Soil solution chemistry is a powerful tool for studying many aspects of soil science. Among several isolation techniques, centrifugation appears most promising as a method of extracting the soil solution in the laboratory. However, some operational conditions must be defined. The present work reports the influence of sample storage on the observed composition of the soil solution of two Brazilian soils submitted to different managements. Since metal speciation in soil solution significantly influences metal bioavailability, a second experiment was conducted to evaluate the effects of storage on Fe, Al, and Mn speciation by size exclusion chromatography (HPLC-SEC). The results showed that the effects of soil handling prior to solution extraction had a significant effect on soil solution composition, mainly when the sample was dried and rewetted. Only the samples that were kept refrigerated (4 °C) for 15 days led to results comparable to those obtained from fresh soils. However, considering the patterns of the UV detection chromatograms and metal distribution, only field moist samples should be used in studies related to Al, Mn, and Fe speciation in the studied soils.

Chlorothalonil, a halogenated benzonitrile compound, is one of the most widely used fungicides in the world. Anaerobic microcosm assays were established to evaluate the combined effect of the initial content of carbon (6.3, 9.45 and 12.6 mg g⁻¹), nitrogen (0.6, 1.8 and 3 mg g⁻¹)and chlorothalonil (432, 865 and 1298 ηg g⁻¹) on the biodegradation of this fungicide by microbiota from an agricultural tropical soil. A Box-Behnken experimental design was used and chlorothalonil depletion was followed by HPLC with UV detection. The initial carbon content and fungicide dose were found to have a significant effect on removal efficiency. After 25 days of incubation, a high chlorothalonil depletion was observed in all biologically active microcosms (56–95%) although abiotic loss in a sterile blank was also notable (37%). The results suggest a high potential for chlorothalonil biodegradation under anaerobic conditions by indigenous microbial communities from soil that has been continuously exposed to high doses of the fungicide.

A statewide total gaseous mercury (TGM) monitoring campaign was conducted from January 1997 to December 1999 in the State of Connecticut, U.S.A. Eight monitoring sites with different characteristics of geographical location (coastal vs. interior) and land use (rural vs. urban) were included in the monitoring program. Statistical procedures were utilized to evaluate the temporal trend and spatial distribution of the TGM concentration in the State, and the influence of long-range transport from non-local sources. The statewide mean TGM concentration was 2.08 ng m⁻³. The annual mean concentration had no significant differences among the three years of measurements for all the sites. Weak seasonal variations were detected in the State with higher ambient TGM concentration found in warmer seasons. Urban areas in general had higher TGM concentrations than rural areas. The effect of site location of the monitoring sites on TGM concentration was interacted with land use characteristics. Waterbury site with extremely high concentration measurements was the major cause for this interaction. The long-range transport of TGM from remote sources showed an important influence on local ambient concentrations, by explaining over 45% of the total variance of the ambient TGM concentration for most sites. Local sources were responsible for the extremely high TGM concentration in the Waterbury site. The TGM concentrations at Voluntown, Hammonasset and Avery Point in southeast Connecticut were likely to be affected by some local sources.

Nitric acid (HNO₃) vapor is a significant component of air pollution. Dry deposition of HNO₃ is thought to be a major contributor to terrestrial loading of anthropogenically-derived nitrogen (N), but many questions remain regarding the physico-chemical process of deposition and the biological responses to accumulation of dry-deposited HNO₃ on surfaces. To examine these processes experimentally, a continuously stirred tank reactor (CSTR) fumigation system has been constructed. This system enables simultaneous fumigation at several concentrations in working volumes 1.3 m dia by 1.3 m ht, allowing for simultaneous fumigation of many experimental units. Evaluation of the system indicates that it is appropriate for long-term exposures of several months duration and capable of mimicking patterns of diurnal atmospheric HNO₃ concentrations representative of areas with different levels of pollution.

Bulk rainfalls were sampled during ten months in the Eastern Channel (Northern France). Chloride and sodium are the heavily loaded major ions in wet deposition, indicating a high influence of seasalt. However, the presence of heavy metals is independent of seasalt emissions and various anthropogenic sources should have an impact on their atmospheric concentrations.The comparison between heavy metals concentrations, always ranked as [Zn] ≫ [Pb] > [Cu] ≫ [Cd], with other values obtained during the same period on European coastal or on urban sites, confirms that ourwestern European station is in a semi-rural area where no local source strongly influences the abundance of atmospheric heavy metals. This semi-rural site could be disturbed by medium and/or long range transportepisodes.The observation of literature data confirms a decrease of Cd, Cu and Pb concentrations in rain waters from the beginning of the nineties. On the other hand, no sharp evolution has been observed for zinc concentrations.The structuring of data by clustering has permitted to extract five clusters, including four different types of origins. Two marine clusters, with relatively low levels of heavy metals, are opposite to three other clusters with higher heavy metal levels and a more important impact of continental polluted sources. In 47% of cases, the heavy metals collected at Cap Gris-Nez could originate from British Islands or north western Europe.Heavy metals fluxes show that this rural coastal European site has a level of contamination higher than those measured in remote area. The wet depositions of heavy metals to the English channel and the southern bight of the north sea are not negligible in the evaluation of global fluxes for this area, representing from 20 to 70% of the total input (riverine, direct and atmospheric inputs).

