Contribution of marine and continental aerosols to the content of major ions in the precipitation of the central Mediterranean

The region of the investigated receptor is situated in the southern part of the Adriatic Sea in the Mediterranean. The measuring station is located on the seashore, which, being considered as a border area, is representative for the qualitative and quantitative estimation of the influence of marine and continental aerosols on the content of major ions in precipitation. In the sampling period, precipitation in the region of the investigated receptor was more abundant during the summer and autumn than during the winter and spring. The most frequent precipitation heights were up to 20 mm, while high precipitation came exclusively from the continental region. The results of the measurements of ions readily soluble in water were used for the differentiation of marine from continental contributions of primary and secondary aerosols to their content in the precipitation. Using PCA, it was shown that main contribution of Cl(-), Na(+) and Mg(2+) came from primary marine aerosols, while the contribution from continental sources was dominant for the content of SO(4)(2-), NO(3)(-), NH(4)(+) and Ca(2+) in the precipitation. The continental origin of Ca(2+) was from a primary source, while SO(4)(2-), NO(3)(-) and NH(4)(+) were representatives of secondary aerosols produced by reactions between acid oxides and alkaline species in the atmosphere, but SO(4)(2-) and NO(3)(-) also exist in the precipitation as free acids. The origin of the trace elements Cd, Cu, Pb and Zn in the precipitation came from anthropogenic emission sources. The results obtained in this work are based on experimental data from 609 samples collected during the period 1995-2000.     

Chemical composition of arctic snow: concentration levels and regional distribution of major elements

At the end of the northern winter 1996/1997, 21 snow samples were collected from 17 arctic localities in Norway, Sweden, Finland, Svalbard, Russia, Alaska, Canada, Greenland and Iceland. Major element concentrations of the filtered (0.45 mum) melted snow indicate that most samples are consistent with a diluted seawater composition. Deviations from this behaviour indicate additional SO(4)(2-) and Cl(-) relative to seawater, suggesting a minor contribution from (probably local) coal combustion emissions (Alaska, Finland, Sweden, Svalbard). The samples with the highest Na and Cl(-) content (Canada, Russia) also have higher Na/SO(4)(2-) and Cl(-)/SO(4)(2-) ratios than seawater, suggesting a slight contamination from (probably local) deicing activities. Local soil or rock dust inputs in the snow are indicated by 'excess' Ca contents (Alaska, Svalbard, Greenland, Sweden). No overall relationship was found between pH (range: 4.6-6.1) and total or non-seasalt SO(4)(2-) (NSS), suggesting that acidification due to long-range transport of SO(2) pollution is not operating on an arctic-wide scale. In a few samples (Alaska, Finland, Sweden, Svalbard), a significant proportion (>50%) of SO(4)(2-) is non-marine in origin. Sources for this non-marine SO(4)(2-) need not all be found in long-range atmospheric transport and more likely sources are local industry (Finland, Sweden), road traffic (Alaska) or minor snow-scooting traffic (one Svalbard locality). A few samples from northern Europe show a relatively weak trend of decreasing pH with increasing NO(3)(-).     

Electrocatalytic reduction of nitrate in water

Nitrate (NO(3)(-)) contamination of groundwater is a common problem throughout intensive agricultural areas (nonpoint source pollution). Current processes (e.g., ion exchange, membrane separation) for NO(3)(-) removal have various disadvantages. The objective of this study was to evaluate an electrocatalytic reduction process to selectively remove NO(3)(-) from groundwater associated with small agricultural communities. A commercially available ELAT (E-Tek Inc., Natick, MA) carbon cloth with a 30% surface coated Rh (rhodium) (1microg x cm(-1)) was tested at an applied potential of -1.5 V versus standard calomel electrode (SCE) with a Pt auxiliary electrode. Electrocatalytic reduction process (electrolysis) of NO(3)(-) was tested with cyclic voltammetry (CV) in samples containing NO(3)(-) and 0.1M NaClO(4)(-). Nitrate and NO(2)(-) concentrations in test solutions and groundwater samples were analyzed by ion chromatography (IC). The presence of Rh on the carbon cloth surface resulted in current increase of 36% over uncoated carbon cloths. The electrocatalysis experiments using Rh coated carbon cloth resulted in reduction of NO(3)(-) and NO(2)(-) on a timescale of minutes. Nitrite is produced as a product, but is rapidly consumed upon further electrolysis. Field groundwater samples subjected to electrocatalysis experiments, without the addition of NaClO(4)(-) electrolyte, also exhibited removal of NO(3)(-) on a timescale of minutes. Overall, results suggest that at an applied potential of -1.5 V with respect to SCE, Rh coated carbon cloth can reduce NO(3)(-) concentrations in field groundwater samples from 73 to 39 mg/L (16.58 to 8.82 mg/L as N) on a timescale range of 40-60 min. The electrocatalytic reduction process described in this study may prove useful for removing NO(3)(-) and NO(2)(-) from groundwater associated with nonpoint source pollution.     

