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.

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.

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).

To date there have only been a few studies that measured mercury emissions from background substrate worldwide, and only a small amount of mercury flux data, from background substrate, exists for the Western United States. Because of this, the database of mercury emissions from background units < 0.1 mg kg⁻¹ mercury) is incomplete. This study focused on the collection of in-situ mercury flux data from representative lithologic units in Nevada. Measured mercury fluxes from substrate with background mercury concentration throughout Nevada were low (mean 2.0 ± 4.1 ng m⁻² hr⁻¹), and ranged from –3.7 to 9.3 ng m⁻² hr⁻¹. The mean measured mercury flux is slightly higher than those measured from background substrate from various locations throughout the world. The mean mercury flux from in-situ mercury measurements from substrate located near altered geologic units across Nevada was 15.5 ± 24.2 ng m⁻² hr⁻¹. These mercury fluxes are higher than the values applied in published global models for naturally enriched geologic units.

[Departement_IRSTEA]RE [TR1_IRSTEA]RIE / PHYLEAU | Passive capillary samplers, which sample water from the vadose zone via a hanging water column in a fiberglass wick, have shown potential to provide better estimates of actual soil percolation fluxes than alternative field methods. Unsaturated and saturated flows (water and solutes) are extracted continuously and without external vacuum generator from a nondisturbed soil volume, through a significant area (typically 600cm2). In order to achieve a minimal disturbance of the native flow regime, the wick type (hydraulic conductivity and section), length and number and the contact area have to be dimensioned to match as close as possible the expected soil pressure/flow conditions. First, the Hydrus 2D code (Simunek et al., 1999) solving the Richards equation for simulating two dimensional unsaturated flow was used to evaluate the uncertainties in flux estimation by such passive capillary samplers. Two sources of uncertainties were examined. Those associated with the theoretical assumptions of the dimensioning of the wick and those associated to experimental uncertainties. A numerical experimentation was conducted on two reference soils submitted to a 11 days actual hyetograph. Results showed that an analytical dimensioning method proposed in the literature is relevant. But significant errors on the observed fluxes occur when the soil and wick properties do not exactly match, which is the common case since the range of available characteristics of fiberglass wicks is limited. Also, uncertainties in the hydraulic conductivity properties of the soil, in wick length appear to have an important influence on the representativity of the wick fluxes against the actual soil drainage fluxes. Elsewhere, eight such samplers have been installed for an in situ long term experimentation ,initiated this year in the Ardière Watershed (France). The objective is to measure water and pesticides percolation fluxes, at a 50cm depth under a grassed strip receiving contaminated runoff. Flow rate and pesticide concentration in surface runoff water are also measured so as to determine the soil boundary condition above each sampler. Soil water content and soil matric potential are measured at three different depth very close to each instrumented profile in order to explain the volumes extracted by each sampler. We present here the experimental methodology and first results obtained with simulated runoff events.

Passive capillary samplers, which sample water from the vadose zone via a hanging water column in a fiberglass wick, have shown potential to provide better estimates of actual soil percolation fluxes than alternative field methods. Unsaturated and saturated flows (water and solutes) are extracted continuously and without external vacuum generator from a nondisturbed soil volume, through a significant area (typically 600cm2). In order to achieve a minimal disturbance of the native flow regime, the wick type (hydraulic conductivity and section), length and number and the contact area have to be dimensioned to match as close as possible the expected soil pressure/flow conditions. First, the Hydrus 2D code (Simunek et al., 1999) solving the Richards equation for simulating two dimensional unsaturated flow was used to evaluate the uncertainties in flux estimation by such passive capillary samplers. Two sources of uncertainties were examined. Those associated with the theoretical assumptions of the dimensioning of the wick and those associated to experimental uncertainties. A numerical experimentation was conducted on two reference soils submitted to a 11 days actual hyetograph. Results showed that an analytical dimensioning method proposed in the literature is relevant. But significant errors on the observed fluxes occur when the soil and wick properties do not exactly match, which is the common case since the range of available characteristics of fiberglass wicks is limited. Also, uncertainties in the hydraulic conductivity properties of the soil, in wick length appear to have an important influence on the representativity of the wick fluxes against the actual soil drainage fluxes. Elsewhere, eight such samplers have been installed for an in situ long term experimentation ,initiated this year in the Ardière Watershed (France). The objective is to measure water and pesticides percolation fluxes, at a 50cm depth under a grassed strip receiving contaminated runoff. Flow rate and pesticide concentration in surface runoff water are also measured so as to determine the soil boundary condition above each sampler. Soil water content and soil matric potential are measured at three different depth very close to each instrumented profile in order to explain the volumes extracted by each sampler. We present here the experimental methodology and first results obtained with simulated runoff events.