Changes in land-use or management practices may affect water outflow, sediment, nutrients and pesticides loads. Thus, there is an increasing demand for quantitative information at the watershed scale that would help decision makers or planners to take appropriate decisions. This paper evaluates by a modeling approach the impact of farming practices and land-use changes on water discharge, sediment and NO3-N loads at the outlet of a 51.29 km2 watershed of central Iowa (Walnut Creek watershed). This intensively farmed (corn-soybean rotation) watershed is characterized by a flat topography with tiles and potholes. Nine scenarios of management practices (nitrogen application rates: increase of current rate by 20, 40%, decrease of current rate by 20, 40 and 60%; no tillage) and land-use changes (from corn-soybean rotation to winter wheat and pasture) were tested over a 30 yr simulated period. The selected model (Soil and Water Assessment Tool, SWAT) was first validated using observed flow, sediment and nutrient loads from 1991 to 1998. Scenarios of N application rates did not affect water and sediment annual budgets but did so for NO3-N loads. Lessening the N rate by 20, 40 and 60% in corn-soybean fields decreased mean NO3-N annual loads by 22, 50 and 95%, respectively, with greatest differences during late spring. On the other hand, increasing input N by 20 and 40% enhanced NO3-N loads by 25 and 49%, respectively. When replacing corn-soybean rotation by winter wheat, NO3-N loads increased in early fall, immediately after harvest. Pasture installation with or without fertilization lessened flow discharge, NO3-N and sediment delivery by 58, 97 and 50%, respectively. No-tillage practices did not significantly affect the water resource and sediment loads. Finally, such realistic predictions of the impact of farming systems scenarios over a long period are discussed regarding environmental processes involved.

1,1-bis(p-chlorophenyl)-2,2,2-trichloroethane (p,p′-DDT) is a recalcitrant organic compound that is difficult to remove from contaminated soil due to its low solubility. In this study we investigated the effectiveness of both cosolvents and surfactants in enhancing the solubility of p,p′-DDT from a soil that has been contaminated with DDT for nearly 40 yr. The presence of selected surfactants removed less than 1 to 11% of p,p′-DDT compared to cosolvents, which removed less than 1 to 77% of p,p′-DDT from the same soil. The low solubility of p,p′-DDT in the presence of surfactants was attributed to the decreased surfactant concentration to below critical micelle concentrationfollowing sorption by soil surfaces. Enhanced solubility of p,p′-DDT was achieved with the use of cosolvents that releasedup to 77% of p,p′-DDT from a contaminated soil. Increasing the solution concentration and hydrophobicity of the cosolvent increased the amount of p,p′-DDT desorbed. For example, the amount of p,p′-DDT desorbed increased in the order 5% 1-propanol << 50% ethanol << 50% 1-propanol. Repeated washing of the soil with various cosolvents, in all but two cases, markedly increased the total amount of p,p′-DDT desorbed from the soil. For example, repeated washing of the soil with 50% ethanol increased the amount of p,p′-DDT removed by 42% while repeated washings of the soil with 50% 1-propanol had little effect on the amount of p,p′-DDT desorbed. Increasing the soil-solution ratio from 1:2 to 1:10 in the presence of 40% 1-propanol increased the amount of p,p′-DDT desorbed by 100%; suggesting that the soil-solution ratio was an important parameterin controlling the amount of p,p′-DDT desorbed.

This study investigated the intrinsic perchlorate (ClO₄ ⁻)degradation kinetics of sediments and soils from multiple sites in microcosm studies, including the influence of varying nitrate concentration (NO₃ ⁻-N from 1 to 22.8 ppm) and up to 300 ppm sulfate. The first-order degradation rates and lag times of both ClO₄ ⁻ and NO₃ ⁻ degradation were site-specific and dependent on environmental conditions such as organic substrate availability, nitrate, initial ClO₄ ⁻ concentration, and prior ClO₄ ⁻ exposure. At an initial ClO₄ ⁻ concentration of 5 ppm, ClO₄ ⁻ degradation rates ranged from 0.13 to 0.46 day⁻¹, and lag times of ClO₄ ⁻ degradation ranged from 0 to 60.0 days; while NO₃ ⁻ degradation occurred at rates ranging from 0.03 to 1.42 day⁻¹, with lag times ranging from 0 to 29.7 days. Under the same treatment conditions, NO₃ ⁻ degradation rates were relatively higher than that of ClO₄ ⁻. Perchlorate degradation rates remained constant at both lower (0.5 ppm) and higher (5 ppm) ClO₄ ⁻ concentrations. Generally, ClO₄ ⁻ rates were affected by the availability of organic substrate, which was represented here by Total Volatile Solids (TVS) of sediments and soils, and not by NO₃ ⁻. Nitrate did increase the lag time of ClO₄ ⁻ degradation, which may account for the persistence of ClO₄ ⁻ in the environment, especially when ClO₄ ⁻ is typically ppb levels in the environment compared to ppm levels of NO₃ ⁻. This study showed rapid intrinsic ClO₄ ⁻ degradation in sediments and soils of contaminated sites, and highlighted the potential for natural attenuation of ClO₄ ⁻ in the environment.

This work aims to identify the sources of nitrogencontamination in nitrate vulnerable zones (NVZs) of Spain by means of the nitrogen isotope method. Three categories of nitrogen sources (synthetic fertilisers, animal wastes, and sludges and effluents from waste-water treatment plants) from three NVZs were analysed for their nitrogen isotopic composition (δ¹⁵N) in order to assess the applicability of the method to the identification of these N sources. The mean δ¹⁵N values were: +1.48‰ for synthetic fertilisers, +15.98‰ for animal wastes and +11.52‰ for sludges and effluents. The synthetic fertiliser sources were significantly different from the organic sources and so, the method can be used for their identification. The highest variability was found within the animal waste category. The range of values found for the different kinds of animal wastes (+5.86 to +36.74) was very wide and overlappedthe range found for sludges and effluents from waste-water treatmentplants (+4.57 to +20.18). Accordingly, these two nitrogen sources areisotopically indistinguishable.

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