Elevated nitrate levels in the groundwater of the Gaza Strip: distribution and sources

Seven years of monitoring groundwater in the Gaza Strip has shown that nitrate was and still is a major groundwater pollutant. The objectives of this research were to study the distribution of NO(3)(-) in the groundwater of the Gaza Strip and to identify the sources of NO(3)(-) in the Gaza aquifer system by assessing nitrogen and oxygen isotopes. The most recent samples collected in 2007 showed 90% of the wells having NO(3)(-) concentrations that are several times higher than the WHO standards of 50 mg/L. Potential NO(3)(-) source materials in Gaza are animal manure N, synthetic NH(4) based fertilizers, and wastewater/sludge. The average concentrations of N in the sludge, manure and soil of Gaza were 2.9%, 1% and 0.08%, respectively. The range in delta(15)N of solid manure samples was +7.5 to +11.9 per thousand. The range in delta(15)N of sludge samples was +4.6 to +7.4 per thousand, while four brands of synthetic fertilizers commonly used in Gaza had delta(15)N ranging from +0.2 to +1.0 per thousand. Sludge amended soil had delta(15)N ranging from +2.0 to +7.3 per thousand. For both delta(18)O and delta(15)N, the ranges of groundwater NO(3)(-) were -0.1 to +9.3 per thousand and +3.2 to 12.8 per thousand, respectively. No significant bacterial denitrification is taking place in the Gaza Strip aquifer. Nitrate was predominantly derived from manure and, provided delta(15)N of sludge represents the maximum delta(15)N of human waste, to a lesser extent from septic effluents/sludge. Synthetic fertilizers were a minor source.     

Sediment treatment with a nitrate-storing compound to reduce phosphorus release

The application of Fe(III), in combination with sediment oxidation by NO(3)(-), is an accepted procedure to manage stratified eutrophic lakes by controlling the phosphorus release from sediments into overlying water. Depox(R), a newly developed compound, consisting of Fe(III) and NO(3)(-), has a storage effect for NO(3)(-). NO(3)(-) is released slowly, hence the disadvantageous high solubility of NO(3)(-) in water can be retarded. The compound was added to water as a suspension which quickly flocculated and precipitated. Within 3 weeks, NO(3)(-) was desorbed from the Depox(R) compound in deionized water. After application in lakes, the NO(3)(-) availability on the sediment surface was prolonged for 2 months. After treatment, P release from the sediment and microbial metabolism were investigated under laboratory conditions as well as in the mesocosm. P release was almost stopped in both cases during the experiment. SO(4)(2-) consumption was significantly lower after Depox(R) addition, and CH(4) production was completely suppressed by Depox(R) treatment in the laboratory, whereas in the enclosures SO(4)(2-) and also CH(4) concentrations at the sediment water interface did not change significantly between treated enclosures and controls.     

Factors affecting removal of selenate in agricultural drainage water utilizing rice straw

Microbial reduction of selenate [Se(VI)] to elemental selenium [Se(0)] is a useful technique for removing Se from agricultural drainage water. A series of batch experiments were conducted in the laboratory to determine the effects of pH (5-10), NO(3)(-) (100-500 mg/l), and SO(4)(2-) (0-5000 mg/l) on the removal of Se(VI) from drainage water with 1000 microg/l of Se(VI) and different amounts (1-4 g) of rice straw. Results showed that rice straw was very effective in creating a reducing environment (Eh=-205 to -355 mV) in the first 3 days of the pH-effect experiments. The optimum conditions for rapid Se(VI) removal from drainage water were a pH range of 6-9, high amounts of SO(4)(2-) (1000-5000 mg/l), low amounts of NO(3)(-) (100 mg/l) and high amounts of rice straw (3-4 g). Under these conditions, it took 5-7 days to reduce 93-95% of the added Se(VI) to Se(0). This study indicates that rice straw may be an inexpensive reducing agent to remediate Se(VI)-dominant San Joaquin Valley drainage water in the field.     

