlorite at pH 8.5 (OMOCl) before the reducible fractions. This study first showed that NaOAc may remove considerable amounts of metals (especially Mn and Zn) in other forms than exchangeable ones. Procedures II and III give similar results for Fe, Mn and Zn forms, which were mainly found in fractions of inorganic soil components, but not for Cu and Pb. Copper distribution was affected by the position of the oxidation step in the sequence. In procedure II, where the oxidation step (OMHyd) ended the sequence, Cu was mainly recovered in the TAMOx fraction. However, in procedure III, where the oxidation step (OMOCl) preceded the NH(2)OH, TAMOx and TAMAs steps, Cu was found in both OMOCl and TAMOx fractions. Lead distribution varied with oxidation reagent: it was partly removed in the OMHyd fraction of procedures I and II, and to a much lower extent in the OMOCl fraction of procedure III, probably due to the alkaline pH of the reagent in the latter case.