Soil remediation has been studied after a spill from a settling pond of a pyrite mine in Aznalcóllar (SW Spain). The affected area was approximately 55 km² and extended about 40 km from the spill. The Pb concentration in soils ranged from 35.8 to 3231.0 mg kg⁻¹, with a mean value of 385.8 mg kg⁻¹. The remediation techniques investigated included: manual and mechanical removal of the contaminated soil, mixing the upper part of the soils by ploughing, and addition of different amendment materials to reduce the Pb solubility, such as carbonates, zeolites, iron-rich soils, bentonites and yeasts. A combination of liming with iron-rich soils proved the most effective treatment.

Concentrations of ozone and nitrogen oxides, together with air temperature and solar radiation intensity, were measured at several heights on a tower standing through the canopy of a red pine forest in summer and in autumn. In the summer observation, the diurnal variation patterns of ozone concentration both above and below the canopy were all similar and parallel to the solar radiation intensity. Using the data collected immediately above the canopy, deviation from the Leighton relationship and variations of concentration sums [O₃] + [NO] and [NO₂] + [NO] were examined, and as a result, it was supposedthat ozone was photochemically formed there in the daytime, probably because hydrocarbons emitted from pine trees broke the photostationary state among ozone and nitrogen oxides. The vertical temperature profile exhibited an inversion at the leaf-layer, which must have hindered vertical mixing of the air and made the trunk space more or less isolated from the upper atmosphere. These observations led to an idea that the similarity of the ozone variation pattern at every height was caused by the photochemical formation that proceeded simultaneously above and below the canopy rather than by vertical transport. Such situations of ozone formation were supported by observation of two maximums in the ozone vertical profile, one immediately above the canopy and another in the trunk space. Another feature of the ozone profile was a deep minimum in the leaf layer, which indicated ozone deposition onto leaf surfaces. This study thus revealed concurrence of ozone formation and deposition, and left two potentially important implications worthy of further investigation: (1) a forest is not always a sink but can be a source of ozone in sunlit conditions, and (2) deposition of ozone to trees can take place not only from outside but also from inside of a forest. In the autumn observation, however, the ozone formation was barely recognizable above the canopy and no longer found in the trunk space; in addition, the ozone concentration minimum in the leaf layer disappeared, suggesting that the deposition or removal was dependent on temperature.

The effect of selected nutrient amendments and temperature on the biodegradation of pentachlorophenol (PCP) within a soil biopile was studied on a laboratory scale. This was accomplished by monitoring microbial populations, the concentration of PCP and the release of inorganic chloride ions in the contaminated soil. It was found that temperatures of 10, 15 and 20 °C had no significant effect on microbial populations and the percentage of PCP remaining in the soil. However, the nutrient amendments did have a significant effect on the parameters measured. The dairy manure, ammonium nitrate fertilizer and control treatments all experienced some fluctuations in the amount of PCP remaining in the soil over the incubation period and may have been due to the release of initially unextractable bound residues. PCP decreased by 76% in the municipal solid waste compost amended soil, while the concentration of inorganic chloride ions increased. The municipal solid waste compost treatment had significantly higher bacterial and fungal populations. Based on the results of this study municipal solid waste compost may be used as an effective supplemental nutrient amendment for the degradation of PCP in soil biopiles.

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.