Evolution of anthropogenic aerosols in the coastal town of Salina Cruz, Mexico: part II particulate phase chemistry

An analysis of atmospheric gases and particles during periods of land and sea breezes in a coastal city in southwest Mexico indicates limited removal of total particle mass by deposition during periods when the air resides over the ocean. The average PM(2.5) mass concentrations for land and sea breeze samples were 25+/-1.0 and 26+/-1.0 microg m(-3), respectively. The average sum of the ion concentrations (NH(4)(+), SO(4)(2-), NO(3)(-), Na(+), Cl(-)) were 10 and 11.8 microg m(-3) for the samples taken during land and sea breeze periods. The average total carbon concentrations were 6.0 and 5.3 microg m(-3) for land and sea breeze periods. The mass of sulfate in particles of ocean origin, 3.3+/-2.8 microg m(-3), is marginally higher than those originating from the land, 2.0+/-0.8 microg m(-3), presumably as a result of the conversion of SO(2) recirculated from the city. The fraction of sulfate, nitrate and ammonium ions in rainwater samples is almost a factor of two higher than the fraction measured on filtered air samples. The rainwater also contains significant concentrations of elemental and organic carbon. This study, although extending over a period of only 15 days, with limited chemical samples, suggests that recirculation of anthropogenic particles from coastal cities should be taken into consideration when diagnosing and predicting air quality in such regions.     

Impact of fertilizer on a small watershed of Lake Biwa: use of sulfur and strontium isotopes in environmental diagnosis

Sulfur and strontium isotopes (delta(34)S and (87)Sr/(86)Sr) were determined in 39 river water samples collected over three different cultivation periods (April, May, and June), and in several materials used for comparison (fertilizers, detergents, soils, irrigation and agricultural waters), to evaluate the impact of fertilizers on a small agricultural watershed of Lake Biwa, in central Japan. delta(34)S values in river water decreased (from +5.8 to -2.0 per thousand) with increasing SO(4) concentrations (3.8 to 93.2 ppm) from upstream to downstream of the watershed. Comparison of river water S isotopes with those of possible source materials indicates that the enrichment of SO(4) can be attributed to the dissolution of two kinds of fertilizers: (1) compound fertilizers commonly used in this area and (2) ammonium sulfate which is applied on a small scale. In contrast, (87)Sr/(86)Sr values of river water decreased with time from April (avg. 0.71163), through May (avg. 0.71139), to June (avg. 0.71127). The tendency of the sample plots on the (87)Sr/(86)Sr vs. 1/Sr diagram suggests a time-dependent increase in the contribution of soil water to the river, which is partly affected by the Sr-bearing fertilizers. It is suggested that a maximum of 25% of dissolved Sr is derived from these fertilizers, while more than 75% of it is of rock origin. Mass balance calculations permitted us to evaluate the proportion of fertilizer contribution in each river. Combined use of S and Sr isotopes together with concentration data could be a new environmental diagnosis technique for rivers and soils in localized watersheds.     

Evaluating the sources and fate of anthropogenic dissolved inorganic nitrogen (DIN) in two contrasting North Sea estuaries

Nitrogen isotope ratios (delta(15)N) were used to help elucidate the sources and fate of ammonium (NH(4)(+)) and nitrate (NO(3)(-)) in two northeastern English estuaries. The dominant feature of NH(4)(+) in the heavily urbanised Tyne estuary was a plume arising from a single point source; a large sewage works. Although NH(4)(+) concentrations (ranging from 30-150 microM) near the sewage outfall varied considerably between surveys, the sewage-derived delta(15)N-NH(4)(+) signature was remarkably constant (+10.6+/-0.5 per thousand) and could be tracked across the estuary. As indirectly supported by (15)N-depleted delta(15)N-NO(3)(-) values observed close to the mouth of the Tyne, this sewage-derived NH(4)(+) was thought to initiate lower estuarine and coastal zone nitrification. In the more rural Tweed, NH(4)(+) concentrations were low (<7 microM) compared to those in the Tyne and delta(15)N-NH(4)(+) values were consistent with mixing between riverine and marine sources. The dominant form of dissolved inorganic nitrogen (DIN) in the Tweed was agricultural soil-derived NO(3)(-). A decrease in riverine NO(3)(-) flux during the summer coinciding with an increase in delta(15)N-NO(3)(-) values was mainly attributed to enhanced watershed nutrient processing. In the Tyne, where agricultural inputs are less important compared to the Tweed, light delta(15)N-NO(3)(-) (ca. 0 per thousand) detected in the estuary during one winter survey pointed to a larger contribution from precipitation-derived NO(3)(-) during high river discharge. Regardless of the dominant sources, in both estuaries most of the variability in DIN concentrations and delta(15)N values was explained by simple end-member mixing models, implying very little estuarine processing.     

Natural denitrification in the Kakamigahara groundwater basin,Gifu prefecture,central Japan

Although nitrate is recognized as the most common groundwater contaminant due to growing anthropogenic sources, such as agriculture in particular, its adverse effects on human and animal health are debatable. The current issue, however, is to control and reduce nitrate contamination with regards to the long residence time of groundwater within aquifers. Denitrification has recently been recognized for its ability to reduce high nitrate concentrations in groundwater. The Kakamigahara groundwater basin, Gifu prefecture, Japan, witnessed rising levels of nitrate (>12 mg/l NO(3)-N) originating from agricultural sources. Chemical analyses for the determination of major constituents of groundwater and delta(15)N of residual nitrate were performed on representative groundwater samples in order to fulfill two main objectives. One is to investigate the current situation of nitrate groundwater pollution. The second objective is to determine whether the denitrification is a potential natural mechanism, which eliminates nitrate pollution in the Kakamigahara aquifer. Agricultural nitrate contamination of groundwater was obvious from characteristically high concentrations of Ca(2+), Mg(2+), NO(3)(-) and SO(4)(2-). High nitrate concentrations were found on the eastern side of the basin in association with vegetable cultivation fields, and decreased gradually towards the west of the basin along the direction of groundwater flow. The decrease of nitrate concentration was conveniently coupled with increase of HCO(3)(-) (the heterotrophic denitrification product), pH and delta(15)N of residual nitrate (due to isotopic fractionation) from east to west. Therefore, denitrification in situ is continuously removing nitrate from the Kakamigahara groundwater system.     

Degradation and byproduct formation of parathion in aqueous solutions by UV and UV/H(2)O(2) treatment

The photodegradation of parathion in aqueous solutions by UV and UV/H(2)O(2) processes was evaluated. Direct photolysis of parathion both by LP (low pressure) and MP (medium pressure) lamps at pH 7 was very slow with quantum yields of 6.67+/-0.33x10(-4) and 6.00+/-1.06x10(-4)molE(-1), respectively. Hydrogen peroxide enhanced the photodegradation of parathion through the reaction between UV generated hydroxyl radical and parathion with a second-order reaction rate constant of 9.70+/-0.45x10(9)M(-1)s(-1). An optimum molar ratio between hydrogen peroxide and parathion was determined to be between 300 and 400. Photodegradation of parathion yielded several organic byproducts, of which the paraoxon, 4-nitrophenol, O,O,O-triethyl thiophosphate and O,O-diethyl-methyl thiophosphate were quantified and their occurrence during UV/H(2)O(2) processes were discussed. NO(2)(-), PO(4)(3-), NO(3)(-) and SO(4)(2-) were the major anionic byproducts of parathion photodegradation and their recover ratios were also discussed. A photodegradation scheme suggesting three simultaneous pathways was proposed in the study.     

Groundwater geochemistry and its implications for arsenic mobilization in shallow aquifers of the Hetao Basin, Inner Mongolia

Arsenic concentrations in shallow groundwaters from the Hetao Basin of Inner Mongolia range between 0.6 and 572 microg/L. High As groundwaters generally occur in the shallow alluvial-lacustrine aquifers, which are mainly composed of black (or dark grey) fine sands in a reducing environment. They are characterized by high concentrations of dissolved Fe, Mn, HCO(3)(-), P and S(2-), and low concentrations of NO(3)(-) and SO(4)(2-). Low SO(4)(2-) coupled with high S(2-) suggests that SO(4)(2-) reduction has been an active process. In the reducing groundwaters, inorganic As(III) accounts for around 75% of total dissolved As. Total As contents in the sediments from three representative boreholes are observed to be 7.3-73.3 mg/kg (average of 18.9 mg/kg). The total As is mildly-strongly correlated with total Fe and total Mn, while a quite weak correlation exists between total As and total S, suggesting that the As is associated with Fe-Mn oxides, rather than sulfides in the sediments. It is found in the sequential extraction that chemically active As is mainly bound to Fe-Mn oxides, up to 3500 microg/kg. The mobilization of As under reducing conditions is believed to include reductive dissolution of Fe-Mn oxides and reduction of adsorbed As. Although exchangeable As is labile and very vulnerable to hydrogeochemical condition, the contribution is relatively limited due to the low concentrations. The competition between As and other anions (such as HPO(4)(2-)) for binding sites on Fe-Mn oxides may also give rise to the release of As into groundwater. Slow groundwater movement helps accumulation of the released As in the groundwaters.     

Greenhouse gas production in a pond sediment: effects of temperature, nitrate, acetate and season

In this paper we investigate the impact of nitrate (NO(3)(-)) concentration and temperature on the production of carbon dioxide (CO(2)), methane (CH(4)) and nitrous oxide (N(2)O). We studied sediment collected during spring, summer and autumn from a constructed pond in South Sweden. Homogenised sediment samples were dark incubated in vitro under N(2) atmosphere at 13 degrees C and 20 degrees C after addition of five NO(3)(-) concentrations, between 0 and 16 mg NO(3)(-)-N per litre. We found higher net production of N(2)O and CO(2) at the higher temperature. Moreover, increased NO(3)(-) concentrations had strong positive impact on the N(2)O concentration, but no effect on CH(4) and CO(2) production. The lack of response in CO(2) is suggested to be due to the use of alternative oxidants as electron acceptors. Interaction between NO(3)(-) and temperature suggests a further increase of N(2)O net production when both NO(3)(-) and temperature are high. Our interpretation of the CH(4) data is that at high concentrations of NO(3)(-) temperature is of less importance for CH(4) production. We also found that at 13 degrees C CH(4) production was substrate limited and that the addition of acetate increased CH(4) as well as CO(2) production. There was a seasonal effect on gas production potential, with more CH(4) and N(2)O produced in spring than in summer. Re-calculation of the gas concentrations into global warming potential (GWP) units (i.e. CO(2), CH(4), and N(2)O transferred to CO(2) equivalents) shows that GWP increases with temperature. However, under environmental conditions generally occurring in South Swedish ponds, i.e. low temperature and high NO(3)(-) concentration during spring and high temperature and low NO(3)(-) concentration during summer, NO(3)(-) concentration is of minor importance.     

Net changes in nutrient concentrations below a point source input in two streams draining catchments with contrasting land uses

We examined net changes in ammonium-Nitrogen (NH(4)(+)-N), nitrate-Nitrogen (NO(3)(-)-N), dissolved inorganic nitrogen (DIN), soluble reactive phosphorus (SRP), and dissolved organic carbon (DOC) chloride-corrected ambient concentrations along a reach located below a wastewater treatment plant (WWTP) input in a non-agricultural (12 dates) and an agricultural (6 dates) stream. Based on those net changes, we estimated processing length (Snet) and mass transfer coefficient (Vf) of the cited nutrients. In the agricultural stream, results suggest that diffuse nutrient inputs from adjacent agricultural fields had a greater effect on water chemistry than the WWTP input, and probably overwhelmed the stream capacity to retain and transform nutrients. In the non-agricultural stream we observed consistent longitudinal trends below the WWTP input only for NH(4)(+)-N and NO(3)(-)-N. The tight coupling between longitudinal NH(4)(+)-N decreases and NO(3)(-)-N increases in the non-agricultural stream, and lack of longitudinal trends of DIN on most dates suggest that NH(4)(+)-N from the WWTP input was being nitrified along the reach. These results suggest that WWTP inputs favor conditions to support hot spots for chemoautotrophic activity.     

The cytotoxicities induced by PM 10 and particle-bound water-soluble species

A 1-year field sampling of PM(10) was performed at a town that usually has the worst air quality in Taiwan to examine if PM(10) is a good indicator for pollutant-induced cytotoxicity. The average PM(10) concentration in summer was the lowest, while the other three seasons did not show statistical difference in their PM(10) means. The pollutant-induced cytotoxicity presented as the cumene-hydroperoxide equivalent concentration (CEC) was found to positively correlate with PM(10) concentrations and this study yielded a yearly average of the seasonal CEC 12.+/-8.54 microM with the magnitudes in sequence for the four seasons as: fall>winter>spring>summer. Positive relationship was also found between seasonal PM(10) and their corresponding CECs. The exponential regression model obtained from this study shows: CEC=3.305 exp(0.0118 PM(10)) (R(2)=0.634). The CEC correlates more significantly with NO(3)(-), SO(4)(2-), NH(4)(+) and Cl(-) (secondary aerosol species) than with the Na(+), K(+), Ca(2+) and Mg(2+) (crust-related species) in PM(10). However, the best multivariable model obtained from this study to relate CEC with the concentrations of PM(10)-bearing water-soluble species shows: CEC=exp(1.4751+0.0470[SO(4)(2-)]+0.0143[NO(3)(-)]) (R(2)=0.550).     

Evaluation of the salt accumulation process during inundation in water resource of Contas river basin (Bahia-Brazil) applying principal component analysis

The high salinization in some reservoirs of the Contas river basin (Bahia-Brazil) has been erroneously attributed only to concentration by evaporation. However, recent studies of this basin have shown that in period of intense rainfalls, occur an increase of the saline concentration in the flowing rivers of the reservoirs. The application of statistical methods (cluster and principal components analysis) have shown that this fact can be attributed to the discharge of saline waters from the small reservoirs of every drained area, provoked by inundation, is also an important factor in the salinization process. Thus the study of the geochemical variables: Na(+), K(+), Ca(2+), Mg(2+), Cl(-), SO(4)(2-) and CO(3)(2-), showed one group formed by Na(+) and Cl(-), attributed to the discharge of saline water provoked by inundation from a small reservoir, and a second group constituted by Ca(2+), Mg(2+), K(+) and SO(4)(2-), due to an increase provoked by the evaporation in the salinization process.     

Sources of nitrate and ammonium contamination in groundwater under developing Asian megacities

The status of nitrate (NO(3)(-)), nitrite (NO(2)(-)) and ammonium (NH(4)(+)) contamination in the water systems, and the mechanisms controlling their sources, pathways, and distributions were investigated for the Southeast Asian cities of Metro Manila, Bangkok, and Jakarta. GIS-based monitoring and dual isotope approach (nitrate delta(15)N and delta(18)O) suggested that human waste via severe sewer leakage was the major source of nutrient contaminants in Metro Manila and Jakarta urban areas. Furthermore, the characteristics of the nutrient contamination differed depending on the agricultural land use pattern in the suburban areas: high nitrate contamination was observed in Jakarta (dry fields), and relatively lower nutrients consisting mainly of ammonium were detected in Bangkok (paddy fields). The exponential increase in NO(3)(-)-delta(15)N along with the NO(3)(-) reduction and clear delta(18)O/delta(15)N slopes of NO(3)(-) ( approximately 0.5) indicated the occurrence of denitrification. An anoxic subsurface system associated with the natural geological setting (e.g., the old tidal plain at Bangkok) and artificial pavement coverage served to buffer NO(3)(-) contamination via active denitrification and reduced nitrification. Our results showed that NO(3)(-) and NH(4)(+) contamination of the aquifers in Metro Manila, Bangkok, and Jakarta was not excessive, suggesting low risk of drinking groundwater to human health, at present. However, the increased nitrogen load and increased per capita gross domestic product (GDP) in these developing cities may increase this contamination in the very near future. Continuous monitoring and management of the groundwater system is needed to minimize groundwater pollution in these areas, and this information should be shared among adjacent countries with similar geographic and cultural settings.     

Electrodialysis and nanofiltration of surface water for subsequent use as infiltration water

In order to achieve stable groundwater levels, an equilibrium between the use of groundwater for drinking water production and natural or artificial groundwater recharge by infiltration is needed. Local governments usually require that the composition of the water used for artificial recharge is similar to the surface water that is naturally present in the specific recharge area. In this paper, electrodialysis (ED) and nanofiltration were evaluated as possible treatment technologies for surface water from a canal in Flanders, the North of Belgium, in view of infiltration at critical places on heathlands. Both methods were evaluated on the basis of a comparison between the water composition after treatment and the composition of local surface waters. The treatment generally consists of a tuning of pH and the removal of contaminants originating from industrial and agricultural activity, e.g., nitrates and pesticides. Further evaluation of the influence of the composition of the water on the characteristics of the artificial recharge, however, was not envisaged. In a case study of water from the canal Schoten-Dessel, satisfactory concentration reductions of Cl(-), SO(4)(2-), NO(3)(-), HCO(3)(-), Na(+), Mg(2+), K(+) and Ca(2+) were obtained by ultrafiltration pretreatment followed by ED. Nanofiltration with UTC-20, N30F, Desal 51 HL, UTC-60 and Desal 5 DL membranes resulted in an insufficient removal level, especially for the monovalent ions.     

Minerals controlling arsenic and lead solubility in an abandoned gold mine tailings

Numerous areas have been contaminated by heavy metals and metalloids due to industrial and mining activities. Studies investigating the behavior of such contaminants in the environment have identified speciation as a key factor controlling their mobility, availability and toxicity. Here we characterize As- and Pb-bearing phases resulting from the oxidation of sulfide-rich tailings of a former gold mine (La Petite Faye, France) in order to assess the risk for water quality. Elements were first pre-concentrated by granulometric fractionation (sedimentation in deionized water) and then investigated using X-ray diffraction and electron microprobe analyses. Two main As-Pb-bearing minerals were clearly identified: scorodite (FeAsO4 x 2H2O) and beudantite PbFe3(AsO4)(SO4)(OH)6. Minor amounts of As and Pb were dissolved in deionized water during granulometric fractionation, indicating the possible presence of other soluble Pb-sulfates which could be some of the primary metastable products of sulfide oxidation. This dissolution also provides information about the fate of these phases in the case of intensive leaching of the tailings. Scorodite may not be considered as a relevant candidate for As on-site immobilization, because its solubility largely exceeds drinking water standards whatever the pH. Since beudantite solubility has not yet been determined, an estimation of its solubility product was obtained using the Gibbs free energy of formation of plumbojarosite [Pb0.5Fe3(SO4)2(OH)6]. This estimation suggests that beudantite should efficiently maintain low Pb concentration in waters. However, Pb dissolution in deionized water during the granulometric fractionation led to Pb concentrations much higher than the French and US drinking water standards (2.4 x 10(-7) mol l(-1)), which may be due to dissolution of the suspected metastable Pb-sulfates. Accurate determination of beudantite solubility is now required to improve the Pb risk assessment on such polluted sites.     

Use of stable nitrogen isotope fractionation to estimate denitrification in small constructed wetlands treating agricultural runoff

Constructed wetlands (CWs) in the agricultural landscape reduce non-point source pollution through removal of nutrients and particles. The objective of this study was to evaluate if measurements of natural abundance of (15)NO(3)(-) can be used to determine the fate of NO(3)(-) in different types of small CWs treating agricultural runoff. Nitrogen removal was studied in wetland trenches filled with different filter materials (T1--sand and gravel; T3--mixture of peat, shell sand and light-weight aggregates; T8--barley straw) and a trench formed as a shallow pond (T4). The removal was highest during summer and lowest during autumn and winter. Trench T8 had the highest N removal during summer. Measurements of the natural abundance of (15)N in NO(3)(-) showed that denitrification was not significant during autumn/winter, while it was present in all trenches during summer, but only important for nitrogen removal in trench T8. The (15)N enrichment factors of NO(3)(-) in this study ranged from -2.5 to -5.9 per thousand (T3 and T8, summer), thus smaller than enrichment factors found in laboratory tests of isotope discrimination in denitrification, but similar to factors found for denitrification in groundwater and a large CW. The low enrichment factors compared to laboratory studies was attributed to assimilation in plants/microbes as well as diffusion effect. Based on a modified version of the method presented by Lund et al. [Lund LJ, Horne AJ, Williams AE, Estimating denitrification in a large constructed wetland using stable nitrogen isotope ratios. Ecol Engineer 2000; 14: 67-76], denitrification and assimilation were estimated to account for 53 to 99 and 1 to 47%, respectively, of the total N removal during summer. This method is, however, based on a number of assumptions, and there is thus a need for a better knowledge of the effect of plant uptake, microbial assimilation as well as nitrification on N isotopic fractionation before this method can be used to evaluate the contribution of dinitrification in CWs.